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Chapter 9.

Reproduction Cutting Methodsfor Naturally Regenerated Pine Stands in the South

James M. Guldin1

Abstract—It is projected that plantations willmake up 25 percent of the South’s forest landarea by the year 2040. Thus the remaining75 percent of that area will consist of naturallyregenerated pine, pine-hardwood, and hardwoodstands. Naturally regenerated pines can bemanaged successfully by even-aged and uneven-aged silvicultural systems when the reproductioncutting method is properly planned and executed,and when there is timely application of sitepreparation, release, and intermediate treatmentsto ensure seedling establishment and development.Attention to residual basal area, seed production,preparation of suitable seedbeds, control ofcompeting vegetation, and timely density controlare important to the successful managementof naturally regenerated stands.

INTRODUCTION

In the last half of the 20th century, the practiceof silviculture in southern pine (Pinus spp.)stands has focused on one silvicultural

system—clearcutting and planting. This focushas been made possible by two great advancesduring that time: (1) the development ofgenetically improved planting stock and (2)the advent of herbicide technology for controlof unwanted vegetation in planted stands. Thesilvicultural system of clearcutting, planting, andassociated herbicide treatments has come to defineintensive forest management. Forest industry,nonindustrial private forest (NIPF) landowners,and Government agencies have all employedvariations of this prescription, and as a resultthe area in plantations in the South has gonefrom virtually none to roughly 12.5 million ha(31 million acres) in the last 50 years (fig. 9.1).

This silvicultural system has become popularbecause of the large total merchantable volume

of wood and wood fiber that can be obtained. In1995, plantations occupied 15 percent of the forestland in the South but provided 35 percent of theharvested volume (Wear and Greis 2002). By 2040,pine plantations will occupy approximately 20million ha (50 million acres), or 25 percent of thesouthern forest area. This will represent roughlyhalf of the projected pine-dominated forest areaat that time (Wear and Greis 2002).

On the other hand, these data also imply that by2040, 75 percent of the South’s forest land will notbe in plantations, but rather in stands of naturallyregenerated origin. Currently more than half ofthe area in the South’s pine-dominated foresttypes is managed by methods other than intensiveplantation culture. Some of this area will not bemanaged at all in a professional sense; it willsimply be allowed to grow as it will and willbe high-graded when an operable commercialharvest becomes feasible. But other areas are,and will continue to be, managed using classicalsilvicultural practices that establish and maintain

1 Supervisory Ecologist and Project Leader, U.S.Department of Agriculture Forest Service, SouthernResearch Station, Monticello, AR 71656.

Figure 9.1—Trends in forest area occupied byforest type and year, 1952–96 (Sheffield andDickson 1998).

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naturally regenerated pine stands. Specifically,these include even-aged reproduction cuttingmethods, such as the seed tree and shelterwoodmethods, and uneven-aged reproduction cuttingmethods, such as the group selection and singletree selection methods.

Management of naturally regenerated standswill have four prominent areas of applicationin the decades to come. The first of these is inmanagement of the forest land owned by NIPFlandowners. Many NIPF landowners choosenot to employ clearcutting on their land, becauseclearcutting requires a large capital investmentin stand establishment. Plantation establishmentcosts can quickly exceed $500/ha ($200 per acre),especially if intensive site preparation includesapplications of chemicals and fertilizer (Dubois andothers 2001). While such costs are easily borne bylarge companies, they are often difficult for NIPFowners of small properties to justify. Managementprescriptions that rely on natural regeneration canbe adapted to make stand establishment costs verylow, although the tradeoff is that it takes longerto develop trees of merchantable size. However,many NIPF landowners find this acceptable,especially in light of the multiple managementobjectives they often seek, within which theaesthetic disadvantages associated withclearcutting do not fit.

The second prominent area of application is inmanagement of large-diameter pine trees and thehigher unit value that sawtimber brings relative topulpwood when trees are harvested. For example,during the past 10 years in Louisiana, prices ofsoftwood sawtimber averaged from 3.2 to 5.4 timesthose of pine pulpwood on an equivalent weightbasis (Louisiana Department of Agriculture andForestry 2002a, 2002b). In multiple-use settings,management of stands to large tree sizecan produce aesthetic, wildlife, and otherbenefits sought by a landowner. Finally, a partof the South’s forest industry will continue toconcentrate on the manufacture of high-qualitydimension lumber, the best source of whichis high-quality trees of sawtimber size.

The third area of application is withinstreamside management zones (SMZs), oftenamong the most productive sites in a forestedownership. Clearcutting is generally avoided inSMZs, because it has adverse effects on waterquality and aquatic systems. High-grading orselective cutting is often used to capture standingvolume of desired species found in SMZs,but experience shows that such practices are

neither sustainable nor grounded in soundsilvicultural practice. One sensible approachto the management of SMZs is to employmanagement prescriptions that naturallyregenerate desired species while maintainingforest cover within the SMZs.

