DOUGLAS-FIRFORESTSManaging for Timber andMature-Forest Habitat

Reprinced fran Journal of Forestry volume 91, no. 12, published by the Society of AmericanForesters, 5400 Grosvenor Lane, Bethesda, ND 20814-2198. Not for further reproduction.

PEER,.EVIEWED

By William C. McComb,Thomas A. Spies, andWilliam H. Emmingham

illions of acres once domi-nated by mature and old-growth forests in westernOregon and Washingtonhave been clearcut and arenow dominated by youngplantations. The point instand development atwhich plantations mightmeet the needs of wildlifespecies associated withmature forests is un-

known. Yet with rotations decreasing to40 years in places and harvestable treesize declining (Sessions 1990), someplantations may not provide, prior toharvest, the structural and compositionalfeatures used by some mature-forest spe-cies. For example, designated conserva-tion areas (DCAs) for northern spottedowls contain many acres of young plan-tations that may not provide suitablenesting or foraging habitat for 80 yearsor more (Thomas et al. 1990, US De-partment of the Interior 1992). Pressuresto remove timber on remaining landsmay be high in order to reduce the eco-nomic impact of spotted owl protection(Greber et al. 1990).

Alternative silvicultural systemsshould be tested to determine if timberextraction can be accomplished whilemeeting habitat needs of wildlife speciesassociated with mature forests. This arti-cle describes a conceptual basis for silvi-cultural systems that integrates mature-forest wildlife habitat and timber objec-tives in managed Douglas-fir (Pseudo-tsuga menziesii) forests of western Ore-gon and Washington. Specifically, it de-scribes the structural and compositionalfeatures of stands associated with abun-dance of mature-forest wildlife; the in-fluence of natural disturbances and past

management practices; how silviculturemay be used to more closely imitate thefrequencies, sizes, shapes, intensities, andpatterns of natural disturbances in theseforests; and how silvicultural systemsthat provide these features can be devel-oped and tested.

Historical PerspectiveMost Pacific Northwest forest manag-

ers have regenerated stands by clearcut-ting during the past 50 years, although aform of selection cutting was tried earlier(Isaac 1956). In the 1930s, diameter-limit cutting (which removed about 35%of the volume in old-growth stands) pro-duced mixed results in western Oregonand Washington Douglas-fir forests(Isaac 1956). Some stands sustained highdamage to residual stems, especially tothin-barked species, and some had highlevels of windfall after harvest (Munger1950). Several stands exhibited decreasedor stable growth rates following cutting(Munger 1950). For a number of reasons,including the failure of diameter-limitcutting to meet timber objectives and therisks of inadequate natural regeneration(Cleary et al. 1978), clearcutting andplanting with Douglas-fir became the pri-mary method of stand regeneration bythe early 1940s.

Following passage of the NationalForest Management Act of 1976 and pur-suant regulations, land managers on na-tional forests faced a new set of manage-ment objectives, including maintenanceof biological diversity. Special treatments(such as retention of 1-2 trees or snagsper acre) were designed to mitigate theloss of mature forest habitat (Neitro et al.1985). In the more recent new forestrypractices (Franklin 1989) trees, snags,and logs are retained during harvest with

Reprinted from the Journal of Forestry, Vol. 91, No. 12, December 1993. December 1993 31

the intent of carrying these featuresthrough the next rotation. This and otheralternatives to traditional plantationmanagement need to be evaluated as tohow effectively they will provide habitatfor mature-forest wildlife.

Mature-Forest Habitat CharacteristicsSpecies associated with mature stands

seem to be associated with certain abioticfeatures—soils, topography, elevation—and biotic structures—large trees of sev-eral species; multilayered canopies; largesnags and logs; and deep forest floor litter(Ruggiero et al. 1991). Although manyspecies use these structures (Brown1985), the abundance of some species hasbeen found to be associated with them(Ruggiero et al. 1991), implying ecologi-cal dependency. No studies seem to haveestablished cause and effect relationships;until these relationships can be quantifiedthrough experimentation, an objective ofa stand-level silvicultural system shouldbe to produce habitat structures associ-ated with the abundance of vertebratesand a complementary, integrated designover the landscape.

