J\[EXASA&M

fiGRILIFE EXTEN SION

SOUTH E

E-129

X RANGELANDS

Brush Management Effects on Deer Habitat s

Much of the rangeland in South Texas Is covered by dense stands of low-growing, thorny shrubs which may limit livestock produc­tion because of reduced her­baceous forage. Large acreages of brushy rangeland have under­gone treatment to check woody plant encroachment and Increase forage production for domestic livestock. In the past, most range improvement efforts in South Texas were directed at clearing pastures of brush through mechanical methods, followed by conversion to tame pasture. Only In the past 1 O to 15 years have the habitat requirements of wildlife

• Extension assistant, Texas Agricultural Extension Service.

calvln L Richardson*

species been considered In brush management programs.

IHabltat Requirements

White-tailed deer are often con­sidered browsers because they consume woody vegetation. In reality, deer prefer forbs (weeds) more than browse but are com­pelled to consume woody species when herbaceous {non-woody) forage Is unavailable or declines In quality. Although forbs are preferred, deer also will eat a broad variety of browse and grass species. Because of this adap-­tabllity, It Is difficult to single out one habitat type that Is greatly su­perior to others.

Good deer habitat contains a diversity of woody plants (brush), forbs and grasses. A variety of food plants allow deer to select high quality forages throughout the year. The greatest forage supply for deer occurs in the early to intermediate stages of succes~ sion before the trees out-compete herbaceous plants for sunlight, water and minerals. This Is the reaspn that brush management (appropriately conducted) tends to increase the availability of deer forage. Fire, herbicides, roller chopping, shredding, etc. tem­porarily "set back" succession and allow herbaceous forage plants to grow.

Cover is also a vital component of deer habitat. In South Texas,

Texas Agricultural Extension Service • Zerle L. Carpenter, Director • The Texas A&M University System • College Station, Texas

brush provides excellent cover forescape and for protection againstweather extremes. An importantaspect of this cover is its structure(height, density and canopy).Brush species with a moderate todense canopy are important inSouth Texas as a source of shade.Escape or screening cover doesnot need to be extremely densebut should be at least 4 feet inheight. Probably more importantthan the extent of the cover is thedegree to which it is interspersedwith feeding areas. For example,habitat with brush mottes andfeeding areas scattered through-out would be far more valuable todeer than habitat with a singlelarge feeding area adjacent to alarge tract of brush. This rathersimple but important principleshould be considered bymanagers implementing brushmanagement practices withwildlife as a priority.

The reason the interspersion offood and cover is so important todeer can be explained by the“edge effect.” Edge is the areawhere two or more vegetationtypes meet and integrate. The sig-nificance of edge is that this regionoften provides a greater diversityof food plants and cover types (es-cape, shade, etc.) to meet deerhabitat requirements. Therefore,the most beneficial brush manage-ment patterns are those that createthe most edge among treated anduntreated areas. Brush manage-ment patterns that leave smallblocks of brush in a checkerboarddesign (Fig. 1) have been usedeffectively in several deer manage-ment programs. However, a strippattern (Fig. 2) of brush treatmentis more common because long,thin strips provide more edge thanblock patterns. Mosaic brushtreatment patterns, which followcontours of the land and certainvegetation or soil types, providethe greatest amount of edge andappear to be the most beneficial to

deer. However, these treatmentsare more expensive and difficult toplan and accomplish.

Deer rarely travel across broad ex-panses of open area without ac-cess to cover. Therefore, a treatedarea should be no more than twicethe distance a deer will move fromcover. Research in South Texashas shown that deer will seldomventure more than 200 to 250yards from cover, so treated stripwidths should be no greater than1/4 mile. It was observed that deerused treated strips more oftenduring daylight hours when stripswere only 200 to 250 yards wide.

Brush strips left for cover shouldbe at least wide enough to allow adeer to disappear from visibilitywhen an observer is standing atthe edge of the cover strip. Brushdensity and height are unique toeach ranch, but this thresholdvisibility distance ranges between30 to 50 yards over much of SouthTexas. Note that this is the mini-mum amount of brush that shouldremain untreated to satisfy thescreening requirement of the

cover strip. It may be necessary toleave more untreated brush inorder to maintain the diversity thatis so essential to good deerhabitat. This is particularity impor-tant with chronic impact treat-ments such as root-plowing orchaining that physically removethe treated brush plants.

The quantity of brush that can beremoved will vary among ranches,depending upon brush charac-teristics. However, most success-ful deer management programsmaintain 40 to 60 percent of theranch in brush. Remember thatonce brush is treated, its composi-tion, structure and density are al-tered for a long period of time.Clearly define the objectives andconsider all options before im-plementing a brush managementprogram.