Finally managers of public forest land in theSouth, especially those who manage national forestlands, are increasingly seeking alternatives toclearcutting (Guldin and Loewenstein 1999). Thistrend has its origins in the fact that the public doesnot like the appearance of clearcutting on publiclands. But it also is seen in modern approachesto management of Government lands by meansof silvicultural prescriptions designed to retainor restore forest stand conditions that benefitunderrepresented plant and animal communities,such as the pine-bluestem habitat restoration inthe western Ouachita Mountains (Stanturf andothers 2004).

Research and practical experience suggestthat both even-aged and uneven-aged reproductioncutting methods can be used in southern foreststands, depending on forest type, prevailingeconomic and ecological conditions, and ownership(Burns 1983). It is likely that the range of potentialapplications will grow wider rather than narroweras a wider variety of practitioners employ awider variety of these methods on a wider varietyof ownerships.

THE ECOLOGICAL BASIS OF NATURALLYREGENERATED PINE STANDS

Reproduction cutting methods that rely onnatural regeneration emulate a continuum ofintensity of natural disturbance. Clearcutting,

with its total removal of all overstory vegetation,approximates the most severe stand-replacementdisturbances, such as the main path of a tornadoor the flare-up of a canopy-destroying wildfire. Butfew ecological conditions in nature are so severethat all living trees are removed. More commonly,some trees remain following disturbance, andthey provide seed to reforest the disturbed area.Reproduction cutting methods that rely on naturalregeneration imitate this dynamic directly.

The even-aged seed tree and shelterwoodmethods approximate disturbance eventssufficiently severe that a new regeneration cohortis established across the entire stand. They differin the number of residual trees remaining on thesite and in the provision of shelter by residualtrees. In the seed tree method, few overstorytrees remain, and microecological conditions for

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seedlings are essentially the same as if the areawere clearcut. In the shelterwood method, moreoverstory trees remain, and their presence slightlyameliorates the microecological condition fordeveloping seedlings.

The uneven-aged methods approximatedisturbance events that open up only part of astand. Thus the new regeneration cohort will befound only in those portions of the stand withinwhich the openings are found, rather than acrossthe entire stand. The group selection methodemulates disturbance events such as beetlespots or locally heavy windstorms that removesmall groups of overstory trees within a stand;regeneration then occurs in that group opening.The single tree selection method imitates thesmallest scale of disturbance, that of the mortalityof one or two mature trees. This creates a smallopening marginally sufficient for development ofa very small cohort of regeneration, provided thatthe species being managed is sufficiently tolerantof shade to develop. Thus the entire gradient ofnatural disturbance events, from severe eventsthat give rise to continuous regeneration cohortsacross the stand to localized events that giverise to discontinuous regeneration cohorts withinthe stand, are reflected in the reproductioncutting methods used to naturally regeneratemanaged stands.

EVEN-AGED REPRODUCTIONCUTTING METHODS

Clearcutting Method

The clearcutting method can be applied in amanner that relies on natural regenerationrather than on planted seedlings to reforest

the clearcut site (Langdon 1981, Smith 1986a).However the circumstances under which thepractice will succeed are highly specialized.One common approach is to configure theclearcut opening so that trees from adjacentstands can naturally seed all parts of the harvestedsite (fig. 9.2). The more risky practice in southernpines, clearcutting using seed-in-place (Smith1986a), relies on the harvest of trees at the pointin the growing season when cones are maturebut not yet opened. Harvest will disperse thosecones across the site, and the warm temperatureregimes that result from clearcutting promotecone scale reflexion and seed dispersal (Sheltonand Cain 2001). This method can succeed onlyif many conditions are concurrently met. Conesmust be present and contain viable seed, harvestmust occur within a 1-month window prior to theautumnal seed fall, seedbed conditions mustbe adequate within the slash resulting from theharvest, seed must remain present and viable

Figure 9.2—The strip clearcutting method demonstrated in aloblolly-shortleaf pine stand, Crossett Experimental Forest, nearCrossett, AR. Photo courtesy of James M. Guldin 2003.

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until germination occurs, and seedlings mustbecome established and must develop properly.The major difficulty is that there is no room foraccident or error, since there is no residual seedsource in the event that the initial cohort does notbecome established.

Seed Tree MethodIn the seed tree method, a small number of

trees are retained on the site after harvest as asource of seed for the harvested area. Seed treesshould be distributed uniformly across the site insuch a way that the entire area of the harvestedstand is within an acceptable dispersal distanceof one or more of the residual seed trees. Areasonable estimate for the number of seed treesdepends on tree size, but it is not unusual toreserve 10 to 25 pine seed trees/ha (4 to 10 treesper acre), with a corresponding residual basalarea from 1 to 3 m2/ha (5 to 15 square feet peracre). The harvest that takes all but the seed treesis called the seed cut, and the subsequent harvestthat removes the seed trees is called the removalcut (Smith 1986a).

