L i vMore Safelyin the Chaparral-UrbanInterfaceKlaus W. H. Radtke

CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1The Chaparral Environment . . . . . . . . . . . . . . . . . . . . . . 1

Chaparral Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . 1Fire and Chaparral . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Problems in Watershed Management. . . . . . . . . . . . . . . 5Dry-Creep, Wet-Erosion Cycle . . . . . . . . . . . . . . . . . . 5Fire-Flood Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Erosion Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Topography . . . . . . . . . . . . . . . . . . . . . . . . . .......10Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...11Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......11Human Interference . . . . . . . . . . . . . . . ... ... ..%.13

Coping with Watershed Problems . . . . . . . . . . . .......14Maintaining Slope Stability . . . . . . . . . . . . . . .......14Controlling Drainage . . . . . . . . . . . . . . . . . . . .......15Controlling Animal Activity . . . . . . . . . . . . . .......16

Landscaping for Fire and Erosion Control . . . .......17Establishing Greenbelts . . . . . . . . . . . . . . . . . .......20Maintaining Compatibility of Plants . . . . . . .......21Choosing Low-Growing Species . . . . . . . . . . .......22

lce Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....27Coyote Brush . . . . . . . . . . . . . . . . . . . . . . . . .......27Rosemary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..27Prostrate Acacia . . . . . . . . . . . . . . . . . . . . . .......28Rockrose . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......28

Periwinkle . . . . . . . . . . . . . . . . . . . . . . . . . . . .......28Ivy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......28African Daisy.. . . . . . . . . . . . . . . . . . . . . . . .......28

Watering Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28Water-Saving Plants . . . . . . . . . . . . . . . . . . .......28Water Requirements . . . . . . . . . . . . . . . . . . .......30Overhead Impact Sprinklers . . . . . . . . . . . .......32

Planning for Home Safety from Fire . . . . . . . . .......32Reducing Fuel Load . . . . . . . . . . . . . . . . . . . . .......33Understanding Fire Behavior . . . . . . . . . . . . . .......34Promoting Fire Safety . . . . . . . . . . . . . . . . . . .......37Clearing Brush Around Homes . . . . . . . . . . . .......40

Treating Newly Burned Chaparral Slopes . . . . .......40Direct Seeding . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . 41

Annual Ryegrass . . . . . . . . . . . . ..... . .. . . .......41Barley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....42

Check Dams... . . . . . . . . . . . . . . . . . . . . . . . . .......43Boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43Jute Matting. . . . . . . . . . . . . . . . . . . . . . . . . . . .......44Chain Link Fence . . . . . . . . . . . . . . . . . . . . . . .......44Sandbags and Deflector Barriers . . . . . . . . . . .......44Drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......45Dry Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......45Plastic Sheeting . . . . . . . . . . . . . . . . . . . . . . . . .......45Guniting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....46

What to Do When Caught in aWildfire . . . . . .......47Before Fire Approaches . . . . . . . . . . . . . . . . . .......47When the Fire Front Arrives and Passes . . . .......47When Caughtin the Open . . . . . . . . . . . . . . . .......48Evacuation and Road Closure . . . . . . . . . . . . .......48

Appendix: List of Species Mentioned . . . . . . . . .......49References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .....50

I n recent years, urban development has extended intorural areas around many of our larger cities. Where the

topography is relatively flat and open, this encroachmentpresents no great difficulty, but where the cities are sur-rounded by steep, brush-covered slopes, development hasresulted in all-too-frequent loss of life and property.Although intense efforts have been made to deal with thisproblem, one pressing need is clear: greater coordination inplanning for fire control and for the prevention of flooding,landslides, and erosion.

The brushland fire-flood-erosion sequence is particu-larly well known in chaparral areas of southern California.Urban encroachment accelerates the cycle and adds thepotential for tragedy. Unless adequate measures are takenin new developments, fire protection and flood controlagencies are hard pressed to safeguard life and property.

When hazardous conditions come about through im-proper land use or lack of planning, they are extremelydifficult to correct by either private or public action.Government agencies should therefore work together toadopt comprehensive protection plans before permission isgranted for wildland development. These plans mustresolve the problem presented by new construction in eco-logically sensitive areas, so that added services for safe-guarding such developments are not paid fur by society as awhole.

Living in the urban-wildland interface creates biologicaland social problems which cannot be readily resolved.Logically, zoning ordinances should exclude developmenton steep chaparral wildlands and in areas where flooding isa common occurrence. But these are also the areas mostdesirable to potential home buyers because they offer aview or serve as secluded, wooded hideaways. Most of thepioneer homeowners who initially settled in these areaswere aware of the danger of fire and flood and were able tolive in closer harmony with natural conditions. Most mod-ern homeowners, however, are ill equipped to live in thewildlands and have come to depend on private and publicorganizations for support and safety. Today’s homeownerswant to live in natural surroundings, but often do not knowhow. To live more safely in the mountains, they mustregain the pioneering spirit of self-help, neighborhood

teamwork, and an understanding of nature’s ways. Toooften, home buyers fail to realize that fire protection agen-cies may not be able to save the “home” from fire, and thatbuilding and safety and flood control agencies may bepowerless to save them from floods and rnudshdes.

This report is intended to bring about greater under-standing of a fragile ecosystem chaparral. It describespreventive maintenance measures that should help reducethe damage from fire and flood. The information providedhere is addressed to homeowners, home buyers, develop-ers, landscape architects, land use planners, wildland man-agers, zoning agencies, city and county boards of supervi-sors, and other interested persons.

Although the report sometimes deals with them separ-ately, protection from fire and prevention of erosion gohand in hand. Fire protection that weakens slopes andcauses slides, or slope protection that increases fire hazard,can give us only a dangerous illusion of safety. From arealistic view, the price we must pay to live in the chaparralis high; it can be lowered only through wise planning andmanagement.

THE CHAPARRAL ENVIRONMENT

Chaparral is a plant community in California that hasadapted over millions of years to summer drought andfrequent fires. Similar vegetation is found in regions ofMediterranean climate throughout the world. These re-gions lie along the western edges of the continents, roughlybetween 28° and 37° latitude in the Southern Hemisphereand between 30° and 43° latitude in the Northern Hemi-sphere. Except in the Mediterranean Sea, the ocean waterin these regions is comparatively cool; cold currents flowtoward the equator, and local upwelling brings cold waterto the surface. In summer, high-pressure systems bring dryair to these regions, but in winter, rain-producing frontsmove in.

Mediterranean regions are found in the countries ofEurope, Africa, and Asia that border the Mediterranean

Sea; in southwest Australia and South Africa; and in Cen-tral Chile, Mexico, and the State of California. The climateis characterized by hot, dry summers and wet, moderatewinters. Rainfall ranges from about 10inches (250 mm) toabove 32 inches (800 mm). The mixtures of plant specieswithin these areas are determined by such factors as aspectand steepness of slope, soils, elevation, fire frequency, andlocal climate.

Chaparral Vegetation

Two distinct subformations of chaparral called “hardchaparral” and “soft chaparral” are clearly distinguished inrecent ecological literature and are commonly referred toas chaparral and coastal sage scrub communities, res-pectively (Paysen and others 1980, Westman 1982). Thisdistinction is important for both fire and slope manage-ment.

The coastal sage scrub community or “soft” chaparral israpidly becoming an “endangered” habitat because it iscommonly found in California’s coastal zone, where mosturban expansion is taking place. It is generally restricted tothe more xeric sites at lower elevations, because of orogra-phic effects, and at higher elevations because of shallowsoils (Miller 1981).The dominant species that compose thecoastal sage scrub community are of smaller stature thanthose in the chaparral community and provide a moreopen habitat that encourages more herbaceous speciesincluding the sages, California sagebrush, and deerweed. IThe chaparral community as a whole is drought-tolerant.In comparison with hard chaparral species, which tend tostart growth in winter, coastal sage species tend to startgrowth soon after the first significant autumn rains. Addi-tionally, both annual plant productivity and wildfires inthis community tend to be related to the amount of rain-fall, whereas hard chaparral species are more independentof rainfall in these respects (Minnich 1983).

Generally, plant adaptations to drought include thickleathery leaves, reduced leaf size, and summer dormancy, acondition which enables the plant to reduce its metabolicfunctions and drop leaves under prolonged drought. Twoadaptations to fire are sprouting and fire-stimulated ger-mination of seeds. Sprouting produces new shoots fromthe roots or root crown after the top has been injured byfire, browsing, pruning, or other means (Sampson 1944).Itmay begin soon after a fire if soil moisture is available tothe deep root system. After an early summer fire, sproutsmay grow more than a foot tall before the first rains comein the fall.

Both sprouting and nonsprouting plant species germi-nate prolifically after fires. The seeds of many chaparral

ICommonpublication.Mentioned,

2

names of plants and animals are used throughout thisFor scientific names, see Appendix: List of Species

species remain viable for a long time; often a thick seedcoat protects the endosperm from drying out. Fire ofteninjures this seed coat so that seeds germinate under properconditions of moisture and temperature. In the air-driedstate, many seeds can tolerate temperatures higher than302° F (150° C) for 5 minutes within the seed zone (tophalf-inch of soil layer), but tolerance to high temperaturesis sharply reduced when seed moisture content is high(Sweeney 1956). Seeds of some plant species may germi-nate readily with or without fire, whereas other specieswith a hard seed coat, such as certain Ceanothus speciesand many legumes, often require very hot fires to germi-nate. Nature has developed a set of survival mechanismsfor the varying fire and environmental conditions in thechaparral region.

Besides the sprouts and seedlings of the perennial chap-arral species, seedlings of herbaceous species are abundantin the first few seasons after fire. Seeds of many of thesespecies lie in the soil for years awaiting stimulation by firefor germination. Fire-dependent annuals and perennialsare responsible for the beautiful array of wildflowers thatcan be seen everywhere the first few seasons after a fire.They provide a natural vegetative cover that helps tempor-arily to reduce the heavy erosion that can be expected fromsteep mountain slopes once existing protective cover hasburned off. These short lived, fire-adapted species convertmineral nutrients to organic form, thus conserving nut-rients that could be lost by leaching and erosion. Somespecies, such as deerweed, are able to obtain mineralizedsoil nitrogen from symbiotic bacteria and nlay be animportant means of returning it to the soil in an availableform for other plants. Nitrogen is the plant nutrient mosteasily lost during a fire.

Many chaparral plants exude chemical inhibitors, com-monly called allelopathic agents. These volatile or water-soluble antagonistic chemicals are carried by the heat ofthe day or by water to the soil and other plants, where theymay effectively stunt growth and reduce or eliminate seedgermination (Muller 1966, Muller and others 1968, Rice1974). Allelopathy is widespread in nature and the chemi-cal agents probably accumulate in the soil from one year tothe next. Allelopathy may function as a plant defensivemechanism that assures availability of the limited moistureand nutrients to the dominant plants on the site. By remov-ing litter and burning the soil surface, fire acts to reduce theeffects of these chemical inhibitors in the soil.

Plant species diversity peaks in the first few seasons aftera fire, but is reduced when, in the years after a fire, thefire-dependent annuals and short-lived perennials fail toreproduce. In hard chaparral, shrub species such as bushpoppy and Ceanothusmay decline in vigor after 10and 20years, respectively, and provide dry, dead fuel for futurefires. Chaparral fires aid in the continued survival of thesespecies. The oldest stands of hard chaparral generally havethe lowest species diversity and tend to be even-aged. Incontrast, most mature coastal sage stands are uneven-agedand have greater species diversity because of seedling

Figure l—The 1923 Berkeley Fire-considered themost devastating in California’s history+roke out inWildcat Ridge (A), reaching the city (B) before finallycoming undercontrol (C).Wind velocityon September

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— Humidity (pet)----- Temperature (“F)

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Fire weather

AB

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8 12 4 8 12 4 8 12 4 8 12 4 8 12 4 8 12MT MT Ml

Saturday Sunday Monday17 was 40 mph (64.4 kph). (Source: Emanuel Fritz, Sept. 15 Sept. 16 Sept. 17University of California, Berkeley).

Figure 2—The Oat Fire in Los Angeles County,whichstarted on October 31, 1981 (A) and burned 15,500acres,was contained during the night (B)despite dan-gerous fire weather conditions characterized by lowrelative humidity. Young age classes (average: 11years) of woody chaparral species offered relativelyhigh resistance to fire spread.

------ Temperature (“F)— Relative humidity (pet) ~.-.,

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Fire weather

12 4 8 12 4 8 12 4 8 12 4 8 12 4 8 12 4 8 12 4 8 12 4 8 1:MT Thursday ‘T Friday ‘T Saturday MT Sunday ‘“

Oct. 29 Oct. 30 Oct. 31 Nov. 1

establishment in the absence of fire and also greater herbdiversity and cover.

Fire and Chaparral

Wildfires in California can occur at almost any time ofyear but are most prevalent during the dry season. Extremefire conditions normally exist from September throughDecember or until the winter rains end the dry season.Fires are more likely to occur during strong Santa Anawinds; these winds, also known as Santana, foehn, devil, orfire winds, blow from the north to northeast out of theGreat Basin of Utah, Colorado, and surrounding northernStates. As the airis compressed and forced southwestwardto lower elevations, it becomes hot, dry, and gusty. WhenSanta Ana winds meet the local mountain winds, unpre-dictable weather patterns are often set up, making erraticfire fronts and spotting ahead of fires a commonoccurrence.

The rapid changes in temperature and humidity before,during, ~nd after- the 1923 Berkeley Fire illustrate theeffects of fire winds on local climate wig. 1).Itwas the mostdevastating fire in California history, with 624 housesburned in a single conflagration. High winds and woodshingles were the major factors in the heavy structurallosses. Within 1hour of the onset of the Santa Ana windsat 8:30 p.m., humidity had dropped from 92 to 25 percent.By midnight, temperature had increased from 63° F (17.2°C) to 82° F (27.8° C).

In southern California, humidity mayapproach 10per-cent, as it did in the 1981Oat Fire in Los Angeles County(iig.2). Most major fires in the chaparral areas of southernCalifornia occur during this extreme fire weather. UnderSanta Ana conditions, wildfires are extremely difficult tocontrol unless the fuel supply is exhausted or the windsubsides. Studies of fire problems in Los Angeles County,particularly the coastal Santa Monica Mountains, pointthis out (Radtke 1978, 1982; Weide 1968). A study offrequency of fires burning more than IOOacresin the Santa

3

Monica Mountains from 1919 to 1982 indicates that thegreater portion of wildland areas have burned at least oncein the last 60years; some have burned more than four times@g. 3).

In the interior mountain ranges of Los Angeles County,fire frequency and number of acres burned are high in thesummer months because of high summer temperatures andoccasional lightning strikes. In the coastal ranges, firefrequency is lower in the summer, and lightning strikes arealmost unknown as causes of fire. The number of acresburned is lower than in the interior ranges because theCatalina eddy, a marine breeze characterized by cool,moist air, penetrates the coastal mountains, primarily dur-ing June and July. This cool air is also responsible for theabnormal air circulation pattern of upslope instead ofdownslope winds during the evenings and into the night. Inboth the inland and coastal regions, the great toll ofacreage burned from late September through December isthe result of the Santa Ana wind, which has its highestfrequency from September to February and is almostabsent in July and August.

The pressure for urbanization of wildlands and openspace is significant in the Santa Monica Mountain range.Before intensive settlement began, the north-facing slopes(those facing the San Fernando Valley) were relatively freefrom fire, but in the last 35 years large fires have greatlyincreased here. Presently the estimated fire-start probabil-ity in coastal sage scrub is about once in 14years and in

chamise chaparral once in 16years (McBride and Jacobs1980). This large increase in fire starts is the result of thepopulation influx: almost every fire is started accidentallyor deliberately by man.

The areas of highest fire frequency are at the fire perime-ters, where fires burn together. In such a high-fire-frequency area, only the first fire burns hot because thequantity of fuel remaining for subsequent fires is reduced.The fire boundaries are determined by fire suppressionactivities, fuel types and their age classes, topography, fuelmodification attempts (firebreaks, roads, and subdivi-sions), and wind conditions. Once a fire perimeter is estab-lished, it normally defines a portion of the boundaries forfires that burn as much as 20 to 30 years later wig. 3). Thisbecomes clear when we realize that chaparral fire intensitydepends on the mixture and age of the individual chaparralspecies. The ratio of dead to live fuel is much greater in oldthan in young chaparral and varies from species to species.Past fire frequencies suggest that under natural conditionschaparral does not become highly fire-prone for about 15to 20 years, or until some of the shorter-lived chaparralcomponents die and increase the dead fuel (Philpot 1977).Coastal sage scrub, because of its shorter lived species andgreater mixture of herbaceous species, can become highlyfire-prone after 5 to 8 years.

The major flammable vegetation types found in theSanta Monica Mountains, namely chaparral, coastal sagescrub, and grassland, also have a direct bearing on fire

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Figure 3-Frequency of fires exceeding 100 acres (40 hectares), in theSantaMonicaMountains(VenturaCounty linetothe San DiegoFreeway),southern California, 1919to 1982.The outline on the leftshowsthe extentof the Da~on Canyon Fire, October 1982.

4

frequency and fire intensity because of their different fuelloads and ease of ignition. For example, the flashy annualgrassland fuel seldom exceeds 5 tons per acre (1 1.2 t/ha)whereas mature chaparral can exceed 30 tons per acre (67t/ha). Grassland fires may be more frequent but are alsomore easily extinguished; however, they often carry the fireinto the coastal sage scrub and chaparral. In any event, thefuels dictate the ease of fire starts and spread rates and thishas a direct bearing on fire frequency. When the grasslandswere grazed, reducing fuel loads, the highest fire frequencywas found in coastal sage. With reduction in sheep grazing,fires in annual grassland, especially along roads and rightsof way, have become the major source of fire starts. Never-theless, fire starts have been historically concentrated inthe coastal sage areas, where development has beengreatest.

The predictable direction of fire spread in the SantaMonica Mountains during Santa Ana winds is south tosouthwest. This spread pattern is primarily influenced byfire winds and secondarily by topography. Because canyonsin the eastern part of the Santa Monica Mountain rangerun in a south to south-westerly direction or parallel withthe fire winds, fire is channeled up the canyons, spreads outas it reaches the ridges, contracts again as it is funneleddownhill through the canyons, and may fan out in eitherdirection as it reaches the beaches. The western portion ofthe Santa Monica Mountains does not have this pro-nounced linearity of canyons and fire winds, however.Fires therefore are more influenced by the direction of thewinds and are more irregular in shape (Weide 1968).

PROBLEMS INWATERSHED MANAGEMENT

A watershed is generally understood to be all the landand water within the confines of a drainage area. Verti-cally, it extends from the top of the vegetation to theunderlying rock layers that confine water movement. Ahomeowner’s watershed is the area of land whose drainagedirectly affects the safety of that person’s property. Fre-quently this area includes adjacent properties over whichthe homeowner has little control. The drainage conditionsmay vary widely. Some homeowners have a well-mani-cured property adjacent to a street where all runoff ischanneled into rain gutters. Others are in a watershed thatincludes steep slopes where most runoff finds its way even-tually into intermittent stream beds. Sometimes the steepslopes are undercut by either natural stream channel ero-sion or development activities. To know how to safeguardtheir properties, homeowners shGtild understand the ero-sional processes affecting a watershed, and the changesbrought about by wildfire and their own actions.

Dry-Creep, Wet-Erosion Cycle

In chaparral, preserving the stability of the slopes is amajor problem. Most chaparral in southern Californiagrows on geologically young mountains where the steepslopes range from 25° to more than 70°. About 25 percentof the chaparral watershed exceeds the angle of repose,that is, the angle between the horizontal and the maximumslope that a particular soil or other material assumesthrough natural processes. On slopes that exceed the angleof repose, gravitational forces are likely to cause soil androcks to slide or fall downhill unless anchored by plants.The angle of repose increases with the compaction of thematerial, with the average size of fragments, with thesurface roughness and cohesion of soil particles, and, insand, with an increase in moisture content up to the satura-tion point. For loosely heaped soil particles the standardangle of repose is approximately 9° for wet clay, 11°to 20°for dry sand and mixed earth, 21° to 25° for gravel, and23° for moist clay (Van Burkalow 1945). Under naturalconditions and where soil is anchored by deep-rootedplants, the angles of repose are much steeper than thosegiven. Occurrence of landslides in chaparral is stronglyrelated to the angle of repose for different soils, oncecover, root depth, and root strength are taken intoconsideration.

On steep, harsh southern exposures, plant cover issparse, and dry creep and dry ravel (downhill soil anddebris movement during the dry season) become majorerosional forces, especially where slopes beyond the angleof repose have been undercut. During low rainfall years,this dry creep and dry ravel often exceed wet erosion ratesduring the winter months. The debris settles at the foot ofthe slopes, where it is flushed out by the rainstorms ofhigher-than-usual intensity, which occur about every 5years. Dry creep and dry ravel can also be greatly acceler-ated by animals, such as deer, rodents, and birds.

The dry-wet cycle on these slopes begins when summerdrought encourages dry creep and dry ravel. The onset ofthe first light winter rains gives the soil cohesion andgreatly reduces dry erosion. If further rains do not followbefore the soil dries out, dry creep and dry ravel againaccelerate. With heavier rains, dry erosion finally stopscompletely, so that erosion is at a minimum during the firstpart of the rainy season. As the rainy season continues,however, the soil mantle becomes saturated and rill andgully (overland) erosion accelerates. Toward the end of therainy season and until the soil surface dries out and loses itscohesiveness, erosion is again low (Anderson and others1959).