Brush management methods thatpresently have the most ap-plicability in South Texas include

Figure 1. Brush management in an alternating block design with clearings that are150-200 yards wide.

IBrush Management Practices

600 • 800 yda ------

D Cleared Area

rl] Brush

Figure 2. Brush management in a large block pattern (A) and strip pattern (B). Al-though approximately the same proportion of brush was cleared in A and B, thestrip pattern results in better deer habitat.

mechanical and chemical techni-ques and prescribed burning.Each method has its strengths andweaknesses and should be con-sidered in relation to managementobjectives.

Mechanical Brush Management

Mechanical brush managementmethods can be classified into twocategories, those designed tosimply remove the aerial parts ofthe plants and those designed toremove the entire plant. Shred-ding and roller chopping are theprimary methods for simple topremoval. The effects of these prac-tices are relatively short-lived sincemost brush species possesstremendous regrowth potential.However, these temporary effectscan improve the accessibility andnutrient content of deer forage.

With shredding and roller chop-ping of mixed brush, a 50 percentcanopy recovery has been ob-served only one year after treat-ment. However, all brush plants intreated areas are accessible to

deer at least during the first yearafter treatment, and usually longer.Brush plants on untreated areasmay be largely unavailable due tothe height and dense growth pat-terns of the mottes. Top removalnot only increases the availabilityof browse species by reducing theplant height, but also increasesbrowse palatability by allowingmore tender regrowth to sprout.Deer readily feed on so-called un-palatable plants when the thornystems are replaced by new, leafyshoots.

Not only is regrowth morepalatable to deer than maturewoody plants, but the nutritionalquality of the immature growth isusually higher. Immature growthstimulated by top removal tends tobe higher in crude protein contentand more digestible than matureleaves or stems. Research hasshown an eight-fold increase in thevalue of brush for forage (browseutilization x frequency of use xplant density) after shredding, anda six-fold increase after roller

chopping. While roller choppingmay be less effective than shred-ding for improving the forage valueof browse, it has the additional ad-vantage of increasing forb produc-tion through soil disturbance.

Although shredding and choppingmay temporarily improve foragevalues, continued top removal ofbrush may result in thickets of root-sprouters such as mesquite andtwisted acacia on the treatedareas. Mesquite mast is con-sidered important to deer duringthe summer and twisted acaciamay be used by deer, but thesespecies usually are undesirable indense stands. Because mostbrush species are prolificsprouters, the effectiveness ofshredding and roller choppingtreatments generally does not lastmore than five years. The greatestforage values of browse speciesare associated with the first yearfollowing top removal treatment.

Grubbing, root-plowing and chain-ing are the primary methods ofphysical plant removal in SouthTexas. Little attention has beenfocused on the effects of grubbingon deer forage since it is an ex-tremely selective method. Themost efficient control by grubbingusually occurs on sites wherewoody plants are widely spacedand large enough to be seen by theequipment operator. Elimination ofa browse species decreases thediversity of available forage andlimits diet selectivity. Cod-seasongrasses may become establishedin pits left by grubbing, but grassesare relatively unimportant for deernutrition.

Most studies on root-plowing havereported that the practice is devas-tating to white-tailed deer habitatbecause it destroys cover andplant diversity, unless brush stripsor blocks are left untreated. How-ever, because brush speciesgenerally constitute a significantportion of the deer diet in South

A B

D Cleared Area II Brush

Texas, root-plowing also has adetrimental effect on the year-round availability of forage. Al-though root-plowing mayessentially eliminate browse andreduce cover, the soil disturbancegenerally stimulates forb produc-tion. Therefore, newly root-plowedareas offer a good source ofseasonal (spring and fall) feed fordeer. However, the root-plowedareas will be used by deer only ifcover is available nearby and thereare alternate food sources to sus-tain the deer herd when forbs arenot present.

Under proper environmental con-ditions, chaining is an effectivemethod of knocking down, uproot-ing, and thinning moderate todense stands of large woodyspecies. Like root-plowing, chain-ing large expanses of brushlandcan be detrimental to deer num-bers, as well as deer nutrition, byreducing or eliminating availablecover and browse species. The ef-fects of chaining are generally notas severe as root-plowing sincethe smaller, more limber brushplants are seldom up-rooted andthe larger shrubs that are brokenoff at the base often resprout withnutritious, palatable shoots. In ad-dition, the low to moderate soil dis-t u r b a n c e ( d e p e n d i n g o ntreatment) will increase forbproduction most years.

Chaining may also result in ex-tremely dense stands of prick-Iypear. A stacker rake must beused (prior to plowing and afterchaining) to avoid this problem.Pricklypear is an important foodplant for deer, especially duringthe summer and winter. However,it is most desirable when inter-spersed with a diversity of otherforage species rather than grow-ing in dense stands.