Large trees. Douglas-fir larger than 40inches dbh are associated with the pres-ence of nesting marbled murrelets (Singeret al. 1991) and northern spotted owls(Forsman et al. 1984). Spotted owls usu-ally nest in broken-topped snags and treeslarger than 30 inches dbh (Carey 1985),although they can use platforms insmaller trees, especially in mixed-coniferforests. Large trees add to the verticalstructure within a stand, and bird diver-sity is associated with vertical complexityin other forest types (MacArthur andMacArthur 1961). Douglas-firs largerthan 40 inches dbh are more abundantin old-growth (more than 200 years,

=7.7/acre) and mature (80-195 years,=1.0/acre) stands than in naturally re-

generated young (40-79 years, =0.2/acre) stands (Spies and Franklin 1991).Many old-growth Douglas-fir stands inthe Coast Range and Cascades of Ore-gon and Washington exhibit an inverse-Jdiameter distribution (US Departmentof the Interior 1992). This size-class dis-tribution also contributes to the verticaldistribution of foliage layers. Large treescan add large surfaces of deeply fissuredor scaly bark that are used by bark-forag-ing birds (Peterson et al. 1989) and cansupport epiphytes eaten by northern fly-ing squirrels (Maser et al. 1981).

Oregon white oaks (Quercus garry-anna) and bigleaf maples (Ater macro-phyllum) larger than 20 inches dbh pro-duce more natural cavities and large deadlimbs (elevated snags) than conifers(Gumtow-Farrior 1991). Pacific ma-drone (Arbutus menziesii) also is cavity-prone (Raphael 1987). Hardwoods andshrubs provide forage, fruits, and foliarinsects that are food resources for manyvertebrates (Martin et al. 1951).

Large dead wood. About 100 species ofvertebrates use snags and 150 use logs(Brown 1985), though use varies by sizeand decay class. Snags larger than 20inches dbh are more abundant in old-growth (R = 4.9/acre) than in mature(R =2.5/acre) or young (R =2.3/acre) un-managed stands (Spies and Franklin1991). Although cavity-nesting birds usesnags (Neitro et al. 1985, Nelson 1989,Marcot 1991), there is little quantitativeinformation for other species, especiallylog-users. High proportions of cloudedsalamanders and Oregon slender sala-manders were captured in or under barkon logs in Oregon forests (Bury and Corn1988). The abundance of marsh shrewscorrelated positively with log densities inOregon (Corn et al. 1988). Old-growthDouglas-fir forests typically have morethan 13.8 tons/acre of dead and downlogs (Franklin and Spies 1991).

Deep litter. Forest floor and below-ground conditions probably influencehabitat quality for ground-foraging andburrowing species. Some terrestrial mam-mals and amphibians are primarily activebelow-ground during the summer. For in-stance, roughskin newts use logs and bur-row systems of voles and shrews as sum-mer daytime refugia. Other species usethe burrow systems of mountain beaver(Aplodontia rufa) and pocket gophers(Thomomys spp.) (Maser et al. 1981), an-imals that also kill some conifer regenera-tion and may maintain small semiperma-nent openings in otherwise homogeneousstands. Litter depth was positively associ-ated with the number of marsh shrews(Corn et al. 1988). The litter layer isdeeper in old-growth =21 mm) than inmature (ic =14 mm) or young =15 mm)stands (Spies and Franklin 1991).

Species-Habitat Matrix ApproachBecause each species has its own habi-

tat requirements and hence responds dif-ferently to various silvicultural practices,managers need tools to predict these re-

sponses. In developing silvicultural sys-tems for mature-forest species, an idealfirst step is to determine the sizes andnumbers per unit area of.habitat struc-tures needed to support self-sustainingpopulations of each species and then sumthe structures over the species in the com-munity—such as Neitro et al. (1985) didfor cavity-nesters. Information on animalhabitat associations may guide silvicul-tural prescriptions for some species thatuse mature and old-growth Douglas-firforests of western Oregon and Washing-ton for at least part of their life cycle(Brown 1985, Ru 14:iero et al. 1991). Un-fortunately, quantitative relationships arelacking for many species. For instance,snags are used by bats and logs by shrew-moles, tailed frogs, and clouded sala-manders; but data are insufficient to pre-dict the needed snag and log density tosupport sustainable populations (Brown1985). Information is unavailable to sethabitat goals for species associated withforest floor litter and burrows.

An alternative is to provide habitat forindicator species and assume that meet-ing the needs of one or several species ina guild (a group of species that share sim-ilar resources) will meet the needs of allothers in a guild. But Mannan et al.(1984) suggested that this may not be avalid assumption. Until data are availableon optimal habitats for each species, newsilvicultural approaches—based on natu-ral disturbances, large conifers and hard-woods, dead wood, and litter—should bedeveloped and tested. Incorporating keyhabitat features into silvicultural pre-scriptions can test hypotheses regardingthe relationships between abundance ofthese features and abundance of the spe-cies they are predicted to support.