The erosion cycle is influenced by topography and vege-tation. A north-facing slope is less exposed to the sun thana south-facing slope, and is therefore more moist for thegreater part of the year. On north exposures, deeper soilsand more dense plant cover of different species have deve-loped over time, and these greatly reduce dry creep andoverland erosion. Dry ravel occurs sporadically but may

5

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Slope (degrees)

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Figure 4-Slope ratio, percentslope, and degree of slope areshownfor somehillsidesof vary-ing steepness. On naturalslopes,thedangerof soilslipfail-ures is related to slope angles.The angle may be expressedasthe ratio of run to rise, either asa percent(rise/run)or indegrees(angle between run and slope)(Campbell 1975).

Figure 5-During heavy rains,the amount of water that infil-trates the soil layer may exceedthe capacity of the parent rockmaterial to transmit water. Azone of supersaturatedsoil maydevelop,with a potentialslipsur-face as the lower edge. Thechances of slope failure are in-creased when de’ep-rooted na-tive vegetation is replaced bymore shallow-rwted plantings.Even though little or no runoffand little erosion may occur atthe surface,slopestrengthat thedeeper levels is reduced.

6

be high during or immediately after a fire; plants that wereanchoring the debris on their uphill side are burned off,and gravitational forces are again influential.

Dry creep is more continuous and at times almostimperceptible, but soil slips and slumps (landslides)—themajor wet erosional processes on mature chaparral water-sheds—are readily visible. A soil slip is a miniature lands-lide caused by downslope movement of soil under wet orsaturated conditions. Slips and slumps account for almost50 percent of the total erosional processes on a watershed(Rice 1974).

Soil failures are most common on slopes that range from25° to 45° ~ig. 4). As the slopes become steeper, thethickness of the soil mantle decreases and rockslidesbecome more common. The minimum angle of soil failureis steeper for chaparral vegetation than for grasses. Slidesoccur primarily during rainfall of high intensity, after thesoil has been saturated from a single major storm or fromseveral medium- to high-intensity storms in close succes-sion. In such cases, the rate of water infiltration into thesoil mantle exceeds the rate of percolation into the underly-ing bedrock. This results in supersaturated soils @g. 5).

Slips and landslides occur more readily when the inter-face of the soil and the parent material is low in shearstrength (resistance to separation), but this is not easy topredict for a particular region. Slides may not add much tothe immediate amount of downstream sediment erodedfrom a particular watershed because the eroded materialmay accumulate at the base of the slope. The sedimenteffect of slides is magnified after a fire because even mod-erately heavy storms can create high-velocity overlandflow of water over bare hillsides, carrying away the accum-ulated sediment. Because flow velocity is further increasedin the streambeds, the water can transport greater amountsof debris.

F iC

The amount of erosion after a fire depends on the stormintensity and the time elapsed since the fire (ruble 1).Postfire erosion may be more than 50 to 100times greaterthan on a well-vegetated watershed. Understanding of thefire-flood cycle is vital to watershed management becausethe peak flows created by fire-denuded hillsides areresponsible for accelerated erosion and flood damage.

Table 1—Amouni of erosion related 10 age of chaparral and maximum24-hour precipitation

Years Erosion at maximum 24-hour precipitation of.sincefire 2 inches 5 inches 1I inches

Yd3/acre1 5 20 1804 1 12 140

17 0 1 285~+ o 0 3

Source: Kittredge 1973

— Runoff: bare ground (fire denuded)

-------- Runoff: forested (chaparral)

I i I i i I‘ Rainfall

Figure 6-Water runoff from a watershed denuded by fire reaches ahigher peak than that from a forested watershed

Peak flow is the point of maximum streamflow, the resultof precipitation that is added to the base streamflow afterimmediate losses for interception, infiltration, and soilmoisture recharge have been satisfied. On bare ground,peak flow increases drastically as the rate of rainfallincreases, and reaches its maximum about the same time asrainfall wig.6). As the rain stops, runoff is greatly reducedand is eliminated within a very short period thereafter. Asshown in the graph, runoff on a well-vegetated watershedis often not noticeable until the storm is well underway. Amuch reduced peak runoff is normally reached at the endof the storm, and the constantly diminishing flow is fed fora considerable period of time. Grassland watersheds havegreater peak flows than forested watersheds.

A well-vegetated watershed thus greatly reduces peakstreamflow by increasing the time before runoff begins,and by spreading it over a longer period of time. Thiseliminates or greatly reduces watershed damage, as fol-lows: Increasing the infiltration rate and lag time by asmuch as four times decreases the peak discharge rate (peakflow) by almost four times. On the other hand, a decreasein lag time and infiltration rate, caused by bare soils,produces a geometric increase in sediment-carrying capac-ity. Thus, as the velocity of the water (v) is doubled, itserosive power is increased 4 times (vz) and its carryingcapacity is increased 32 times (vS).This carrying capacitydictates the quantity and size of material that can be car-ried by a given amount of water and adds to its destruc-tiveness (Leopold 1980).

Of the wet erosional processes, scouring out of streamchannels after fires accounts for the greatest sedimentyield. Overland flow causing rill and gully erosion is next inimportance. The debris that clogs a stream channel bedand is scoured out has been accumulating since the last fireand was reduced by intermittent nonfire-related floodpeaks. Thus, even during nonfire years, channel scour is amajor source of sediment. Both channel scour and over-land flow increase with storm intensity, channel scour

7

being responsible for two to three times more sedimentthan overland flow in almost all situations. The amount ofchannel scour depends on stream discharge and, therefore,the capacity of moving water to hold and carry sediments.Overland flow depends on other factors, such as the infil-tration rate of the soil (related to soil texture and aggrega-tion), the percolation and water storage capacity (relatedto soil texture and depth), the steepness of the slope, theheat of the fire (which affects development of water-repellency in soil layers), and the splash effect during heavyrains (which clogs the pores of fine-textured soils).

The production of water-repellent (hydrophobic) soilsby hot fires is an important factor in overland flow ~g. 7).In nature, many soils are water-repellent to some degree, asa result of the breakdown of organic material and thepresence of certain chemicals in the plant litter. Often firevolatilizes these chemicals and the resultant gases pene-trate into the soil, where they cool, coat the soil particles,and reduce water penetration through the soil layer thathas been affected. Water-repellency is more acute in coarse(sandy) soils than in fine (clay) soils. Fine soils have agreater surface-to-volume ratio, so that more of the water-repellent gases per unit area of soil are needed to coat allsoil particles effectively. Depending on the heat of the fire,the water-repellent layer may be found almost at the sur-

Osborn and others 1967).Nonwettable soils reduce germi-nation and establishment of plants on sloping groundbecause of the lack of adequate soil moisture.

Immediately after afire, the water-repellent layer acts asmulch by preventing evaporation from the lower wettablelayer. Chaparral that resprouts during the hot summerafter a fire draws moisture from the rock crevices and thewater remaining in the lower wettable layer. With the onsetof rains, the surface wettable layer becomes saturated;further precipitation cannot infiltrate except through thebreaks in the water-repellent layer. The resulting overlandflow is magnified by successive storms. However, if thefirst few winter rains are light and the thin wettable surfacelayer does not dry out between rains (that is, in cool,overcast weather), then the water-repellent layer becomeswettable from slow absorption of moisture from above.Once moist throughout, it retains its infiltration and perco-lation capacity. Surface runoff from later storms is greatlyreduced as long as the layer does not dry out and becomenonwettable again. Mechanical disturbance breaks up thenonwettable layer even more readily than gentle rains. Theeffect of water repellency is much lower after the first yearand becomes negligible after 5 to 10 years (DeBano andRice 1973). Such changes in soil nettability may partlyexplain the great differences observed in overland flow

face or down as far ‘as 2 inches (5 cm) (DeBano 1969, after a fire.

After fire

Waterrepellentlayer

Wettablesoil laYOr

Bedrock

Thin wettablesur-face layer

Break inwaterrepel-Ient layer

Runoff

Lateralflow

Figum7—Theeffectsof heatonthe soil may increase the depthof the water-repellent layer, andincrease repellency, so thatwater does not penetrate well toplant rmts. Thus the establish-ment of seedlings is sloweddown until the water-repellentlayer is broken up. Water fromfrequent heavy rains flows over-land, and rill and gully erosion isincreased.With time, the water-repellent layer again becomeswettable.

8

During the season after a fire, if rainfall is low and stormintensities are light, overland flow and channel scour arelessened. Dry creep, dry ravel, and occasional landslideswhich started on steep slopes during the fire may then bethe primary agents of erosion. On the other hand, dryerosion may be greatly reduced if the fire occurs imme-diately before the rainy period or between rainy periods.

Increases in landslides during the rainy period followinga fire could be caused by well-spaced storms that permeatethe nonwettable layer and completely recharge the water-holding capacity of the soil. Once the soil moisture isrecharged, a high-intensity storm could quickly supersatu-rate the soil, thereby accelerating wet creep, startingslumps and slides, and greatly increasing overland flow.Under these conditions, postfire rainy season slumps andslides have a tendency to occur more frequently on a southslope than a north slope. On south slopes, a sparse prefirevegetative cover, coupled with thin soils and a smaller rootnetwork, provides less soil-binding and water-holdingcapacity.

Postfire slips and slumps during the first few years aftera fire may be greatly reduced on nonwettable soils if highintensity storms follow each other in close order, therebyreducing rainfall penetration through the nonwettablelayer. The soil below the nonwettable layer would remaindry, eliminating landslides, but the greatly increased over-land flow would result in highly visible rill and gully ero-sion and would increase channel scour.

Erosion Factors

Erosion is the product of six factors: soils, climate,vegetation, animal activity, topography, and human activ-ity. The climate, the degree of slope of the land, and the soilphysical characteristics cannot be directly controlled toreduce soil erosion, but can be modified through soilsengineering, whose principal aim is to change slope charac-teristics so that the amount and velocity of runoff islessened.

SoilsSoil is developed through physical and chemical weather-

ing of a thin surface layer of rock and mineral fragments(soil parent material). Soil texture, structure, depth, andfertility determine what kind of plant life a soil can supportand ‘what its infiltration rate, percolation rate, and waterholding and water storage capacities will be. Soil textureand structure determine the erosiveness of soils. Texture isthe proportion of mineral particles of various sizes in thesoil; structure is the degree of aggregation of theseparticles.

In order of decreasing particle size, soil texture classesare sand, silt, and clay. Sand particles are visible to thenaked eye; individual silt and clay particles are visible onlyunder the microscope. Sandy soils are referred to as coarsetextured, loamy soils as medium textured, and clay soils asfine textured. Generally, soils composed of coarser parti-

cles drain water more rapidly than soils composed predom-inantly of finer particles. Sandy soils allow fast waterinfiltration and percolation, but little storage; clay soilsallow slow infiltration and percolation and greater storage.Sand, silt, and clay are easily eroded if the particles are notbound into stable aggregates. Organic materials and col-loidal clays are primary cementing agents. Soils high inclay content and organic material are among the leasterodible and most fertile soils. Sandy soils low in clay andorganic material tend to have high erosion rates.

Good soil structure contains much airspace, whichallows ready water infiltration into the soil, water percola-tion through the soil, and higher water storage capacity.Soils that have blocky or prismatic aggregates or thatcontain a high fraction of gravel (rock fragments largerthan 2 mm) have higher infiltration rates than soils that areplaty, such as most clay soils, or granular, such as someloamy soils.

Although geological relationships are too complex toanalyze here, review of some geologic terms and principlesshould clarify the direct implication of geology in slopemanagement. The type of rock and parent material presentare good indicators of the weathering of rocks, the soil-forming processes, and erosion. The rock hardness, thesize of the crystals, and the degree of crystal bonding andcementation are all important factors. For example, manygranitic rocks erode rapidly because of weak crystal cohe-sion and large crystal size. This makes our granitic soilshighly erodible. Rhyolite rocks weather more slowly, pro-ducing finer crystals, and soils derived from these rocks aretherefore less erodible. Basalt rocks have even finer crys-tals that weather very slowly and soils derived from theserocks are less erodible still.

Generally, metamorphic rocks (rocks that were alteredin form under extreme heat and pressure) are harder thanigneous rocks (rocks formed by cooling and solidificationof molten lava) and sedimentary rocks (rocks which werebroken down by weathering and deposited by water, wind,and gravity and then consolidated by heat or pressure orcemented by silica, lime, or iron solutions).

ClimateThe major climatic factors in erosion are precipitation,

temperature, and wind. Precipitation, viewed as the inter-play of amount, intensity, and duration, rather than asaverage rainfall, is the greatest erosional factor. The firstrainfall after a dry period saturates a bare soil surface,causing little erosion. After that, raindrops hit the soil-water surface, causing breakdown of the soil aggregates.Splashing causes muddy water, in which the smaller soilparticles are held in suspension. When this muddy waterenters the soil, the pores become clogged; infiltration slowsdown and may almost stop. Amount and velocity of runoffare increased, causing surface erosion, rills, and finallygullies. If the runoff water is concentrated long enough ona particular portion of a slope, the soil becomes saturatedand mud flows result.

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Temperature and wind have some erosional effects.High temperatures have an indirect effect in creating aharsh environment for plants, so that revegetation is slowand there is little soil binding. Wind erosion at the surfaceis most critical on fine-grained dry soils devoid of vegeta-tion. When large areas become exposed, as on recentlytilled fields or sandy deserts, or in dry, overgrazed regions,wind erosion may become the dominant process.

TopographyTopography can be directly controlled or permanently

altered to reduce soil erosion. Changes in topographyinfluence climate (rainfall), soils, and vegetation. Degreeand length of slope, the two most important factors thatdetermine the amount of runoff and soil erosion (ruble2),can often be manipulated. Cover crops, such as grasses,help to offset the effect of slope on surface erosion andcontours can be very effective in reducing soil erosion andrunoff. Rains of high intensity cause much greater amounts

of erosion than do low intensity rains under similar slopeconditions. Two rules of thumb emphasize these importantrelationships: doubling the degree of slope increases theerosion two to three times, and doubling the horizontallength of the slope increases erosion two to three times.

To visualize the amounts of sediment carried away byerosion, note that 1mm (0.04 inch) of soil erosion approx-imates 2 tons of topsoil per acre (4.6 t /ha) or up to 4 cubicyards (3 mj) of wet soil. Thus, 0.04 inch (1 mm) of soilerosion per acre equals about one large dump truck ofdebris. These estimates would be affected by the type ofsoil and the rainfall intensity. During high intensity rains,runoff and erosion increase with length of slope and shal-lowness of soil, because at high intensities there is less timefor infiltration and water storage. For low intensity rains,runoff and erosion decrease greatly (lab/e2). If the soil hasa low infiltration rate and low water storage capacity,excessive runoff and slope damage can be reduced onlythrough engineering practices, such as installation of ter-

Table 2—Effecis on erosion and runoffproducedb.vslopecharacteristics.protectivecover, and rainfall intensit.)l

Erosion factor,soil. location,

time Deriod. croKI

SlopeSteepness(Shelby loam, Montana,

1918-35,corn, clean tilled):

Length (Shelby silt loam,Montana, 1934-35,corn,clean tilled):

Direction (Marshall siltloam, Iowa, 1933-35,corn,clean tilled):

On contourUp and down

Protective coverPalouse silt loam, Washing-

ton, 1932-35wheat):FallowBare

Rainfall intensity(Marshall silt loam, Iowa,

1932-34)

Source: Bennett 1939

Annual\nnual Slope Slope soil Waterrainfall steepness length loss loss

Inches Degrees Feet Tons/acre Pet rain

4035

333333

2727

2222

(2)(2)(2)(3)(3)(’)

2 91 20 295 73 69 28

5 90 24 195 180 54 215 270 66 24

55

1717

012

928

0.112

925

5 158 9 115 315 18 185 630 33 205 158 8 285 315 6 175 630 6 14

IRainfall in southern California is generally more concentrated and of higher inten-sity than in Montana or Iowa, and often causes more erosional damage than indicatedhere.

‘High intensity ❑ rains considerably exceeding infiltration capacity of the soil.JLOWintensity = rains twice the duration of high intensity rains and only slightly

above the infiltration capacity of the soil.

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races and drains which take the water off the slope before itcan do any damage. Compaction of the soil reduces infil-tration and surface roughness increases it.

Terracing reduces the length of the slope, mitigates thedegree of slope, and disperses the water at a lower velocity,thereby reducing its cutting action. The greatly reducedrunoff reduces the amount of soil eroded. Significantreduction in total runoff from terraced land comparedwith that from nonterraced land can be achieved; the soilbecomes more permeable because the reduced velocity ofthe runoff allows more time for infiltration (table 2).

Spacing of terraces is determined primarily by the slopeof the land. Spacing is also influenced by the ability of thesoil to absorb water and transmit it through its profile, andby the plant material that covers the slopes. Permeablesoils of high water storage capacity, erodible soils, soilsunderlain by weak bedrock, and soils on steep slopesrequire close spacing of terraces. In areas of intense rain-fall, and in residential areas, concrete terraces (benchdrains) and down drains are used to channel the water offthe slope, but may not prevent slippage. During the inter-mittent high-intensity rains that occurred in southern Cali-fornia in the spring of 1978and 1980, I noted many slopefailures on manmade slopes despite concrete terraces.Slope failures often occurred on permeable soils on steeperslopes that were planted to grasses and shallow-rootedvegetation instead of deep-rooted plants. In areas of high-intensity rains, both concrete terraces and deep-rootedvegetation are therefore necessary. Bench drains, gener-ally, should not be installed on natural slopes steeper than20° because there may be weakening of slope stability atthe steeper angles.

Contour planting, a system of small earth terraces con-structed around the slope so as to follow the contour of theland, is used as a soil conservation measure. It is mostsuccessful on permeable soils during average storms ofmedium duration. Heavy, intense storms allow contours tobreak and permit the water to concentrate in channelsdown the slope. Grains such as barley have been usedsuccessfully for over 50 years in initial contour stabiliza-tion of highly erosive fill slopes of good permeability untildeep-rooted, woody plant material has become estab-lished.

VegetationA good vegetative cover can greatly offset the effects of

climate, soil, and topography on erosion. Vegetationachieves this effect by intercepting rainfall, and by decreas-ing the velocity of runoff and the cutting power of water,thus allowing more time for water to infiltrate. In addition,vegetation increases soil particle aggregation and porosity.Roots bind the soil particles and anchor the soil to theparent material. Transpiration through the leaves dries outthe soil, enabling it to absorb more water.

Different types of vegetation reduce erosion to differentdegrees. Plants with interwoven rhizomes, plants that forma tight mat, or those that produce much litter and have

tight aerial crowns normally decrease surface erosion morethan plants that lack these characteristics. Most grasses aretherefore well suited for surface erosion control, and deep-rooted woody plants for permanent slope stability espe-cially on slopes with deep soils. This fact was reemphasizedin studies which showed that during moderate- to high-intensity storms, soil slippage (shallow mass soil move-ment) was inversely related to the rooting pattern, size, anddensity of vegetation (Bailey and Rice 1969, Rice andothers 1969, Rice and Foggin 1971). Analysis of the soilslips by vegetative types showed slippage on about 25percent of the barren or sparsely covered natural slopessituated on harsh southern and eastern exposures. Theroots of the sages, the predominant vegetation on thesesites, are shallow and spread laterally through shallow soilinstead of into bedrock. Slippage occurred on 12percent ofthe area converted from brush to perennial grasses, but ononly 6 percent of the area converted to annual grasses.Apparently a higher density and greater below-groundroot biomass of annual grasses compared with perennialgrasses more than compensates for their more shallow rootsystem. On slopes converted from chaparral to grass, soilslip patterns were thus related to root patterns, whereas onnatural slopes they were related to soil factors.

In all chaparral vegetation types combined (chamise,oak, broadleaf) there was slippage in less than 2.5 percentof the area. These vegetation types are characterized byplants with deep tap roots. California scrub oak with rootsextending more than 30 feet (9 m) deep and occupyingmesic northerly and easterly aspects, is one of the vegeta-tive types least susceptible to slippage. Overall, densebroadleaved chaparral, which prefers the more mesicnorthern exposures, is much less susceptible to slippagethan the more sparse chamise chaparral predominantlyfound on harsher southern exposures.

Vegetation, in general, increases the moisture storagecapacity of the soil, particularly when plants are vigorouslygrowing and transpiring. Most chaparral plants are ever-green and active in winter, thereby increasing the capacityof the soil for greater soil moisture storage during thecritical winter period.

Any good vegetative cover will greatly reduce erosionduring intense rainfall of short duration or extended rain-fall of low intensity. In southern California’s Mediterra-nean climate, however, almost yearly storms of high inten-sity and long duration are characteristic. Therefore, themost effective plant material possible is needed, along withproper land use planning. In chaparral, nature has pro-vided a watershed cover that has become effectivelyadapted to dry, hot summers and long periods of summerdrought. Modifying this cover for fire protection createsmany problems.

AnimalsThe influence of animals on erosion is closely linked to

that of vegetation. For example, beneficial soil fauna suchas earthworms and beetles are more abundant under a

11

good vegetative cover. They greatly improve soil structureby mixing humus with subsurface soil layers and by creat-ing channels in the soil which increase soil permeability. Amoderate number of rodents, such as pocket gophers, arealso useful for this purpose. Too many rodents can be anuisance, however, creating soil instability by damagingroot structure, tunneling large underground waterways,and concentrating water in sections of hillsides. Theseconditions can induce slippage problems.

