Chapter 4€¦ · Chapter 4 Longleaf Pine Regeneration Ecology and Methods Dale G. Brockway, Kenneth W. Outcalt, and William D. Boyer ... composition, and density (Platt and Rathbun

Chapter 4

Longleaf Pine Regeneration Ecologyand Methods

Dale G. Brockway, Kenneth W. Outcalt, and William D. Boyer

Introduction

Regenerating longleaf pine (Pinus palustris) iskey to its long-term sustainable production offorest resources and its perpetuation as thedominant tree species in a variety of importantecosystems ranging from xeric to mesic to hy-dric site conditions. Early regeneration prob-lems and the subsequent efforts to overcomethese are significant features of the continu-ing longleaf pine saga. This chapter discussesrecent restoration relevant to longleaf pineregeneration, disturbance dynamics includingfire as an ecological process and describesthe uniqueness of longleaf pine’s regenerationenvironment. Fundamental information con-cerning reproductive biology (including genet-ics, flowering, pollination, fertilization, coneproduction, and seed dispersal) and seedlingdevelopment (including germination, shootgrowth, rooting, sprouting, competition, ini-tiation of height growth, effects of fire, andseedling morality) is then presented. Variousaspects of natural regeneration and artifi-cial regeneration are discussed and the even-aged (i.e., clearcutting, seed-tree and shelter-wood) and uneven-aged (i.e., group selectionand single-tree selection) forest reproductionmethods are introduced. We conclude by high-

Dale G. Brockway and William D. Boyer � Southern Research Station, USDA Forest Service, Auburn, Alabama36849. Kenneth W. Outcalt � Southern Research Station, USDA Forest Service, Athens, Georgia 30602.

lighting recent work that calls for applicationof silviculture techniques that more closelymimic natural disturbance regimes.

Ecological Relationships

Indispensable Nature ofRegenerationSuccessful reproduction is essential to perpet-uate any population of organisms. Indeed, if anexisting generation is unable to produce a suc-ceeding generation, then the existing genera-tion can appropriately be considered an eco-logical and evolutionary “dead end” for thatpopulation and perhaps the entire species. De-spite the extended longevity of many treespecies, some approaching 500 years, all in-dividual organisms eventually die. If none ofthe offspring survive to the age of reproductivematurity, then the entire species will eventu-ally perish. If the species is a dominant organ-ism, then entire ecosystems will be degradedor lost, potentially threatening the survival ofassociated plant and animal species.

While species extinction and ecosystem lossmay seem like rare events in the shorter termof human experience, from the longer-term

95

96 II. Ecology

FIGURE 1. Naturally regenerated even-aged second-growth longleaf pine forest on mesic uplands. Photocourtesy of the Forestry Images Organization.

perspective of geologic time, such events havenot been uncommon. The survival of speciesand sustainability of ecosystems cannot al-ways be assumed, even under the best cir-cumstances. And when new species and/orcultures encounter native ecosystems, newpressures can stress the indigenous organismsand threaten ecological sustainability. Such hasbeen the case in the southern United States,where the Age of Discovery and the IndustrialRevolution brought substantial change to na-tive longleaf pine forests (Frost this volume).Effective means of regenerating longleaf pineare important for continuation of this speciesand the long-term sustainability of longleafpine forest ecosystems.

Declining TrendLongleaf pine ecosystems were once amongthe most extensive in North America, occu-pying about 37 million ha prior to Europeansettlement (Frost 1993, Landers et al. 1995).While the initial impact of immigrants during

the eighteenth and nineteenth centuries wasgenerally modest, as populations grew and log-ging activity expanded during the late nine-teenth and early twentieth centuries, most na-tive longleaf pine forests were harvested. Theland was often converted to agricultural, resi-dential and urban uses or planted with planta-tions of other easier-to-establish, faster grow-ing trees such as slash pine (Pinus elliottii)and loblolly pine (Pinus taeda) (Croker 1987,Outcalt 2000). Although many second-growthlongleaf pine forests naturally regenerated fol-lowing this initial harvest (Fig. 1), recoverywas impaired by irregular seed production,with good seed years occurring at intervalsof five or more years (Boyer 1990a). Wherelongleaf pine seedlings did survive logging,they were often consumed by feral hogs (Susscrofa), causing many areas of potential lon-gleaf pine forest to be lost (Schwarz 1907,Croker 1987, Simberloff 1993, McGuire 2001).As the southern landscape became increas-ingly domesticated, the modified structureof expansive agricultural areas and linear

4. Longleaf Pine Regeneration Ecology and Methods 97

transportation corridors fragmented previ-ously contiguous habitat, thereby impedingthe movement of natural surface fires acrossthese lands (Walker 1999). During the twen-tieth century, organized programs of fire sup-pression and policies of fire exclusion from theforest further interrupted natural fire regimes(Croker 1987). Since the absence of frequentsurface fires impedes the natural regenerationof longleaf pine and allows invasion of long-leaf pine sites by hardwoods and more ag-gressive southern pines, interruption of nat-ural fire regimes is believed to be the mostecologically significant cause for its continu-ing decline (Wright and Bailey 1982, Landerset al. 1990, Pyne 1997, Gilliam and Platt 1999).Longleaf pine forests have undergone a steadydecrease to 8 million ha in 1935 (Wahlenberg1946), 2 million ha by 1975, 1.5 million ha in1985 (Kelly and Bechtold 1990) and less than1.2 million ha currently (Outcalt and Sheffield1996). Occupying less than 3% of their originalrange (Ware et al. 1993), longleaf pine ecosys-tems are now recognized as being at high risk(Noss et al. 1995, Kush 2002). Unfortunately,area reductions continue for stands in everydiameter class below 41 cm (Kelly and Bech-told, 1990), an indication that most remaininglongleaf pine forests are aging without replace-ment.

Ecological RestorationExtending along the Gulf and Atlantic CoastalPlains from Texas to Virginia and inland tothe Piedmont and mountains in Alabama andGeorgia, longleaf pine forests, woodlands, andsavannas may occupy a wide variety of sites,ranging from wet poorly drained flatwoodsto mesic uplands, xeric sandhills, and rockymountain ridges (Boyer 1990a; Stout andMarion 1993). Distinguished by a generallyopen, parklike stand structure (Schwarz 1907;Wahlenberg 1946), naturally regenerated lon-gleaf pine forests are typically an uneven-agedmosaic of even-aged patches distributed acrossthe landscape, which vary in size, structure,composition, and density (Platt and Rathbun1993; Brockway and Outcalt 1998) and con-tain numerous embedded special habitats such

as stream bottoms, wetlands, and seeps (Hilton1999). The natural variability of these ecosys-tems makes them excellent habitat for a varietyof game animals and numerous nongame andrare wildlife species (Kantola and Humphrey1990; Engstrom 1993; Guyer and Bailey 1993;Crofton 2001; Engstrom et al. 2001; Brockwayand Lewis 2003; Means this volume).

The complex natural patterns and processesunique to longleaf pine forests create ex-traordinarily high levels of biological diver-sity in these ecosystems, with the great num-ber of plant species per unit area qualifyingthese as among the most species-rich terres-trial ecosystems outside the tropics. As manyas 140 vascular plant species have been ob-served in a 1000 m2 area and equally impres-sive counts of more than 40 species per m2

have been recorded (Peet and Allard 1993),a large number of which are restricted toor found principally in longleaf pine habi-tats. Habitat reduction resulting from declineof longleaf pine ecosystems has caused theincreased rarity of 191 vascular plant taxa(Hardin and White 1989, Walker 1993) andseveral vertebrate species. Concern over lossof this unique ecosystem (Means and Grow1985; Noss et al. 1995) has led to many effortsfocused on effectively restoring longleaf pineecosystems (Walker and Boyer 1993; Walker1995; Kush 1996, 1998, 1999, 2001; Johnsonand Gjerstad 1998, 1999; Brockway et al. 1998;Seamon 1998; Outcalt et al. 1999; Brockwayand Outcalt 2000; Provencher et al. 2001a,b;Mulligan et al. 2002). Since longleaf pine stilloccurs in isolated fragments over most of itsnatural range, it is reasonable to concludethat restoration of these ecosystems is possible(Landers et al. 1995). Effective methods for re-generating longleaf pine will no doubt play akey role in ecological restoration efforts.

Disturbance Dynamics and Fireas an Ecological ProcessLongleaf pine ecosystems exist in an envi-ronment influenced by large-scale catastrophicdisturbance, such as damaging tropical storms.Lightning is an important agent in individ-ual tree morality and creation of small-scale

98 II. Ecology

disturbance in longleaf pine forests (Komarek1968; Taylor 1974). The structure, pattern, anddiversity of longleaf pine ecosystems are main-tained by a combination of site factors andperiodic disturbance events, including light-ning strikes, tree mortality, and animal inter-actions at local scales and tropical storms, soils,and hydrologic regimes at broader scales. Dis-turbances across site gradients provide largeliving trees, snags, coarse woody debris, for-est canopy gaps, and hardwood thickets thatsupport numerous plant and animal speciesadapted to these disturbance-prone, yet largelystable ecosystems.

Longleaf pine is closely associated withwiregrass (Aristida spp.) in the eastern partand bluestem grasses (Andropogon spp. andSchizachyrium spp.) in the western portion ofits range. The understories of longleaf pineforests are typically dominated by herbaceousplants because these bunchgrasses facilitate theignition and spread of frequent surface fires(Landers 1991). In these ecosystems, longleafpine and bunchgrasses function together askeystone species that facilitate but are resis-tant to fire (Platt et al. 1988; Noss 1989). Theyalso exhibit substantial longevity and demon-strate nutrient and water retention to a de-gree that reinforces their site dominance andminimizes change in the plant community fol-lowing disturbance (Landers et al. 1995). As akey ecological process and disturbance agent,the benefits of periodic fire include (1) main-taining the physiognomic character of longleafpine ecosystems through excluding invasiveplants that are ill-adapted to fire, (2) preparinga seedbed favorable for the establishment oflongleaf pine seedlings, (3) reducing the den-sity of understory vegetation thus providingmicrosites for a variety of herbaceous plants,(4) releasing nutrients immobilized in accu-mulated phytomass for recycling to the in-fertile soil and subsequently more rapid up-take by plants, (5) improving forage for graz-ing, (6) enhancing wildlife habitat, (7) control-ling harmful insects and pathogens, and (8)reducing fuel levels and wildfire hazard (Mc-Kee 1982; Wade and Lewis 1987; Boyer 1990b;Wade and Lundsford 1990; Dickmann 1993;Brennan and Hermann 1994; Brockway andLewis 1997).

Regeneration EnvironmentDifficulties encountered during early attemptsto regenerate longleaf pine impeded its recov-ery and contributed to its historical decline(Croker 1987). Erratic seed production, poorseedling survival, and slow early growth ofseedlings discouraged forestland managersfrom investing in longleaf pine. Managementpolicies based on these initial observationsfurther contributed to the decrease of longleafpine forests, as harvested stands were deliber-ately converted to other southern pine speciesrather than being regenerated with longleafpine. Fortunately, later research illuminatedthe ecological mechanisms and identifiedsilvicultural methods for effectively regener-ating longleaf pine by natural and artificialmeans (Boyer and White 1990; Barnett et al.1990; Kush 2002) and the earlier policies offorest type conversion have now been largelyreversed.

The unique structural and process dynam-ics characteristic of longleaf pine forests pro-vide both challenges to and opportunities forapplying science and adapting technology toefficiently obtain regeneration. Foremost, alllongleaf pine forests are obligatorily pyro-phytic ecosystems. Therefore, all regenera-tion techniques employed must be compati-ble with periodic surface fires. Longleaf pineforests are disturbance-prone and naturally re-generate in a variety of configurations rang-ing from relatively small circular or ellipticalcanopy gaps and attenuated strings to largerareas of partially blown down or almost com-pletely blown down overstory trees (Crokerand Boyer 1975; Palik and Pedersen 1996;Brockway and Outcalt 1998). As a tree speciesthat is intolerant of competition, whether forlight, moisture, or nutrients (Boyer 1990a),its seedlings become established and flourishas opportunists responding to resource avail-ability. Although longleaf pine displays manytraits consistent with an intolerant, early seralspecies, its seedlings often persist in the for-est understory for prolonged periods similarto those of more tolerant, late-seral species.Suppressed longleaf pine seedlings will not re-spond with improved growth until releasedfrom competition with overstory trees and


long-suppressed individuals are, through time,increasingly prone to mortality. Whether a spe-cific longleaf pine seedling survives to eventu-ally become a dominant member of the forestcanopy may depend as much on stochasticevents (i.e., drought severity and duration,fire intensity and season, disturbance that re-sults in timely release from competition) asit does on the competitive vigor (i.e., geneticattributes) of the individual. Whether by ar-tificial or natural methods, by even-aged oruneven-aged silvicultural techniques, not onlyis efficiently regenerating longleaf pine feasi-ble, it is also imperative for achieving ecologicalrestoration and ecosystem sustainability goals.