Professional application of the seed treemethod bears little resemblance to retention ofseed trees under the old seed tree laws. Thoselaws, which mandated retention of a few trees/haafter harvest, had the effect of leaving the poorestphenotypes of marginal size to reforest the site.Many attributes of interest to foresters, such ascone production, straightness, and branchiness,are highly inherited traits, and trees that displaysuch attributes are likely to pass them along.Thus proper application of the seed tree methoddictates the retention of trees with good form,acceptable branch characteristics, and evidenceof past seed production. These attributes areeasier to determine in some species than others.For example, in shortleaf pine (P. echinata Mill.),cones tend to persist for a number of yearsafter seeds are shed (Lawson 1990), whereasloblolly pine (P. taeda L.) tends to drop its conesafter seed fall (Baker and Langdon 1990). Inshortleaf pine stands, marking crews can usethis information about cone persistence to helpdetermine which trees to retain.

The biggest limitation on the effective use ofthe seed tree method is the production of seed bythe parent tree. Of the four major southern pines,the seed tree method works best in applicationto loblolly pine, especially in the west gulf regionwhere abundant seeds are produced with greatregularity (Cain and Shelton 2001). Adequate seedproduction translates to adequate seed fall and

the likelihood of effective catch of seed by the site.Unfortunately, seed production in longleaf pine(P. palustris Mill.) is highly periodic, and useof the seed tree method is rarely successfulwith this species. One way to compensate forerratic cone production is to plan to retain seedtrees for a long period of time, in the hope ofcontinued recruitment into the regenerationcohort. Empirical evidence suggests that theseed tree method can also be made to work inshortleaf pine, which falls between loblolly andlongleaf in periodicity of seed fall (Guldin andLoewenstein 1999).

As seed fall from seed trees becomes marginal,the need for effective site preparation increases.One main element of site preparation is thecreation of a suitable seedbed. This, for southernpines, generally means the scarification of theforest floor to expose mineral soil. Typically, thelogging activity associated with a seed treeharvest provides sufficient scarification foracceptable establishment of seedlings duringbumper seed crops (Baker and others 1996).If seed crops are marginal, supplementalscarification may be required. However, noamount of supplemental scarification will helpif seed crops are a failure. As a result, earlydetection of impending seed crops is importantto help schedule the amount of site preparationnecessary to ensure acceptable seedlingestablishment. Since pine cones take 2 yearsto develop, one can get an early estimate ofcone production expected for given autumn byinspecting tree crowns for conelets in the spring ofthe previous year. While this approach offers onlya rough prediction of adequate to bumper crops,one can easily see when a cone failure is imminent.That information can then be used to schedule ordefer site preparation treatments in the summeror autumn immediately prior to seed fall.

When properly applied, the seed tree methodhas a number of advantages. Enough residualtrees should be retained to allow an operableharvest of the parent trees 5 to 10 years afterthe seed cut. That operable harvest can alsoprovide a desirable precommercial thinning inthe regeneration cohort, by felling the seed treesamidst the regeneration and by the passage ofthe equipment used to harvest and skid the felledlogs to the logging deck.

An outstanding example of the seed treemethod in application to southern pines exists inthe loblolly-shortleaf pine type in the upper westGulf Coastal Plain (Zeide and Sharer 2000) (fig.9.3). No southern pine is easier to regenerate

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naturally than loblolly pine, which dominates thisforest type; seed crops that are adequate or betteroccur 15 years in 20 in mature loblolly-shortleafpine stands (Cain and Shelton 2001). For a numberof decades, the silvicultural guidelines for a majorindustrial forestry landowner in the region calledfor use of the seed tree method, leaving 2.3 to 4.5m2/ha (10 to 20 square feet per acre) of basal areaof trees with good form and with diameter atbreast height of 40 to 50 cm (16 to 20 inches).2 Theseed trees were usually taken in a removal cut 3 to5 years later, which produced an operable harvestof from 2.9 to 8.8 m3/ha (500 to 1,500 board feet peracre) of saw logs. Removal of the seed trees alsothinned the excessive pine regeneration that wascommon in this forest type. The first commercialthinning occurred between the ages of 17 and 20years, leaving about 16 m2/ha (70 square feet per

acre). The next thinning, at age 25, included somesmall saw logs, and subsequent thinnings on a 5-year cycle averaged 11.7 m3/ha (2,000 board feetper acre) in each thinning. The final seed cutproduced between 29.2 and 40.8 m3/ha (5,000 to7,000 board feet per acre). Thus growth for therotation averaged > 1.75 m3/ha (300 board feetper acre) annually. Late-rotation thinning alsoreleased the crowns of the seed trees, whichincreased cone and seed production. Regularlyscheduled prescribed fires on a 3- to 5-year cycle,coupled with hardwood control on a 5- to 10-yearcycle, promoted visibility within the stand thatenhanced subsequent thinning treatments, and ifcarried through the end of the rotation, reducedthe need for intensive site preparation in thesubsequent rotation.