Animals, like plants, require a definite set of habitatconditions. A change in habitat often directly affects popu-lation dynamics. In an informal study made of a 90- by150-foot (27.4 by 45.8 m) chaparral-covered urban water-shed that was fenced but had not burned in 40 years,various changes in animal populations were observed. Thechaparral was pruned for fire safety in 1977and 1978andthe understory was thinned, thereby destroying the habitatfor pack rats. T’he resident rattlesnake, measuring 44inches (111.8 cm), was removed from the site. Theunderstory was planted to low fuel plants, which werereadily clipped by pack rats and mice that reinvaded fromsurrounding areas. California quail moved onto the site,but no California ground squirrels were sighted.

Within a year after the partial brush clearance, theOctober 1978Mandeville Canyon Fire denuded the studyarea and surrounding watersheds. This prompted a ratinvasion into nearby residential areas and created the openhabitat preferred by ground squirrels. During July andAugust, 1979, 17ground squirrels were trapped within thestudy area, accounting for 100 percent of the populationsighted. Four rattlesnakes were also removed during thesummer months. One rattlesnake was killed onsite; itsstomach contained the remains of four gophers. With theremoval of the rattlesnakes, the gopher population ex-ploded with serious detriment to the reestablishment of thelow fuel plants. Three western racers, two gopher snakes,and one mountain kingsnake were spotted during 1979,but these are no match for a mature gopher in its naturalunderground habitat.

From July 1 to August 15, 1980, 39 ground squirrelswere trapped, accounting for every ground squirrel withinthe study area at the time. Trapping was continued onSeptember 1 and an additional 15 ground squirrels werecaught within the next 2weeks. The<great influx of groundsquirrels into the area was supported by juvenile animalsthat moved into areas of low population densities createdthrough trapping. It is estimated that 90 percent of theadult ground squirrels would need to be trapped every yearto maintain effective population control. Rabbits weresighted for the first time, and along with rats and mice, areheading towards a population explosion. A coyote wasobserved to raise a litter each year during 1978-80,near thestudy area.

In this example, human interference changed the bal-ance of nature by changing the natural habitat. Thechanges in the predator population resulted in increasingthe gopher, rat, mouse, ground squirrel, and rabbit popu-

lations. This had an immediate detrimental effect on thewatershed through reduction of ground cover and under-mining of slope stability.

The detrimental effect of rodents on slope stability isalso pointed out in hillside grading guidelines (Los AngelesCounty 1975) which specify that “fill slopes steeper than2:1 (20percent, 11°) with a grading project located next toundeveloped land infested by burrowing rodents, shall beprotected from potential damage by a preventive programof rodent control.”

Observations by the Los Angeles County AgriculturalCommissioner’s Office in Calabasas Park confirmed thatground squirrels were at least a significant contributingcause of a massive slope failure that cost more than$500,000 for rehabilitation. Control of rodents affectingsloping land is therefore a cost-effective undertaking.

Trapping and population control is most successful’when the life history of the animal is known. The Califor-nia ground squirrel causes extensive hillside damage wig.8) because it digs burrows from 5 to 39 feet (1.5 to 12 m)long, almost 5 inches (13 cm) in diameter and up to 4 feet(1.2 m) deep (Grinnel and Dixon 1918).ColoniaI burrowsused by both sexes and their young may be more than 130feet (40 m) long. At any time there are more burrows thanindividual squirrels, because the squirrels construct newburrows from time to time to have additional escape routesand probably to leave most of their fleas behind in the oldnest. These fleas can be the carrier for the bacillus of thebubonic plague. Minimal handling of ground squirrels istherefore advisable.

The California ground squirrel was an asset to the Indi-ans because both its fur and meat could be used. Thesquirrel became a pest when the settlers drove out theIndians and destroyed many other natural enemies such asthe golden eagle, redtailed hawk, coyote, badger, wildcat,weasel, rattlesnake, and gopher snake. The importance ofnatural enemies for population control is well documented.One study showed that a nest of golden eagles consumed 6ground squirrels per day for a total of about 540 squirrelsduring a 3-month period (Grinnel and Dixon 1918).Inten-sive agriculture also supplied a dependable food source forthe ground squirrels; thus two primary factors of popula-tion control, seasonal scarcity of food and natural enemies,were greatly reduced or eliminated.

In the wildlands, ground squirrels gather almost anyseeds and fruits available, but prefer the young leaves andseeds of alfilaria, star thistle, and bur clover. The animalsare also fond of prickly pear. In urban areas and agri-cultural lands they gather grain and grass seeds. Successfulrevegetation methods with grasses can therefore contributeto population explosions by providing a plentiful seedsource from early ripening seeds. Among cultivated nuts,ground squirrels prefer almonds and walnuts, and amongfruits they like apples, prunes, peaches, apricots, figs, andolives. Poultry and wild bird eggs, as well as potatoes, arealso sought after. Grapes, if harvested while ripening, arenormally safe from ground squirrels.

12

The breeding season of the California ground squirrelextends from about February until April. At higher alti-tudes and in colder climates, the breeding season is laterand shorter. A litter varies from 4to 11and averages 7or 8.Under favorable conditions of climate and food supply,two litters are produced in 1 year. The gestation periodlasts about 30days and the young are born towards the endof March. They may appear above ground near their bur-rows towards early May. They start digging their ownburrows within 4 to 6 weeks thereafter, and fend for them-selves from then on. If the population density is too highlocally, they migrate by July and August. By September,the young have matured.

HumanInterferenceThe homeowner must remember that on steep terrain

almost every stone and plant has its place. Anything thatchanges the natural relationships of soil, vegetation, andrunoff may create a potential hazard. Random clearing ortunneling or other disturbance of the soil may-channeloverland flow or groundwater seepage in such a way as toweaken slopes and eventually lead to failure of an entireslope. Undercutting of the toe of a slope is one of the majorreasons for eventual slope failures. Development abovesuch slopes should be severely restricted unless the slopecan be totally restabilized by mechanical means. Restabili-zation should be a logical prerequisite for issuing a build-ing permit. With the rapid mobility of the urban popula-tion, the original owner and builder are seldom faced withthe hillside problems and financial losses they helpedcreate,

The urban hillside homeowner normally lacks the know-ledge necessary and year-round commitment to propertymanagement, so that small problems magnify and water-shed deterioration progresses from year to year. Forexample, a bench drain—a concrete sidehill drain—that ispartially blocked by soil, or a pipe filled with leaves, willeventually cause uncontrolled overland runoff, supersa-turated soils, and slope failures. Slopes cleared of deep-rooted vegetation but not properly replanted will slowlyweaken because the strength of the remaining root systemis steadily deteriorating. Root decay starts rapidly with thedeath of the plant and is completed in about 10years (Riceand others 1982). Since landscape plants that replacenative plants take a longer time to provide an equal bio-mass of live roots to the soil, it is therefore best to thin andprune, leaving deep-rooted native plants alive as~erman-ent specimens or at least until the replacement vegetation iswell anchored.

A row of water-demanding landscape plants, such asroses or fruit trees, planted along the edge of a slope may beresponsible for supersaturated soils during intense rains.Backyards that are leveled to accommodate lawns mayberesponsible for channeling water over the slope. A brokenor leaky pipe or sprinkler system or improperly laid outdrains are causes of slope failures, especially in olderdevelopments. Improper or looseiy compacted fill maysettle, thereby often breaking drainage pipes laid across orthrough them. The displacement of natural enemies ofslope-damaging rodents increases their population andalso accelerates their damage potential. Any hillside devel-opment has the potential for creating serious problems for

Figure 8-Hillsides in southernCalifornia are often damaged byground squirrels that burrowdeep into the soil and dig fordis-tances up to 40 feet (12.2 me-ters).

lower-lying homes; however, the unwillingness of a down-slope or sideslope resident to provide drainage easementmay affect the drainage patterns of the whole watershed,and dangerously undermine its stability.

On a larger scale, the hydrologic characteristics of awatershed can be altered in two ways by urbanization(Strahler and Strahler 1973):

1. The percentage of surface runoff made imperviousto infiltration is increased through the construction ofbuildings, driveways, and so on. This leads to increasedoverland flow (runoff) and greater discharge directly intostreams, increased flood peaks, and reduced recharge ofgroundwater.

2. Storm sewers allow storm runoff from paved areasto be taken directly to the stream channels (or the ocean)for discharge.

The effects of these two changes combine. Runoff timeto the stream channels is shortened at the same time thatthe proportion of runoff is being increased. The lag timebetween precipitation and runoff is reduced, therebyincreasing peak flow and frequency of floods.

Two basic methods of control are possible to decreasepeak flows that exceed the stream channel capacity (Satter-lund 1972):

1. Increase the capacity of the channel to handle excessflow, as by dredging, building levees to increase bankheight, widening the channel or straightening it to increasespeed of flow.

2. Decrease the volume of water so that it does notexceed the capacity of the channel, as by means of reser-voirs, spreading grounds, and diversion overflows.

Sometimes it is possible to shift a problem from oneplace to another. This approach is useful if the problem isshifted away from a high value area to a low value area.Problems arise, however, when determining what can bedone if homes are located at the edge of a streambed, at themouth of a channel, or on a flood plain. In such flood-hazardous locations proper flood control then becomesimpractical if not impossible and should be thought of asflood reduction rather than flood control.

COPING WITHWATERSHED PROBLEMS

Maintaining Slope StabilityIf slopes on a particular property range from about 25°

to 45° (47to 100percent), landslides maybe the major longterm erosional process (Campbell 1975). They can bereduced by maintaining deep-rooted woody vegetation,such as chaparral, on the hillside. The deep roots serve thedual function of anchoring the soil and pumping the waterout of the deeper soil layers. Woody chaparral vegetation ismore deeply rooted than any other low-fuel plant vegeta-tion that could replace it, and also has an extensive, strong

lateral root system. Therefore, chaparral should not begrubbed out. Occasionally the volume of fuel should bereduced through pruning that removes dead material,trims lower branches, and tops larger branches, andthrough occasional thinning of crowded plants. The chap-arral plants should be interspersed with deep-rooted,drought-tolerant low-fuel plants of somewhat similarwater requirement or tolerances that will form low-growing, dense ground covers. Sprinkler irrigation may benecessary until the low-fuel plants are well established;after that, they can be given a few deep waterings in thesummer. Proper watering of new plantings may have to becontinued throughout the winter season if rainfall is sparseor intermittent. If drought-tolerant landscape plants areheavily watered, they may not be able to use all of the waterso that the soil mantle is partially saturated at the%tart ofthe rainy season, with greater likelihood of soil slips andslides. Water-demanding plants should therefore not beused for hillside planting.

When chaparral is thinned or removed for fire protec-tion, great care must be taken not to remove plants overmore area than can be safely replanted and covered withlow-fuel plants the same season. Any disturbance or remov-al of the native vegetation represents at least a temporaryinstability in a particular portion of the watershed. Erosionduring brush conversion can be severe on even moderatelysteep slopes of about 15° (27 percent). First-year erosionrates on such slopes can exceed 1 inch (2.54 cm) of loosetopsoil. On an acre basis ( 1 acre ❑ 0.4 ha), this wouldamount to as much as 100 cubic yards (76 m3) of soil(enough to fill up to 25 dump trucks) that would find itsway into properties at the base of the slope. Such heavy soilloss can be greatly reduced through the use of erosionnetting, such as jute matting, which is very effective inprotecting soil from washing away. Erosion netting shouldbe used at planting time whenever it is anticipated thatheavy rains will return before a plant cover can be reestab-lished. The loss of topsoil in itself is very critical becausetopsoil contains more nutrients, has better structure, agreater infiltration rate, and more water storage capacitythan subsoil and is therefore more capable of producingvigorous, rapidly growing plants.

Brush conversion on slopes approaching 30° (58 per-cent) should not be attempted unless appropriate soilsengineering practices such as terracing are used or unlessthe slope is short. In some instances slopes are steeper thanthe natural angle of repose for the geologic material. Formost standard soils on natural slopes, this angle is about34° (67 percent), but it depends on the many factors dis-cussed earlier. Because of internal static friction, the angleof maximum slope (angle at which slope failure occurs)may be up to 10° greater than the angle of repose. LosAngeles County Grading Guidelines ( 1975)also emphasizethe maximum slope angle by stating the “cuts shall not besteeper than 1.5:1 (34°) unless the owner furnishes a soilsengineering or soils geology report. . certifying that a cut ata steeper slope will be stable and not create a hazard to

14

Figure 9--Rock strata can con-tribute to hillside problems. Abreakinthepavement nefltothehouse (A) caused by sewer orwater linescanleadtomajorslip-page. More slippage murs onthe right side of this hill than onthe left.

❑✘❞✌Original ridge top

/A\

H

Section of slope\

/’ \ may slip

a

public and private property.” Even so, the building inspec- requirements spelled out in the Los Angeles Countv ~rad-tor has the right to insist on a more gentle slope if necessaryfor stability and safety. Large-scale brush conversion forfire safety should not be attempted on slopes beyond theangle of repose, because the soil will slide under the force ofgravity once the plant cover is removed. Most landscapeplants cannot establish themselves unless the hillside isreshaped. If this cannot be done, permanent acceleratederosion results, leading to eventual large-scale slope fail-ures if the underlying parent material is unstable.

The bedrock from which most soils are derived is impor-tant to slope stability. For example, fractured rocks, orrock layers that are parallel to the slope, especially on anorthern exposure, cause more hillside problems than con-solidated rock or rock layers at right angles to the slopewig. 9). Soil stability can be greatly reduced by an underly-ing clay bed; this acts as a lubricating agent once it is wet.High rates of water infiltration cause local soil saturationthat may result in mudflows and major slides, especiallywhen they occur on geologically unstable material. There-fore erosion and slope problems will be accelerated if wateris concentrated on any particular portion of a slope, unlessthe water finds its way immediately into storm drains orrain gutters.

Controlling Drainage

Homeowners must understand the purpose of gradingregulations and should not defeat their intent throughignorance or lack of maintenance. Much of the hillsidedamage in the Los Angeles area in the 1978, 1980,and 1983floods could have been reduced by homeowners throughpreventive maintenance and by following the grading

.-ing guidelines, summarized below:

. A 2 percent overall gradient must be maintainedfrom the rear of the lot to the curb or drainage structure.

. A berm must be installed at the top of the slope toprevent water from draining onto the slope.

. A 1percent flow line is required around the house toa drainage structure or the street.

● No roof drainage over slopes is permitted.. Any gradient greater than 5percent that carries yard

drainage must have a paved swale (wide open drain withlow center line) or V driveway.

. When fill is used to repair even a small slip on a slope,benches are required if the natural slope exceeds 5:1 (20percent or 11°).

. Cut slopes more than 5feet (1.5 m) high or fill slopesmore than 3feet (O.9 m) high must be planted with grass orground cover. Slopes more than 15feet (4.6 m) in verticalheight must also be planted with shrubs not more than ICfeet (3 m) on center or trees not more than 20 feet (6 m) oncenter, or a combination of shrubs and trees at equivalentspacing in addition to grasses or ground covers.

● Irrigation must be provided covering all portions ofthe slope.

To protect the homeowner from damage caused bynearby developments, the guidelines stipulate that “nograding permit shall be issued for work to be commencedbetween October 1of any year and April 15of the follow-ing calendar year unless the plans for such work includedetails of protective measures, including desilting basins orother temporary drainage or control measures or both asmay be necessary to protect adjoining public or private

15

property. . . .“ Additionally, a standby crew for emergencywork must be made availabk by the builder at all timesduring the rainy season, and necessary materials must beavailable immediately when rain is imminent. Further-more, all removable protective devices must be in place atthe end of each working day when the 5-day rain probabil-ity forecast exceeds 40 percent. A guard must be on sitewhenever the depth of water in any device exceeds 2 feet(61 cm). A 24hour emergency phone number of the personresponsible for the project must be listed when submittingthe temporary erosion control plans. (It is wise also to postthis number on the construction site at all times.)

A field inspector visits building sites periodically, butwould not be aware of any accelerated erosion problemsunless requested by a homeowner to make an emergencyinspection of a property, or unless an inspector is checkingthe building site to make sure that drainage plans have beenadhered to. Concerned neighbors may also call the fieldinspector to point out erosion problems on constructionsites. A final inspection is done at the time the land isoccupied, and the inspector does not return unlessrequested to do so or unless a construction permit is takenout for improvements. Under these circumstances, newowners may not be aware of the consequences of anyadditional work they are doing, however minor. Forexample, major slope failure affecting several propertieswas observed after the heavy 1980rains. The homes had anadequate setback from the slopes and the canyon below,but the large backyards and lawns sloped more than 1percent toward the rear, thereby draining all excess waterdown the hill. Chances are that the backyard landscapingwas done after the final inspection and the result was adisastrous financial loss to the owners. In another newerhome extending over a hillside, part of the roof drainedonto the slope, Apparently this was a late change in thedesign, or it would not have passed inspection. Again, theresult was major slope failure with great financial loss.

Even gently sloping hillsides are not immune from slopefailure. Therefore, hillsides sloping more than 5percent forany appreciable distance should not be planted to lawns.The slope should be broken up by terraces or stone walls sothat the actual lawn is level or has a very gentle slope.

Weakening the slope structure through undercutting ofits toe, as for further development below a steep property,should be avoided at any cost. Retaining walls may reduceslide hazard, but are very costly and rarely can duplicatethe stability of the natural toe of a slope. If a slope is beingundercut by a small stream, it maybe possible to rechannelthe stream and reduce its velocity in the affected area.Streambank control is often a more feasible alternative.

Vegetation, as described earlier, can reduce both wet anddry erosion. Overland erosion in the form of rills andgullies can be greatly reduced by maintaining a thickground cover on the slopes and allowing plant litter toaccumulate. Once gullies have started, they cut rapidly intothe soil mantle and should be immediately controlledthrough small check dams, stacking of cut brush, and

temporary soil-binding cover, such as grasses, Dry creepand dry ravel on steep slopes where vegetation is sparse canbe reduced by use of plants adapted to harsh sites with thinsoils; these add cohesion to the soil.

The annual weed clearing of hillsides down to mineralsoil for fire hazard reduction is a source of acceleratederosion. Weedy flash fuels such as introduced annualgrasses and wild mustard are well adapted to the climateand soils of southern California. Clearing them on a yearlybasis with handtools removes much valuable soil whileestablishing an excellent seedbed for the next weed crop,which becomes quickly established with the onset of winterrains. Motor-powered machines that use nylon filamentsfor weed trimming cause less erosion than handtools do,because a small stubble of the plant is left to protect the soilsurface. Nevertheless, yearly eradication of annual flashfuels around homes is a never-ending task; such areasshould be planted to low-growing, drought-tolerant groundcover, interplanted if necessary with deep-rooted vegeta-tion such as chaparral or carefully selected introduced treesand shrubs.

Controlling Animal ActivityRodent activity should be reduced and controlled. It

adds to slope instability by reducing the cover of low-fuelplants while weakening their root system. Water is concen-trated on the particular parts of the slope where rodentshave been active, Hillside animal pests can be controlledmost effectively by their natural enemies. If these are notpresent, cats can effectively control rodents, includinggophers and ground squirrels. Cats and dogs also manageto keep the rabbit population under control.

Occasionally, the homeowner must act to minimize hill-side damage by animals. Instruments that send shockwaves through the soil, such as noisemaker windmills at-tached to metal rods that send out electrical impulses, havebeen used with varying success on hillsides for rodentcontrol, especially for gophers. They may be worth tryingbecause they require little maintenance once installed.Control of pests that have reached epidemic proportions,such as ground squirrels, is best achieved through poisonsplaced in strategically located bait stations. Gopher poisonplaced directly into the rodent runways is effective. Adviceon the use and availability of poisons is available from thelocal office of the Agricultural Commissioner; in LosAngeles County, these offices provide rodent control ser-vice for a minimal fee based on the size of the problem andthe followup service reqllired. Some poisons can be boughtwithout a license, but in using these poisons, extreme caremust still be taken to ensure that natural predators anddomestic animals are not affected.

Trapp@g is often effective in animal control. To catchgophers, small box traps work occasionally and Macabee2

2Trade names and commercial enterprises or products are mentionedsolely for information, No endorsement by the U.S. Department ofAgriculture or the County of Los Angeles is implied,

16

traps have worked well. The Macabee traps are used toblock both sides of the major underground tunnel; thesmall box traps are placed at the end of a side tunnel.Larger box traps placed above ground and baited withapples work well for rabbits; ground squirrels prefer pea-nut butter or nuts but can also be caught with fruits,especially when these are not in season. For catching rab-bits, the traps should be hidden under larger shrubs; forcatching ground squirrels, they can be left in plain view.These traps also easily catch young gophers and otherunderground rodents when they wander above the groundin search of food. Rats, mice, occasionally a bird, and evena young curious cat, may enter the traps. Live traps such asthe “have-a-heart” traps (standard size, 30inches long by 7inches high) are also effective for the small, curious groundsquirrels. The larger traps are better suited for largeranimals.

Effectiveness of traps tends to vary with the season, theanimal, and the bait used. Maintenance of these trapsrequires frequent walking on hillsides which acceleratessoil erosion. Daily disposal of the animals is a chore thatfalls upon the trapper.

Shooting, where permissible, is also an effective way tocontrol most animal pests. Homeowners must be aware ofthe danger of firearms and must comply with local ordi-nances concerning their ownership and use.