Reproductive Biology

GeneticsLongleaf pine is a tree species of consider-able genetic diversity, with variation amongindividuals typically greater than that amongstands or geographically different seed sources(Snyder et al. 1977; Lynch 1980). Although ge-netic variation among populations is thoughtto be a result of the diversity of environmentsin which longleaf pine occurs throughout itsnative range (Boyer 1990a), measures of ge-netic diversity appear unrelated to climatevariables (Schmidtling and Hipkins 1998).While the pattern of genetic variation for long-leaf pine is similar to that of other south-ern pines (Schmidtling 1999), its unique pat-tern of allozyme variation is indicative of avery different history during the recent IceAge (Schmidtling et al. 2000). Unlike otherpines, longleaf pine appears to have migratedeastward across the southeastern United Statesfrom a single refuge in southern Texas and/ornortheastern Mexico after the Pleistocene(Schmidtling and Hipkins 1998). The pro-gressive decrease in allozyme diversity fromwestern to eastern longleaf pine populationsrepresents a loss in genetic variability fromstochastic events during migration.

Longleaf pine may form a natural hybridwith loblolly pine, referred to as “Sondereg-ger pine” (Pinus sondereggeri). Since floweringof these two species frequently overlaps, there

is no phenological barrier to natural cross-ing (Boyer 1990a). Hybridization between lon-gleaf pine and slash pine is far less likely be-cause of differences between their dormancyand heat requirements for flowering (Boyer1981); however, artificial crossing can be easilyachieved. Hybrids between longleaf pine andshortleaf pine (Pinus echinata) have not beenobserved in nature but have been artificiallyproduced (Snyder et al. 1977).

With a pattern of genetic variation similarto that in other southern pines, longleaf pineis suitable for genetic improvement. However,the effort expended on this species is easilydwarfed by the immense resources devotedto loblolly pine and slash pine improvementprograms (Schmidtling 1999). Traditional treeimprovement approaches, which select “plus”trees in the forest based on size and form, havenot proven to be suitable for longleaf pine.Variation in the “grass” stage of longleaf pinemakes it impossible to determine the true ageof a tree and thus its true growth potential.Therefore, tree improvement programs forlongleaf pine have shifted their emphasis to aprogeny test approach, with the duration of thegrass stage and resistance to brown-spot fun-gus (Mycosphaerella dearnessii) the most impor-tant inherited traits of interest. When focusingefforts on accelerating the early height growthof longleaf pine, one of the greatest dangersis the possibility of incorporating loblolly pinegenes that will result in a hybrid that beginsgrowing earlier but has poor form and in-creased susceptibility to fusiform rust fungus(Cronartium quercuum f. sp. fusiforme). Thereis no ecotypic differentiation in longleaf pinebased on site conditions and no important dif-ference in survival or growth between east-ern and western populations, as occurs withloblolly pine (Schmidtling 1999).

Flowering, Pollination, andFertilizationLongleaf pine is monoecious, with male strobili(catkins) predominating in the lower crownand female strobili (conelets) occurring mostfrequently in the upper crown of the same tree(Schopmeyer 1974). Development of catkins

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FIGURE 2. Elongated catkins, subtending a terminalbud, shown after their pollen has been shed. Photocourtesy of the Forestry Images Organization.

(Fig. 2) and conelets (Fig. 3) is initiated dur-ing the growing season before buds emerge,with catkins beginning to form during Julyand conelets being formed during a short pe-riod in August (Boyer 1990a). First appearingat the base of vegetative buds between mid-November and early December, purple catkinsremain dormant for several weeks before re-suming development between late Decemberand early February (Boyer 1981). Conelet budsappear in January or February and conelets,upon emerging from the bud, are red untilpollinated, after which they fade to yellowishgreen. The development rates of both catkinsand conelets are almost entirely dependent onambient temperature (Boyer 1990a).

The number of flowers produced appears re-lated to weather conditions during the yearof initiation. Catkin production is favored byabundant rainfall throughout the growing sea-son, while conelet production is promoted by a

wet spring and early summer followed by a dryperiod in late summer (Shoulders 1967). Be-cause of the differential conditions that favoreach sex, large crops of male and female flow-ers do not necessarily coincide (Boyer 1990a).Heavy annual losses of longleaf pine coneletscan usually be expected, with observed lossesranging from 65% to 100% (Boyer 1974a;McLemore 1977; White et al. 1977). Insects,weather extremes, and insufficient pollen ap-pear to be the primary causes for these losses,which primarily occur during spring pollina-tion or the following summer.

Peak pollen shed and conelet receptivity typ-ically vary from late February in the southernportion of the native range to early April inmore northern areas (Boyer 1990a). Althoughpollen shedding and receptivity coincide on in-dividual trees, there appears to be very littlesynchrony among trees in a longleaf pine for-est, with some trees being consistently earlyand others being consistently late and over-all dates highly influenced by air temperaturesbefore and during the flowering period. Pollenshedding typically occurs during a period of 5to 21 days, with an average of 13 days (Boyer1981). Year-to-year variation in the time ofpollen shedding appears to be related to ac-cumulation of degree-day heat sums, with alltemperatures greater than 10oC after January1 promoting development of the male strobili(Boyer and Woods 1973; Boyer 1973, 1978).

While pollination takes place in late winteror spring, fertilization does not occur until thefollowing spring. Conelets grow rapidly afterfertilization, increasing in length from 2.5 cmto 18 cm by May or June (Boyer 1990a). Conesreach maturity between mid-September andmid-October of their second year and range inlength from 10 cm to 25 cm. Although conecolor changes from green to brown as theyripen, cones may be ripe before changing color(Schopmeyer 1974).

Cone Production and SeedDispersalLongleaf pine cone crops are highly variablefrom year to year (Fig. 4), with 1860 cones/ha


FIGURE 3. Conelets, located peripherally to terminal buds, are most often observed in the upper crown.Photo courtesy of the Forestry Images Organization.

(e.g., 30 cones/tree and 62 seed trees/ha) nor-mally required for successful natural regen-eration (Boyer 1996). While cone productionmay be influenced by the density of airbornepollen during flowering, low cone crop fre-quencies appear to be more a result of flowerlosses rather than a failure to produce flow-ers (Boyer 1974a, 1987a). Since 1986, conecrops on coastal plain sites from Louisiana toNorth Carolina have increased to an average of36 cones/tree from an earlier average of only14 (Boyer 1998). This increase in cone pro-duction appears to be a result of both an in-crease in flower production and an increasein the fraction of flowers surviving to becomemature cones. Cone production of individualtrees is influenced foremost by genetics andsecondarily by tree size, crown class, standdensity, and site quality. The greatest coneproduction occurs on dominant, open-grownlongleaf pines having large crowns (Crokerand Boyer 1975). Trees of 38–48 cm diam-

eter at breast height produce on average 65cones/year compared with 15 cones/year fromtrees in the 25–33 cm diameter at breast heightsize class (Boyer 1990a). The number of vi-able seeds per cone varies with the seed cropfor a specific year, ranging from 50 seeds/conein good years to 35 seeds/cone during averageyears to 15 seeds/cone in poor years (Croker1973).

Peak seed production is observed in lon-gleaf pine forests having stand densities be-tween 6.9 and 9.2 m2/ha, when principallycomprised of dominant and codominant treesof cone-bearing size (Boyer 1979). Such standsproduce seed crops adequate for natural re-generation once every 4 to 5 years on aver-age (Croker and Boyer 1975). When forestsof substantially greater density are thinned tothis level, increased cone production resultingfrom decreased intraspecific competition doesnot occur for three growing seasons (Croker1952). Release following conelet initiation

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0

30

60

90

120

150

1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003

Year

Co

ne

s p

er

Tre

e

FIGURE 4. Example of high temporal variability for longleaf pine seed production: Cone crops at theEscambia Experimental Forest, southern Alabama, 1957–2003.

benefits the crop only by reducing moisturestress during dry periods (Boyer 1990a). Seedsare dispersed by wind during a 2- to 3-week pe-riod between late October and late November,depending on weather conditions. Longleafpine seeds are the largest of the southern pinesand their dispersal distance is limited, with71% of sound seeds falling within 20 metersof the base of a parent tree (Croker and Boyer1975).

Seedling Development

Germination and Shoot GrowthLongleaf pine seeds typically germinate (Fig. 5)within a week of contacting the ground (Boyer1990a). While rapid germination may be anadaptation to reduce the risk of exposure toseed predators, newly germinated seedlingsare also vulnerable to mortality from animals,pathogens, and adverse weather conditions

(Croker and Boyer 1975). Although germina-tion and establishment require that seeds con-tact mineral soil, the large seed and wing canimpede penetration through dense grass or ac-cumulated litter on the forest floor. Root sys-tems of premature germinants fail to reachmineral soil and readily die from desiccation.The risk of regeneration failure can be signifi-cantly reduced by using mechanical treatmentand/or prescribed fire to prepare a suitableseedbed before seedfall. Germination beginswith emergence of the radicle and an almostsimultaneous elongation of the cotyledons(Allen 1958). Hypocotyl elongation beginssoon after radicle emergence but is limited.Growth of the cotyledons lifts the seedcoatfrom the ground. Limited hypocotyl growthcauses the cotyledons of new germinants toremain at or near the ground line. Newly ger-minated seedlings are relatively inconspicuouswith their small primary needles. Althoughsecondary needles appear within 2 months,the epicotyl reaches a length of only 0.38 cm


FIGURE 5. Newly germinated longleaf pine seedlings emerging from thin forest litter (foreground) andamong cones fallen from the parent trees. Photo courtesy of the Forestry Images Organization.

and, during the next 8 weeks, does not elon-gate as in other pines. This stemless condi-tion is one of the unique characteristics of lon-gleaf pine, commonly referred to as the “grassstage” (Fig. 6). Depending on ambient condi-tions, longleaf pine seedlings may remain inthis stage for 2 to as long as 15 years, duringwhich they are most susceptible to their ma-jor disease, brown-spot needle blight (Boyer1990a).

Roots and SproutsWhile in the grass stage, longleaf pine seedlingsdevote much of their energy to root produc-tion. Following germination, the radicle formsa taproot that develops very rapidly. Growthrates may be as high as 50 cm in 15 days follow-ing germination in sandy soils under green-house conditions (Wahlenberg 1946). More

typical rates are 0.8 cm/day during the first60 days (Allen 1958). Taproot developmentis inversely related to moisture conditions,with greater root elongation occurring in driersoils. The general root structure of naturalseedlings is unaffected by soil conditions, butthese seedlings have slower root growth thanthose measured in greenhouse tests. The rootsystem of a typical 1-year-old seedling con-sists of a taproot 60–70 cm long and a numberof strong laterals 50–60 cm long in the uppersoil layers with numerous attached feeder tips(Wahlenberg 1946). Laterals extend outward,and though they often change direction due toobstructions, they remain at a uniform depthfrom origin to tip (Heyward 1933). On wet-ter flatwoods sites, root systems have the samegeneral architecture, but root distribution is re-stricted mostly to surface horizons, above thespodic layer that occurs in soils typical of these

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FIGURE 6. Longleaf pine seedling in the grass stage. Photo courtesy of the Forestry Images Organization.

areas. Even in well-drained sands, 90% of alllateral roots are found in the upper 30 cm ofthe soil.

Longleaf pine seedlings can sprout from theroot collar if the top is killed. Under naturalconditions, sprouts often result following topkill from fire. This sprouting ability diminishesrapidly once seedlings emerge from the grassstage and begin stem elongation. As many as40% of the grass-stage seedlings that werecut off at the groundline have been foundto have living sprouts 1 year later (Farrar1975). Only 14% of the seedlings, that hadinitiated height growth but were less than1.37 m tall, produced sprouts when cut atthe groundline. None of the trees more than1.37 m tall produced sprouts after cutting.Three years after cutting, 30% of the grass-stage seedlings still had surviving sprouts, butthese were growing very slowly. Althoughfewer of the seedlings that had begun heightgrowth sprouted, those sprouts were muchlarger 3 years after treatment. Sprouts from

smaller seedlings are rather weak and oftendie following subsequent fires.