Shelterwood MethodThe shelterwood method is similar to the seed

tree method in that residual trees are retainedto reforest the site after harvesting occurs, butmore trees are retained. In his description of theshelterwood method, Smith (1986a) includes threespecific elements: (1) the preparatory cut, (2) theseed cut, and (3) the removal cut.

The preparatory cut removes competitors offuture seed trees, which then expand their crownsand root systems, thereby enhancing the potentialfor cone development. In southern pines, the late-rotation thinning commonly conducted in pinesawtimber stands generally fulfills the intent ofthe preparatory cut. During the seed cut, 35 to 75pines/ha (15 to 30 trees per acre), having 4.5 to 9.0m2/ha (20 to 40 square feet per acre) of basal area,are selected for retention. Favorable traits forresidual pines include stem form, windfirmness,and evidence of past seed production. The removalcut harvests the seed trees after the new stand hasdeveloped past the point of risk from seedling-related mortality.

One operational advantage of the shelterwoodover the seed tree method in southern pines is thatthe volume of the residual trees in the shelterwoodis greater than that of the seed tree method and is,thus, more likely to attract interest from loggersduring the removal cut. Conversely, if carelesslydone, logging during the removal cut can adverselyaffect stem density of the regeneration, especiallyat higher residual basal areas. Depending onmanagement objectives, the final harvest may bedeferred for half or more of the rotation length,resulting in a two-aged stand; this method isreferred to as an irregular shelterwood (Helms1998, Smith 1986a).

2 Lovett, Ernest. 2003. Letter dated September 29 toJames M. Guldin. On file with: Arkansas Forestry SciencesLaboratory, 114 Chamberlin Forestry Building, Universityof Arkansas at Monticello, Monticello, AR 71656.

Figure 9.3—The seed tree reproduction cutting methodapplied operationally in a loblolly-shortleaf pine standmanaged by forest industry, Ashley County, AR. Photocourtesy of James M. Guldin 1984.

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Under traditional application of theshelterwood method, microclimatic ecologicalconditions are ameliorated relative to those foundin fully open conditions; e.g., see Valigura andMessina 1993. Thus one reason to apply theshelterwood method is to moderate conditions thatmight be too harsh for seedlings to survive under aclearcut or a seed tree prescription. As a practicalmatter, the shelterwood method is popular forspecies in which seed production is erratic orunreliable; the added numbers of seed treesthat remain in the shelterwood often make thedifference between adequate stocking and less-than-adequate stocking.

Among the most prominent examples ofthe shelterwood method in southern pines isthe experience with longleaf pine in southernAlabama (fig. 9.4). Longleaf pine has the deservedreputation of being the most difficult of thesouthern pines to regenerate naturally, but cleverresearch has identified the practices needed tonaturally regenerate the species using theshelterwood method (Boyer 1979, Croker and

Boyer 1975). First, seed production in longleafis optimal when the seed cut retains 6.9 to 9.2 m2/ha (30 to 40 square feet per acre) of basal area(Maple 1977). Fewer trees result in fewer conesper unit area, and more trees do not enhance coneproduction. Second, prescribed fires are essentialto control brown-spot needle blight (Mycosphaer-ella dearnessii Barr.) and, thereby, to releaseseedlings from the grass stage (Boyer 1979).Third, seedling mortality is highest beneath thecrowns of residual trees, because the buildup ofpine straw promotes prescribed fires sufficientlyintense to kill them. All of these factors have ledscientists to conclude that the need for availablegrowing space, the need for frequent prescribedfire, the optimal development of cones in thecanopy, and the ability to store seedlingsin a seedling bank beneath the overstory oflongleaf pine could be achieved using theshelterwood method.

UNEVEN-AGED REPRODUCTIONCUTTING METHODS

P revailing wisdom suggests that uneven-agedreproduction cutting methods, especially thesingle tree selection method, are best for

shade-tolerant species (Smith 1986a). As a result,the use of uneven-aged silviculture to manageshade-intolerant species such as the southernpines is often criticized. But historical experiencesuggests that the method can work with pines,subject to certain considerations. The Dauerwald,among the first applications of uneven-agedsilviculture, was imposed in plantations of Scotspine (P. sylvestris L.) on poor sites in Germany(Troup 1952); some of its attributes still applyto current uneven-aged methods (Guldin 1996).Pearson (1950) applied a selection method toponderosa pine (P. ponderosa Laws.) stands onthe Fort Valley Experimental Forest in Arizona,thus laying the groundwork for contemporaryapplication of that method in the American West(Becker and Corse 1997).