Raptor (bird of prey) roosts are used effectively by LosAngeles County foresters to control rodents in young treeplantations. In areas where no natural resting sites, such astrees, are present, the roosts serve for sighting, attacking,and devouring of prey. A homemade raptor roost is easilyinstalled and should consist of a vertical post or pipe atleast 15feet (4,6m) tall on which a wooden crossbeam 3 to5 feet (0.9to 1.5m) long is mounted horizontally. The pipeshould be in one piece, or it may break at a joint from windaction. (A completed roost looks like an elongated letterT.)

Eradication attempts by homeowners are normally ofshort duration and poorly organized. Continuous effort isnecessary for long-term population control and hillsidesafety, as demonstrated by the following projection forground squirrels:

The projection assumes that one litter of eight young israised each year, there is no natural mortality, plenty offood is available, and the rodents can freely emigrate. Amated pair of ground squirrels present on a watershed inearly spring will then increase its population to 10 bysummer. If an eradication program is 80 percent efficient, 2animals are left at the end of the first season. If there is nofollowup campaign, the population climbs back to its orig-inal 10 at the end of the second season, to 50 the thirdseason, 250 the fourth season, 1250 the fifth season, and6250the sixth season. Because, during a lifespan of 5years,the original pair could be responsible for 6250 offspring,the initial intensive eradication campaign was responsiblefor limiting the population to 1250at the end of the fifthseason: a difference of 5000 animals. However, even the

relatively low number of 50 animals on an acre of urbanwatershed could greatly undermine the hillsides. Neigh-borhood teamwork is therefore essential to keep hillsidepests under control and eliminate the breeding populationon a regular basis. Just eliminating the young will notprevent reinfestation.

LANDSCAPING FOR FIREAND EROSION CONTROL

When a community greenbelt or a homeowner’s undevel-oped acreage is to be planted for minimum maintenanceand little irrigation, the most important considerationshould be low fuel volume. On hillsides, low-fuel Iandscapeplants should form a solid cover; they should thereforehave a spreading and not mounting growth habit. This willsuppress weeds and reduce the dry flash fuel. Droughttolerance and resprouting ability are other important con-siderations. Ground covers like ivy and vincas, low-growing shrubs like coyote brush, hedges such as oleanderand myoporum, and even a conifer like Canary Island pine(the only fire-sprouting conifer readily available from nur-series) do not need to be replanted. They all readily sproutafter fires, thereby assuring that the greenbelt reestablishesitself at little or no cost. The resprouting ability of groundcovers is extremely important on steep slopes. Chances arethat with additional watering after afire, ground cover thatwas well established can partially reestablish itself within 3or 4 months, often in time for the winter rains. Chaparralplants should not be overlooked in this respect. All aredrought tolerant and most resprout.

Scrub oak, Ceanothusspecies, chokecherry, and sugar-bush can be readily shaped into beautiful short-stemmedtrees. At distances of about 25 feet (7.6 m) or more apartthey can be kept relatively fire retardant by occasionalpruning. Oak, California pepper, Brazilian pepper, Cali-fornia laurel, sycamore, and black locust, to name a few,are trees that can be effectively blended into a landscapesetting. They all resprout after fire. However, trees gener-ally have greater fuel volume than shrubs and receive lesspruning. For fire safety, trees can be planted farther apartthan shrubs.

Often overlooked in landscaping are the vinelike low-growing natives, such as honeysuckle, which are quitedrought tolerant, have a low fuel volume, and are excellentfor slope stabilization. They will resprout after fire.Resprouting ability also allows the plant to recover fromgopher and other rodent damage.

The choice of plants for landscaping is related directly tofire safety and protection from erosion. All plants burnduring extreme fire weather conditions, specifically, hightemperatures, strong winds, and low relative humidity, Thelabeling of plants as highlyJammable, @reretardant, orfire resistant,is therefore misleading. For many years, the

17

term “fire resistant” or “fire tolerant” has been used inecological literature to denote plants that are adapted tofire and can survive it. For example, a nonsprouting pinesuch as ponderosa pine is called fire resistant because treesat maturity are protected from firekill by their thick bark.Coast live oak is a fire-resistant (fire-tolerant) tree becauseit readily resprouts from dormant shoots underneath thebark; however, a mature oak located next to a home,because of its fine dead aerial fuel that consists of twigs andbranchlets, can readily catch fire and produce flames thatare two or more times greater than its height and diameter.Some plants that do not sprout, such as MediterraneanCistus species (many of which are highly flammable butused in landscaping), and also many native Ceano[hus

Table 3—Chemical composition of 11 low-fuelplant species

Species and plant part! —

Prostrate acaciaLeavesStems

Twin peaks coyote brushsLeavesStems

Carmel creeperLeavesStems

Green galeniadLeavesStems

Descanso rockroseLeavesStems

Purple rockrose7LeavesStems

Prostrate rosemarysLeavesStems

Chilean saltbushbLeavesStems

Green saltbush7LeavesStems

Mueller’s saltbush$LeavesStems

Gray santolinaj

species are fire adapted, because they readily reestablishthemselves from seeds stimulated by fire. Thus, if properlyused and maintained, plants can reduce the spread of fire; ifimproperly used, they may increase fire spread. Properchoice of plants for landscaping depends on specific condi-tions, but must be combined with measures to improve thefire safety of the structure itself.

The term fire retardanr,as used in a flammability con-text, means that the plant so described is less flammablethan another that contains the same amount of fuel. Thisdifference may be due to the proportions of live and deadfine fuel present, to the oil and mineral content (ash) of thefoliage, to the percent fuel moisture, or to the age of theplants. For example, the needles of plants like pines, cham-

Moisture Crude Crude CrudeLength, typej content~ Ash’ fat~ protein4 fibed

12 in,, H to SW

4 in.. H to SW

H to SW

8 in., H to SW

H to SW

H to SW

8 in., H to SW

Sw

Green to H

4 in., H to SWComDosite

275215

335277

225200

221198

226187

239226

349242

337216

527401

392353322

2.51.9

4.33.9

2,62.3

10.910.0

7.12.6

7.25.3

4.33.2

10.53.3

9.26.5

10.58.19.1

Per(ent

5.86.4

9.85.2

4.32.5

3.51.5

3.32.1

4.54.2

12.14,2

3.3I.4

1.91.1

2.51.8

111

16.210.9

14.78.3

10.85.7

18.212.1

10.15.7

10.56.4

8.83.3

24,313.1

27.112.3

20.612.516,4

15,730.7

I 1.721.1

14.126.5

9.717.8

26.513.5

13.128.9

15.147.3

6.329.1

8.326.4

7.324,716.6

ILate fall growth of tip cuttings consisting of leaves and small twigs was analyzed.Large seasonal !ariations in moisture content and fat, protein and fiber contents areoften encountered.

2H = herbaceous, SW = semiwoody, W = woody, Composite ❑ herbaceous to semi-woody tip cuttings consisting of leaves and stems.

]Moisture content of the living plant sample as percentage of its oven dry weight.4Percentage of dry residue in relation to the total oven dry weight of plant sample.SPlants that are inherently flammable (high oil content) but low in fuel volume.dFire retardant plants: low in fat (oil) and high in ash.7Arelated species, gum rockrose, which grows 6 to 8 feet tall, is often recommended

for low fuel planting, but it has a high crude fat content ( 14.9 percent) and is highlyflammable.

Table 4—Heat values of four w,ildlandfuels

Species, fuel type

Annual grassEarly greenIn bloomMature, dry

Blue gum eucalyptu!Leaf litterBarkDuffBranches/twigs

ChamiseLeavesTwigsBranches

Scrub oakLeavesTwigsBranches

Heat value

Kcal/g Btu/lb

o.41g 7531.668 3,0053.956 7,128

5.732 10,3284.616 8,3175.454 8,2724,591 8,272

5.439 9,8005.009 9,0254,742 8,544

4.571 8,2364.480 8,0724,490 8,090

Source: Agee and others 1973

18

400 -

100 -90-80-

Figure 10-Seasonal fuel moisture content 70-of foliage (leaves and current year’s stem 60-growth)of sevennativeand introducedshrub 50-speciesvarieswidely among species,and by Aug. Septseason. 7971

.................... Allscale saltbush—-— Fourwing saltbush-------- Creeping sage

Descanso rockrose ..”””””’”.Rosemary

... ..— -- ...--------- Chamise ...

..””“....

...

..”” ...... ...

.......””

,~4\...”

/

.../:,#,””..#..

......”

..””/

#t...” It..” #

/

IR.....”” It

--&’ ,1”......

,..

./ .I I I I I I I (

ise, and rosemary have a high oil content and fine fuelcharacteristics. They are therefore inherently more flam-mable during the fire season than saltbushes, which havebroad leaves and lower oil content, with higher ash content(table 3). Other plants fall into intermediate categories.

Some other plants used in landscaping may be just asflammable as chamise, one of the most flammable chapar-ral species. The heat content of bluegum eucalyptus iscomparable to that of chamise (table 4). So, once ignited,both species may burn equally hot, and the eucalyptus maypresent added problems of greater fuel volume and litterproduction. During the 1977 Santa Barbara Fire, 244houses were lost when sundowner winds (downhill eveningwind patterns) carried the fire from tree to tree and fromone wood shingle roof to another.

Live fuel moisture is important because plants withhigher fuel moisture ignite less readily. For example, thelive fuel moisture of many saltbushes that are recom-mended as “fire-resistant plants” is higher than that of mostchaparral species except for succulents. Live fuel moisturecontent of such wildland fuels may be low from June toNovember and high from December to April wig. 10).Thelate summer and fall Santa Ana (fire winds) coincide withthis period of low fuel moisture. Within a few hours thedry, hot winds can reduce fuel moisture of fine dead plantmaterial to the critical level for ready ignition and canfurther decrease live fuel moisture by a few percentage

Oct. Nov. Oec. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct

1972

points over several days. The amount of fine, dead fuelsdetermines rate of fire spread because such fuels dryrapidly, ignite quickly, and preheat live fuels to the ignitionpoint.

It is clear, then, that inherent fire-retardant characteris-tics of landscape plants cannot be depended on to preventignition during severe fire weather. Young plants and newshoots on pruned plants have a high moisture content, andcan be considered slow burning (fire retardant), but asthese plants become older and more woody and theamount of dry fuel and dead litter increases, they becomemore flammable. This fact may explain some of the con-tradictory literature about “fire retardant” plants. Forexample, old man saltbush is often recommended in Cali-fornia as a fire-resistant plant. In Tunisia, the plant isgrown as firewood because it is excellent for baking breadin the traditional domestic ovens and also for charcoal. Inwell-managed, nonirrigated plantations, it can produce upto 17 tons/acre (38.25 t/ha) of firewood during the firstyear after outplanting, and 30 tons/acre (67 t /ha) within 2years (Franclet and LeHouerou 1974).With irrigation, thewood production is even higher. In Australia, where theplant is browsed periodically by sheep, it is kept vigorous,and does not readily contribute to fire spread.

Other plant species often mislabeled as fire resistant orfire retardant are rosemary, coyote brush, and rockrose.The foliage of these plants has a high oil content, and once

19

ignited burns readily. Nevertheless, these plants aredrought tolerant, esthetically pleasing, very versatile forlandscaping, generally low growing (except for gum rock-rose), and well adapted to southern California’s climate.Their rooting depth approaches that of coastal sage spe-cies. Prostrate coyote brush resprouts readily after a fire,and it is an excellent candidate for erosion control on thesteeper hillsides as it does not require replanting after fire.

The fire resistance of plants is relative and depends onfuel moisture and the amount of dead fuel. Generally, alow-growing plant has an inherently lower fuel volumethan a taller plant, and therefore has less fine dead fuel.Two key factors of fire control and fire safety are relateddirectly to low fuel volume:fueldiscontinuity, whereby thecontinuity of any flammable cover is broken up, andreductioninfuel load,whereby plants are pruned and deadfuel is cleared away.

The low fuel volume objective suggests creation ofgreenbelts around subdivisions and individual homes. Asspace permits, these areas could include flammable fuelssuch as chamise, eucalyptus, coyote brush, and rosemary,as well as relatively fire-resistant fuels such as ice plants.Aerial fuel (trees) can be kept reasonably fire retardantthrough periodic pruning; however, the general tendency isto leave them unpruned and they are therefore more flam-mable and carry fire more readily than low-growing plants.Conifers should not be planted close to a home, becausetheir needles have a high resin content, provide fine fuels,are quite flammable, and are likely to be on the roof whenfire strikes. However, both conifers and broadleaf treesplanted a distance away from the home can serve theimportant function of channeling the initial convectionheatwave away from a home and thereby perhaps saving it

(assuming, of course, that the flames from the burning treescan be extinguished before they ignite the house).

Brush clearance ordinances are based on the low fuelconcept and are good guidelines for reducing fire hazard.They are self-defeating if they do not take into account theincreasing flammability of many landscape plants as theygrow and mature, and ignore the danger of potential slipsand slides on steep slopes owing to the removal of thedeep-rooted chaparral vegetation.

Establishing GreenbeltsHomeowners trying to comply with the brush clearance

ordinances and faced with a brush surcharge on their fireinsurance policies should reduce the unwanted native vege-tation in an ecologically sound way. They must realize thatit may not be possible to reduce flammable fuels-on slipareas and on erosive, steep, and unstable terrain to thepoint of receiving a favorable insurance rate. The addedexpense of paying the surcharge then becomes one of thecosts of living with nature and may be much cheaper, evenin the long run, than slope failures caused by improper orexcessive clearing of native vegetation.

There are several alternative methods of reducing flam-mable fuels and establishing a greenbelt. The first is toeliminate the native vegetation and relandscape a greenbeltbuffer strip of 100 to 200 feet (30.5 to 61 m) around thehome. This practice may also be the only possible solutionwhere the developer or builder has already eliminated mostof the native plants, or where, because of harsh climate orsite characteristics, only highly flammable vegetationexists. This method is effective if the native plants can bereadily replaced by drought-tolerant vegetation of less fuel

Figura n-Native plantscan beused effectively as foundationplants in landscapes. To sepa-rate ground fuels from aerialfuels, prunethelowerbranchletsand thin the plant. Yearly lightpruning can make it difficult forsuch plants to burn and supwrta fire.

volume and similar rooting characteristics. Moreover,more gentle terrain with deep soils is often well suited forthe establishment of a wider greenbelt buffer zone that mayinclude recreational facilities and commercial agriculturesuch as orange or avocado groves. This requires strongcommunity support and long-range planning but may bethe most effective way of separating wildland fuels fromflammable structures.

A second alternative for landscaping in wildland areas isto reduce the fuels of the native vegetation and use theremaining plants as foundation plants in the landscapesetting ~ig. 11). To do this, an expert familiar with thenative plants of the area should be consulted to oversee theselection of plants, thinning, pruning, and relandscaping.All native vegetation that is not to be removed during theinitial thinning should first be identified. The unwantedvegetation should then be removed. The consultant who isselected should be well trained in the principles of pruningfor fire safety and should oversee the pruning of all desira-ble woody overstory plants into upright short-stemmedtrees. On multistemmed plants, several stems should beselected and the plant so pruned that a fuel separation iscreated between the overstory canopy and the groundcover that is to be planted next. This method works well inareas where the native vegetation has not been disturbed byfire for about 7 to 10years, and where the fire frequency islow.

The careful selection of native plants as a foundation forlandscaping is critical, because of differential wateringrequirements, differences in year-round appearance,growth, flowering habits, resprouting characteristics, androoting depth. For example, native mountain lilacs (Cea-nothus species) come in many shades of color from white todeep blue, and even the highly flammable chamise, left as aspecimen plant, is delightful when displaying its attractivewhite flowers. Chokecherries, toyon, elderberry, and Cali-fornia walnut provide food for wildlife. When there isdoubt about what plant to retain, it is best to choose asprouting plant over a nonsprouting one.

Native understory plants can add accent to the landscapesetting but can also act as ladder fuels to the woody over-story vegetation. Highly flammable plants such as sages(white, black, purple), buckwheat, California sagebrush,and deerweed should therefore be eradicated whereverpermanent slope stability permits. Woody perennials suchas fuchsias and gooseberries and even woody-based peren-nials such as sunflowers that die back to the base every yearshould be included in the landscape setting because theyare low-fuel plants with showy flowers and provide foodfor wildlife. Perennial grasses should not be eradicated.

Once thinning and pruning of native plants is completed,erosion netting should be spread and anchored on steeperslopes and erosive soils. This is especially critical if slow-growing ground cover such as coyote brush is interplantedamong the native plants or if the ground cover chosen willnot grow fast enough to cover the soil surface by late fall. A“noncompetitive” protective cover crop such as alyssum

can be sown in the fall for temporary control of surfaceerosion and rilling. When heavy first-year planting failureshave occurred through such conditions as lack of propermaintenance, rodent activity, or browsing, it may be neces-sary to sow highly competitive annual grasses with thecoming of the winter rains. These should be immediatelyeradicated in the spring, when replanting should begin.

Ideally, the greenbelt should be established early inspring, or even towards the end of winter, when soil mois-ture has been fully recharged through rainfall. Regularwatering will be needed to get the plants established, espe-cially the ground covers planted from flats, as these have avery shallow root system at first. Early establishment pro-vides a better rooted cover before the hot weather andsummer drought return. With this technique, less wateringis required during the summer, and water can be withheldfrom plants earlier in the fall. The soil moisture is then wellbelow field capacity when the winter rains return. Well-established plants several years old should not receive deepwatering after mid-September. If plants are not establisheduntil summer, more frequent watering is needed and anabundant late weed crop may compete vigorously with theplanted stock.

When planting is done in early spring at the end of therainy season, weed killers or preemergent herbicides thatselectively kill spring weeds can be used to full advantage.A reduced crop of winter weeds will still germinate andhelp cover the slope until the ground cover becomes fullyestablished. Using selective weed killers for fall planting onhillsides is not advisable unless slopes are covered with jutematting, because the newly established ground cover willnot prevent excessive erosion. For hillside use of preemer-gent herbicides or herbicides that kill the seedlings as theygerminate, follow these four rules:

1. Select a herbicide that does not affect the plantedstock.

2. Treat a small test area first.3. Always use less than recommended.4. Do not use a preemergent herbicide whose effective-

ness lasts for more than one season.

Maintaining Compatibility of PlantsA critical concept when establishing a greenbelt is the

compatibility of landscape species and native plants, espe-cially in regard to watering and maintenance requirements.

Information on the compatibility of existing nativeplants and introduced species is scant, but the moisture andhabitat requirements of native plants often provide a clueto their tolerance. In general, native plants found in moistcanyons and draws have a higher tolerance to landscapeirrigation than plants on north and east slopes. These, inturn, seem to have a higher tolerance than plants on harshexposures such as south-to-west slopes and thin soils.

Among individual species, those with higher moisturerequirements also seem to have greater tolerance to lands-cape irrigation than the most drought-tolerant species. The

21

time and amount of watering also plays a critical role.Occasional deep watering during the summer at nighttimewhen the exotic plants show signs of wilting, such as droop-ing of leaves, is less damaging than intermittent, moreshallow watering in the daytime. Heat and moisture bothencourage root rot, so that plants growing in heavy soils,such as those with a high clay content, or in dark soils thatheat up more readily, seem to be most affected. Examplesto clarify the above points are given below.

Sumac species, such as laurel sumac, sugarbush, andlemonade berry, are quite drought tolerant and deeprooted. These native plants make excellent landscape spec-imens, but do not tolerate the watering required wheninterplanted with more water-demanding plants. The com-bination of sumacs with a surrounding groundcover ofAfrican daisy, ivy, or vinca is likely to result in root rot anddeath of the sumacs within a few years because regularwatering is normally required to keep these ground coversalive. On the other hand, interplanting the sumacs withTwin Peaks coyote brush for groundcover may not adverse-ly affect the sumacs if the coyote brush is watered onlyenough to keep it alive. Native oaks are also very suscepti-ble to watering of an understory ground cover or surround-ing lawns. A good technique which allows the use of morewater-demanding plants is to keep an unplanted andunwatered buffer near the base of the intolerant shrubs andtrees. However, situations can be found where the above-named plants seem to be compatible with landscapeground covers. Examples are long, steep slopes on north oreast exposures, where, due to deep soils, water seepagefrom above and the shading of the native plants, the under-story groundcover needs little or no watering. These situa-tions are common when one owner has managed the prop-erty for many years. A change of ownership and a differentmanagement regime that results in increased watering maycause root rot and mortality of the woody native species.The soil around most native plants is normally well aeratedand covered with litter and humus. Soil compactionaround these plants may therefore also affect them moreadversely than it would landscape plants.

Laurel sumac is of great interest in landscaping withnative plants because it is an excellent soil binder on steeperslopes and harsher sites. Its prolific resprouting ability andfast growth enables it to survive in areas of repeated distur-bance by fire and grazing. This resprouting ability fromroots and root crowns makes it a nuisance plant in alandscape setting. However, once the soil surface aroundthe plant is shaded with a noninvasive ground cover such asTwin Peaks coyote brush, and any disturbance has stopped,the resprouting will also greatly decrease or stop. Thisgreatly reduces maintenance. When laurel sumac andsugarbush grow close to each other on nonerosive, moder-ately steep slopes, it may be better to select sugarbush as afoundation plant because it is usually much slower grow-ing and does not require regular maintenance. It is alsoesthetically more pleasing throughout the year. Further-more, laurel sumac is not cold-tolerant and freezes. All of

the sumacs tend to be susceptible to insects and disease andpruning of dead material is therefore recommended.