CompetitionLongleaf pine seedlings are intolerant ofinterspecific and intraspecific competition(Harrington, this volume). Seedling growthrates improve as the distance from adult pinesincreases, with the suppressive effect fromstands of overstory trees adjacent to clearcutstrips being greater than that from single over-story trees (Boyer 1963). The relationship ofdeclining seedling growth rates with increasingamounts of overstory competition (i.e., over-story basal area) follows that of a general expo-nential decay curve. The root collar diameterfor 4-year-old seedlings has been reported tosharply decrease from 1.2 cm to 0.7 cm as over-story basal area increased from 0 to 6.9 m2/ha.More recent work has substantiated the sup-pressive effect of overstory adults upon long-leaf pine seedlings on redhills sites (Grace and


Platt 1995) and flatwoods sites (Gagnon et al.2003, 2004) and the exponential relationshipbetween seedling growth and overstory basalarea (Palik et al. 1997).

Overstory hardwood trees are even greatercompetition for longleaf pine seedlings. While60% of the seedlings in the 0–3 m zone nearadult longleaf pines reached sufficient root col-lar diameter by age 9 to begin height growth(Smith 1962), only 24% of the pine seedlingsnear oak trees had initiated height growth. Re-moval of overstory oaks significantly improvedheight growth of longleaf seedlings (Walker1954). Understory vegetation, including otherlongleaf pine seedlings and herbaceous plants,also competes with longleaf pine seedlings.Single season growth increases of 18% weremeasured in seedling densities of 247,100/haand increases of 64% were observed atdensities of 2471/ha (Pessin 1938). Whenherbaceous competition was removed, growthincreased by 25 and 456% for the same respec-tive seedling densities. Thus, intraspecific com-petition in the understory appears much lessimportant than competition from other speciesin this layer.

Ascertaining the underlying causes ofseedling growth reduction has proven chal-lenging. Root competition was believed tobe much more important than light becausegrowth depression extends well beyond theheight of adjacent overstory trees (Walker andDavis 1956; Croker and Boyer 1975). This in-hibitory effect is also greater on sites withpoor soils, another indication of belowgroundcompetition. The importance of belowgroundcompetition was more recently substantiatedby research on xeric sandhills sites in Florida,where total daily light influx did not differ sig-nificantly with distance from adult trees, butthe fine root biomass of overstory trees diddecline with distance (Brockway and Outcalt1998). Others working on more fertile soilswith higher densities of woody plants haveshown that light does increase with distancefrom gap edge (Palik et al. 1997; McGuire et al.2001; Gagnon et al. 2003). Palik et al. (1997)also documented a positive relationship be-tween available N and seedling growth. Lon-gleaf pine seedling growth was found to be

significantly related to N, soil water, and theirinteraction in a greenhouse study (Jose et al.2003). Light was important only if water wasnot limiting. Therefore, competition affectinglongleaf pine seedling growth follows the fun-damental principle of limiting factors, withgrowth most impaired by whichever essentialfactor is most limited in a specific environment.

Initiation of Height GrowthAlthough varying considerably, longleaf pineseedlings usually begin emerging from thegrass stage when their root-collar diameterreaches about 2.5 cm (Boyer 1990a). Infec-tion by brown-spot needle blight can substan-tially delay grass stage emergence. The heightgrowth of seedlings also depends on the in-tensity of competition in the ambient environ-ment (Ramsey et al. 2003). Therefore, treat-ments that reduce competition will increasethe proportion of seedlings that emerge fromthe grass stage (Haywood 2000). Differences inlevels of intraspecific and interspecific compe-tition and individual genetic control of growthrates and resistance to brown-spot infection re-sult in considerable variation in emergence oflongleaf pine seedlings from the grass stage.This high within-stand variation is actuallybeneficial as it leads to the early establish-ment of dominant seedlings, preventing standstagnation even when seedlings occur at veryhigh densities. The key to height growth ini-tiation is accumulation of carbohydrate re-serves in the root sufficient to support rapidupward expansion of the stem. This intervalis known as the bolting stage in which rapidgrowth of the needle-covered stem occurs withlimited lateral branch development, produc-ing the characteristic “bottlebrush” structure(Fig. 7). Under favorable conditions, longleafpine seedlings can grow 30–90 cm in a singleseason (Wahlenberg 1946).

Effects of FireLongleaf pine evolved in ecosystems subjectto frequent low-intensity surface fires andhas developed many adaptations for enhanc-ing survival and growth in this environment(Landers 1991). Although newly germinated

106 II. Ecology

FIGURE 7. Longleaf pine seedlings in the boltingstage. Photo courtesy of the Forestry Images Orga-nization.

and small grass-stage seedlings are suscepti-ble to fire-caused mortality, once they attaina root-collar diameter of 1.3 cm, they becomequite fire-resistant (Boyer 1974b). Such largergrass-stage seedlings have thicker bark and alarge tuft of needles that protect the centralmeristem (Fig. 8) and, as noted previously,even if the top is killed, they will often sprout.However, since many natural seedlings do notattain this size until they are 2 or 3 years old,mortality from fires can be quite high. A sin-gle growing-season fire, at age 2, can result inas much as 80% of the total seedling mortal-ity for the 3-year period following germina-tion. Fire can also be beneficial to longleaf pineseedlings by consuming brown-spot-infectedneedles. Fire stimulates height growth (Grelen1983) by reducing competition and releasingnutrients immobilized in organic matter.

When initiating height growth, seedlingsonce again become more susceptible to fire-

FIGURE 8. This larger grass-stage longleaf pine sur-vived a recent fire; note the thick root collar and par-tially consumed needles that adequately protectedits terminal bud. Photo courtesy of the Forestry Im-ages Organization.

caused mortality. During this stage, the termi-nal bud is situated directly in the flaming zone,where it may be exposed to maximum tem-peratures. These seedlings are especially vul-nerable during early season bud break whenthe candles are rapidly expanding and thereis very little protective needle mass. Once theyhave bolted above the flame zone (about 1 m),seedlings are again quite resistant to fires ofmoderate intensity. Although fire does not killmany longleaf pines once they reach this smallsapling stage, burning can still cause reductionsin growth (Boyer 1987b).

Seedling MortalitySeedlings are susceptible to losses fromfrost heaving, flooding, disease, logging, fire,


FIGURE 9. Close-up view of longleaf pine needlesinfected with brown-spot fungus; note highly var-iegated color tones and distinctive dark spots onthe needles. Photo courtesy of the Forestry ImagesOrganization.

drought, and animals. As expected, losses aregreatest during the first growing season. Frostheaving is a threat only near the northern limitof the natural range on finer-textured soils.Flooding can be a problem on wet coastal plainsites where prolonged standing water can killnewly germinated seedlings (Croker and Boyer1975). Brown-spot needle blight (Fig. 9) mayat times become so severe that it destroys allthe foliage and directly kills the seedling. Moreoften, the seedling becomes so weakened thatit dies during the next fire. While dependingon the harvest method, season, and volume oftrees removed, losses from logging generallyaverage about 50% (Boyer 1990a). To mini-mize logging losses, harvesting should be donewhen seedlings are in the grass stage. As notedabove, fire is a significant cause of seedling

mortality during the first 2 years, where lossesup to 90% may often occur (Grace and Platt1995; Provencher et al. 2001b). The probabil-ity of seedling mortality from fire is greatest inthe zone around adult trees, because greaterneedle litter accumulations there often resultin hotter fires. Higher intraspecific competi-tion in this zone also results in slower seedlinggrowth, thus predisposing them to higher ratesof fire-related mortality. Before the first fireoccurs, seedlings growing close to adult pinesrarely attain the 1.3 cm root-collar diameterneeded for survival.

Drought can cause significant losses of first-year seedlings, especially on sandhills siteswhere 50% mortality is common during thespring drought period. Many of the seedlingsthat perish during dry periods are growing onlocations where the forest floor is somewhatthicker. Although bare mineral soil is ideal forlongleaf pine germination and growth, suffi-cient moisture is all that is needed to initiatethe germination process. Therefore, many ofthe seedlings that germinate on thicker for-est floor material in the fall, fail to survivethe spring drought because their root systemhas not penetrated sufficiently into the min-eral soil to obtain adequate moisture. Litterfallis of course not distributed evenly, but ratheris highest near adult trees. The greater for-est floor thickness, increased root competition,and reduced rainfall from crown interceptionall combine to substantially lower the prob-ability of longleaf pine seedling survival nearadult overstory trees. This typical spring mor-tality significantly contributes to developmentof the often-observed zone of seedling exclu-sion near adult pines (Brockway and Outcalt1998).

Both wild and domestic animals can deci-mate stands of longleaf pine seedlings. Locallyhigh populations of rabbits can cause signif-icant damage to newly germinated seedlingsby clipping off the needles (Croker and Boyer1975). Local losses can also result from pocketgophers feeding on the starch-laden roots ofgrass-stage seedlings. While cattle will alsograze on longleaf pine seedlings, most damageand mortality results from trampling wheresites are allowed to suffer from overstocking

108 II. Ecology

and excessive use. However, the most destruc-tive of all animals is the wild hog, a nonna-tive species introduced from Europe. The rootsof grass-stage seedlings, rich in starch, are afavorite food of wild hogs. A single hog canuproot and consume a great many seedlingsin a single day. The destructive power of thevast herds of wild hogs was noted in theearly 1900s (Schwarz 1907). An early fenc-ing study demonstrated their effect on longleafpine seedling densities, with 14,826 stems/haoccurring within the protective fence and amere 20 stems/ha surviving outside (Mattoon1922). In some locations, wild hogs still posea problem for regeneration. However, remov-ing hogs for only 2 years resulted in successfulregeneration of longleaf pine in the South Car-olina Coastal Plain (Lipscomb 1989).

Natural Regeneration

Regeneration ProblemsPerhaps the greatest impediment to wider ac-ceptance of longleaf pine, as a tree worthyof forest management investment, is its rep-utation as a difficult species to successfullyregenerate, whether by natural or artificialmeans. Schwarz (1907) was among the first toidentify poor regeneration as a major threat tothe future of longleaf pine. Insufficient num-bers of seed trees, infrequent seed crops, coneinfestation by insects, limited dispersal dis-tance of heavy seeds, seed predation, seedperching in litter above mineral soil, vulner-ability of early germinating seed to tempera-ture extremes, brown-spot fungus infection,slow early seedling growth, untimely fires,and fire exclusion favoring competing speciesare among the primary reasons for regenera-tion failure of longleaf pine (Wahlenberg 1946;Croker and Boyer 1975; Boyer 1979). Fortu-nately, the extensive research conducted onlongleaf pine regeneration during the secondhalf of the twentieth century has now re-duced these problems to considerations thatcan be effectively addressed through appropri-ate management strategies and practices (Kush2002).

Regeneration RequirementsWhen the fundamental requirements can bemet, natural regeneration is a practical andinexpensive management option for existinglongleaf pine forests (Boyer 1993a). The fore-most requirements for successfully regenerat-ing longleaf pine by natural means are an ad-equate seed source and a receptive seedbed(Boyer and White 1990). A sufficient num-ber of sexually mature parent trees, havingdesirable characteristics and being well dis-tributed throughout the area, typically servesto meet this need (Dennington and Farrar1991). Since longleaf pine seed crops are infre-quent, averaging one every 5 to 7 years, annualmonitoring of conelet and cone production isnecessary to appropriately forecast years whenadequate seed will be available (Boyer 1996).For initiating even-aged stands, the size, num-ber, and distribution of seed-bearing trees mustbe such that a minimum of 1860 and prefer-ably 2470 or more cones/ha will be provided(Boyer and White 1990). Peak seed productionmay be encouraged in future years by reduc-ing stand density to between 6.9 and 9.2 m2/ha(Boyer 1979).

One of the most pervasive problems imped-ing the natural regeneration of longleaf pineis high-density understory and midstory lay-ers dominated by woody plants. If preestablish-ment competition control is not achieved, lon-gleaf pine regeneration success will be highlydoubtful (Boyer and White 1990). Therefore,competing hardwood trees and shrubs mustbe effectively controlled before seed disper-sal. The presence of competing woody plantsis not only deleterious to seedlings as theyare becoming established, but may also inter-fere with dispersed seeds as they attempt toreach mineral soil. Although prescribed fireconducted well in advance of seedfall maybe sufficient to control these woody plants,herbicide application or mechanical treatmentmay also be necessary to obtain adequate con-trol under certain circumstances (Croker andBoyer 1975).