In the South, the best long-term uneven-ageddataset comes from the Good and Poor FarmForestry Forties of the Crossett ExperimentalForest (CEF) in southern Arkansas. Establishedin mixed loblolly-shortleaf pine stands on thewest Gulf Coastal Plain in 1937, the Good andPoor Farm Forestry Forties have yielded datathat were summarized after four decades (Baker1986, Reynolds and others 1984). Other long-termexamples are the quarter-century summary fromthe Farm Forestry Forties at Mississippi StateUniversity (Farrar and others 1989) and the 33-

Figure 9.4—The shelterwood reproduction cutting methodapplied in a research study on the Escambia ExperimentalForest, near Brewton, AL. Photo courtesy of James M.Guldin 1982.

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year record from the University of Arkansas’sHope Farm Woodland at Hope, AR (Farrar andothers 1984). Empirical evidence suggests thatthe selection method can be made to work withlongleaf pine in the lower Coastal Plain of Floridaand Alabama (Farrar 1996), and with shortleafpine in the Interior Highlands of Arkansas andOklahoma (Guldin and Loewenstein 1999, Lawson1986). In short, the selection method can beadapted to southern pines if attention is paidto marking, regeneration, and stand structure(Guldin and Baker 1998).

The general experience with uneven-agedsilviculture in intolerant pines would lead oneto suspect that group selection, with its largeropenings (fig. 9.5), would be more effective thansingle tree selection, with its minimal canopyopening. Certainly some evidence suggeststhat in longleaf pine, group selection may be aneffective reproduction cutting method (Brockwayand Outcalt 1998, Farrar 1996, Farrar and Boyer1991). On the other hand, Russ Reynolds, thescientist who pioneered the research at CEF, didnot distinguish specifically between single treeselection and group selection; he spoke instead ofusing whatever size of openings was indicated bylocal stand conditions (fig. 9.6). Whether groupselection or single tree selection is preferred, anumber of considerations should receive specialattention when selection methods are appliedto southern pines: initial stand conditions,regeneration, developmental dynamics, applicationof marking rules, and residual stand structure.

Initial Stand ConditionsCircumstantial evidence suggests that early

20th century southern pine stands were largelyeven-aged before they were high-graded.Loblolly pine was known as old-field pine,and early photographs show that virgin uplandpine-hardwood stands in the west gulf regionhad an open understory (Reynolds 1980).

Figure 9.5—The group selection method in application tolongleaf pine in a Farm Forestry Forty demonstration on theEscambia Experimental Forest, near Brewton, AL. Photocourtesy of James M. Guldin 1982.

Figure 9.6—Stand structure in a stand under management using the selection method,Good Farm Forestry Forty demonstration, Crossett Experimental Forest, near Crossett, AR.Photo courtesy of James M. Guldin 1984.

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Similarly, virgin shortleaf pines in the OuachitaMountains grew in open forest consisting of widelyspaced overstory trees and little undergrowth(Smith 1986b).

Naturally occurring loblolly-shortleaf pinestands in the west gulf region originated afterthe first cutting of virgin forest in the early 1900s.In 1915, the Crossett Lumber Company, whichowned the virgin forest land that would laterbecome the CEF, harvested the area using a38-cm (15-inch) stump limit cut, which wasroughly equivalent to a 30-cm (12-inch) diameterlimit cut. Between 1915 and 1934, no deliberatemanagement was undertaken. The area supportedoccasional harvest of small hardwoods for chemicaldistillation and periodically was subject to arson

fires. The company leased the 680-ha (1,680-acre)tract to the U.S. Department of Agriculture ForestService (Forest Service) in 1934 for establishmentof the CEF. While the company was interested inresearch information on management of second-growth forests, they also thought that ForestService research staff could help prevent arsonor control the resulting fires (Reynolds 1980).

Thus the use of uneven-aged silviculture insouthern pines originated as a result of selectivecutting. In 1937, the CEF Forties were stockedwith scattered residual overstory trees that hadsurvived the 30-cm (12-inch) diameter limit cuttingin 1915, and the second-growth seedlings, saplings,and poles that seeded in after the cut and grewuntil 1937. On average, the stands were about40 percent stocked by then (Reynolds 1969). Thediameter distribution of the pine component in theCEF Good and Poor Forties in 1937 showed thereverse J-shaped curve typical of uneven-agedstructure (fig. 9.7). This description of selectivecutting and its effects on stand conditions atCEF was typical of that in the region; the standsin the Farm Forestry Forties and Hope FarmWoodland demonstrations had a similar historyand initial condition. Because the stands in thesedemonstrations were relatively understockedwhen the selection method was initially appliedto them, their rapid recovery to fully stockedconditions under the selection method shows thatuneven-aged silviculture is a powerful tool forbringing understocked or cutover standsto full stocking within a short time (Baker andBishop 1986; Farrar and others 1984, 1989).