On steep, erosive slopes, laurel sumac should not bereplaced with landscape plants. For its fuel volume, theplant is one of the deepest rooted and most drought-tolerant plants available to the homeowner. Its reputationhas been tainted by labeling as extremely flammable,because the species has been observed during wildfire asbursting into flames. Actually, in comparison to manyother chaparral species of the same stature, fuel loading,and age, individual plants are quite fire-resistant. Exceptwhen the plant freezes, the dead-to-live fuel ratio is oftenmuch lower than that of other species. More important,perhaps, in fuel moisture it ranks among the highest ofnative plant species during the high fire weather conditionsencountered in late fall. (Under wildland conditions, highfuel moisture of leaves and stems requires that the plant bepreheated to higher temperatures, than for example, cham-ise, mountain mahogany, and most Ceanothusspecies, inorder to ignite or burst into flames.) Once the surroundingfuels are removed and laurel sumac is pruned to treelikeform, the understory vegetation rarely will preheat it to theignition point. Leaves may be totally scorched by the heatof the fire, without the plant carrying the fire. Thus, thedifferent ignition requirements of individual species andplants are the key to flaming and firespread.

Choosing Low-Growing Species

Ideally, plants should be selected for these qualities: (1)low growth habit, (2)drought tolerance, (3) fire retardance,(4) deep rooting habit, (5) esthetically pleasing effect, and(6) compatibility among different species wig. 12). Theusefulness of some commonly used low growing landscapeplants and other plants in particular situations, withemphasis on southern California, was evaluated accordingto their suitability for various sites and conditions, growthcharacteristics, and fire retardance (table 5). The table is ageneral guide, but cannot substitute for onsite professionalopinions rendered by expert consultants familiar with spe-cific sites and problems. Homeowners who must deal withindividual landscaping problems should make their owndecisions from the table and descriptions, using the generaladvice on fire safety and more effective watershed man-agement given elsewhere in this report.

The plant species listed, except where indicated, are ableto forma solid ground cover for the slopes recommended.However, there is no guarantee that the species preventslippage when the soil becomes saturated. Interplantingground covers with shrubs and trees, as discussed earlier,will maximize slope stability. Landscape plants that requirehigh maintenance or that are readily browsed, such as mostprostrate Ceanothusspecies, are not included in table 5.

The columns in table 5 headed “aspects,” “soil depth,”and “if irrigated” should be read as a unit. The values forsoil depth apply to medium textured, loamy soils. Thosefor irrigation apply to coastal regions of southern Califor-

22

&

Figure 12—A greenbelt of coy-ote brush surrounds the houseat the top. Trees provide addedslope stability, but will increasethe fire hazard as they grow. Agreenbelt of African daisy plantsprovides minimal fire safety forthe flammable house at the bot-tom. The probability of damagefromfireand soilslippageishigh,

23

w& Table 5—Evaluation of 20 low-growing planrs used in wi[dland-urban hillside Iandscapingl

Species

Aaron’s beard

Acacia ongerup,prostrate

African daisy

Algerian ivy(freeway ivy)

Australiansaltbush

Capeweed

Carmel creeperceanothus

Effective . Characterized by

On aspects At soil depths If irrigated At Growth Fire Re- Rooting CommentsIn slopes (degrees) (feet) . . . summer elevations habit, retardance sprouting depth (ft)

<25 25-35 >35 N-E s-w <I 1-3 >3 to fa112 (feet) height (inches) ability (effective)

x x >2 M Low maintenance.Little foot traffic. Spreads byx x IMx x

underground runners. Good soil binder. Invasive if2-3 S up to Spreading If

Xxz xxwell watered. Yellow flowers. Draws bees. Sun to

IW 4000 shrub, Medium watered <3x x

shade.<1 w 12-24

x x IM

x x <1 M Low maintenance. No foot traffic. Showy yellowx x Low; flowers. Draws bees. Most drought-tolerant andx x o up to Spreading decreases quickest-spreading woody plant tested. Full sun.

XXY xx >1 M 2000 shrub, with increase Poor >6 Spreads to more than 8 feet in diameter in full sunx x 12-30 in fuel and deep soils.x x 1s

x x 2M Moderate to high maintenance. Tolerates some footx x traffic. Showy white flowers and other hybrid colors.x Y <1 M up to Trailing Medium If Freezes at 25”F. Fertilize and water regularly. Full

XYZ Yx IW 2000 groundcover, to watered 3x

sun to partial shade.x 2M <12 high

x x 1-2 M

x x IW Low maintenance. Tolerates foot traffic. Excellent forx x IM minimizing erosion on long, steep cuts. Leaves willx Y 2s up to Trailing If burn if watering is neglected. Excellent understory to

XXY YY 2000 groundcover, Medium watered 34 a variety of trees. No flowers. Full sun to shade.x x 2M 8-12x x IM

x x 1s Low to medium maintenance. Moderate foot traffic.x x o Readily established from seeds. Naturalized on harsh,x z up to Trailing Generally Resprouts rocky sites. May not form persistent solid cover

XXY xx 1-2 s 2000 groundcover, high even on 34 because it is affected by disease if overwatered orx x o to 12 dry sites crowded (variety corra may be disease resistant). Rel-X x 0 atively short lived (5 years +). Full sun (no north

slopes).

x x 1-2 M Very low maintenance. Takes occasional foot traffic.

x x IM Showy yellow flowers. Weedy in manicured setting.x x 2s up to Spreading If Frost sensitive. Draws bees. Spreads by runners. Full

XY xx 2M 2000 groundcover, High watered I-3 sun to partial shade.x x IM 6-8x x <1 M

x x <1 M Moderate maintenance (renovate occasionally byx x <1 M Low to med- If thinning old branches). No foot traffic. Readilyx x 2s up to Spreading ium; decreases watered browsed. Showy blue flowers. Draws bees. Full sun

XXY xx IM 4000+ shrub, with increase after light 6 to partial shade.x x <1 M 18-30 in fuel firex x <1 s

.“ -.

Table5—Evaluation of 20 low-growing plants used in n,ildland-urban hillside landscapinft (Continued)

Species

Coyote bush(brush)

Creeping sage

Descanso rockros

Green lavendercotton

Ice plants

Lippia

Periwinkle

1< = less than

Effective Characterized by

On aspects At soil depths If irrigated At Growth Fire Re- Rooting Comments

)n slopes (degrees) (feet) summer elevations habit, retardance sprouting depth (ft)

<25 25-35 >35 N-E s-w <1 I-3 >3 to fall? (feel) height (inches) ability (effective)—

x x <1 M Prune back every 5 years or less often. No foot traf-

X x fic. Inconspicuous flowers. Hard to establish from

x x o up to Spreading flats in midsummer. Healthy green color. Sensitive to

XXY YY >1 M 4000 shrub, Low Vigorous 6 herbicides. Full sun. Spreads to more than 5 feet

x x 12-24 across in full sun and deep soils.

x x Isx x >1 s Low maintenance. Tolerates some fnot traffic. Stem

x x o layers readily. Prefers acid soil. Excellent understory

x x o 2ooo- Trailing Medium If in pine plantations. Readily killed by overwatering

XXY Xz 6000 groundcover, to watered 34 and heavy soils. Sensitive to herbicides. Needs exten-

X x >1 s <6 high sive seed scarification. Showy blue flowers, Draws

x x Is bees.Sun to shade.

x x IM Medium to low maintenance. No foot traffic. Showy

x xx x

pink flowers; draws bees. Ground cover for easily

o up to Semi-upright Low accessible dry site areas. Attractive if watered; unat-

Xxz xx <;2 M 4000 shrub, to Poor 3-4 tractive if not maintained. Full sun.

x x 12-24 medium

x x 1-2 s

x x IM Medium maintenance. No foot traffic, Does not stem

x x layer. Excellent for border effect. Clip back dead

x x o up to Semi-upright Low Resprouts flower stalks every year to maintain higher fire

Xxz xx 2M 4fm3t3+ shrub, to even on 3-5 retardance. Yellow flowers. Draws bees. Full sun to

x x 16-30 medium dry sites partial shade.

x x <1 M Low maintenance. Nn foot traffic. Showy multi-

X Y colored flowers. High foliage moisture and weak root

x x o up to Trailing Generally Depends on system causes slippage on steeper slopes, especially

x See text xx IM 2000 groundcover, high severity I-2 fills. Full sun to partial shade,

x Y 4-18 of fire

x Y ‘l-2 s’

x x 2M Low maintenance. Tolerates foot traffic. Takes neg-

X x Iect and will recover with watering. Good soil binder

x x <1 s up to Trailing If among pruned shrubs. Excellent drysite lawn. Lilac

XYZ xx lw 2000 groundcover, High watered <3 to rose flowers. Draws bees. Mow off flowers to elim-

X x <4 inate bees. Full sun to partial shade.

x x >2 M Low maintenance. Occasional foot traffic. Showy

x x up to Trailing If blue flowers. Does well under partial overstory where

Xxzx x <1 M 4000 groundcover, Medium watered 3

Y x

somewhat neglected. Excellent understory ground

<18 cover. Sun to shade.

x x 1-2 M

ZO= None

> = greater tban I = Once

X = suitable 2 ❑ Twice

Y = not totally suitable W = Week

Z ❑ not recommended M = Month

S = Summer

No entry ❑ intermediate watering schedule (see entry above or below)

Table 5–Evaluation of 20 low-growing plants used in wi[dland-urban hillside Iands<apingl (Carrlinued)

Species

Point Reyesceanotfrus

Prostrateceanothus

Prostratemyoporum

Prostrate rosemar

Silver saltbush

Wavy leaf saltbusk

1< = less than

Effective Characterized by

On aspects At soil depths If irrigated At Growth Fire Re- Rooting Comments

In slopes (degrees) (feet) . summer elevations habit, retardance sprouting depth (ft)

<25 25-35 >35 N-E s-w <1 1-3 >3 to fa112 (feet) height (inches) ability (effective)

x x <1 M Moderate maintenance (renovate occasionally byx x thinning old branches). No foot traffic. Readilyx x o up to Spreading Low browsed. Showy bright blue flowers. Draws bees. Full

XXY XY IM 4000+ shrub, to Poor 6x

sun to partial shade.x 8-24 medium

x x 1s

x x >1 s Low maintenance. Tolerates some foot traffic. Stemx x 1s layers readily. At lower elevations in southern Cali-X x 0 4ooo- Trailing Generally fornia plant prefers north slopes. Best on coarse tei-

XXY XY <1 M 7000 groundcover, high No 34 tured soils. Needs extensive seed treatment. White tox x o >4 blue flowers. Draws bees. Sun to shade.x x o

x x IM Low maintenance. No foot traffic. Stem layers. Whitex x flowers. Draws bees. Full sun to partial shade.x x 2s up to Spreading Generally

XYZ xx 2M 2000 groundcover, high No 3x x <6x x <1 M

x x <I M Low maintenance. No foot traffic. Stem layers read-X xx x

ily. Hardy plant with dark green needle foliage.1s up to Spreading Low; decreases Showy blue flowers. Draws bees. Prefers full sun.

XXY xx 2M 4000+ shrub, with increase No 3-5x x 12-24 in fuelx x <1 M

x x Is Moderate maintenance (renovate occasionally). Nox xx o Low to med- Without foot traffic. Stem layers, underground runners. Seedsx x o up to Spreading ium; decreases water germinate readily and are preferred by birds. Deer

XXY XY 2s 2000+ shrub, with increase after 6 browsing maintains vigor, low growth, greater firex x o 16-30 in fuel light fire retardance (less fuel). Loamy to sandy soils. Flowersx x o inconspicuous. For dry site landscaping away from

house. Full sun.

x x 1s Moderate maintenance (renovate occasionally). Nox x o Low to med- Without foot traffic. Stem layers. Moderately browsed whenx x o up to Semi-upright ium decreases; water young. Avoid heavy soils. Flowers inconspicuous.

XXY XY ‘2 s’ 3000 shrub, with increase after 6-9 Good for dry site landscaping away from house, Fullx x o to 36 in fuel light fire sun.x x o

ZO= None> =.greater than I = Once

X = suitable 2 ❑ TwiceY = not totally suitable W = WeekZ = not recommended M = Month

S = SummerNo entry = intermediate watering schedule (see entry above or below)

nia and attempt to show relative watering needs of theplants listed. These values assume that soil moisture isrecharged to 12-inch (30.5 cm) depth during watering. Inreality, this goal is rarely achieved through overhead water-ing because of sprinkler design and time period necessaryfor irrigation. The effective rooting depths indicated in[able5 are based on moisture withdrawal by roots after soilmoisture has been depleted in the upper soil layers.

The term “fire retardance” as used in table 5 reflectsdifferences in fuel volume, inherent flammability charac-teristics of the plant, and ease of fire spread. For example,under extreme autumn fire conditions, on steep slopes withnongusting winds of 30 mph (48.3 kph), a 2-foot (61 cm)tall solid ground cover with “high” fire retardance isexpected to produce a flame less than 10feet (3 m) long andto reduce the rate of fire spread. Under similar conditions,a plant with “low” fire retardance may ignite readily, willcarry the fire, and can produce flames approaching 25 feet(7.6 m) in length. For comparison, mature chaparral underthese conditions can produce flames exceeding 80feet (24.4m) in length.

The following example for capeweed will illustrate theuse of table 5. Column 1 shows that the species is mosteffective for planting on slopes not exceeding 25°, but maybe used on a limited scale on slightly steeper slopes. Theshallow root system of capeweed may trigger soil slippage.The next three columns of data are to be read as a unit andshow the relationship between aspect, soil depth, and irri-gation requirements. For example, the first line shows thaton a north-to-east aspect with less than 1foot of soil depth,established plants require summer irrigation once or twicea month.

The importance of microclimate should be kept in mind.A north or east slope provides an opportunity for using lessdrought-tolerant plants, such as vinca or ivy, whereas theharsh south- and west-facing slopes are best suited for themost drought-tolerant plants. Canyons and valleys pro-vide for a wide choice of plant species, but may alsoincrease the danger of frost due to cold air drainage.

Plants suitable to landscape needs can be identified bytheir performance in the neighborhood. Comparisonsshould take into account such variables as steepness andexposure of slopes, soil type and depth, and wateringschedule. Further advice is available at nurseries and inliterature on landscaping in California (Williamson 1976).The plants described in the rest of this section are ratedaccording to the six qualities listed earlier.

IcePlantsIce plants (Carpobrotus, Delosperma, Drosanthemum

spp.) generally are rated excellent in low growth habit, fireretardance, and esthetics, but fail in deep rooting habit.The coarse-leaved “freeway ice plants” (Carpobrotus,for-merly classified as Mesembryanthemum) are recom-mended for soil binding of marginal, seldom-watered butnot steep areas; white trailing ice plant (Delospermaalba)for soil binding of steeper slopes, and finally Drosanthe-

mum species for soil binding of steep slopes even where soilis very poor (Williamson 1976). Professional landscapersrecommend ice plants for extensive plantings on slopes assteep as 25° or more and these plants do an admirable jobmost of the time. However, when high-intensity stormsoccasionally follow each other in short order, dumpingadditional rain on supersaturated soils, by far the greatestproportion of soil slips in landscaped areas occurs onslopes planted with ice plant, As a general rule, a writtenopinion by a geologist should be obtained before ice plantsare used extensively on landscaped slopes of more than15°. Exceptions are extremely harsh slopes where only iceplants would grow anyway. Ice plants are so extensivelyused because the plants cover quickly, soon giving theappearance of a completed landscape job. Unfortunately,the combination of a weak root system with high foliagemoisture that adds weight may produce slope failures (Ilch1952).

CoyoteBrushCoyote brush (Baccharispilularisvar. prostrata or cul-

tivar Twin Peaks) rates excellent in drought tolerance,deep rooting habit, and esthetics. Its flowers are inconspic-uous. The plant is prostrate to semiprostrate but is deeprooted and quite drought tolerant. In coastal areas ondeeper soils it requires little, if any, summer watering.Mature coyote brush is highly flammable once ignited butresprouts readily after fire. It is therefore recommended forsteeper slopes even in chaparral areas because its highflammability is countered by its relatively low fuel volume.The plant should not be planted too close to the house,however. Initially slow growing and therefore hard toestablish, a 5-year-old plant may measure 6to 8feet (1.&t>2.4 m) in diameter on better soils, and its compact growthwill eliminate weeds almost completely. Plants will moundafter they have grown together and thinning out may berequired. When coyote brush becomes overmature andquite woody (usually within 5 to 10 years, depending onsoils, watering, and exposure) it should be cut back to a fewinches above the base in the springtime toward the end ofthe rainy season. Regrowth will be rapid, and during theregrowth period the plant will be essentially fireproof.Most of the slope will again be clothed before the rainsarrive; thus, occasional renovation of coyote brush shouldbe considered. Only the prostrate variety is recommended.On slopes, it does not exceed 12to 18inches (30.5 to 45.7cm) in height. Other varieties may grow to be more than 4feet (1.2 m) tall.

RosemaryThe prostrate variety of rosemary (Rosmarinusofficina-

Zis)also rates excellent in drought tolerance, deep rootinghabit, and esthetics, but does not spread as extensively ascoyote brush and therefore should not be used for large-scale slope plantings where weed control is necessary. It isalso highly flammable but has low fuel volume (semipros-trate). It will not resprout. Its blue flowers are quite attrac-tive and lure bees.

27

ProstrateAcaciaProstrate acacia (Acacia rodelens cultivar ongerup)

rates excellent in drought tolerance, deep rooting habit,and esthetics. Mature plants are flammable and have agreater fuel volume than prostrate coyote brush. Wherefire danger is not great, in many ways the plant is superiorto coyote brush. In coastal regions it is the most drought-tolerant, quick-spreading, low-growing woody plant testedunder wildland conditions. With adequate rainfall andgood soils, it can forma thick mat 3 to 4feet (0.9 to 1.2m)in diameter within 1 year and up to 15 feet (4.6 m) indiameter within 5 years. In late spring the plant is coveredwith showy yellow flowers. It may mound to 4 feet (1.2 m)high (thereby greatly increasing fuel volume), if its growthis obstructed. Thinning is then required. This species is themost underrated and underplanted species for greenbeltestablishment that our research has encountered in 5years.Its one drawback is the lack of resprouting ability; how-ever, some of its seeds develop true to the prostrate habit.

RockroseMany species of rockrose (Cisrus spp.) are available.

They are rated good in drought tolerance and esthetics,and have beautiful showy white or pink flowers. In growthform they range from semiprostrate to over 6 feet (1.8 m)tall. The genus is flammable but generally has low fuelvolume; the major exception is gum rockrose, which hasthe highest oil content (crude fat) of any plant listed intable 3, The genus is recommended for border effect butnot for mass planting because its semiprostrate-to-uprightgrowth form does not eliminate weeds. It also aids fire-spread (Laure and others 1961, Martin and Juhren 1954,Olsen 1960).

PeriwinkleThe Vincas( Vincamajor, V.minor) are rated excellent

in low growth habit, and esthetics. They are fairly deeprooted and somewhat drought tolerant. They form anexcellent weed-free cover, will readily resprout after fire,and have showy flowers. Vincasare well adapted as anunderstory cover to deep-rooted vegetation, especially onnorthern and eastern exposures when deeper soils are pres-ent. Without an overstory, they may require frequentwatering in the summer. The taller-growing periwinkle( Vincamajor) is more drought tolerant and is a better soilbinder on slopes than the smaller-growing dwarf runningmyrtle ( V. minor). On fertile soils with ample soil mois-ture, periwinkle covers the soil faster than any other spe-cies discussed in this section. However, it can become anunwanted nuisance similar to ivy.

IvyAlgerian ivy (Hederacanariensis)and English ivy (Hed-

erahelix) are the two species of ivy most commonly used inlandscaping. They form an excellent weed-free cover.Algerian ivy, known as freeway ivy, is more commonlyplanted and also more drought tolerant and more deeply

rooted than the more dainty English ivy. Because of itsaggressiveness, it may be considered a nuisance in mani-cured landscape settings and it chokes out other plants.However, because of its climbing habit, it can effectivelycover old fences and keep them standing, and reduce ero-sion scars on very steep slopes as it climbs downward, It isexcellent for erosion control and its fuel buildup with age isnot considered a major problem if the plant is kept awayfrom the home. Frequent watering is required in summer.The daintier-looking English ivy is more shallow rooted,and also needs constant watering in the summertime or itsleaves will be sunburned. It should, therefore, not beplanted on south slopes or in harsh areas and does bestunder partial overstory.

AfricanDaisyAfrican daisy (Osteospermumfruticosum) is a trailing

ground cover with very showy flowers. It is somewhatdrought tolerant but is best planted in full sun and onmoderate slopes with good soil and ample soil moisture.Overwatering in hot weather may cause disease, This plantis not suitable for harsh cut slopes or other harsh sites, suchas south-to-west exposures with thin soils. It does best inthe vicinity of the coast and freezes at about 25° F (-4° C).After fires, it reestablishes prolifically from seeds. Two tothree years after establishment, it may require regularmaintenance such as fertilization and thinning of diebackcaused by drought, cold, and fungus.

Watering Plants

Proper watering is the key to maintaining healthy andfunctional plants anywhere, even in a drought-tolerantgreenbelt in the chaparral-urban watershed. Ideally, such agreenbelt should require no supplemental irrigation, buteven the most drought-tolerant plants require a minimumamount of rainfall for survival.