Longleaf pine seeds need to be in contactwith mineral soil for successful germinationand establishment (Boyer and White 1990).


Since seed supplies are typically limited, a well-prepared mineral seedbed is necessary to pro-vide optimum opportunity for regenerationsuccess. A suitably prepared seedbed can becreated by a prescribed fire conducted within1 year prior to seedfall. Such a fire will removeenough forest litter to double the rate of lon-gleaf pine seedling establishment compared tounburned sites. While only 14% of longleafpine seeds became established as seedlings onunburned areas, 36% became established onwinter-burned areas and 24% became estab-lished on fall-burned areas (Croker 1975). Thelower establishment level on fall-burned areasis believed to result from lighter subsequent lit-ter accumulation causing higher rates of seedpredation by birds.

Successful regeneration requires an ade-quate number of established seedlings well-distributed throughout the area (Boyer andWhite 1990). Although exact criteria must beleft up to individual land managers with spe-cific management objectives, a reasonable goalwhen using the shelterwood method might beabout 14,800 established 1-year-old or olderseedlings per hectare. This standard allows forabout 50% mortality among seedlings, whenthe stand is later logged, and anticipates highrates of mortality from other sources, espe-cially brown-spot fungus, during the earlyyears following establishment. It is reasonableto expect that at least 1235 well-distributedseedlings per hectare could result that areabout 1 m in height and therefore free frombrown-spot infection and relatively safe fromdamage by fire (Croker and Boyer 1975).

Since longleaf pine is highly sensitive tocompetition, established seedlings develop op-timally in the absence of competitors. Al-though hardwood trees and shrubs comprisethe most severe competition for young longleafpine, these should be largely eliminated duringpreestablishment treatments. While eliminat-ing all competitors is not practical, action toobtain postestablishment competition controlis indicated when hardwood densities exceed2.3 m2/ha (Boyer and White 1990). Herba-ceous understory plants and adult longleafpine trees in the overstory typically remain asthe major competitors for newly established

seedlings. Seedling growth beneath adults re-mains inhibited until nearby overstory treesare removed (Boyer and White 1990). Peri-odic prescribed fire should adequately curtailunderstory plants, with herbicide applicationreserved for use under specific circumstances.

Control of the brown-spot fungus, the mostserious pathogen of longleaf pine, is essentialfor successful natural regeneration (Boyer andWhite 1990; Boyer 1990a; Dennington andFarrar 1991). Timely application of prescribedfire, which consumes the infected needles,is the most effective remedy for this needleblight. In newly established seedlings, pre-scribed fire should be deferred until an ade-quate number of the seedlings reach a fire-resistant size. Unfortunately, seedlings beneathadult trees grow slowly and delaying fire couldallow brown-spot needle blight to spread in astand, further inhibiting seedling growth. Thisrisk can be abated by maintaining relativelylow basal areas where seedlings are less likelyto be suppressed by overstory trees.

Young seedlings must also be protected fromhogs, which can rapidly destroy seedlings byconsuming them while in the grass stage(Boyer 1990a; Boyer and White 1990). Cattlegrazing will also reduce the fine fuel needed toeffectively carry fire in these ecosystems andmay directly damage seedlings if conducted athigh intensities (Dennington and Farrar 1991).Regenerating longleaf pine by natural meansrequires careful attention to details relevantto advanced planning, monitoring site condi-tions, prescription development, and timing ofcultural treatments. Through identifying thearea, assessing the seed source, monitoringcone crops, controlling competition, preparinga suitable seedbed, conducting regenerationsurveys of seedlings, appropriately adjustingoverstory density, and conducting postestab-lishment burns and other treatments, the like-lihood of successfully regenerating longleafpine forests will be substantially increased.

Unique ConsiderationsLargely as a result of ignorance concerningthe unique life history of longleaf pine, mis-management may be the rule rather than the

110 II. Ecology

exception (Kush 2002). Unlike other south-ern pines, longleaf pine is both resistant to anddependent on fire and its seedlings must passthrough a stemless grass stage. If unwise man-agement or the absence of management allowscompeting species to grow freely while lon-gleaf pine is in the grass stage, then it can be lostfrom a site and will not become reestablishedand regain dominance without interventionthat provides the requisite disturbance regime.Although periodic surface fires are essen-tial for sustaining longleaf pine forests, thesemust be prudently timed because longleaf pineseedlings remain highly vulnerable to fire-caused mortality until they reach a ground-line diameter of 7.5 mm and a height of 1 m(Kush 2002). Because of their high suscepti-bility to competition for aboveground and be-lowground resources, their slower growth nearadult trees, and the greater needle litter (i.e.,fuel) accumulation under tree crowns, longleafpine seedlings located beneath adult trees aremore vulnerable to mortality from fire than arethose in openings (Croker and Boyer 1975).Prescribed burning, with the objectives of ade-quately reducing fuels and competition whileaffording protection for seed-bearing trees andseedlings, should be conducted within 2 to3 days following a saturating rain, at tem-peratures no greater than 27◦C, with relativehumidity higher than 40% and wind speedssteady at 8–13 kph (Croker and Boyer 1975).

Longleaf pine is a competition-intolerantspecies, with its regeneration largely confinedto canopy gaps (Wahlenberg 1946). Abun-dance and growth of seedlings have long beenreported to be negatively related to the pres-ence of adult longleaf pine (Walker and Davis1954; Davis 1955; Smith 1961), with the com-petitive influence of individual trees and forestedges on seedlings observed to extend up to16 m (less on better quality sites) from adultsinto forest gaps (Smith 1955; Walker and Davis1956; Boyer 1963). This competitive effect is sopronounced that the most frequently survivingand vigorous growing longleaf pine seedlingstypically cluster near the center of canopy gaps(Brockway and Outcalt 1998). Although lon-gleaf pine seedlings may persist for years be-neath the crowns of adult trees, their growthis impeded by competition from adults and

continuing long-term suppression makes themhighly vulnerable to mortality from a vari-ety of individual and cumulative stress factors(Boyer 1974b; Boyer and White 1990). There-fore, unless natural or anthropogenic distur-bances remove nearby adults from the canopy,it is doubtful that seedlings present beneathmature pines will ever ascend to become dom-inant members of the forest canopy.

The impoverished (low available moistureand nutrients) and relatively simple (veryfew woody plants other than longleaf pine)ecosystem represented by the well-drainedand somewhat excessively drained, coarse-textured soils in north central Florida pro-vided a unique opportunity to assess the re-sults of gap-phase regeneration in longleafpine that are the cumulative product of re-source competition and repeated fires overseveral decades. In examining these long-termpatterns of natural longleaf pine regenerationin numerous naturally occurring forest gaps,Brockway and Outcalt (1998) observed thatmost surviving longleaf pine seedlings aggre-gated near the center of canopy gaps and wereencircled by a zone approximately 12–16 mwide from which they were generally absent.This “seedling exclusionary zone” (SEZ) wasfound to spatially coincide with an area ofgreater fine root biomass and relatively in-tense intraspecific root competition betweenadult and juvenile longleaf pines. The cen-ter of the canopy gap, where most longleafpine seedlings cluster, spatially coincides witha fine-root gap, where seedlings are under lesscompetitive stress and thus enjoy higher ratesof survival and growth. Although all three fac-tors are no doubt of some degree of impor-tance, in these relatively open longleaf pinestands (57% cover) growing on xeric sand-hills, competition for soil moisture and possiblycompetition for nutrients appear to be propor-tionally more important than competition forlight.

Others studying gap-phase regeneration inlongleaf pine have typically examined short-term responses of planted seedlings on higherquality forest sites (Palik et al. 1997; McGuireet al. 2001; Gagnon et al. 2003). On moremesic sites, with richer soils resulting in higherstand density and a greater number of woody


plants with roots innervating the surface soillayers, various root clusters are not readily dis-tinguishable and a SEZ was not identified. Onthese better sites, competition for light and nu-trients is reportedly more important than com-petition for soil water. Should the root geom-etry characteristic of xeric sites eventually de-velop on these mesic sites, it is likely that theresulting SEZ would be considerably narrower(i.e., shorter foraging distance for adult roots),perhaps only 5–10 m wide, making its effectsdifficult to distinguish from the influence ofthe 4–7 m radius directly beneath the crownof a mature longleaf pine tree.

Survival and growth of longleaf pineseedlings is negatively influenced by the den-sity of adult trees in the canopy and the prox-imity of adults to the seedlings (Palik et al.1997; Brockway and Outcalt 1998; Gagnonet al. 2004). Timely seedling release from in-traspecific competition is essential to achievesuccessful natural regeneration. Although re-lease can be affected through stand treatmentsthat thin the forest to a uniform overstorydensity (i.e., even-aged management meth-ods), recent appreciation for the ecological val-ues protected by maintaining an uneven-agedstructure has increased interest in achievingnatural regeneration through selection silvi-culture techniques (Farrar 1996). Group se-lection, which mimics the natural stand re-placement dynamics of gap-phase regenera-tion, may be one of the most useful ap-proaches for regenerating longleaf pine forests.Although canopy gaps created on xeric sand-hill sites should perhaps range from 0.13 to0.8 ha (radius = 20–50 m) to sufficiently re-duce the competitive influence of adults onseedlings (Brockway and Outcalt 1998), gapsas small as 0.1–0.14 ha (radius = 18–21 m)may be suitable for regenerating longleaf pineon mesic sites (Palik et al. 1997; McGuire et al.2001; Gagnon et al. 2003).

Artificial Regeneration

Direct SeedingInitiating a stand of longleaf pine from seedsown directly onsite can be a cost-effectiveregeneration method, especially for small

landowners. However, this approach is poten-tially quite risky. Many longleaf pine standshave been successfully established by directseeding, but there have also been many fail-ures resulting from adverse weather, seed pre-dation, or simply not following the requiredprocedures. The first step in attempting toachieve successful regeneration by this methodis proper seed selection. Longleaf pine has fiveseed zones and seed should not be transportedfor use more than one zone in any direction(Schmidtling 2001). Since there is no geneticevidence for east–west or ecotypic site vari-ation, seed can be collected from anywherewithin a zone for use in that zone. Seed fromone zone warmer should grow faster and seedfrom one zone colder will typically grow slowerthan local seed.

Seedlots should be 95% pure and have agermination rate of at least 75% (Barnett et al.1990). To obtain this germination rate, conesmust not be collected until they are fully ma-ture (Barnett and McGilvray 2002). Maturecones have a specific gravity of 0.89, whichcan be determined by the water displacementmethod (Barnett and McGilvray 2002). Guide-lines specify that cones should not be collecteduntil 19 of 20 cones have a specific gravityequal to 0.89, which means the averagespecific gravity will be about 0.81 (Wakeley1954). Cones must be stored in a dry locationhaving adequate ventilation. Cone storage fora short period will increase seed yields, butstorage beyond 4 weeks may reduce seed qual-ity. Cones will dry in a kiln within 24–48 hoursdepending on initial moisture and weatherconditions. Kiln drying temperatures shouldnot exceed 45◦C (Barnett and McGilvray2002). Once cones are dry and open, seedmay be removed by using a tumbler.

Newly extracted seed will have a relativelyhigh moisture content and, therefore, shouldbe refrigerated and then dried to an 8–10%moisture level. Dewinging the seed requiresappropriate equipment and processing tech-niques to prevent damage and a correspond-ing decline in quality (Barnett and McGilvray2002). The wing is not really removed, butrather reduced to a stub. Debris is removedby screening and air, followed by removal ofempty and partially filled seeds on a gravity

112 II. Ecology

table. Processed seed can then be stored inmoisture-proof containers at no more than 2◦Cfor up to 3 years. Storage for longer periods re-quires a temperature of-18◦C.

Seed should be tested for its germinationrate prior to use or sale. Since longleaf pineseed is nondormant, stratification is not neces-sary. However, a 10-minute drench with beno-myl fungicide prior to sowing will improvegermination. Since longleaf pine seed is quitelarge and nutritious, some type of repellent isneeded to deter consumption by birds and ro-dents (Nolte and Barnett 2000). On most sites,seed is best sown during the fall, when mois-ture is adequate and the maximum daytimetemperature is below 29◦C (Dennington andFarrar 1991). On other sites, such as those innorthern areas with finer-textured soils proneto frost heaving or those having high rabbitpopulations that may damage new seedlings,seed should be sown in late winter or earlyspring. Seed can be broadcast onsite by air orground equipment. Since most sites are nowrather small, aerial seeding is rarely employed,but ground application with a cyclone seeder isa commonly used method. Row and spot seed-ers operate more slowly, but use less seed perunit area and provide increased spacing con-trol. Following dispersal, the seed can be cov-ered with soil, which improves seedling stock-ing especially on dry sandy sites.