Additional research illustrates not only thespeed of the recovery, but also the degree ofunderstocking from which recovery can occur.Baker and Shelton (1998a, 1998c) reportedthat stands with 20- to 30-percent stockingcould develop acceptable stocking and basalarea within 15 years, provided that competingvegetation is controlled with herbicide application.These threshold levels are lower than previouslythought, and lower than threshold levels in thelong-term demonstrations.

This suggests a strategy for implementinguneven-aged silviculture in southern pines across aforested ownership in the public or private sector.If the ownership supports both fully stocked even-aged stands and stands that for one reason oranother are understocked, the best approachwould be to convert the understocked standsrather than the fully stocked even-aged stands.Figure 9.7—Diameter distributions of the Good Forty and the

Poor Forty on the Crossett Experimental Forest in the first 35years of the demonstration—(A) Good Forty in 1937, 1951,and 1971; (B) Poor Forty in 1937, 1951, and 1971.

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RegenerationThe importance of regeneration in these

demonstrations is poorly documented for tworeasons. First, there is no record of regenerationdevelopment in the 20- to 40-year period betweenthe initial high-grading and demonstrationestablishment. Second, because regenerationwas so abundant, the scientists who establishedthe demonstrations paid little attention to it.

Reynolds (1959, 1969) reported that pineregeneration was established as a result ofremoval of poorer hardwoods of large and mediumsize, continuing fire protection, and control ofsmall hardwood stems. He also noted that pineseedlings, saplings, and poles typically are foundin small openings and often directly under high-crowned larger stems. This is apparent in thediameter distributions of the Good and PoorForties during the first 20 years of management(fig. 9.7). The continued ingrowth into the 10-cm(4-inch) class during this period resulted fromrecruitment of saplings from the smallerdiameter classes.

Thus obtaining regeneration and promotingits development through the seedling and saplingclasses are critical for successful uneven-agedmanagement (Shelton and Cain 2000). The initialcohort of reproduction should be established orreleased at the first cutting-cycle harvest in orderto meet two goals: (1) the need for reproductioncutting to result in regeneration, and (2) theneed to establish three or more distinct age classesin the uneven-aged stand (Helms 1998). If theestablishment of the initial regeneration cohortis delayed, the conversion period will becorrespondingly lengthened.

Residual Basal AreaIn southern pines, regeneration establishment

and development are strongly related to the basalarea of the merchantable component of the stand.Data from the CEF and elsewhere suggest thatuneven-aged stands can be managed successfullywithin a range of residual basal area from 10 to17 m2/ha (45 to 75 square feet per acre) (Bakerand others 1996; Farrar 1996; Farrar and others1984, 1989). At residual basal area levels < 10 m2/ha (45 square feet per acre), the overstory isunderstocked and growth will not be optimal(although such stands can be rehabilitated tooptimal production easily, as discussed earlier).At residual basal areas > 17 m2/ha (75 squarefeet per acre) at the end of the cutting cycle,regeneration development is adversely affected.

The residual basal area target immediatelyafter harvest must be established in conjunctionwith the expected length of the cutting cycle,the expected growth of the residual stand, andthe upper basal area limit for the species. Forexample, basal area growth of uneven-agedloblolly-shortleaf pine stands at CEF is 0.5 to 0.7m2/ha (2 to 3 square feet per acre) annually. If a 5-year cutting cycle is planned, the target residualbasal area immediately after the cutting cycleharvest must, therefore, be 14 to 15 m2/ha (60 to65 square feet per acre), so that stand basal areadoes not exceed 17 m2/ha (75 square feet per acre)at the end of the cutting cycle. Longer cuttingcycles require lower residual basal area levels.

Thus managing for the proper residual basalarea is an important element of uneven-agedsilviculture. This is one reason why structuralregulation using the basal area, maximumdiameter, and q-ratio or the BDq method (Bakerand others 1996, Farrar 1996, Marquis 1978)has become popular. The CEF experience andother work suggest that BDq is more than analphabetical ranking; this order reflects thepriority for implementation (Baker and others1996, Farrar 1996). The importance ofmaintenance of stand structure is based onobtaining the appropriate basal area; retaininga specified maximum diameter class or a givenq is much less important (Guldin and Baker 1998).