A practical rule of thumb is that most drought-tolerantlandscape shrubs can survive on %inch (12.7 mm) of waterper week during the hot summer months but may require agreater amount of water where esthetics are important.Most other landscape plants can survive on about 30inches (762 mm) of supplemental irrigation per year. Sincethe average household uses more than 60inches (1524mm)of watqr per year for landscape irrigation, this represents atremendous saving to the homeowner as well as to society.In California, where future water shortages are foreseen,such saving has great importance, and can be achievedsimply by sharply reducing and thoughtfully regulatingwatering in the late winter and spring months when plantshave plenty of ground water.

Water-SavingPlantsWhen soil moisture is recharged to field capacity late in

the season, even chaparral plants can be moderately heavywater users. They can transpire more than 5 inches (127mm) of water per month (zab/e6). Most chaparral plants

28

are true water savers (hydrophytes), however, and are ableto conserve water by restricting transpiration before per-manent wilting occurs; they may become dormant in thesummer (table 6). Miller (1979) showed that in a stand ofchamise chaparral on a southern exposure, maximumtranspiration was slightly over 1 inch (25.4 mm) in June,but dropped to less than ~ inch (6.4 mm) in October beforethe fall rains. Maximum transpiration on north slopes wasmuch higher than on south slopes; the maximum of 1.7inches (43.2 mm) per month was reached a month later.The transpiration rates reached a minimum of 0.0024inches (0.06096 mm) in October, primarily because the soilmoisture had been used up.

In order to survive for several months on practically nosoil moisture uptake, after being a moderately heavy wateruser just weeks before, water-saving plants have developedeffective drought-adaptive mechanisms (Rundel 1977).These include

. Leaves which are small, thick, and leathery (havingthick-walled cells) and high in oil content, all of which tendto reduce transpiration. Relative vertical orientation of

leaves so as to present the edge but not the surface to thesun, as well as changes in the angle of leaves in response tosunlight regulate the uptake of solar radiation and waterloss.

. Stomata (minute openings in the leaf surface) thatopen during the daylight only for a short period of time andare able to close quickly, thus reducing water loss; stomatamay be recessed and have cavities covered with hairy pro-trusions, which aid in reducing water loss.

● Cutin (a waxy substance on the leaf) that reducestranspiration to a much greater degree after the stomatahave closed.

● Reduction of exposed leaf surface, as through shed-ding, rolling, or folding of leaves.

. Reverse transpiration—the ability of leaves to takeup atmospheric moisture.

In general, the major means of control of water loss arethe stomata; the other mechanisms help control water losseven further. Additionally, the gradient of increasing arid-ity and lack of available ground water supply betweenevergreen shrub communities and summer deciduous

Table 6—Rates of transpiration and evaporation on loamy soils, Call~ornia

Plant or surface

Lawn grassesBermuda grass

Weedy herbs

Brush 5 ft tall:Chamise, sage,Yucca

Reeds, tules

Mixed chaparral:Desert buckbrush,Scrub oak

Chamise chaparral

Navel orangetrees, mature,10ft spacing

Bare ground

Swimming pool

Evaporation pan

Time Rate ofLocation Conditions of year transpiration Source

Coastal zoneSanta Ana

River Valley

Santa AnaRiver Valley

San Bernardino

Temescal Creek,Corona

Northern exposure

Southern exposure

Santa AnaRiver Valley

Santa AnaRiver Valley

Coastal zone

Coastalzone

Riverside (“desert”)

Water table:2 ft3 ft

Level

Soil moisturerecharge to fieldcapacity in MayStreambed

Before fall rain

Before fall rain

Level

Water table:2 ft2 ft3 ft4 ft

—

SummerSummer

Winter

Apr.JuneJulyApr.-May

JulyOct.

JuneOct.Jan,Mar.MayJulySept.Nov.

W’interSummerJan. -Apr.SummerSummer

[ncheslmo

4,0

6.55.52.0

3.03.95.2

12.9

1.70.00240.01.10.21.01.62.13.12.01,5

0.30.80.10,05-10

140.0

167.0

Williamson 1976

Blaney andothers 1930

Blaney andothers 1930

Blaney andothers 1930

Blaney andothers 1930

Miller 1979

Miller 1979

Blaney andothers 1930

Blaney andothers 1930

Klaus W. H.Radtke

Strahler andStrahler 1973

Blaney andothers 1930

[Per year

29

coastal scrub communities is reflected in a change fromdeep, penetrating roots to shallow, fibrous roots and anincrease in shedding of leaves. Furthermore, some plantssuch as hoary-leaf ceanothus make more complete use ofthe available moisture by starting their active growingseason early in the year during the cooler temperatureswhich normally coincide with the onset of the fall or winterrainy season. Chaparral plants that have deep root systemsdraw moisture even from deep rock crevices. Manydrought-tolerant plants are also able to lower the soilmoisture percentage well below the so-called wilting point,at which water absorption by roots theoretically stops andleaf turgor cannot be maintained even in the absence oftranspiration.

WaterRequirementsThe ability of most chaparral plants to extract the max-

imum amount of moisture possible leaves the soil mantleand rock crevices dry to absorb moisture when the winterrains return. Proper watering of greenbelts should, there-fore, be patterned after this natural water withdrawal-recharge cycle. The yearly irrigation requirements oflandscape plants depend on the amount and distribution ofrainfall and are governed by the timing of the last effectiverain in the spring and the first effective rain in the fall. Such

rainfall is sufficient to be absorbed by plants. The time offirst summer irrigation depends on the amount of moisturestored in the soil at the end of the rainy season, and on theroot depth and moisture requirements of plants (table 7).During years of well-distributed rainstorms, most of thewater infiltrates the ground and recharges the soil moistureto field capacity throughout the plant root zone; moisturefor evaporation and transpiration is thus supplied through-out the winter months. During years when the rainstormscome early and are more closely spaced, more water perco-lates below the root zone and is lost to the plant. Soilmoisture recharge occurs less often and much available soilmoisture is used up early in the season by evaporation andtranspiration. On deep soils, less water penetrates belowthe root zone, but on coarse soils, there is greater moisturepercolation to the underground water table. The approxi-mate amount of water available per foot of soil is as-follows(Stefferund 1957):

Soil type: Available water (irrches/ft)Sand 0.25-0.75Loamy sand 0.75-1.25Sandy loam 1.0 -1.5Fine sandy loam 1.5 -2.0Clay loams 1.75-2.25Clays 2.0 -3,0

Table 7—H~,pothetical water use b.v nine species of chaparral plants and ground cover, based on soilmoisture recharge to field capacity b,v March 15, coastal zone, Call~ornia

Plant

Lawn grassPeriwinkle

Algerian ivyDescanso rockrose

Australiansaltbush

Coyote brush

Californiabuckwheat

Prostrate acacia

Laurel sumac

Zffectiverootingdepth

Feet23

45

6

7

8

9

20

HInches Avg. inches/mo

3.5 3,5 4.55.25 2,5 3.5

6.75 2.5 3.58.25 1 2

9.25 1 0,5

10.25 1 1.5

11.0 1 1.5

1.75 1 I .5

7.0 3 2.5

Apr. 15May 22

June 5Sept. 1

None

None

None

None

None

Resp,~nseto

drought

Plant diesLeaves go limp,above-ground portionsdie, root systems usu-ally survivePlant diesPlant goes partiallydormantPlant drasticallyreduces transpiration,“shuts down”Plant drasticallyreduces transpiration,“shuts down”Plant drasticallyreduces transpiration,“shuts down”Plant drasticallyreduces transpiration,“shuts down”Plant drasticallyreduces transpiration,“shuts down”

IFrom August 15to October 15transpiration for all species increases drastically if soil moisture is readilyavailable.

zSee /able 8 for available moisture by soil profile.

30

Sandy soils have the lowest moisture-holding capacityand release the available water most easily, Clay soils havea greater water-holding capacity but do not release thewater as easily because water is more tightly held byadsorption to the smaller soil particles. Plants compensatefor the lower water-holding capacity of sandy soils with awider root network, but are restricted in their root penetra-tion and water withdrawal on shallow, compacted or heavysoils. Plants do not withdraw moisture at equal rates fromall depths of the root zone, but initially concentrate with-drawal on the upper half of the root zone. When theavailable moisture is withdrawn from any appreciable partof the root zone, growth slows down. As more moisture iswithdrawn, the soil layer reaches the point at which nofurther moisture uptake is possible by the plant roots of theparticular species. Before this point is reached, however,most plants show that they require water. For example,temporary wilting of the plants during the daytime indi-cates water need; this wilting is readily apparent in thewater-demanding plants such as periwinkle and ivy. Otherplants may change leaf color from green to yellowish. Onceplants are well established, irrigation should be sparingenough to reduce the available soil moisture to the point atwhich plant growth is reduced without permanent injury.Growth stops as the wilting point is approached, but againincreases rapidly for most landscape plants after irrigation.

Because of the many variables, a specific watering sched-ule for each plant species cannot be given here. Generalwatering recommendations for plant species (tables 5, 7)take into account such variables as soil depth, rootingdepth, and transpiration rates. The minimum hypotheticaltranspiration rates and rooting depths given in table 7forground covers and chaparral species suggest how soonafter the last effective rains the landscape plants may needirrigation. Transpiration rates depend on the total leafstructure area of the plant as well as its growth rate, with

greater growth resulting from a larger area and volume offoliage, Humidity, wind, and temperature are also impor-tant; for example, at constant relative humidity, transpira-tion of English oak was found to be five times greater at104° F (40° C) than at 68° F (20° C) (Kittredge 1973). Ingeneral, transpiration is related to the species and age ofthe plant and to the site. Water requirements are less perunit volume on good soils, but the total transpiration isgreater because the plants grow better and have more leafsurface area.

During dry years, or when rains have come late in thewinter season, fairly complete soil moisture recharge isinitially necessary through irrigation. One deep wateringearly in the summer may be required by the most drought-tolerant species. When late winter rains have recharged thesoil to field capacity, no watering maybe required at all, ora more shallow watering to perhaps 1foot (30.5 cm) depthlate in summer may be sufficient for plant survival. Mois-ture withdrawal by plant roots will then leave the soil dry,ready for heavy winter rains that may come early in therainy season.

Under the conditions shown in tables 7, 8, Algerian ivywould require watering by about mid-May to remain tur-gid. This is within 9 to 10weeks after the last storm (mid-March) recharged the soil moisture to field capacity withinthe root zone of the plant. By this time, approximately 3inches (76 mm) per month of spring transpiration wouldhave used up the 6.75 inches (171 mm) of available soilmoisture to a depth of 4 feet (1.2 m). The plant wouldattempt to send out new roots into the deeper moist soillayer, but transpiration needs of the leaves would soonoutstrip the capacity of the roots to expand. Moistureabsorption for all practical purposes stops and the plantdies unless irrigated.

Periwinkle, like ivy, is a water loving plant, and its waterneeds also increase throughout the spring and summer

Table 8— Water availability is determined by root depth and d~ferences in moisture availabilityihroughoul the soilprofile, Data are based on soil moisture recharge tofield capacit) b), March 15(see table 7)

Soil profile Total available(depth in feet) Available moisture moisture Species and root depth

123456

J789

10111213141516

Inches/f! soil Inches Feet1.751.75 3.5 Lawn grass. . . . . . . . , ., , . . 21.75 5.25 Periwinkle. . . . . . . . . . . . . . 31.5 6.75 Algerian ivy. . . . . . . . . . . . . 41.5 8.25 Descanso rockrose. . . . . . . . 51 9.25 Australian saltbush. . 61 10.25 Coyote brush. . . . . . . . . . . . 70.75 11.00 California buckwheat. . . . . 8

.75 11.75 Prostrate acacia. . . . . . . . . . 9

.75 .- ..

,75 -- --

.75 .. --

.75 -- --

,75 -- --

.75 .- --

.75 17,0 Laurel sumac. . . . . . . . . . . . 20

31

months. On deeper soils, however, and especially in par-tially shaded areas, its root crown can survive withoutsummer irrigation and can send out new shoots whenwinter rains return. It is, therefore, an excellent groundcover for neglected areas.

Prostrate acacia and coyote brush are two deep-rootedground covers that have drought-adaptive mechanismssimilar to chaparral plants and can drastically reducetranspiration as the wilting point is approached. Thus,once these plants are established, irrigation is hardly neces-sary. Prostrate acacia and coyote brush have the addedadvantage of being esthetically pleasing despite droughtshutdown.

OverheadImpactSprinklersFor both initial establishment and later maintenance of

hillside ground covers, overhead impact sprinklers anddrip irrigation systems are recommended. They are easy toinstall, maintain, and inspect. Overhead sprinklers are notefficient water users when compared to drip irrigation.

Great care should be taken in designing the irrigationsystem, so that it will evenly cover the affected areas with-out causing undue erosion. When there is doubt about howto design a hillside irrigation system, an expert should beconsulted. A well-designed system will pay off over theyears in water saved and possible damage to hillsidesavoided.

The greatest efficiency rate or maximum spacing is nor-mally achieved by spacing impact heads at 60 percent oftheir throw diameter. Thus, 60 percent of a 72-foot-diameter sprinkler would be 43 feet. For tight soils andinitial establishment of ground covers, impact heads thatdeliver only about 0.1 inch (2.5 mm) of water per hour, or

2.5 - \ -.–.-. Coarse-textured soil I-6.25!I (sandy loam)

2.0

c“g1.0mk=E .5

- \\— Fine-textured soil(clay loam)

i.

.-. —---- .-. — --------

o .5 1 1.5 2

HoursFigure 13-infiltration rates for coarse-tefiured soilsare higher than thatfor fine-textured soils.

that rotate quickly, can be used. Such heads greatly reducethe impact of the falling water drops on the bare soil,preventing damage to soil structure and allowing forgreater infiltration and therefore less runoff. These areimportant considerations for compacted fills that normallyhave a much lower infiltration rate than chaparral soils.

Once the ground cover is well established, the nozzle ofthe impact head can be changed to deliver approximately0.2 inch (5 mm) per hour. For soils that have a highinfiltration rate, sprinklers are available to deliver as muchas 0.4 to 0.5 inches (10 to 12,7 mm) per hour. When usingthese sprinklers, it may be advisable to irrigate severaltimes a day to replenish soil moisture to the desired depth.Infiltration into soils is high during the initial wateringperiod, but levels off very quickly as the soil surfacebecomes well moistened ~g. 13), as a result of closing ofsoil pores by soil particles or swelling of colloidal clays. Forhome use, high impact sprinklers are not normally recom-mended because they may saturate soil if left on too long.When sprinklers are automatically timed, there is dangerthat too much water may be applied and that a broken pipemay go unnoticed until hillside slippage occurs. Drip irri-gation allows for deep watering with a minimum amount ofwater. Thus, a superior root system is developed.

To summarize, the proper watering of newly establishedgreenbelts does not accelerate the natural erosion rates nordamage the soil structure. Deep watering is more beneficialto hillside plants than shallow watering because it rechargessoil moisture more completely throughout the root zoneand encourages some plants to develop a deeper root syrs-tem. Water should be withheld from mature plants as muchas possible to force slowdown of growth, which also resultsin reduction in transpiration. Water should be withheldtowards the end of summer, allowing plants to harden offwhile they can still withdraw moisture from their rootzones. Withholding water as fall approaches leaves the soilrelatively dry at the onset of the rainy season and allows itto absorb water readily to greater soil depths. Constantshallow watering, on the other hand, only partially re-charges the root zone, wastes water through evaporation,and may induce a more shallow root system that makeshillside plants less drought-tolerant. Deep watering shouldnot be done after about mid-September. If effective rainsdo not occur until late in the season, occasional shallowwatering may then be required to keep the more-water-demanding plants alive.

PLANNING FOR HOME SAFETYFROM FIRE

In most cases the fire safety of a home can be greatlyimproved. There are, however, special conditions of topog-raphy, wind, and heat patterns under which, in spite of allprecautions, a home may literally explode inflames during

32

a wildfire disaster. Through neighborhood teamwork,community action, and proper land use planning, the like-lihood of such events can be reduced, but homeownersmust realize that there is a risk in living in chaparral areas.

Reducing Fuel LoadFire safety around a home is achieved by reducing the

fuel load and breaking the fuel continuity, and by buildinga “fire safe” home in an area where it can be defended fromwildfires. Landscaping to lessen the fire without fireproof-ing the home itself may be a futile effort. This was dramati-cally demonstrated during the June 22, 1973, CrenshawFire in Rolling Hills, Los Angeles County, where 12homesburned, 11of which had wood shingle roofs. The shinglescaught fire, even though most homes were surrounded byan excellent green belt. The fire burned through 897 acres(359 ha) of light fuel which consisted of grass, mustard, andcoastal sage.

The California State Resource Code 4291 is the basicvehicle for creating minimum fire safety by reducing thefuel load and breaking the fuel continuity. The coderequires that all flammable vegetation must be cleared to adistance of 30 feet (9.1 m) around a structure. If additionalhazards exist, the Director of the California Department ofForestry can require clearance up to 100 feet (30.5 m).Individual fire jurisdictions may differ as to the enforce-ment of the 30-to-100-foot-clearance law. For example, theCounty of Los Angeles brush clearance law (Section 27301of the Los Angeles County Fire Code) requires a minimum

of 30 feet legal clearance, but the Fire Chief can enforceclearance of up to 100feet. The City of Los Angeles brushclearance law (Section 57.21.07) is more inclusive andrequires the removal of all native brush (specimen plantsexcluded) and other flammable vegetation to a distance of100feet. The Chief Engineer has the authority to insist onmore extensive brush clearance beyond 100feet.

Homes burned in the 1961 Bel Air Fire showed theinterdependence of brush clearance and roof type (Howardand others 1973). The destruction rate for homes withwood roofs ranged from 14.8percent with brush clearanceover 100 feet (legal clearance limit) to 49.5 percent withclearance of Oto 30feet. Nonwood roofs of approved typesfared much better; the corresponding rates were 0.7 and24.3 percent. With a legal brush clearance of 100 feet, ahome with a wood roof therefore may be 21 times morelikely to burn during a wildfire than a home with a non-wood roof. Gable roofs, large wooden overhangs (eaves),wood siding, large picture windows facing in the directionof the fire hazard, and houses located too close to a slopeare some of the additional safety hazards that need to beeliminated in fire-prone areas. Pressure-treated woodshingles cannot be considered fire resistant indefinitely,because the safety edge wears off with time through weath-ering. Placing wood shingles over a layer of nonflammablematerial gives an individual home an added safety margin,but adds to fire spread by producing airborne incendiariesand creating radiation and convection heat that affectsneighboring homes.

When a home with a nonwood roof and brush clearanceof more than 100feet (30.5 m) ignites, other conditions are

Figure 14--Winds tend tochan-nel through chimneys, makingnarrow canyons and saddlesparticularly fire-prone.

\ —

33

responsible, the most critical being topography. Topog-raphy is becoming increasingly important as homes arebeing built in areas that are often indefensible from fire.Such areas include natural chimneys (narrow canyons thatconcentrate heat and updraft) (fig. 14), saddles (low pointsin a rolling landscape) wig.15),steep canyons, and ridges~ig. Z6). Analysis of the apparently random burning ofhomes in the 1961Bel Air Fire in Los Angeles showed thatalong Roscomare Road the burning was not random butwas directly correlated with the intersection of a tributarycanyon and the main canyon (Weide 1968). Wind eddiesand associated fire winds quite common in such situationsare normally found on leeward sides of objects that create abarrier to airflow. They can, therefore, be expected on thelee side of ridges, hills, large rocks, and even vegetation. Ifthe prevailing wind is either up or down canyon, the eddiesare magnified behind spur ridges, at sharp bends in thecanyons, and especially in areas where two or morecanyons meet (Countryman 1971). In very steep and nar-row canyons the heat may also be a major factor in firespread and home losses. In the areas considered indefensi-ble from fire, a safety margin can nevertheless be createdby reduction of brush and other fuel beyond the legal100-foot clearance. Terrain permitting, this can be donethrough wide fuelbreaks surrounding the larger devel-opments.

Understanding Fire Behavior

Understanding the basics of fire behavior will provehelpful to the homeowners. They will be able to judge fuelsaround their homes in terms of flammability, heat inten-

sity, heat duration, and fire spread. A fire can be visualizedas the flame, heat, and light caused by burning (oxidation)after an object has reached ignition temperatures and hasbeen ignited. Ignition temperatures are influenced by therate of airflow (supply of oxygen), rate of heating, and sizeand shape of the object. Once ignition has occurred, sus-taining combustion requires a continuous supply ofoxygen.

The different major wildland fuels, such as grasses, coast-al sage scrub, chaparral, and trees, have various ignitionrequirements. Heat of ignition is greatly influenced by fuelparticle size distribution, live-to-dead ratio of these parti-cles and moisture content of live and dead tissues. Thephysiologica~ condition of the living tissues greatly affectslive fuel moisture. A vigorous growing plant has high livingtissue moisture and a plant under stress or in poor vigor hasrelatively lower living tissue moisture. For example, grow-ing grass has a living tissue moisture content greater than100 to 150 percent of dry weight. Dead tissue moisturecontent is determined by the ambient air moisture andtherefore changes rapidly. Dry grass has the lowest heatrequirements for ignition and is therefore easily ignited; ithas the longest fire season and also the highest fire fre-quency. Coastal sage scrub, because of its summer dor- ‘mancy, its high amount of fine dead fuels, aromatic oils,and the relatively short life cycle of individual species, isnext in heat requirements for ignition and in fire frequency.Woody chaparral shrubs in coastal areas have a higher livemoisture content than the same vegetation inland andnormally do not become dangerously dry until late summeror fall. However, even among these plants, several species,such as chamise, have greater amounts of fine fuel and tend

Figure 15-Natural saddles arewide paths for fire winds, andvegetation growing there willnormally ignite first,

34

to have more flammable secondary compounds during theannual dry season.