Direct seeding should not be attempted onpoorly drained soils or sites having a high wa-ter table, because new germinants are highlysusceptible to mortality from wet conditions(Dennington and Farrar 1991). Steep siteswhere seed is likely to be displaced down slopeand deep sands during drought periods are alsopoor candidates for direct seeding. Preparingthe site prior to sowing, by burning, chemical,or mechanical means to reduce plant competi-tion and expose mineral soil, will increase theprobability of regeneration success. If compe-tition is mostly composed of herbaceous plantsand low shrubs, a prescribed fire in the springor summer prior to sowing may be useful(Mann 1970). On sites with substantial compe-tition from woody plants, mechanical or her-bicide treatments may be required, before firecan be effectively used to prepare the seedbed.

A scalper attachment may be used with therow seeder to remove competition from thearea being seeded. Recommended minimumseeding rates are 32,000 repellent-treated vi-able seeds/ha for broadcast application. Whenrow seeding, use 16,800 seeds/ha with oneseed placed every 23–30 cm within a row.When spot seeding, 5–6 seeds should be de-posited at each spot with spots arrayed at a2 × 2 m spacing. Covering seeds lightly withabout 6 mm of soil improves germination andestablishment success (Barnett et al. 1990). Inassessing seeding success, a minimum of 100survey plots (each 4 m2) per site is recom-mended (Mann 1970). If seedling stocking isgreater than 50%, then a suitable stand of lon-gleaf pine should develop.

Bare-Root Nursery SeedlingsThe nursery management objective is toproduce high-quality longleaf pine seedlingswith a root-collar diameter of 10 mm, atleast six primary lateral roots, a stout taproot,well-developed terminal bud, and manyneedle fascicles (Barnett et al. 1990). The firststep in this process is to select good-qualityseed with 95% purity and a germinationrate of at least 75% (Cordell et al. 1990).A benomyl application to seeds will reducefungal pathogens and improve seedling es-tablishment in the nursery bed (Barnett etal. 1999). Seedbeds should consist of sandyor loamy sand soils with a pH of 5–6. Weeds,insects, and pathogens are reduced by seedbedfumigation prior to sowing. If mulch is used, itshould also be fumigated to prevent introduc-tion of pathogens. Seed may be sown in eitherfall or spring, although fall sowing will usuallyproduce larger seedlings (Barnett et al. 1990).However, a cold winter can damage youngseedlings so spring sowing may be favoredat more northerly locations. Longleaf pineseedlings should be grown at a density of 108–160/m2. Seedlings produced at higher densi-ties have lower survival following outplant-ing, while growing them at lower densitiesincreases the per unit cost of production. A pre-cision sowing machine greatly aids in obtainingthe desired planting density in the seedbed.


Irrigation and fertilization must both becarefully controlled to produce good-qualitylongleaf pine seedlings (Cordell et al. 1990).Too much water will promote disease, whiletoo little will impede growth and develop-ment. The pH of irrigation water must also becontrolled, maintaining it at 5–6. Substantialpractical experience is needed to develop theskill necessary to determine when seedlings re-quire watering. Fertilization decisions shouldbe based on a chemical analysis of the soiland seedling nutrition requirements. Gen-erally, numerous smaller applications ratherthan fewer larger inputs of nutrients are pro-vided, with the highest rates applied during thephase of rapid growth. Although most largenursery operations use soluble fertilizers ap-plied from tank sprays or as injections intothe irrigation system, dry fertilizers can also beused. Standard practices should be followed forreducing fertilization during the seedling hard-ening phase.

Pruning of both vertical and horizontalroots improves longleaf pine seedling survival(Cordell et al. 1990). For production of 1-0seedlings, two root-pruning treatments ap-plied in August and October are recom-mended. Root pruning should be followedwith irrigation to settle the soil and reducedesiccation. Needle clipping just before lift-ing can improve survival on dry sites (Barnettet al. 1990). The best lifting time is Januaryand early February, but lifting should be co-ordinated with planting schedules to reducetime in storage. Care must be exercised dur-ing lifting to limit root system damage. Sur-vival is improved by application of benomylfungicide to the packing medium or as a rootcoating at the time of packing (Barnett et al.1988). Grading should normally not be nec-essary if proper seedbed densities, fertiliza-tion, and irrigation have been used. If prob-lems caused by nonuniform growth arise, thenall seedlings with a root-collar diameter lessthan 7.5 mm should be discarded. Bare-rootseedlings should be stored and transported inrefrigerated containers maintained at a tem-perature of 1–3◦C. Seedlings are best plantedas soon as possible after lifting, with the dura-tion in cold storage limited to 1 week. Seedling

health declines rapidly when kept in cold stor-age longer than 2 weeks and survival becomescorrespondingly low (White 1981).

Containerized NurserySeedlingsSuperior containerized longleaf pine seedlingsare best grown outdoors in full sunlight. Dur-ing initial germination, a 30% shade cloth isused to prevent seed wash from containers(Barnett and McGilvray 2000), but this ma-terial should be removed as soon as germina-tion is complete. A 1:1 mixture of sphagnumpeat moss and number 2 grade vermiculite isan optimum growing medium. Prior to mixing,the peat moss should be screened to removelarge sticks and woody fragments. If necessary,medium pH should be adjusted to 4.5–5. Con-tainers having a minimum depth of 11 cm, vol-ume of 100 cm3, and density of less than 535seedlings/m2 are recommended for growinglongleaf pine (Barnett and McGilvray 1997). Ifpossible, good-quality seed with a viability ofat least 80% should be sown. Treatment withbenomyl prior to sowing will reduce pathogensand improve germination, especially for lowerquality seedlots. Seeds should be sown dur-ing spring, from March to May, putting oneseed per cavity for good-quality seedlots ortwo per cavity if viability is 65–80% (Bar-nett and McGilvray 2000). The seed is thencovered with a thin 3-mm layer of growingmedium, grit, or vermiculite. Seedlings shouldbe thinned to one per cavity when seedcoatsare being shed.

Because longleaf normally germinates inthe fall, it will do best if sown during coolertemperatures when the daily range is 15–27◦C and the mean is 22◦C. During the ger-mination phase, seedlings need frequent butlight watering. Following germination, waterapplication is based on container weight. Aweight of 80–85% of field capacity duringrapid growth and 70–75% during the hard-ening phase is a good guideline for deter-mining when water is needed. Sufficient wa-ter is typically added to wet the entire plug(Starkey 2002). While many nursery managers

114 II. Ecology

now incorporate slow-release fertilizers intothe growing medium, water-soluble fertiliz-ers can also be applied as needed. Starkey(2002) recommends starting with three fertil-izer applications per week, adjusted as neededfor rainfall amounts, using a balanced N-P-Kfertilizer like 20-20-20 or 15-15-15. After ger-mination is completed, use 50 ppm for 2 weeksduring the establishment phase, followed by200 ppm for 14–16 weeks and then 25–50ppm during the hardening phase. If weeds be-come a problem, oxyfluorfen should be ap-plied at about one-fourth the recommendedrate to prevent seedling damage (Barnett andMcGilvray 2000).

Watering to field capacity makes plug ex-traction easier. Poor-quality seedlings, wherethe root plug does not hold together or root-collar diameter is less than 7 mm, should beculled. Good-quality seedlings are then putinto cardboard boxes and placed in cold stor-age at 1–3◦C. Storage intervals in excess of2 weeks should be avoided, as seedling qual-ity will decline. Containerized seedlings can beplanted in Florida during July and August be-cause rainfall is normally plentiful. In other ar-eas, seedlings should be planted in the fall assoon as soil moisture is adequate, to reduce therisk from freezing winter temperatures (Bar-nett and McGilvray 2000).

Planting Longleaf Pine SeedlingsIn the past, longleaf pine was often not cho-sen for reforestation because high mortalityshowed it to be very difficult to establish us-ing bare-root seedlings and, even if survivalwas acceptable, many seedlings remained inthe grass stage for extended periods. More re-cently, however, longleaf pine has been shownto survive well and begin height growth quiterapidly if seedlings are planted properly. Suc-cessful regeneration with bare-root seedlingsrequires healthy, fresh planting stock and pre-cision planting on a well-prepared site (Barnett1992). The average survival and growth ofcontainerized longleaf pine, however, remainsbetter than those of bare-root seedlings. At fivelocations in Georgia, containerized seedlingsurvival was 76%, while that for bare-root

seedlings was only 51%, after 5 years (Boyer1989). Although containerized seedlings aremore costly, they are clearly the better choiceespecially on droughty sites prone to moisturestress and when planting outside the normaldormant-season period (Barnett 2002).

Since longleaf pine is sensitive to compe-tition, some form of site preparation is re-quired before seedlings are planted. Prescribedburning may be all that is required if the sitehas been regularly burned and is dominatedby herbaceous species. On sites with heavycompetition from woody plants, mechanical orherbicide treatments will be required. Inten-sive mechanical site preparation is often a poorchoice for longleaf pine ecosystems because itdestroys most native understory plants, canpromote rapid growth of annual weeds, andmay lead to soil erosion. Herbicide and fire ina combination sequence of “brown then burn”treatments may be used to prepare harvestedsites for planting. A combination of herbicideand strip scalping works well on sites with na-tive understory plants. The herbicide shouldtarget woody species, while the scalp reducesherbaceous competition within the plantingzone. The native grasses will recover and reoc-cupy the scalped strip, providing the fuel nec-essary for future management with fire (Out-calt 1995). Herbicide and scalping is also a veryeffective site preparation technique for old-field sites (Hainds 2001).

Longleaf pine requires careful handling andseedlings must be kept in cold storage untilthey are planted. For small operations, balesor boxes of seedlings can be brought to theplanting site a couple of times each day andkept in the shade until planted. For large op-erations, it is best to have a refrigerated truckpresent onsite. Both bare-root and container-ized seedlings can be hand or machine planted,although machine planting is preferable forbare-root seedlings because of their large rootsystem. Bare-root seedlings should be rootpruned before lifting and not in the field. Ob-vious culls, which are too small or have poorlyformed root systems or plugs, should be dis-carded. Planting depth is a critical factor insurvival and growth. The bud of bare-rootseedlings should be placed at ground level or


slightly below to allow for soil settling (Barnettet al. 1990). Shallow planting, with the budabove the soil surface, is better for container-ized seedlings that have smaller buds moreprone to being buried (Hainds 2001).

Containerized seedlings can be planted any-time from July to March, when soil mois-ture is adequate. Winter planting should beavoided in northern portions of the range be-cause cold temperatures may lead to mortalityfrom freezing. Bare-root seedlings should beplanted only during the dormant season fromDecember to February, with January the bestmonth in most areas. The planting objectiveis typically 740 well-distributed seedlings/ha,which means 1000–1200 seedlings/ha mustbe planted, assuming a survival rate of 60–75%. If the survival rate is lower, container-ized seedlings can be used to fill in or, if sur-vival is very low, the site can be burned and re-planted the next season (Barnett et al. 1990).Seedling surveys, conducted 1 year afterplanting between October and February, arevery important. Some sites may require postplanting treatments to control competitionand speed seedling emergence from the grassstage.

Forest ReproductionMethods

Concern for renewing the forest, throughtimely and successful regeneration, is the mostsignificant difference between silviculture andexploitive logging. Reproduction methods de-scribe the manner in which forests will becut to ensure regeneration and are a com-ponent of silvicultural systems that define ina more comprehensive way the manner inwhich forest stands will be tended, harvested,and replaced (Daniel et al. 1979). Reproduc-tion methods that are effective in achievingsuccessful regeneration are not only importantfor the continuation of overstory tree species,but also have a profound impact on composi-tion and structure of the understory plant com-munity which provides habitat for numerousassociated species and indicates to a substantial

degree the ecological health of an ecosystem.Properly selecting and implementing forest re-production methods that contribute to numer-ous conservation and utilitarian goals requiresextensive knowledge of longleaf pine ecology,silviculture, and the variation in longleaf pineecosystems across an extensive natural range.Although no single approach to obtaining lon-gleaf pine regeneration can be appropriatelyprescribed everywhere, methods that seek toholistically sustain longleaf pine ecosystemsneed to be compatible with (1) frequent useof surface fires, (2) maintaining native un-derstory vegetation, (3) retaining appropriatenumbers of overstory trees onsite well beyondeconomic maturity, and (4) creating and main-taining small-scale canopy gaps interspersedamong forest patches of varying ages within anuneven-aged landscape mosaic at larger scale(Landers et al. 1990).