Developmental DynamicsBy definition, uneven-aged stands have

three or more distinct regeneration cohorts;so, if one begins with an even-aged stand or anunderstocked stand, conversion to an uneven-agedstructure is a long-term proposition. A minimumof two cutting-cycle harvests will be needed torecruit two additional cohorts of regeneration,and a third cutting-cycle harvest will be neededto avoid suppressing this new regeneration,especially with shade-intolerant southern pines.For the 5- to 7-year cutting cycles used for loblolly-shortleaf pine stands at CEF and elsewhere,it will be 20 to 30 years before even-aged orunderstocked stands are minimally reconfiguredto uneven-aged structure. For species such asshortleaf pine in the Interior Highlands, where7- to 10-year cutting cycles are common, theconversion period will be 30 to 40 years. Theseestimates are confirmed in data from the CEFGood and Poor Forties, where the time fromhigh-grading harvests in 1915 to initialdevelopment of full stocking was 36 years.

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Marking RulesWhen conducting a cutting-cycle harvest in an

uneven-aged southern pine stand, the guidancegiven to field crews can be summarized by a simplerule: cut the worst trees and leave the best (Bakerand others 1996; Farrar 1996; Farrar and others1984, 1989; Guldin 1996; Reynolds 1959, 1969).When stands have developed an uneven-agedstructure through time, tree size generallybecomes correlated with age across the diameterdistribution (Baker and others 1996). Marking apercentage of the poorest trees in each diameterclass improves the average tree quality withineach class, and over time only the best trees ofhighest quality attain the largest size. As a result,one attribute of the selection method is thatover time, it produces large sawtimber that hashigh quality.

In stands being converted from even-agedto uneven-aged structure, size is not correlatedwith age, because the smaller trees may be of thesame age as the larger trees. This means that mosttrees in the left-hand tail of a normal bell-shapeddiameter distribution may in fact be the worsttrees in the stand. Strict adherence to the rule ofcutting the worst and leaving the best may resultin an effect similar to thinning from below, wheremost of the smaller trees are removed. This ispreferable to retaining poorer trees in smallersize classes at the expense of better trees in largerclasses simply to achieve a target structure. Ifthe best trees are being retained below themaximum diameter and are retained in a mannerthat allows development of subordinate stemsand newly established regeneration cohorts, aperfectly balanced stand structure is immaterial.

Marking crews need guidance in judgingwhether an intermediate tree in the pulpwoodsize class can respond to release if it is allowedto remain in the stand. Reynolds (1959) notedthat loblolly pine in the west gulf region couldrespond to release, even at advanced age. Bakerand Shelton (1998b) observed that if a loblolly pinehad a 20-percent live crown ratio and good apicaldominance, it should satisfactorily respond torelease, even if it developed in the lower crownclasses of fully stocked, uneven-aged stands for upto 40 years; anecdotal evidence for longleaf pine issimilar. Different standards would probably applyfor other southern pine species and for trees fromlower crown classes in even-aged stands.

To a certain extent, the group selectionapproach to management of uneven-agedstands violates the rule of cutting the worst

trees and leaving the best. Group selectionusually prescribes cutting of all trees, best andworst, if they are within the group. The degreeof conflict depends on how the groups are located.If groups are identified independently of densityor stocking, for example, by systematicallyinstalling groups of similar size and shapeaccording to a predetermined pattern, theopportunity to cut the worst and leave the bestis seriously compromised. Conversely, if groupsare established in understocked portions of thestand, without regard for size, shape, or patternof group opening, the number of best trees thatmust be cut will be reduced. Group selectionwith reserves (Helms 1998) is probably the best,though least often prescribed, method to minimizeconflicts with the “cut the worst and leave thebest” axiom, provided that reserved trees withinthe group are the best trees and do not adverselyaffect regeneration establishment or development.

OTHER ELEMENTS

Additional silvicultural considerations areimportant in the management of naturallyregenerated stands by even-aged or uneven-

aged methods.

Seedbed preparation is critical. Southernpine seeds germinate best on exposed mineralsoil. In southern pine types that produce prolificseed crops, such as the loblolly-shortleaf pinetype in the west gulf region, the scarificationassociated with logging provides enough exposureof mineral soil to promote establishment ofregeneration. For other species, such as longleafpine, supplemental mineral soil scarification isoften recommended. Prescribed burning canalso be used to prepare seedbeds.

The relative competitive abilities of pinesand hardwoods after a harvest dictate thatforesters must pay attention to relative growthrates and intervene if necessary. After a seedcut or cutting-cycle harvest, the intent is to allowpine seed to germinate on exposed mineral soil,become established, and be free to develop.However, hardwoods cut during harvest orsubsequent site preparation will sprout andquickly outgrow seed-origin pines. Similarly,under certain circumstances grasses and otherherbaceous plants may become sufficiently denseto impede pine seedling development, and controlof grasses may also be necessary. Therefore sitepreparation or release treatments are often anintegral part of effective silvicultural prescriptionsfor natural regeneration.