Heat transfer is by conduction, convection, and radia-tion. The flame is the visible burning gas produced by thefire and provides (along with airborne sparks) a directignition source for fuels that have reached ignition tempera-tures.

Convection heat is the transfer of heat by atmosphericcurrents and is most critical under windy conditions and insteep terrain. With light wind and on level terrain, theconvection heat column is almost vertical, and radiationheat becomes a critical factor in fire safety. Radiation heatis transfer of heat by electromagnetic waves and can, there-fore, travel against the wind. For example, it can preheat tothe ignition point the hillside opposite a burning slope in asteep canyon ~g. 17). Conduction is the direct transfer ofheat by objects touching each other. It is not a criticalprocess during a fast-moving wildfire but can be responsi-ble for igniting a home, as when burning firewood stackedagainst the side of the garage causes the house to catch fire.

The interaction of the three types of heat transfer withtopography can be illustrated by visualizing a burningmatch ~ig. 18). When the match is held up, heat transfer isby conduction only, and the match burns slowly. This iscomparable to a wildfire burning downhill. If the match isheld horizontally, heat transfer is by conduction and radia-tion, and the match burns a little faster. When the match isheld down, it is consumed rapidly because conduction,convection, and radiation heating are occurring together.The situation is comparable to a wildfire burning uphill,and such a fire travels much faster than one on level groundor burning downhill.

The key objective in breaking up the fuel load and fuelcontinuity around structures is to reduce the amount andduration of thermal radiation the home or the firefighterreceives. For a point source of radiation this heat intensitydecreases with the square of the distance from the source.The radiation intensity 100feet (30.5 m) from the burningbrush or landscape plants is therefore only one-fourth thatat 50feet (15.2 m). A tree burning within 20feet (6m) froma roof or picture window transfers only one-fourth of theheat to the house compared with a tree burning within 10feet (3 m), and only one-sixteenth the heat compared with atree within 5feet (1.5 m) ~g. 19). A line source of radiationsuch as a burning hedge of junipers or cypresses is evenmore critical than a point source of radiation because thehouse receives heat from all points along the line wig. 19).In this case, intensity varies with the distance instead of thesquare of the distance, so that the intensity at the homelocated within 20 feet from the burning hedge is still one-half that at 10 feet. Increasing the number of flammablelandscape plants around the home and increasing thenumber of trees, or both, will make a house more fire-prone, despite legal brush clearance.

During a wildfire, flames more than 100 feet (30.5 m)long can roar over homes on ridgetops and consume seem-ingly safe homes a distance away. These flames directlytransmit the greater part of the thermal heat of the radiat-ing source (wildland fuel) to the home and thus ignite it.Flame length is controlled by the height and density of theradiating source, by windspeed, steepness of the slope, liveand dead fuel moisture, fire spread, and such other specificcharacteristics of the fuel as ash and oil content and thearrangement and amount of fine fuels present. Reducing

Figure 16-On narrow ridges,homes without adequate set-backs, such as those depicted,are especiallyvulnerable to fire.

3

[11ConductionSfowest

J\.

andconvection \\-

= ,x. Conduction and radiation

k\*\Conduction,radiation, \>

\Fastest \

Figure I&Theinteraction ofthree types ofheat transfer—conduction, ra-diation, mnvec-tion—is illus-trated by threeburning match-es.

Figure 17—Radiation transfersheat in all directions—evenagainstawindsweeping throughacanyon. Intheprocess, the hill-side opposite a burning slopecan be ignited.

&foot-tall (1.8-m-tall) chaparral to 2-foot-tall (O.6-m-tall)low fuel plants on a 45° slope can reduce flame length byone-third—a powerful incentive for fuel modification(Albini 1976) (table 9).

Wildland fires that produce flame length greater than 30to 35feet (9.1 to 10.7m) are considered to be burning out ofcontrol. In &foot-tall chaparral this critical flame length isalready reached at a windspeed of less than 10mph (16.1kph), whereas in 2-foot-tall low fuel volume plants thewindspeed would have to approach 50 mph (80.5 kph) toproduce flames of this length (table 8). Low fuel volumeplants thus reduce but do not completely eliminate the riskof a wildfire conflagration; they do allow the fire to becontained in a shorter time.

Insurance companies realize that the many factors dis-cussed above have to be taken into consideration for firesafety and therefore affect calculation of brush surchargeon insurance rates. Where there are slopes of more than30° below the home, twice the IO@foot(30.5m) legal brushclearance distance may be required to qualify for the sameinsurance rates wig. 20). This approach, so vital for firesafety, works against maintaining slope stability, as dis-cussed earlier.

The 1983 insurance rates in brush areas in southernCalifornia ((able 10) show that the rates are primarilydetermined by the protection class of the area and the

36

distance of brush to the building. Roof types are not ade-quately accounted for; with brush clearance less than 30feet (9. 1m), costs for unapproved roofs are only 25percenthigher. Surcharges are eliminated with 40@foot (122-m)clearance for both approved and unapproved roofs, eventhough unapproved roofs can readily ignite from flyingembers. This is poor incentive for a homeowner to includea more fire-safe roof in plans for building or remodeling. Ahomeowner who is concerned with tire safety thereforesubsidizes a careless homeowner. Making insurance ratescorrespond closely to the risk factors is a good way toprovide greater fire safety. More direct attempts at regula-tion tend to fail because building and zoning codes reflectpolitical realities. Insurance incentives have been used tosome extent: reductions in rates maybe gained by having aswimming pool with an electric, gas, or battery-drivenpump or other safety devices. An insurance agent canprovide further details.

Promoting Fire Safety

Principles of topography, vegetation, and architecturaldesign can be applied to improve the fire safety of aplanned or an existing home @gs. 21, 22). Drastic fuelreduction on steeper slopes will result in slope instability(at least temporarily) unless the new vegetation offers thesame network of root strength and depth. A basically“fire-safe” home design gives greater flexibility in fuelmodification, thereby retaining slope stability to a greaterdegree,

Table9—Effect of windspeed andfuel height onflame lengthl

Windspeed at midflame I Iheight (mph)

51015202530354045

2-ft low-fuel plants 6-ft chaparral

Flame length ft)9.1 27,7

12.9 39.516.2 49.919.3 59.522.1 68.324.7 76.627.2 84,429.6 91.931.9 99.1

50 34.1 106.0

ISource: Albini 1976;adapted by Ronald H. Wakimoto, University ofMontana.

Exterior materials used on wildland homes should havea minimum fire-resistive rating of 1hour. This requirementis especially critical for parts of a home exposed to windsfrom the north or east, and for homes positioned at the topof a slope, stilted or cantilevered sideslope, or without aslope setback. For further information applicable to resi-dential development see the fire safety guides issued by theCalifornia Department of Forestry (1980).

Homes can be designed with specific features to promotefire safety ~ig. 19). Reduced overhangs or boxed eaves canprotect the house from ignition and heat or flame entrap-ment. Under eaves, vents should be located near the roof-line rather than near the wall. Exterior attic and underfloor

.

Figure 19--Fire satetyisdirectlyaffected by the intensity and du-ration of thermal radiation that ahome receives from flammablefuels.

37

~––––.._I tw ;

I~~ I

II -11A

“@”

Al150rl Iooft

Gan

~ ~ush line B 1——————— —————.—————.— J

SectionA-A’

SectionB-B’

Figure 20--Minimal safety dis-tances from a building to brushrecommended by insurancefirms will vary by the slope of theland.

vents should not face possible fire corridors and should becovered with wire screen (not to exceed YQinch mesh).Picture windows and sliding glass doors should be made

Table 10—Insurance surchar~e rates for homes in brush areas with only of thick, tempered safety glass and protected with.,approved roofs (composition, rock, tile, slate, asbestos, or metal) andfornonapproved roofs (wood shingle, wood shake), b} exposure distance tobrush andproteciion class, Counties of Los Angeles, Santa Barbara, SanBernardino, und @ntura, in southern California, 1983

Protection classl

Exposure 1 to 4 5 and 6 7 and 8 9 and 10distance tobrush (ft) A’ B3 A B A B A B

I AnnuaIcharge(dollars for$lM property valuation)Approved roofs

O-29 0.40 0.40 0.48 0.49 0.64 0.64 1.28 1.2830-59 .28 .36 .36 .48 .56 .64 1.28 1.2860-99 .20 .28 .24 .32 ,32 .48 1.28 1.28

100-199 .08 .16 .12 .24 ,24 .32 .96 1.12200-299 0000 ,16 .24 .64 .80300-399 000000 .32 .48400-over 000000 00

Nonapproved roofsO-29 .50 .50 .60 .60 .80 .80 1,60 1.60

30-59 .35 .45 .45 .60 .70 .80 1.60 1.6060-99 .25 .35 :30 .40 .40 .60 1.60 1,60

100-199 .10 .20 ,15 .30 .30 .40 1.20 1.40200-299 0000 .20 .30 .30 1.00300-399 000000 .40 .60400-over 00000000

IInsurance representatives have listings of the protection class of yourarea.

IFire station within 5 miles; access road; public water hydrant with4-inch main with 2~-inch outlet within 1,000 ft.

]One or more of the above requirements not met.

fire-resistive shutters. Stone walls can act as heat shieldsand deflect the flames. Swimming pools, decks, and patioscan be used to create a setback safety zone as well as toprovide safety accessories. Pools can provide a convenientauxiliary water source, often of critical importance forfirefighters or homeowners before and during a fire, butshould not be in lieu of an adequate community watersystem. Fire engines should be able to get within 10 feet(3 m) of the pool because this is usually the optimumdistance for the drafting hose. If this is not possible, thepool should have a bottom drain and pipe system thatterminates horizontally or below pool level in a 2 M-inchvalved standpipe equipped with a fire hydrant withnational standard thread. This is the thread which mostfire equipment in southern California can hook up towithout adapters. (The local fire protection agency canspecify the thread used and provide other suggestions. ) Afloating pool pump or portable gasoline pump with asuction hose that can reach the bottom of the pool canassure a usable water source, even when water pressure andelectricity fail. A fire hose and nozzle are also needed.

Fabric fire hoses are fine for high pressure equipmentsuch as pool pumps that are designed for firefighting, butshould not be used on home faucets because such hosesreadily kink as water pressure drops. All outdoor faucetsshould be equipped with strong Ya-inchrubber hoses thatwill not burst when the nozzle is shut off. This system of

38

hoses should be able to reach any part of the house androof. A ladder should always be available to reach the roof,and should be placed against the part of the house leastexposed to fire.

In summary, fire risk can be reduced by installing:

. Fire-resistive roof—preferably Class A, such as tile.● Stucco or other fire-resistive siding of at least 1hour

fire-resistant rating.. Reduced overhang (preferably closed eaves with

vent covers).● Roof slanted to accommodate convection heat.. Safety zone (slope setback of at least 30 feet (9.1 m)

for single story home.● Pool used to create safety zone.. Shrubs and trees not directly adjacent to home nor

overhanging the roof.● A deck with exterior materials of at least 1 hour

fire-resistant rating.

Overhead (roo~ sprinklers can increase the fire safety ofan existing home. Under favorable conditions, they canprovide fire protection by keeping the roof and surround-ing landscaping wet (Fairbanks and Marsh 1976),but theycan not take the place of a fire-safe building design. Thehigh winds normally associated with wildfires often pre-vent the water from effectively wetting the roof. Also, thesystem will break down if there is no water pressurebecause of power failure or heavy demand on the watersupply. Systems that can operate on minimal water pres-sure, such as full circle, low-pressure impact sprinklers,provide added safety.

The extensive use of water by many neighbors canquickly drain the community water supply, leaving little orno water or pressure for fire suppression use. Fire suppres-sion agencies, therefore, may not recommend the use ofroof sprinklers operated by the community water system.

If water is available from an auxiliary source such as aswimming pool, roof sprinklers could be installed in con-

Figure 21—Fire safety can beincreased by reducing fuel totwice the legal minimum dis-tance of 100 feet (30.5 meters).Tomaintain slope stability,retainnative plant species within the18-foot (5.5 m) recommendeddistance for fuel separation.Flame length is still mntinuous,but the amount and duration ofheat output is less than whenbrush is clearedto the legal min-imum.

Figure 22—Homeowners canmodify their homesto overumenegative characteristics. Buttheyshouldseekthehelpofgeo-Iogical,engineering,anderosioncontrol specialists when plan-ning intensive fuel modificationon steep slopes. Drastic fuel re-duction can lead to slope insta-bility.

39

junction with a portable pump utilizing the water from theswimming pool only. However, roof sprinklers cannotoffer the degree of fire protection obtained by a fire-safebuilding design.

Modifications to an existing property ~ig. 22) thatcould overcome negative characteristics include:

Negative characteristics ~odl~carions1. Wood shingle roof Fire-resistive roof2. Wood siding Fire-resistive siding (or

fire-resistive paint)3. Large overhand Reduced overhang

(open eaves) (closed eaves); vent cov-ers for tire emergency

4, High gable roof Redesigning may be tooexpensive

5. No safety zone Create setback with a(no slope setback) deck where exterior

material has a fire-resistant rating of 1hour or more

6. brge picture Install fire-resistivewindows shutters

7. Tree crown over- Prune treeshanging the roof

Clearing BrushAround Homes

Some typical fire hazard reduction requirements are setforth below. Local homeowners may receive such informa-tion from their jurisdictional fire agency or the CaliforniaDepartment of Forestry. Residents of fire-prone areasshould be aware of the local ordinances that require suchhazard reduction, should understand them and help makethem applicable to their particular area. Living more safelyin chaparral areas requires a balance of both watershedand fire safety. Clearing brush according to local ordi-nance will not in itself guarantee fire safety @g. 23). Othermeasures described in this report should be followed. For

additional guidance on fire safety, see reports by the Cali-fornia Department of Forestry (1980), Moore (1981),Perry and others (1979).

You are only required to clear your own property.Clearance on other property is the responsibility of theowner. Contact your local forestry or fire personnel if suchclearance is needed.

1. Clear all hazardous flammable vegetation to min-eral soil for a distance of 30 feet (9 m) from any structure.Cut flammable vegetation to a height of 18inches (45 cm)for another 70 feet (21 m). Exception: This requirementdoes not apply to single specimens of trees, ornamentalshrubbery or cultivated ground cover such as green grass,ivy, succulents, or similar plants used as ground cover,provided that they do not form a means of readily trans-mitting fire from native growth to any structure.

2. Remove limbs within 10feet (3 m) of the chimney.Cut away dead branches and limbs that overhang the roof.

3. Screen the chimney outlet to prevent sparks fromigniting the roof or brush. Use Yz-halfinch mesh.

4, Clean leaves, needles and twigs from roof guttersand eaves.

5. Clear flammable vegetation within 10feet (3 m) ofliquefied petroleum gas storage tanks.

6. Stack wood piles away from buildings, fences andother combustible materials.

TREATING NEWLY BURNEDCHAPARRAL SLOPES

After brush fires, erosion from burned watershedscovered with natural vegetation may be more than 20times

k House built too close to Palm=

1 LargepicturewindowFacing slope

Figure 23-Fire cantravel uphill16times faster than downhill. Atwind speeds of 50 mph (80.5kph),flames producedby a solidcover of chaparral can exceedthe 100-foot (30.5 meter) lengthof brush clearance.Therefore, asolidflame front will be producedthat reachesfromthe edgeof thechaparral (A) over the low-fuelplants to the house(B).

40

greater than from unburned watersheds, although it isnormally much less. Fire intensity, steepness and length ofslope, soil type and parent material, and intensity, dura-tion, and frequency of winter rains all affect the amount oferosion. In any event, immediate action by the homeowneris imperative to reduce property damage from the winterrains. But, what to do? Some suggestions are illustrated infigure 24. Additional information can be gathered fromother sources (for example, Amimoto 1978, Los AngelesCounty 1982, Los Angeles Dep. Bldg. and Safety 1978,Maire 196Z Zinke 1962). The appropriate County FloodControl office can provide immediate help when need isurgent.

Direct SeedingAfter major fires, Federal, State, and local agencies may

immediately start aerial seeding of the hillsides with annualryegrass (Blanford and Gunter 1971).This is an emergencymeasure and often seeds exposed on the soil surface willnot germinate and start rooting unless encouraged by 4 or

5days of moist weather. Much of the season’s rainfall maybe passed before the seeded grasses become well estab-lished. Seeds of resident annual grasses, when they arepresent, germinate more quickly because many of the seedsare buried in the soil layer and therefore have moistureavailable. This abundant seed source quickly germinateswherever moisture collects. Perennial grasses will resproutsoon after the first winter rains.

AnnualRyegrassAerially seeded ryegrass is less effective on steep slopes

and needs fertile soils (provided by nature after a fire),moisture (rain or sprinklers), and warmth to germinate.When ryegrass is used by the homeowner the best course isto seed the slopes by hand, preferably raking the grass seedin, and then installing a sprinkler irrigation system. If theslope is to be replanted immediately with landscape plants,ryegrass must be seeded in contour rows or it will chokeout the newly planted stock. To germinate the seeds beforethe winter rains, the first few inches of the soil surface must

/seeded byr in anw

Chaparralwildlands

hAj

/

Checkdarns in

/;”+yAcanyonto reducedebrisflow

Woodendeflectorca[cn r0cK5

barricadesnear basaof slope

nce to

Figure 24-immediately after a fire, emergency measures should betaken to rehabilitatea chaparralwatershed.They includethe useofdirectseeding, check dams, hards, jute matting, chain link fences, sandbagsand deflector barriers, drains,dry walls, plasticsheeting, and guniting onslopes.

41

be kept moist through frequent light watering. Deep water-ing should be avoided.

Seeds can be pregerminated to save water, to preventoverwatering of slopes, and to assure a good, quick cover(Esplin and Shackleford 1978,Radtke 1977)@g. 25). Thisis readily done by putting the seeds into gunnysacks (sand-bags) and soaking them thoroughly in large containers,such as trash cans that have small holes or openings fordrainage. The excess water, which may contain germina-tion-inhibiting chemicals leached from the seed coat,should be channeled into the street gutter. After the seedshave been kept moist in the sacks for about 1 day, theyshould be hand seeded on the hillsides or raked in. Theywill germinate immediately if moisture is continuouslysupplied.

Ryegrass should be viewed by the homeowner as a man-agement tool for temporary emergency surface erosioncontrol of bare slopes during the immediate rainy season.Eradicating the ryegrass plants on landscape slopestowards the end of the rainy season, before they go to seed,and replanting the areas to deep-rooted low-fuel plants canbe an effective method for reducing topsoil erosion. Theryegrass treatment greatly reduces surface erosion but cancompete heavily with the deeper-rooted woody plants.Spring and summer annual grasses will become dry, weedyflash fuels. New seeds germinate year after year as long asthe soil is disturbed. Perennial ryegrass should not be used,as it can become a weedy pest.

R,.

m,Not.rc.,o,kti

3 day,

\

.(.1) -

(Xt) cP,.,

3 day,

!I

@d

Figure 25-Soaking barley andryegrass seeds stimulates pre-germination, thereby hasteningrooting and establishment asground cover.

igure 26-Barley planted on ~ntours is effective in minimizingerosion.

Homeowners should avoid broadcast seeding or contourseeding grasses on recent slippage areas or act~velyslidinghillsides. The additional infiltration of water into the soilby the shallow-rooted grasses may cause local soil liquefac-tion and further slippage and mudflow. Plastic sheetsshould be spread over these areas until a proper slopeengineering job can be done.Barley

Hand planting of barley in contours spaced about 3 feet(0.9 m) apart has proven very effective in minimizing ero-sion, even on steep slopes ~ig. 26). The ridges and trenchesof the contours form a series of miniature terraces thatallow water to infiltrate the soil. This increases plantgrowth, reduces runoff, conserves soil moisture, and pre-”vents soil loss. On slopes with lower infiltration rates, suchas steep, long slopes and hillsides with finer, less coarsesoils, contours should be spaced more closely than onwatersheds with high infiltration rates. Similarly, contoursshould be closer in areas where the runoff problems arecritical, as near homes at the base of the slopes.

Strip cropping could also be practiced by interplantingthe barley rows with rows of low-fuel ground covers incatching and holding water and soil. This method allowsfor reestablishment of ground covers while at the same timegreatly reducing postfire soil erosion. Several years cantherefore be saved in relandscaping of fire-prone hillsides.Quick cover and healthy plants are produced through sav-ing the topsoil which is so valuable for plant growth.

For seeding barley, recommended rates are about 150pounds of barley per acre (167 kg/ha) with about an equalamount of diammonium phosphate fertilizer added to therows at planting time. Barley is readily available from feedstores and can be ordered immediately- after a fire. Careshould be taken to order only recleaned barley, as rolled

42

Figure 27-Check dams can reduce gully erosion,

barley (used for feed) will not germinate. Recleaned barleymay be cheaper than ryegrass when the demand for it islow.