Clearcutting MethodThe clearcutting method consists of removingall overstory and midstory trees, resulting in anopen site that is influenced little by the edgeof adjacent forests. The principal objective ofclearcutting is to establish a new forest standthat will have an even-aged structure (Danielet al. 1979). Clearcutting may be prescribedfor removing stands in poor condition owingto damage by insects, pathogens, or fire andmay also be used to quickly remove an over-story composed of undesirable species prior toreforesting a site with longleaf pine. An areaso cleared may more easily be treated withmechanical site preparation and subsequentlyregenerated by artificial means. Clearcuttingmay also be combined with natural regener-ation, through application of alternative-stripor progressive-strip clearcutting. However, ap-plication of these techniques is somewhat chal-lenging, considering the short dispersal dis-tance of large longleaf pine seeds and the carethat must be taken to protect the usually scarceadvanced regeneration (Kush 2002).

Certain disadvantages of the clearcuttingmethod suggest that it should not be appliedto perpetuate existing longleaf pine forests ingood condition. Clearcutting mature longleaf

116 II. Ecology

pine stands can destroy much of their ad-vanced reproduction (Boyer and Peterson1983), thus requiring reliance on more ex-pensive planted seedlings rather than estab-lished natural regeneration. Managing lon-gleaf pine in accordance with a “clearcut andplant” model is very expensive, because ad-vanced regeneration is destroyed and all standestablishment costs must be carried through along rotation period until harvest. Althoughlongleaf pine is a competition-intolerant treespecies, its does not require complete canopyremoval to regenerate and its need for sun-light cannot be used as an appropriate ratio-nale for implementing the clearcutting method(Brockway and Outcalt 1998). Also, completecanopy removal through clearcutting can di-minish aesthetics and degrades habitat qualityfor certain at-risk species. If clearcut longleafpine sites are somehow captured by other treespecies, not only does this contribute to furtherattrition of these endangered ecosystems, butplant community succession on such areas willbe driven along very different trajectories thatcan fundamentally alter important ecologicalprocesses and structures (Brockway and Lewis2003).

Seed-Tree Method

The seed-tree method consists of removingmost of the mature overstory while leavingenough good seed-producing trees scatteredacross a site to ensure acceptable future stock-ing (Daniel et al. 1979). The 20–25 trees/hatypically left as residuals afford some degreeof site amelioration and ensure an even dis-tribution of seed over the area (Kush 2002).The residual seed-trees can provide a moreaesthetic appearance and improve composi-tion of the future stand if good-quality phe-notypes (and presumably genotypes) are se-lected. The seed-trees are typically harvestedafter regeneration becomes established; how-ever, in a variation of this method known as“deferment” cutting, these residuals may beretained onsite along with the regenerationthroughout the entire next rotation (Smithet al. 1989). While the objective of the seed-

tree method is usually to establish a new for-est with an even-aged stand structure, use ofthe deferment-cut variation will result in morethan one age-class present in the future forest.

The seed-tree method has a number of dis-advantages for longleaf pine. Very rarely willthe low number of residual overstory trees becapable of producing sufficient quantities oflongleaf pine seed to obtain satisfactory natu-ral regeneration. Therefore, a longer time pe-riod will typically be needed to achieve re-generation success with the seed-tree method.The limited seed dispersal distance of longleafpine seed requires that cleared areas be withinabout 30 m of residual seed-trees (Boyer andPeterson 1983). If a good seed crop does notoccur for a number of years, open areas can be-come occupied by competing hardwoods andother southern pines. The sparse longleaf pineoverstory will produce very little needle lit-ter, resulting in surface fires that may burnwith insufficient intensity to satisfactorily con-trol this competition (Kush 2002). If these in-vaders escape to grow to fire-resistant size,then chemical and/or mechanical treatmentsmay be necessary (Boyer and Peterson 1983).Also, seed-trees retained onsite represent atimber volume loss to managers interestedin maximizing the output of forest products(Kush 2002). However, the greatest problemwith application of the seed-tree method inexisting longleaf pine forests is that most orall of the large overstory trees will be re-moved, changing ecosystem structure and de-grading habitat that supports numerous at-riskspecies.

Shelterwood MethodThe shelterwood method consists of remov-ing a moderate portion of the overstory whileretaining onsite sufficient numbers of seed-bearing trees so that regeneration becomes es-tablished under the protective partial shade ofmature residual trees (Fig. 10). Compared withthe relatively rigid conditions resulting fromapplication of clearcutting and seed-tree meth-ods, the shelterwood method is the most flexi-ble method for establishing new forests of lon-gleaf pine having an even-aged structure and is


FIGURE 10. Longleaf pine forest being regenerated by the shelterwood method; an overstory of 60 trees/hahaving a basal area of 7 m2/ha remains following the seed cut. Photo courtesy of the Forestry ImagesOrganization.

capable of producing a variable degree of siteamelioration (Daniel et al. 1979). When ap-plied in longleaf pine forests, the 50–62 resid-ual trees/ha typically produce an abundanceof seed that is uniformly distributed across asite (Kush 2002). Selecting high-quality phe-notypes as residual trees provides an oppor-tunity to improve genetic composition of thefuture stand. With no large areas left barren,a substantial forest canopy deposits sufficientneedle litter to support surface fires with inten-sities high enough to control competing woodyplants (Kush 2002). The more substantial for-est canopy of this method also enhances envi-ronmental aesthetics and improves habitat fornumerous wildlife species. The principal dis-advantages of most forms of the shelterwoodmethod are related to the eventual removalof all overstory trees. During overwood har-vest, excessive damage may occur to estab-lished longleaf pine seedlings and, followingoverstory removal, forest structure is substan-

tially transformed and habitat quality for at-risk species may remain reduced for decades.

The shelterwood method can be applied onlyin existing stands with sufficient dominantand/or codominant trees of seed-bearing size(Boyer and Peterson 1983). The most com-monly used approach is the uniform shelter-wood method, which may be implementedwith either a two-cut or three-cut technique.As the name suggests, each cut in the uni-form shelterwood method is applied through-out the entire stand resulting in a uniformappearance and even-aged structure. If aforest is highly stocked and requires thin-ning or improvement cutting, the three-cuttechnique is necessary. The first cut in thethree-cut technique is the preparatory cut,which is optional in regularly tended standsand normally performed 10 years before theplanned overwood harvest. The preparatorycut should leave a well-distributed populationof dominant and codominant trees totaling

118 II. Ecology

13.8–16.1 m2/ha (Boyer and Peterson 1983).This will promote crown development and en-hance cone production in the residual seed-bearing trees. If the density of competingwoody plants is greater than 2.3 m2/ha, her-bicide and/or fire treatments should be imple-mented (Kush 2002).

The second cut in the three-cut techniqueand the first cut in the two-cut technique is theseed cut (Croker and Boyer 1975). The seedcut is performed 5 years or more before theplanned overwood harvest to reduce the standdensity to 6.9 m2/ha, leaving well-distributedhigh-quality seed-bearing trees in the over-story (Kush 2002). The most desirable resid-uals are trees equal to or greater than 40 cmdiameter at breast height that have evidenceof past cone bearing ability. Large hardwoodand other undesirable trees may also be re-moved during the preparatory cut, and smallerhardwoods can subsequently be controlled byprescribed fire conducted during the growingseason (Boyer and Peterson 1983).

Seed crops are then monitored by annualspringtime counts of flowers and conelets,watching carefully for crops that produce1860–2470 cones/ha, the range typically re-quired for adequate natural regeneration(Boyer and Peterson 1983). Once an accept-able cone crop is noted, a seedbed preparationburn can be conducted during the year priorto seedfall (Kush 2002). While prescribed fireduring summer or autumn will control woodyplant competition better than earlier cool-season burns, increased seed predation by birdshas been associated with fire during the fallseason. Annual seedling surveys are also con-ducted to assess the degree of regeneration suc-cess, the principal criterion being a minimumof 9880–14820 seedlings/ha that are at least1 year old and well distributed across the site(Boyer 1993a). This abundance provides suffi-cient seedling numbers to compensate for fu-ture mortality during overwood removal andfrom other factors (Kush 2002). Once an ad-equate number and distribution of establishedlongleaf pine seedlings are present, the residualseed-bearing trees in the overstory may be har-vested by the removal cut (Boyer and Peterson1983). Although longleaf pine seedling sur-

vival beneath overstory trees may be unaf-fected for 8 or more years, seedling damageduring overwood harvest is minimized if theremoval cut is conducted when seedlings areno more than 2 years old and in the stemlessgrass stage (Boyer 1975, 1993a). While over-wood harvest may be scheduled with a reason-able amount of flexibility to meet economicand other management objectives, conduct-ing the removal cut on overstories of higherdensity above seedlings of increased size willresult in substantially greater seedling mor-tality rates (Maple 1977). When the residualoverstory density is equal to or greater than9.2 m2/ha, overwood harvest is best accom-plished by two separate removal cuts. The prin-cipal postharvest need is application of pre-scribed fire to control competing plants and thebrown-spot fungus; however, timing is cru-cial, since mistimed fires can harm vulnera-ble seedlings (Boyer and White 1990). Pre-scribed burning should be avoided during thefirst 2 years following the removal cut, becauseaccumulated logging slash will produce firestoo hot for newly released seedlings (Boyerand Peterson 1983). Periodic burning shouldgenerally not resume until dominant longleafpine seedlings have attained a root-collar di-ameter of 7.5 mm (Boyer 1979). Prescribedfire is indicated when surveys reveal a brown-spot fungus infection rate of equal to or greaterthan 20% among dominant seedlings (Boyer1993a).

Variations of the shelterwood method in-clude its application in block, strip, and groupconfigurations (Boyer and White 1990; Boyer1993a). The block approach is associated witheven-aged forests and identifies stands typi-cally from 4 to 40 ha as management units de-lineated by various natural or artificial bound-ary features such as creeks and roads. Whileeach unit may be regenerated individually,several adjacent blocks could also be treatedat the same time, resulting in a relatively largearea being in the same stages of regeneration.The progressive strip approach can convert alarge even-aged stand into a number of smallereven-aged stands covering an entire range ofage-classes from seedling to mature. Stripscreated by cutting are long and narrow, not


exceeding 60 m in width, so that most or all ofthe strip will be within seed-dispersal range ofthe adjacent mature trees. Within each strip,the uniform shelterwood method is applied asdescribed above, using either the three-step ortwo-step technique. When the seed cut is madein the first strip, a preparatory cut is made inthe second strip. When seedlings are estab-lished in the first strip, a removal cut is madethere, with a seed cut then made in the sec-ond strip and a preparatory cut made in an en-tirely new third strip. Thus, a “rolling wave” ofregeneration may proceed indefinitely acrossthe landscape. The group approach is appliedto management units that are too small to beconsidered blocks, typically 0.2–2 ha. Usingthis approach, numerous patches are treatedwith either the three-step or two-step tech-nique. When the first patches are treated witha seed cut, the second group of patches istreated with a preparatory cut. Once seedlingsare established in the first patches, they aretreated with a removal cut, the second patchesare treated with a seed cut, and a third groupof patches are treated with a preparatory cut.The substantial dispersion and smaller size ofareas under treatment at any one time allowthis shelterwood approach to more closelyachieve management objectives related to aes-thetic and ecological values. However, even-tually removing all canopy trees still raises ob-jections from those concerned about the rar-ity of older forests and welfare of associatedspecies.

By contrast, the irregular shelterwoodmethod retains a moderately light (less than7 m2/ha) canopy of mature trees onsitethroughout an entire stand rotation. Thismethod may be applied using any of the abovetechniques and variations, except the removalcut is mostly or entirely eliminated (Boyer1999). Unlike the uniform method, the irregu-lar shelterwood method can maintain a resid-ual canopy of mature trees onsite over manyrotations and potentially in perpetuity. Ma-ture overstory residuals plus newly regener-ated seedlings initially comprise a two-agedforest that may be maintained by thinningfrom below or allowed to eventually achievean uneven-aged structure, as successive waves

of regenerating seedlings establish and developduring ensuing decades. With this method,overstory residuals may range in age fromnewly mature (50–100 years) to very mature(300–400 years), depending on the health ofindividual trees and specific management ob-jectives. Although the growth of longleaf pineseedlings will no doubt be slowed by compe-tition from residual adult trees (Table 1), thecontinuously maintained forest canopy is ben-eficial in sustaining species dependent on suchstructural conditions (Boyer 1993b). The ir-regular shelterwood method is the most rapidway to convert an even-aged longleaf pine for-est (or plantation) to a two-aged and even-tually an uneven-aged stand structure (Boyer1999).