Chaining treatments reduce thedensity of most species, but dif-ferential reaction among speciescauses post-treatment com-

munities to differ considerably incomposition. The relative impor-tance (density, frequency, size) ofmesquite changes little after chain-ing. Although each additionalchaining treatment decreases thedensity, frequency and size ofmesquite, it remains an importantpart of the woody plant com-munity. Lime pricklyash tends tobe more susceptible to chaining,and its relative importancedecreases with additional treat-ments. Spiny hackberry (gran-jeno), a high quality browse,increases in importance with addi-tional chaining treatments.

Prescribed Burning

Fire in South Texas brush com-munities significantly reduceswoody cover during the first yearafter the burn. However, generallyless than 15 percent of the woodyplants are actually killed. Althoughfire does not kill many brushspecies, prescribed burning canreduce brush cover, alter brushcomposition and structure, and in-crease herbaceous cover. A majorconstraint to effective prescribedburning in South Texas is theamount and distribution of fine fuelrequired to carry the fire. A brushcontrol treatment before burningmay be required to produce ade-quate amounts and distribution offine fuel. Therefore, prescribedburning often is used in combina-tion with other brush managementpractices and as a maintenancemeasure. Fire has proved to bemore effective on areas wherelarge brush mottes were firstknocked down by mechanicalmeans. The reduction of brushcover by chopping or shreddingtwo to three years before the fireallows grass and forbs to grow,which provide fuel for a firethroughout the mottes. In addition,the chopped portions of old brushtops provide additional fuel for theburn. A rest-rotation system ofgrazing also is necessary to

promote adequate amounts of finefuel .

Because brush species resproutfrom buds located on the stembase and below the soil surface onroots or on rhizomes, the effect offire on these plants is similar to thatof any method of top removal. Inother words, prescribed burningreduces brush cover, especiallyfollowing mechanical or herbicidetreatments, and increases theforage value (availabil i ty,palatability, nutrient content) ofbrush. Increased browseavailability and quality can benefitwhite-tailed deer, provided thatother habitat components are ade-quate to allow utilization of thebrowse. Huisache pIants that areburned tend to have higher levelsof crude protein and phosphorusthan unburned plants during thefirst six months after burning. Thegreatest differences in nutrientlevels between burned and un-burned plants occur during thefirst month of growth. The greatestutilization by deer and other brow-sers occurs during the first twomonths following the burn. Burnedhuisache plants tend to producefive to six times the number of“browsable” twigs as unburnedplants. Maintenance of huisacheplants in a low-growing bushystate can be achieved by burningat two-to three-year intervals. Liveoak thickets respond in a similarfashion.

A mosaic of brush cover patternsusually will result from burning inSouth Texas because of fuel loaddiscontinuities associated witharid conditions and moderate toheavy grazing. This variability as-sociated with “brush country”burns is often desirable for creat-ing high quality deer habitat sinceit results in a vegetation “mosaic.”Deer tend to benefit most fromsmall, hot burns within brushdominated habitats. This patternincreases forbs and valuable

browse regrowth while maintain-ing security cover. Prescribedburning may even restore broad-Ieaved plants to a range whererepeated herbicide use has greatlyreduced the forb population.White-tailed deer make heavy useof burned areas in South Texas,especially in early spring whensucculent forb growth is available.

Herbicide Brush Management

Broadcast herbicide applicationscan have negative effects on deerhabitat, but if applied properly theycan improve the quality andavailability of food plants and im-prove the overall habitat. Treatingrelatively large acreages with her-bicides may temporarily reducewhite-tailed deer numbers. Al-though the standing remains ofdefoliated brush offer screeningcover for deer, herbicides canreduce the diversity of browsespecies and the abundance ofshade cover. In addition, broad-cast herbicide applications reducethe diversity and abundance offorbs. Deer numbers may return tonormal by the third growingseason after broad-scale brushspraying. Generally, deer usegrasses only in small amounts inthe spring and fall; however, theymay consume more grasses inareas sprayed with a herbicide dueto a lack of browse and forbs. Insuch cases, deer may suffer nutri-tionally since they have a lowdigestive capacity for grasses.

Research in the northern RioGrande Plain showed that a sub-stantial portion of the deer popula-tion evacuated a pasture where 80percent of the brush was strip-treated with herbicides. However,when the forbs recovered andbrowse regrowth developed, deerreturned in greater than normalnumbers. A study in the coastalbrushland found that spraying 80percent of mature brush in alter-nating strips did not change deer

numbers. The treated and un-treated strips were 200 yards and30 yards wide, respectively. Theunsprayed strips apparently fur-nished adequate forbs which wereimportant deer food items in thisarea. Spraying 100 percent of anadjacent pasture resulted in a 40percent reduction in deer num-bers. After two years, deer num-bers approached pre-treatmentlevels.