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For example, competing hardwoods, as wellas nonnatives such as privet (Ligustrum vulgareL.) and honeysuckle (Lonicera japonica Thunb.),commonly inhibit the development of pineregeneration (Shelton and Cain 2000). Giventhe slow rates of height growth of pine seedlingsand the competition provided by hardwood sproutsand invasive nonnative plant species, herbicidesare critically important in managing stands ofnaturally regenerated pines, and may be moreimportant to the establishment and developmentof naturally regenerated pine seedlings thanto the survival and development of planted pineseedlings. The use of herbicides has in factbeen an element of every successful long-termdemonstration of uneven-aged silviculture insouthern pines, including the successful practicalexperience of which the author is aware. Periodiccontrol of hardwoods by applying herbicides atroughly 10-year intervals was an element ofuneven-aged silvicultural prescriptions at CEF(Baker 1986). Farrar and others (1984) noted thatdeficits in the smaller diameter classes in uneven-aged stands were due in part to the failure ofrecruitment from regeneration to pulpwood-sizeclasses, which was attributable to hardwoodcompetition and the presence of privet. Farrarand others (1989) reported that control ofhardwoods by cutting, girdling, or herbicidetreatments occurred in the past on the uneven-aged Mississippi State Farm Forestry Forties, andwas recommended in the future for all hardwoodstems > 1.0 cm (0.4 inch) in diameter. Prescribedfire and herbicides were used in much the sameway in stands regenerated using the shelterwoodmethod on the Escambia Experimental Forest(Croker and Boyer 1975). Their use has beenrecommended in industrial seed tree silviculturalguidelines for south Arkansas and north Louisiana(see footnote 2 and Zeide and Sharer 2000).Prescribed fire, which does not kill largerhardwoods, probably cannot completely eliminatethe need for herbicides in naturally regeneratedstands, especially in uneven-aged stands.

Finally control of regeneration density isfundamental to the successful application ofnatural regeneration in managed stands.Regeneration development in loblolly pine isimproved by early precommercial thinnings tocontrol stem density (Cain 1995). Neverthelessregeneration density will always be less uniformlydistributed in naturally regenerated stands than insuccessfully established planted stands. Industryforesters in the west gulf region observed a long-term average rate of understocking of 7 percent of

the stand area in managing naturally regeneratedstands (see footnote 2). Invariably, one of thechallenges in managing naturally regeneratedstands is the likelihood of damage to regenerationwhen conducting removal cuts or subsequentcutting-cycle harvests. In situations whereregeneration is far in excess of desired density,such logging-related precommercial thinningmay actually be desirable. However, the situationis more critical when regeneration density ismarginal prior to the removal cut or to subsequentcutting-cycle harvests. Careful supervision oflogging operations is needed in such situations.

SUMMARY

Successful use of natural regeneration inmanaging southern pines depends on anumber of factors. The establishment and

development of pine regeneration is critical.Prescriptions must leave a sufficient numberof seed trees to adequately regenerate the siteduring an average or better seed year. Sitesmust be properly prepared to be receptive to pineseed, and timing of harvests and site preparationmust optimize the establishment and developmentof regeneration.

In even-aged stands, late-rotation thinningsor preparatory cutting is recommended to expandcrowns of future seed trees and to promotecone production. The seed cut must create anappropriate balance of residual trees and seedproduction capacity per tree to ensure adequateseed fall, and site preparation must be timedto that seed crop. In uneven-aged stands, thefirst cutting-cycle harvest must be heavy enoughnot only to create conditions suitable for theestablishment of regeneration, but also to preventsuppression of regeneration before the secondcutting-cycle harvest occurs. Subsequent cutting-cycle harvests must continue this developmentalpattern. Regardless of system, herbicides willalmost certainly be needed to control competingvegetation and enable young pine cohorts todevelop successfully.

Experience and research suggests that allfour major southern pines can be managed usingone or more of the even-aged or uneven-agedreproduction cutting methods that rely on naturalregeneration. Certainly some forest types, such asthe mixed loblolly-shortleaf pine type in the westgulf region, are amenable to any of the even-agedand uneven-aged prescriptions, whereas in otherforest types, such as longleaf pine, the range ofavailable options is perhaps narrower and requires

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greater care in application. Each of the systemsmust be implemented in a manner that takesinto account the silvical characteristics of thespecies in question. Choosing which method touse in a particular forest type depends on properapplication of available research and experiencewith the desired species in specific situations.Overall, these methods present feasible andeconomically viable alternatives to clearcuttingand planting for public land managers, forestindustry foresters, and NIPF landownersin the South.

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