Uneven-Aged SilvicultureIn the most recent decade, ecosystem man-agement policies have substantially increasedinterest in managing forests through uneven-aged silviculture (Guldin 1996). The chapter byGuldin (this volume) discusses uneven-agedsilviculture of longleaf pine forests in greaterdetail. Protecting the native plant community,maintaining a continuous forest canopy, andfacilitating development of large, old trees areamong the desirable habitat features poten-tially resulting when uneven-aged silvicultureis applied in an adaptive ecosystem manage-ment framework. Interest has also grown inmethods for converting even-aged stands touneven-aged forests, like uniform partial cut-ting and patch cutting combined with thin-ning (Nyland 2003). Whether by even-agedor uneven-aged methods, silviculture is fun-damentally applied at varying spatial and tem-poral scales to mimic disturbance and guidesuccession in a forest. Considering the widenatural variation in frequency, intensity, andarea impacted by disturbance, forests tendedaccording to ecosystem management princi-ples might well contain a mixture of even-aged and uneven-aged stands. Where stagesof advanced succession are sought and perpet-uating those stages is desirable (and ecolog-ically feasible), uneven-aged silviculture can

120 II. Ecology

TABLE 1. Inhibitory influence of residual overstory trees on stand growth during a 40-year period (1957–1996) for longleaf pine forests treated with the uniform shelterwood (initial basal area = 0) and irregularshelterwood (initial basal area > 0) methods (tree dbh > 8.9 cm).

Residual pine Ingrowth pine Total pineInitial standbasal area Basal area Volumea Basal area Volumea Basal area Volumea

(m2/ha) (m2/ha) (m3/ha) (m2/ha) (m3/ha) (m2/ha) (m3/ha)

Block A0 0 0 18.2 131.9 18.2 131.90 0 0 17.0 125.7 17.0 125.7

2.1 2.2 18.6 11.7 70.4 13.9 89.04.1 7.3 62.0 6.8 30.1 14.1 92.16.2 8.9 74.7 2.3 6.2 11.2 80.98.3 12.9 109.6 0.8 4.4 13.7 114.0

10.4 15.4 126.8 0.2 1.1 15.6 127.9

Block B0 0 0 20.1 139.9 20.1 139.9

2.1 2.5 21.4 11.8 68.7 14.3 90.14.2 6.3 53.7 4.6 17.6 10.9 71.36.2 9.3 78.8 1.8 5.2 11.1 84.08.3 12.7 106.9 0.4 1.5 13.1 108.4

10.4 16.1 135.8 0.1 0.2 16.2 136.0

a All volumes reported as inside bark and derived from local forest volume tables.

be used to achieve such conditions (Guldin1996).

Uneven-aged silviculture affords a majoradvantage, in that natural regeneration ismore or less continuous, as late succes-sional forest dynamics are emulated (Guldin1996). The Dauerwald (i.e., continuous for-est) of Germany is a prime example of theuneven-aged, continuously regenerating for-est that can result (Schabel and Palmer 1999).Loblolly pine and shortleaf pine, growing ongentle terrain, under aggressive or limitedcompetition, with the worst trees cut and thebest trees left to serve as seed-bearing residuals,have been successfully managed with uneven-aged methods (Guldin 1996). Although lon-gleaf pine was formerly thought to be toocompetition-intolerant for uneven-aged silvi-culture, recent evidence suggests this to be aviable and desirable forest management alter-native (Farrar and Boyer 1990; Farrar 1996;Palik et al. 1997; Brockway and Outcalt 1998;McGuire et al. 2001; Gagnon et al. 2003). Thegroup selection method and the single-treeselection method are the principal means bywhich uneven-aged silviculture can be prac-ticed.

Group Selection MethodAs an uneven-aged mosaic of even-agedpatches distributed across the landscape(Platt and Rathbun 1993), natural longleafpine forests maintain a continuous over-story canopy while establishing naturallyregenerated seedlings in canopy gaps cre-ated by lightning and other local disturbanceagents. Of all available forest reproductionmethods, group selection most closely mim-ics this natural gap-phase regeneration pat-tern and is perhaps best suited in the longterm for sustaining the ecological character oflongleaf pine ecosystems (Brockway and Out-calt 1998). The group selection method canbe used to create circular, elliptical, and ir-regularly shaped gaps ranging from 0.1 to 0.8ha distributed throughout the forest to effec-tively simulate the desired uneven-aged mo-saic (Fig. 11). If volume control is preferred,the volume-guiding diameter limit (V-GDL)and basal area-maximum diameter at breastheight-q (BDq) stand regulation procedures ina modified group selection method are suitablefor managing longleaf pine forests, when usedin combination with prescribed fire on a 3-year


FIGURE 11. Longleaf pine regeneration freely ascending within a forest canopy gap (background); notenumerous seedlings that remain suppressed by intraspecific competition from nearby adults (foreground).Photo courtesy of the Forestry Images Organization.

cycle to control competing vegetation andmaintain seedbeds in appropriate condition(Farrar and Boyer 1990; Farrar 1996). Alterna-tively, longleaf pine stands may be quite easilyregulated using an area control procedure.

Group selection implementation begins dur-ing year 0, with an entry to create the firstseries of canopy gaps by cutting groups ofoverstory trees, placing emphasis on removingpoor-quality trees and retaining good-qualityseed-bearing trees around the periphery ofeach gap (Table 2). Ideally, gaps should be cutin areas where advanced longleaf pine regen-eration is already present, thereby decreasingthe likelihood that newly created gaps will be-come occupied by competing woody species.Gaps should be created of sufficient size (atleast 0.1 ha) to minimize the suppressive ef-fects of intraspecific competition between lon-gleaf pine adults and seedlings. The forest willbe burned several times during this decade tomaintain good-quality seedbeds and control

woody competitors. If a 10-year cutting cy-cle is used, the forest will be again enteredduring year 10 to create a second series ofgaps. If longleaf pine seedlings are establishedin the first series of gaps, they can be pro-tected by skipping one fire cycle, if necessary,and allowing dominant seedlings to reach amore fire-resistant size. Overstory trees imped-ing seedling development along the gap pe-riphery may now be removed. During year 20,another entry is made to create a third series ofgaps in the canopy. Periodic surface fires needto be conducted throughout this decade. Theseedlings in the first series of gaps should besapling size by now and young seedlings maybe present in the second series of gaps. Com-peting adults may be removed here as needed.During the next entry in year 30, a fourth se-ries of canopy gaps is initiated. Seedlings maynow be present in the third series of gaps andcompeting adults along the periphery may beremoved where necessary. Seedlings in the

122 II. Ecology

TABLE 2. Schedule for implementing the Group Selection Method using a 10-year cutting cycle during thefirst 100 years of application.

Seedlings established inCreate gaps; retain openings; may remove Saplings Sawlogscone-bearing trees adjacent size adults; Seedlings grown grown to Poles grown continue to

Year along edges skip one fire cycle to sapling size pole size to sawlog increase in size

gap series0 1st

10 2nd 1st20 3rd 2nd 1st30 4th 3rd 2nd 1st40 5th 4th 3rd 2nd 1st50 6th 5th 4th 3rd 2nd 1st60 7th 6th 5th 4th 3rd 2nd70 8th 7th 6th 5th 4th 3rd80 9th 8th 7th 6th 5th 4th90 10th 9th 8th 7th 6th 5th

100 11th 10th 9th 8th 7th 6th

second series of gaps should be sapling sizeby now while saplings in the first gap seriesshould have grown to pole size. By year 40, afifth series of gaps will be created, seedlingsshould become established in the fourth se-ries of gaps, saplings will have developed inthe third series, poles will have grown in thesecond series, and sawlogs will have emergedin the first series of gaps. If retained for a pro-longed period, these sawlogs will eventuallybecome very large trees. This continuous se-rial pattern of entry, cutting, and reproductionin the longleaf pine forest may be continued,along with application of periodic prescribedburning and other cultural treatments, to cre-ate a potentially infinite series of regenerat-ing canopy gaps that indefinitely sustain anuneven-aged mosaic.

The principal advantages of the group se-lection method include (1) high-forest coveris constantly maintained with no degradationof habitat for at-risk species, (2) the diver-sity of tree size-classes results in an aesthet-ically pleasing environment, (3) regenerationis continuous and not confined to short high-risk periods, (4) regeneration develops undereven-aged conditions within canopy gaps, (5)the larger openings permit establishment of in-tolerant species, (6) more concentrated har-vest results in lower logging costs, less damageto seedlings and residual overstory trees, andeasier conduct of inventories compared to the

single-tree selection method, (7) full stand reg-ulation is more easily achieved, with area con-trol being an easier-to-apply procedure thanvolume control procedures (i.e., BDq, V-GDL),(8) even small areas can be economically man-aged for regular, even product flow, (9) largertrees may be grown by adjusting the cut-ting cycle and/or maximum diameter at breastheight with no change in stand area, and (10)the stand is afforded a greater degree of pro-tection from disturbance-induced losses, be-cause regeneration is present to replace fallenoverstory trees (Daniel et al. 1979; Farrarand Boyer 1990; Farrar 1996; Kush 2002).Among the disadvantages of group selectionare (1) if healthy groundcover is not main-tained through periodic prescribed burning,gaps without advanced regeneration may be-come occupied by woody competitors, neces-sitating costly mechanical or herbicide treat-ments, (2) need for periodic vegetation controltreatments other than prescribed fire (e.g., her-bicide application every 20 years) on betterquality sites with more severe woody plantcompetition, (3) higher management costs,greater inventory information needs and lowerproduct outputs relative to even-aged manage-ment methods, (4) higher logging costs andgreater logging damage of residuals comparedwith those for even-aged methods, and (5) itcan be difficult to apply on sites with severeunderstory competition such as saw palmetto


(Serenoa repens) dominated flatwoods (Farrarand Boyer 1990; Farrar 1996; Kush 2002).

Single-Tree Selection MethodIn the single-tree selection method, individ-ual trees are removed from the forest canopyand regenerating seedlings become establishedin their place. Since only small openings arecreated by this method, it is best applied totree species that are tolerant of competition forsite resources (Daniel et al. 1979). Individualtrees are harvested in a series of partial cutsthat typically occur in a stand at 10-year inter-vals (though the actual cutting cycle may besomewhat shorter or longer). Application ofthis method results in development and main-tenance of an uneven-aged forest structure,having a reverse-J size-class distribution thatcan be quantified by the diminution quotient,q. The q factor is derived from de Liocourt’slaw, ranges from 1.2 to 1.5, and is applicableto all uneven-aged forests (de Liocourt 1898;Meyer 1952).

Selection was first applied in southern pinesusing annual harvests for the initial 15 years,followed by periodic cuts every 5–7 yearsthereafter (Reynolds 1969; Reynolds et al.1984). Although this approach was neithergroup selection nor single-tree selection, vol-ume control was successfully achieved inloblolly pine and shortleaf pine stands by usingthe V-GDL regulation procedure and followingthe rule of “cut the worst and leave the best”trees (Guldin 1996). The keys to successful re-generation with application of the single-treeselection method in this forest type are reg-ulation of stocking and stand structure, care-ful logging, and control of competing vegeta-tion (Shelton and Cain 2000). Uneven-agedstands are generally easier to create and main-tain on poor-quality sites because of less com-peting vegetation and greater ease of obtain-ing natural pine regeneration. Implementingthe single-tree selection method with the BDqstand regulation procedure calls for postcut-ting guidelines of 10–14 m2/ha for basal area,35–55 cm for maximum diameters, and a q fac-tor of about 1.2 for 2.5 cm diameter at breastheight size classes (Shelton and Cain 2000).