Brush management in drainagehabitats should be carefully con-sidered since these sites (such asmesquite drainages) are con-sidered the most important type ofhabitat for deer in South Texas.The structural features of thesesites are preferred by deer for mid-day loafing and bedding. In addi-tion, these moist, ferti lebottomland sites have great poten-tial for producing nutritious deerforage. Indiscriminate broadcast-ing of herbicides on these siteswould be detrimental to deer num-bers and/or nutrition. Brush treat-ment to thin dense stands orcreate small clearings would bemore appropriate. Research inSouth Texas has shown that spray-ing 70 percent of a mesquite bot-tomland was not detrimental towhite-tailed deer. Any reduction incover screen may have beenmitigated by a general increase inquality, quantity and availability ofbrowse. The three- to ten-fold in-crease in grass production mayhave improved conditions for deerby reducing cattle use of forbs andbrowse.

Broadcast application of soil-ap-plied herbicides at a rate of twopounds per acre or more in-creased forage production andbotanical composition within twoyears in the northern and centralRio Grande Plain and in the Coas-tal Prairie. Although aerial applica-tion of these herbicides at twopounds per acre effectively con-trolled whitebrush, rates as low as

one pound per acre weredetrimental to forb production anddiversity. Rates that were highenough to partially controlmesquite (4 lbs/acre) nearlyeliminated forb production for twoyears following application.

One of the most beneficial her-bicide applications for deer is thevariable rate pattern (VRP), inwhich different rates of herbicideare aerially applied in strips at rightangles to each other. This patterncreates numerous small blocks ofvegetation treated with differentherbicide rates ranging from noneto heavy and results in a diversityof vegetation responses (Fig. 3).This type of pattern provides deerwith a good selection of foodplants at various successionalstages, while leaving scatteredblocks of mature brush for cover.

The effects of brush managementon white-tailed deer habitat cannotbe determined simply in terms ofthe amounts, kinds and nutrientcontent of forage species present.Cover (for shelter and screening)is a dominant factor influencing theuse of potential feeding areas bydeer. A tremendous diversity ofnutritious forbs on a large root-plowed and raked area is of littlevalue to deer unless there isscreening cover nearby. Conver-sely, a vast thicket of densewhitebrush cover is of little value todeer if forbs and browse speciesare unavailable. Diversity and in-terspersion of cover and foragespecies are essential componentsof deer habitat.

Indiscriminate brush treatmentcan reduce the availability of primeloafing or bedding sites of deer, aswell as decrease the availability ofcritical forages. However, careful-ly selected brush management

I Conclusions and Management Implications

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0 l l 4 2 Herbicide RalM (2nd flight)

!'Igwe 3. Variable ,_ palNrn (VRP) herbicide treatment ltl0Wing the variety of

specific area, it is necessary to un­derstand the response to the treat­ment as influenced by soil moisture, soil type, climate and types of brush, Also, it may be Important to consider how range conditions could make the response on one ranch differ from the response on a neighboring ranch. How fast will a range In good condition respond com­pared to an overgrazed range? How will animal diets differ on ran­ges in different conditions and what effect will the treatment have on their diets? Once these ques­tions are considered and under­stood, It Is possible to select an appropriate treatment to ac­complish a specific management objective. cumulatiw rat8S for the two perpendicular flights (A) and the almulated vegetation

resporllN (B) .

practices and treatment sites can Improve deer habitat and Increase the quality and availability of forage, especially In areas where dense brush limits herbaceous production. Mechanical treat­ments such as root-plowing or chaining may disturb deer habitat by suddenly removing cover screen and shade. However, mechanical strip or mosaic clear­ing appears to be a feasible brush management approach when deer habitat is a concern. The respon­ses from herbicide treatments are more subtle and gradual than broad-scale mechanical treat­ment. It Is extremely important to

RANGE

know before treatment what the plant and animal responses should be and what effect the treat­ment will have on other ranch resources. Strip spraying and aerial VA P are the most effective herbicide applications for deer management. Prescribed burning also is a feasible approach to brush management that is highly compatible with requirements for high quality deer habitat. Burning is particularly valuable when used as a follow-up treatment or main­tenance measure.

To determine the most appropriate brush management practice for a

Regardless of which brush management practice (or com­bination) is selected, the treat­ments that will benefit deer most are the ones that stimulate an in­crease in forb production during the growing season, while main­taining a diversity of browse and cacti for forage when forbs are not available. In addition, any treat­ment that stimulates the sprouting of browse species will benefit deer nutrition through Increased quality and availability of browse. And finally, where possible, numbers and kinds of herbivores may have to be manipulated to reduce com­petition for the available, high quality forage species.

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