For quick establishment, barley seeds should be pre-germinated no longer than 1 day and should be coveredwith soil to a depth not exceeding 2 inches (5 cm). Seedslightly covered with soil germinate with the first winterrains, whereas seed lying on the soil surface need anextended period of moist weather for germination, Com-pared with ryegrass, barley germinates and grows morevigorously in cooler weather. Broadcast seeding (sowingthe seeds on the slope without covering them) is less effec-tive with barley than with ryegrass seeding. Barley seedsare much larger than ryegrass seeds, and very seldom findenough moisture at the soil surface to allow germination.Rodents and birds also tend to eat the seeds before theyhave a chance to germinate. Even after the barley plantdies, the strong roots can hold the surface soil for another 2years. When reseeding is not desired, the plants should becut in the spring before they go to seed. Barley is an annualplant and becomes a flashy fuel after it dies in late spring orearly summer.

Check Dams

The object of check dams is to hold back rocks, brush,and other debris, and to slow down the flow of water incanyons or large gullies (fig. 27). Reseeding and replanting

should go hand in hand with these temporary erosioncontrol measures. Check dams should be repeated aboutevery 50 ft (15 m). Small mesh fencing will act to impedewater flow. Additional information regarding liability todownstream residents may be obtained from local floodcontrol officials.

Boards

Redwood boards as thin as 1inch (2.5 cm) can be usedeffectively to stabilize steep slopes before planting and tokeep existing soil slips from getting worse wig. 28). Theboards are the homeowner’s emergency soils engineeringtools to reduce the effective length and steepness of hill-sides by dividing a larger watershed into smaller sections.Boards can be very effective if well engineered and sup-ported by a proper plant cover, but should not be lookedupon as a substitute for permanent soils engineeringmethods. Boards should not be placed closer than 5 feet( 1.5m) vertical distance and should be held by old pipes orrebars at least 4feet ( 1.2m) long and about 1inch (2.54 cm)or more thick (old pipes may be gathered from a localplumber). Rebars are round, solid construction steel barsthat are ridged and anchor themselves in the soil moreeffectively than smooth pipe, provided the soil is firmlytamped around the rebar after it has been hammered intothe ground.

A board 10 feet (3 m) long and 1 foot (30.5 cm) highshould be held by a minimum of three rebars. Unless theboards are used as terraces, there should be 1or 2feet (30.5or61 cm) of clearance between horizontally placed boards.

Figure 28-Pretreated or redw~ bards help stabilize the face of soilslips.

43

Figure 29-Jute mating reduces surface erosion

Boards minimize slippage during heavy rains, when bothsoil and excess water can ooze out between the boards.Remember that a supersaturated slope will slip.

Localized slope instability may result if the pipes thathold the boards are hammered into highly fractured andweak bedrock, especially in areas where such rock layeringparallels the slope. Pipes may also fail to hold the boards,especially on steep slopes with thin soils, if much new soil isplaced behind the boards to establish a foothold for newplants.

Jute Matting

Matting made from natural fibers can be bought incarpetlike rolls. It is unrolled over the slope and anchoredwith pins in areas where heavy erosion is expected ~g. 29).Every square of the matting acts as a miniature check damand effectively catches soil particles. The matting eventu-ally decomposes but holds long enough for plantings tobecome established. Information on how to to use thematting is obtainable from a nursery. Potato sacks (gunnysacks) can be effectivdy used for both erosion control andweed control of smaller areas.

Chain Link Fence

Where life and property are endangered by falling rocks,chain link fencing can be useful wig. 30). The chain link isflexible enough to catch even large boulders. When theseare likely to fall, steel posts or telephone poles should beinstalled to anchor the fence, but not 4-by-4 wooden posts,because a rock has a better chance of glancing off a roundobject than a square one without breaking it. Telephonepoles should be buried at least 3 feet (0.9 m) deep. Profes-

sional help is advisable when designing a chain link fencesystem to reduce the danger from falling rocks.

Sandbags and Deflector Barriers

Sandbags are used to direct the flow of mud and water toareas where they will do less harm @g. 3J). The flow ofmud away from one home should not be directed towardanother, however. Sandbags can be used effectively tobuild a berm at the top of slopes to prevent water fromrunning downhill. Channeling water down the slope causessupersaturated soil and slippage.

After major fires, a limited number of sandbags may besupplied by fire protection agencies or the flood controldistrict. The sandbags should be filled half full with sand orsoil, and the flaps tied and folded under, pointing towardthe direction of water flow. When one layer of bags is inplace, bags should be stomped on to eliminate spacesbetween them. The next layer of bags should be staggered.Sandbags should never be more than three layers highunless they form a pyramid or unless a building is used asbacking.

Wood deflector barricades may need to be used in criti-cal areas where emergency revegetation may not be veryeffective. They serve the same purpose as sandbags but aresemipermanent structures. The local flood control districtoffice can provide expert advice regarding these diversiondevices.

Figure 30-Chain-link fences stop rocks, even large boulders.

44

Drains

Concrete bench and downhill drains reduce the effect oftopography on erosion wig. 32). They reduce runoff anderosion by dividing a portion of a large watershed intosmaller watersheds and by removing excess water safelyfrom a slope. Every year before the rains return, all drainsin the neighborhood should be inspected and cleared ofdebris. Clogged drains are a major cause of flood damageand hillside slippage. All drains should be reinspectedbefore sandbags are placed in position and after everyheavy rain, especially the first few years after a fire.

Dry Walls

Where slippage has occurred or is imminent, dry wallscan be effectively installed, provided they have a firmfoundation, as at the base of slopes wig.33). Dry walls canbe made from unwanted concrete pieces from patios ordriveways, and the wall can then be put up piece by piecewithout cement. Such materials are free, except for haul-ing. No cement is needed and there is no mess. Such a wallmay last a lifetime and is more effective than a block wallduring an earthquake. If the wall is more than several feet

tall, it should be sloped slightly toward the hill as newlayers are added. Dry walling against a fill slope leads toslope failure (mudflow) during intense rains unless the fillis well compacted, anchored by plants, and only a few feethigh. Lateral drains inserted 20 feet or more horizontallyinto the slope will lessen the chance of slope slippage bydraining the excess water out of the slope.

Plastic Sheeting

Plastic sheeting can keep a slope relatively dry duringheavy rains and prevent surface erosion especially after afire in late fall wig. .34. After a slippage, it will preventfurther saturation and movement of the soil. The entireslope or slope area should be covered with the plastic sothat water is not channeled from one part of the slope toanother. The flow of water at the base of the plastic must becontrolled to avoid damage to homes below. Improperlyplaced sheets that concentrate runoff in selected areas orthat cover only portions of a hillside area leading cause ofslope failure. Therefore plastic spread on hillsides must beproperly tied down or constantly maintained throughoutthe rainy season. Broken pieces should be replaced andwindblown sections retied. The thicker 6-roil (0.00&inch)

Figure 31—Sandbags divert flow mud.

I I

Figure 32-Drains mntrol water flow and reduce excesssurface runoff.

45

plastic is preferred because it rips less easily and covers theslope better, thereby reducing maintenance problems.Sandbags partially filled with soil are used to anchor theplastic. On steeper slopes, sandbags should be tied to ropesthat are anchored at the top of the slope. Rocks or stakesshould not be used to anchor the plastic because rocks wearthrough the plastic and stakes are ineffective when windswhip underneath the plastic. Rainstorms bring rain andwind. The plastic sheets must therefore be sealed on alledges and on overlaps, to prevent them from becomingsails as the wind whips underneath them.

Guniting

Guniting of slopes above or below homes or on road cutsis the most effective way to eliminate soil erosion in areaswhere plants are ineffective because slopes are steep andsoil erosion is rapid. In effective guniting, a network ofconstruction steel is anchored into bedrock and concrete ispoured over this web of steel after drain pipes have beeninstalled at appropriate intervals. The unattractive effect ofthe gunited hillside can be greatly reduced by coloring theconcrete approximately the natural soil color of the areaand planting trailing groundcovers at all edges. For safedisposal of the runoff water, the base of gunited slopesmust be tied into permanent steel, asphalt, or concretedrains.

Guniting is most effective on slopes not exceeding 25feet(7.6 m) in vertical distance. It requires a high initial invest-ment but is cost-effective in the long run. It is often the onlyeffective way to stabilize steep roadcuts and slopes alreadyundercut by roads when building is begun. Without treat-ment, debris from steep or undercut slopes settles at thefoot of the slope. Although this process eventually estab-

1--1

Figure 34-Plastic sheets remove further rainfall from saturated soils.

lishes a new, stable slope angle, the debris may also par-tially block the road and need to be cleared and hauledaway periodically. This process continuously undercuts theslope causing further accelerated erosion and larger slides.Building should therefore not be allowed on top of anyundercut slope unless the cut is first completely stabilizedor unless it consists of a solid rock cliff. Retaining walls andguniting are only a partial solution to hillside problems.

The suggestions made here are quick self-nelp methodsfor the homeowner, using materials often readily available.Planting of woody plants, such as shrubs and trees, is noteffective as erosion control in the season after a fire. Thesedeep-rooted plants are needed, however, to minimize slip-page on steeper slopes, and herbaceous cover such as

.

IFigure 33-Dry walls can stabilize the toa of slopes.

46

grasses is needed to reduce surface erosion. Shrubs and

trees must be replanted if the burned woody plants do not

resprout. Research has shown that converting chaparral tograss covered watersheds after a burn greatly reduces ero-sion for the first 5 years or more, as compared with theuntreated stand where chaparral is resprouting. After this,erosion on the grass-covered site greatly increases becausethe old chaparral roots that were still holding the hillsidehave finally rotted away and the grass root zone becomessupersaturated and slips out (Corbett and Rice 1966).Thus, the homeowner must be careful in landscaping ahillside after fire. Steep hillsides converted from chaparralto low-fuel plants often show little subsurface instability inthe form of slips and dides for some years. The slips andslides that occur during high intensity rains 5 to 10yearslater are therefore seldom attributed to the earlier brushconversion, but they can be prevented.

WHAT TO DO WHENCAUGHT IN A WILDFIRE

If your home is threatened by wildfire, you may becontacted by a fire or law enforcement official and advisedto evacuate. If you are not contacted in time to evacuate, orif you decide to stay with your home, the following sugges-tions will increase your chances of safely and successfullydefending your property.

Before Fire Approaches

1. If you plan to stay, evacuate your pets and all familymembers who are not essential to protecting the home.

2. Be properly dressed to survive the fire. Cotton andwoo! fabrics are preferable to synthetics. Wear long pantsand boots anct carry with you for protection a long-sleevedshirt or jacket, gloves, a handkerchief to shield the face,water to wet it, and goggles.

3. Remove combustible items from around the house.This includes lawn and poolside furniture, umbrellas, andtarp coverings. If they catch fire, the added heat couldignite your house.

4. Close outside attic, cave, and basement vents. Thiswill eliminate the possibility of sparks blowing into hiddenareas within the house. Close storm shutters.

5. Place large plastic trash cans or buckets around theoutside of the house and fill them with water. Soak burlapsacks, small rugs, large rags. They can be helpful in beatingout burning embers or small fires. Inside the house, fillbathtubs, sinks, and other containers with water. Toilettanks and water heaters are an important water reservoir.

6. Locate garden hoses so they will reach any place onthe house. Use the spray-gun type nozzle, adjusted to aspray.

7. If you have portable gasoline-powered pumps totake water from a swimming pool or tank, make sure theyare operating and in place.

8. Place a ladder against the roofofthe house oppositethe side of the approaching fire. If you have a combustibleroof, wet it down. Do not waste water. Waste can drain theentire water system quickly.

9. Back your car into the garage and roll up the carwindows. Disconnect the automatic garage door opener (incase of power failure you could not remove the car). Closeall garage doors.

10. Place valuable papers and mementos inside the carin the garage for quick departure, if necessary. Any petsstill with you should also be put in the car.

11. Close windows and doors to the house to preventsparks from blowing inside. qlose all doors inside thehouse to prevent drafts. Open the damper on your fireplaceto help stabilize outside-inside pressure, but close the fire-place screen so sparks will not ignite the room, Turn on alight in each room to make the house more visible in heavysmoke.

12. Turn off all pilot lights.13. If you have time, take down your drapes and cur-

tains. Close all venetian blinds or fire-resistive windowcoverings to reduce the amount of heat radiating into yourhome. This gives added safety in case the windows give waybecause of heat or wind.

WhentheFireFrontArrivesand Passes

As the firefront approaches, go inside the house. Staycalm, you are in control of the situation. After the firepasses, check the roof immediately. Extinguish any sparksor embers. Then, check inside the attic for hidden burningsparks. If you have a fire, call the Fire Department andthen get your neighbors to help fight it until the fire unitsarrive. The water in your pool and the water in yourgarbage cans, sinks, toilet tanks, etc., will come in handynow. For several hours after the fire, recheck for smokeand sparks throughout the house.

In a major conflagration, fire protection agencies willprobably not have enough equipment and manpower to beat every home. You cannot depend totally on their help.One of the firefighter’s principal responsibilities is to stopthe spread of fire from house to house. Therefore, if onehome is on fire, firefighters might have to pass it by to saveanother in the path of the fire. Your careful planning andaction during a fire can save your home. Be prepared. Talkwith your neighbors to see what resources you have. Askyour fire or forestry personnel for professional advice andassistance,

When Caught in the Open

When you are caught in the open, the best temporaryshelter will be found where fuel is sparse. Here are com-ments on some good and bad places to go:

47

. Automobile: Move the car to bare ground or sparsefuel areas, close all windows and doors, lie on the floor andcover yourself with a jacket or blanket. The fuel tank of thecar will normally not explode until the car is well on fire ormay not explode at all. So, keep calm and let the fire pass.

. Road cut: If you are caught without shelter along aroad, lie face down along the road cut or the ditch on theuphill side (less fuel and less convection heat). Cover your-self with anything that will shield you from the heat of thefire.

● Canyons: Never be caught by fire in canyons thatform natural chimneys. These are narrow, steep canyonsthat concentrate heat, explosive gases, and updraft. Withinchimneys, temperatures may exceed several thousanddegrees Fahrenheit during a fire.

. Saddles: When you are hiking out of an area wherefire is in progress, avoid topographic saddles if possible.Saddles are wide natural paths for fire winds, and vegeta-tion here will normally ignite first.

. Other areas: Look for areas with sparse fuel (forexample, soft chaparral such as black sage or grasslandrather than chamise chaparral), if possible, within adepression. Clear as much fuel as you can while the fire isapproaching and then lie face down in the depression andcover yourself with anything that will shield you from theheat. Smoke may create as great a survival problem as theflames do. If you are caught on a steep mountaintop orsharp ridge, the back side away from the approaching firewill be safer than the front side. Be aware, however, thatfire eddies often curl over sharp or narrow ridges.

Before you hike in fire-prone areas, seek additionaladvice from wildland firefighting agencies. They maysupply pamphlets and can give you specific tips for wild-land fire survival.

Evacuatio-nand Road Closure

Fire protection agencies are responsible for determiningwhen the need for evacuation exists, and the jurisdictionallaw enforcement agency is responsible for carrying out anordered evacuation. The purpose of evacuation is to pro-tect people from life-threatening situations. Section 409.5of the California Penal Code provides the legal authority

for law enforcement officers to close and restrict access todisaster areas. The news media are legally exempt from thisprovision.

Owners have the right to stay on their property if they sodesire, if in doing so they are not hindering the efforts offire personnel or contributing to the danger of the disastersituation. In fires or floods, able-bodied persons who wishto remain may be able to aid fire personnel in saving theirproperty, and those who are desirous of remaining may bepermitted to do so.

In a fire or flood, there maybe several different phases ofroad closure within the disaster area: (a) in an area thatforseeably could be involved inthedisaster, but presently isnot, people without purpose will be restricted from entry toreduce traffic problems or the potential for looting; (b) inan area of imminent danger with limited access or egress,people would be discouraged from entry, though they livein the area, and those who are adamant after beinginformed of the danger would be permitted entry; (c) in anarea presently involved in the emergency where extremedanger to life exists and where traffic must be restricted dueto movement of emergency vehicles, people, including res-idents, will be refused entry.

Road closures around emergency incidents are essentialto the expeditious movement of persons leaving the areaand mobility of emergency equipment. On major incidents,closures become immediately essential to permit accessibil-ity of firefighting forces, orderly evacuation, and exclusionof unauthorized persons.

In summary, here is what you should do:. Notify the local fire protection agency.. Stay calm—you are in control of the situation.● If you decide to stay with your home during a wild-

fire, evacuate all family members who are not essential toprotecting the home.

. Dress properly to shield yourself from the heat andflames.

. Take steps to prepare your home for the approachingfire.

. If caught in the open, seek shelter where fuel issparse.

. Remember-wildfire is erratic, unpredictable, andusually underestimated. Life safety is always the mostimportant consideration.

48

APPENDIX

List of Species MentionedFlora (native or naturalized)l

CommonnameAaron’s beardAcacia ongerup, prostrateAfrican daisyalfilariaAlgerian ivy (freeway ivy)alyssumannual ryegrass (H)Australian saltbushbarley (H)Bermudagrassblack locust (P)black sagebluegum eucalyptusBrazilian pepperbuckwheat

bur cloverbush pOppyCalifornia buckwheatCalifornia laurelCalifornia pepperCalifornia sagebrushCalifornia scrub oakCalifornia walnut (D)Canary Island pinecapeweed (P)Carmel creeperceanothuschamiseChilean saltbushchokecherry (P)coast live oakcoyote brush (Twin Peaks)creeping sagecurrant, gooseberrycypressdeerweedDescanso rockrosedesert buckbrushdwarf running myrtleelderberryEnglish ivy (P)english oakeucalyptusfuchsiasgooseberriesgray santolinagreen acaciagreen galenia (P)lgreen lavender cottongreen saltbush

ScientificnameHypericum calycinumAcacia rodelens cultivar ongerupOsteospermum fruticosumErodium speciesHedera canariensisAlyssum specieshlium multl$orumAiriplex semibaccataHordeum vcdgareCyrrodon dactylon -Robinia pseudoacaciaSalvia melhyeraEucalyptus globulusSchinus terebinihl~oliusEriogonum wrightii ssp.subscaposumMedicago hispidaDendromecon rigidaEriogonum JasciculatumUrnbellulariacall~ornicaSchinus molieArtemisia call~ornicaQuercus dumosaJuglans ca[l~ornicaR“nuscanariensisArctoiheca calendulaCcanothus crisseusCeanothus speciesAdenoslomafasciculatumAtriplex undu[ataPrunus species@ercus agr~oliaBaccharispilu[aris var. pilularis

Salvia sonomensisRibes speciesCypress speciesLotus scopariusCistus crispusCeanothus greggiiVincaminorSambucus speciesHedera helix@ercus roburEucalyptus speciesFuchsia speciesRibes speciesSantolina chamaecyparisAcacia speciesGalenia pubescensSantolina virensAtriplex glauca

—

‘Tucker and Kimball (1978)P = plant parts poisonous to ingestD = may cause dermatitisH ❑ may readily cause hay fever or other allergic reaction

gum rockrosehoary-leaf ceanothushollyleaf cherryhoneysuckleice plants

junipersknotweedlaurel sumac (D)lawn grasslemonade berry (D)lippiamountain lilacmountain mahoganyMueller’s saltbushmyoporum, prostrate (P)

navel orangeoakold man saltbusholeanderperiwinklepinesPoint Reyes ceanothusponderosa pineprickly pearpfostrate ceanothuspurple rockrosepurple sagereedrockroserosemary, prostrate

rosesryegrass, annual (H)sagessaltbushscrub oaksilver saltbushstar thistlesugarbosh (D)sugarbush (D)sunflowerssycamoretoyon, christmasberry (P)wavy leaf saltbushwhite sagewhite trailing icepiantwild mustardyucca

FaunabadgerCalifornia ground squirrelCalifornia quailcoyotegolden eaglegopher snakemountain kingsnakepack ratpocket gopherrabbitrattlesnakered-tailed hawkweaselwestern racer snakewildcat

Cistus ladanl~erusCeanothus crassl~oliusPrunus illicl~oliaLonicera speciesCarpobrotus, Delosperma, Dro-samhemum speciesJuniperus speciesPoiygonum equisil~ormeRhus laurinaCynodon dactylonRhus integrifoliaPhyla nodlflora (Lippia repens)Ceanorhus speciesCercocarpus speciesAtriplex mue[[eriMyroporum parvi~oliumcultivar horshumCitrus sinensis@ercus speciesAtriplex nummulariaNerium speciesVinca major

R“nus speciesCeanothus gloriosusPinus ponderosaQuntia speciesCeano~husprostratesCisIus vi[[osusSalvia leucophyllaArundo speciesCislus speciesRosmarinus officinalisvar. prostratesRosa specieshiium mulllflorumSalvia speciesAtrip{ex species@ercus dumosaAtriplex rhagodioidesCenlaurea speciesRhus speciesRhus ovataHeIiarrlhusspeciesPlatanus racemosaHeteromeIes arbutl~oliaAtriplex undulataSalvia apianaDelosperma albaBrassica speciesYuccaspecies

Taxidea taxusOtospermophilus beecheyiLophorlyx call~ornicaCanis IatransAquila chrysaetosR“tuophismelanoleucusLampropeltis zonataNeotomafuscipes~omomys speciesSylvilagus speciesCrotalus viridisButeo borealisMustelafrenataColuber constrictorFe[is lynx

49

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