However, since the q factor is the most dif-ficult to control (and least important of thevariables), most operational-scale applicationsresult in pine stands consisting of multiple sizeclasses, rather than strictly corresponding toa classically balanced reversed-J distribution.With seed-bearing trees greater than 40 cmdiameter at breast height favored as residualoverstory trees, basal area should not exceed17 m2/ha to limit the adverse influences ofshading and root competition on regeneratingseedlings (Shelton and Cain 2000). Applica-tion of the single-tree selection method resultsin a pine stand with an irregular canopy andmany gaps of various sizes, up to 0.1 ha. Al-though seedlings become established through-out stands managed under single-tree selec-tion, those in gaps created by harvest are ofgreatest interest since they have the greatestpotential to eventually ascend to a dominantposition in the forest canopy.

Application of the single-tree selectionmethod in longleaf pine forests has receivedless study than other southern pines. The in-frequency of good seed years and inclina-tion of seedlings to be suppressed by com-petition from nearby adults, appears to makelongleaf pine a less suitable candidate for ap-plication of the single-tree selection method.Guidance for implementing the single-tree se-lection method in longleaf pine forests em-phasizes thinning removal of individual trees(especially those of poor quality) on a 10-year cutting cycle, establishment of seedlingsin small gaps, and removal of adjacent over-story trees to progressively enlarge these gapsthereby releasing seedlings from competitionwith adult longleaf pine trees (Moore 2001).Although each tree is marked and harvestedas an individual, application of this guidanceeventually results in the removal of groups ofoverstory trees, creating canopy gaps that ap-proach the dimensions of those created by thegroup selection method. The principal differ-ence is that two or more stand entries are re-quired to create sufficiently large gaps usingthe single-tree selection method, while onlya single entry is typically needed using thegroup selection method. Such dependence onmultiple stand entries for multiple-tree gap

124 II. Ecology

creation to achieve successful regeneration,raises concerns regarding suitability of thesingle-tree selection method for regeneratinglongleaf pine forests. Nonetheless, a manage-ment approach identified as “the single-treeselection method” has been applied for sev-eral decades on quail hunting plantations insouthern Georgia (Nature Conservancy 2002).While regeneration has been obtained on thesesites, the absence of an objective stand regu-lation procedure, such as V-GDL or BDq, im-pairs reliable replication of management re-sults among different practitioners.

Advantages of the single-tree selectionmethod include (1) forest cover and habitat forat-risk species is constantly maintained, (2) thevariety of tree sizes creates high-quality aes-thetics, (3) regeneration is continuous, (4) fullstand regulation is easily and rapidly achieved,(5) small areas can be economically managedfor regular, even product flow, (6) large treescan be produced by increasing the cutting cycleor maximum diameter at breast height with-out changing the stand area, and (7) the standis afforded a higher degree of protection fromwindthrow, insect, pathogen, and fire losses,since regeneration is always present to replacedamaged overstory trees (Daniel et al. 1979;Farrar and Boyer 1990; Farrar 1996; Sheltonand Cain 2000; Kush 2002). The disadvantagesof single-tree selection are (1) requirementof well-trained staff, highly skilled in apply-ing more difficult stand management conceptsand procedures, (2) large amounts of stand in-formation from inventory examinations andgrowth and yield projections that are difficultand time-consuming, (3) crop trees are scat-tered throughout the stand resulting in higherlogging costs, greater logging damage to residu-als, and lower product outputs relative to otherforest reproduction methods, (4) very smallsingle-tree gaps provide conditions unfavor-able for establishment and growth of intoler-ant longleaf pine, (5) the resulting forest envi-ronment may be less suitable for some wildlifespecies, such as bobwhite quail (Colinus virgini-anus) that prefer low vegetation and edge ar-eas created by other methods, (6) fire dam-age of pine seedlings that are often present inthe youngest and most vulnerable size-classes,(7) need for periodic vegetation control other

than prescribed fire on better quality sites withmore severe woody plant competition and thedifficulty in efficiently applying area-wide me-chanical and chemical treatments, and (8) it isvery difficult to apply on sites where intensecompetition from native plants, such as sawpalmetto, or exotic plants, especially vines likekudzu (Pueraria lobata) and Japanese honey-suckle (Lonicera japonica), severely limit pineregeneration success (Daniel et al. 1979; Far-rar and Boyer 1990; Farrar 1996; Shelton andCain 2000; Kush 2002).

Since little saleable product results, interme-diate cuts in the younger-age classes necessaryfor maintaining an uneven-aged stand struc-ture have a tendency to be neglected (Danielet al. 1979). Also, among the most seriousdangers inherent in the single-tree selectionmethod is the always present temptation to vi-olate the “cut the worst trees first and leavethe best” rule. In not observing this discipline,errant practitioners will harvest the best treesfirst, thereby allowing the single-tree selectionmethod to degenerate into exploitive timber“high-grading” (Farrar 1996). Finally, it is im-portant to note that applications of the selec-tion methods in longleaf pine forests are stillin their infancy and flawless results cannot beexpected without substantially more scientificstudy and management experience.

Silviculture that Mimics NaturalDisturbanceThe above forest reproduction methods werefirst developed by foresters in Europe duringthe eighteenth century, when the newly cre-ated profession of forestry was confronted withthe challenge of repairing the extensive dam-age done to forests by centuries of exploitivelogging (Daniel et al. 1979). During the en-suing 300 years, various clearcutting, seed-tree, shelterwood, and selection methods havebeen employed by foresters in Europe and onother continents to regenerate and rehabili-tate many forest types. Although their princi-pal focus was often limited to renewing the for-est overstory, many early foresters can rightlybe considered among the first practitionersof restoration. With ecologists, foresters, and


wildlife biologists more recently broadeningthe focus of forest management to includeunderstory flora and fauna, appropriate for-est reproduction methods applied through thepractice of silviculture remain the fundamen-tal means by which forest ecosystems will berestored and sustained.

Despite longtime recognition of the inher-ent efficiency of working in concert with na-ture, silviculture has traditionally placed littleemphasis on the importance of natural dis-turbance dynamics in the development andmaintenance of forests. Indeed, forest man-agement has often implemented silviculturalsystems that prescribe stand homogeneity tooptimize stand-level tree growth. However, asthe primary emphasis on timber productionhas shifted to also include the stewardshipgoals of sustaining ecological functions, con-serving biological diversity, and protecting at-risk species, natural disturbance has becomerecognized as a potential source of guidancefor forest management (Coates and Burton1997). The fundamental hypothesis for suchan approach is that the species, structures, andprocesses that characterize natural ecosystemsare more likely to persist in managed forestsif anthropogenic disturbances like logging andprescribed burning mimic the dynamics of nat-ural disturbances (Mitchell et al. 2002). Thegreater spatial and temporal heterogeneity ofnatural disturbance regimes cause higher vari-ation in the size and age structure of livingtrees and distribution of dead woody debristhan typically result from application of tradi-tional silviculture (Franklin et al. 1997; Spies1997). Silviculture might achieve a more nat-ural basis by striving to mimic this heterogene-ity and leaving onsite appropriate patterns andsuitable numbers of residual trees, snags, logs,and other woody debris as biological legacies(Mitchell et al. 2002). These legacies of the pastcan substantially influence forest developmentfollowing disturbance and contribute to futureconservation of biological diversity (Palik et al.2002).

The forest reproduction methods of tradi-tional silviculture are in some ways analo-gous to various natural disturbance events.The clearcutting method eliminates or greatlyreduces the forest canopy, with results simi-

lar to those caused by a powerful windstorm(e.g., hurricane) or other large-scale distur-bance (Fig. 12). However, tree removal fromthe site is not normally associated with suchnatural events and the magnitude and patternof accompanying soil disturbance are very dif-ferent (e.g., skid trails from logging rather thantip-up mounds from windthrow). Results ofthe seed-tree method are also like those pro-duced by major windstorms, where a few largetrees remain scattered across a site. Once again,removal of trees from the site and the resultingsoil disturbance pattern are unnatural conse-quences. The shelterwood method is thoughtto closely mimic stand replacement dynam-ics following a damaging tropical storm, leav-ing the forest canopy moderately intact andfacilitating prolific regeneration (Croker andBoyer 1975). While this may be true for theirregular shelterwood method (where seed-bearing trees of the overwood are retained on-site as biological legacies), eventual harvest ofthe overstory trees makes the uniform shel-terwood method appear less similar to naturaldisturbance. The two selection methods resultin stand conditions not unlike those created bysmall-scale disturbances (e.g., lightning, local-ized fire, disease, or insect outbreaks), whereindividuals or groups of trees suffer mortalityand fall from the forest canopy. The major dif-ference between these two methods is relatedto gap size and dispersion pattern. Group se-lection normally results in canopy gaps of atleast 0.1 ha and well dispersed, while single-tree selection produces smaller gaps less than0.1 ha (and often as small as the area underan individual tree crown about 0.01 ha) re-quiring less dispersion. As additional overstorytrees are removed through time, these smallergaps may coalesce, forming larger gaps difficultto distinguish from those created by the groupselection method. Although tree removal fromthe site and periodic soil disturbance are alsounnatural aspects of both selection meth-ods, the abundant biological legacies retainedonsite following each harvest make both ofthese methods appear consistent with the char-acteristics of a more natural version of silvicul-ture that mimics natural disturbance.

As in numerous tropical and other tem-perate forest types (Brokaw 1985; Denslow

126 II. Ecology

FIGURE 12. Naturally regenerating even-aged longleaf pine stand following Hurricane Camille. Photocourtesy of the Forestry Images Organization.

1987; Spies and Franklin 1989; Veblen 1989;Liu and Hytteborn 1991; Lertzman 1992), theimportance of canopy gaps as fundamentalecological structures in the natural regenera-tion of longleaf pine ecosystems has also beenrecognized (Palik et al. 1997; Brockway andOutcalt 1998; McGuire et al. 2001; Gagnonet al. 2003). Canopy gaps are essential in main-taining the fine-scale variability created bysmall-scale natural disturbances and are alsogenerated by forest reproduction methods thatremove overstory trees in a patch configura-tion (Coates and Burton 1997). Forests hav-ing a wide range of gap sizes afford a diver-sity of microenvironments for regeneration,with habitat conditions varying among gaps,within gaps (gap centers versus gap edges),and beneath the forest canopy. The resultingvariation in available light, soil moisture, andnutrient resources will differentially affect re-generation success, as will the presence of ad-

vanced regeneration prior to gap formation.Gap sizes and distribution resulting from ini-tial harvest and subsequent stand entries willhave a substantial influence on the coloniza-tion of individuals and development of ad-vanced regeneration, therefore the type andtiming of silvicultural treatments will have im-portant impacts on forest population dynamics(Coates and Burton 1997).

Canopy gaps in longleaf pine forests nat-urally result from a variety of disturbanceagents that operate over a wide range of spa-tial and temporal scales (Palik and Pedersen1996). Disturbances that remove single treesultimately create canopy gaps of suitable sizefor unimpaired growth of regeneration (about0.14 ha) as effectively as single events that re-move groups of trees, a major difference beingthe longer time required for many episodes ofsingle-tree removal to occur (Palik et al. 1997).Although different pathways are followed,


the essential result is that similar outcomesfor stand structure are eventually obtained(Palik et al. 2002). Thus, silviculturists mayvalidly apply either the group selection methodor single-tree selection method in achievingstructures representative of natural forests aslong as canopy gaps of sufficient size to facili-tate regeneration are created.

Silviculture, because of social, economic,and other constraints, may be unable to per-fectly emulate the forest ecosystem structuresand processes sustained by a natural distur-bance regime (Palik et al. 2002). However,improvements can be obtained by mitigatingthe negative effects of logging on understoryplants, forest floor, and soil structure, and in-corporating knowledge concerning ecosystemdisequilibrium dynamics, the importance of bi-ological legacies and the vital role of gap-phasereplacement into appropriately implementedforest reproduction methods. The applicationof silviculture will then result in environ-mental conditions that more closely approx-imate those produced by natural disturbanceand improve the likelihood that multipleconstituencies (i.e., environmental, conserva-tion, utilitarian, and industrial groups) will beserved as longleaf pine forests are effectivelyregenerated and sustained in the future.

Acknowledgments

The authors express their appreciation toBecky Estes for assistance in searching the lit-erature to identify numerous relevant publica-tions. We are also grateful to Shibu Jose, EricJokela, Dennis Hardin, Larry Bishop, and oneanonymous reviewer for comments helpful inimproving this manuscript.

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Chapter 4€¦ · Chapter 4 Longleaf Pine Regeneration Ecology and Methods Dale G. Brockway, Kenneth W. Outcalt, and William D. Boyer ... composition, and density (Platt and Rathbun