Natural Disturbance inDouglas-Fir Forests

Disturbances occur over a range ofspatial scales, from coarse (thousands ofacres) to fine (less than 1 tree height inwidth). Coarse- and fine-scale distur-bances have affected the establishment,development, and at times destruction ofunmanaged Douglas-fir forests. Datafrom stands sampled during the Old-Growth Habitat Relationships Program(Ruggiero et al. 1991) illustrate how dis-turbances influence the presence andabundance of habitat features (table 1)."Patch" describes a homogeneous unit ofvegetation that is different from the ma-

32 Journal of Forestry

Table 1. Comparison of natural disturbances and three silviculturel systems that consider both timber removaland mature-forest wildlife in Douglas-fir forests.

Disturbance characteristicNatural disturbances

Managed standCoarse Fine

Coarse Fine Single-story Few-storied Many-storied

Generalized sizePatchl (acres)Stand2 (acres)

Stand-scale intensityResidual live treesResidual dead woodRange of tree coverthroughout cycle (%)

Frequency rate (% of standdisturbed/year)

Return frequency todisturbed portions

Harvest entries/100 yrs

>10>10

Low-moderateModerate-low

10-95

0.5-1.0

100-500+

<0.5 >10 >10>10 >10 >10

High Low ModerateHigh Low Moderate

70-90 10-95 25-95

0.1-0.8 1.3 0.4/1.53

100-500+ 754 75/14031-2 1-2

0.5-2>10

HighModerate-high

50-90

0.5-1.0

100-2004-10

1 Area disturbed.2The area that includes the patch.

30veistory/understory.4Some residuals may be left to develop a sparse emergent layer.

trix in which it occurs. Patches may occurat many scales: a canopy gap is a patchwithin a stand, and a stand is a patchwithin a landscape.

Coarse-scale disturbances. Except incoastal forests, fire was the most frequentand widespread coarse disturbance atscales up to 250,000 acres. The fire re-gime of the western Douglas-fir region iscomplex and includes varying frequen-cies, intensities, sizes, and patterns. Re-turn frequencies for stand-replacementfires range from about 450 years atMount Rainier National Park (Hem-strom and Franklin 1982) to 200 years inthe central Oregon Cascades (Morrisonand Swanson 1990). Smaller ground firesreturn more frequently—every'years (Stewart 1986, Morrison and Swan-son 1990).

The first diagram in figure IA showsthe diameter distribution of a naturalone-story, 100-year-old stand in thesouthern Oregon Cascades. A severe fireprobably killed most trees in the previousstand, initiated establishment of Dou-glas-fir and western hemlock seedlings,and caused the hardwoods to sprout.This stand will probably develop old-growth structure at 150-250 years in theabsence of management (Spies and Fran-klin 1988). Snags and logs probably in-creased following the fire, and will de-crease until gap disturbances producelarge dead wood late in stand develop-ment (Spies et al. 1988).

Lower-intensity fires usually killedtrees in smaller patches (1-100 acres).For instance, the old-growth, few-storiedstand in the Oregon Coast Range (the

first diagram in figure 1B)probably devel-oped after such a fire, followed by newtree establishment in the burned patches.A stand of various tree sizes and largesnags produced a multilayered canopysooner than in the one-story scenario,perhaps in as little as 80-100 years; in-puts of dead wood were more constant(Spies et al. 1988).

Wind may cause either coarse- or fine-scale disturbances. Areas of high wind,such as the Pacific Coast and the Colum-bia River Gorge, can produce large wind-fall after a small part of a stand is opened.Wind fetch along the windward edge of astand increases as the stand progressivelyblows down (Ruth and Yoder 1953).Elsewhere, wind disturbance usually con-sists of single trees or small patches (lessthan 10 acres) of broken or blown-overtrees. Rarely are all trees blown over, andlarge amounts of dead wood remain(Spies et al. 1988).

Fine-scale disturbances. The diameterdistribution of a natural old-growth,many-storied stand in the southern Or-egon Cascades (fig. 1C) was probablyproduced by fine-scale disturbances suchas suppression mortality, root rots(Phellinus spp.), localized windthrow,and light ground fires. These distur-bances led to the death of individual orsmall groups of trees, producing an in-verse J-shaped distribution typical of anuneven-aged stand.

Gap formation rates are relatively lowin old-growth Douglas-fir stands com-pared to other old-growth forest types(Runkle 1985). Canopy gaps are the sitesof snag and log production and tree re-

generation in mature stands, particularlyfor shade-tolerant species that can be re-leased by gap formation (table 2, Stewart1986, Spies et al. 1990). Mortality ratesfor dominant trees more than 36 yearsold in a 500-year-old Douglas-fir/westernhemlock stand were 0.75%/year, butmortality was balanced by recruitment ofshade-tolerant species (Franklin and De-Bell 1988). Gaps might be slow to fill,however, because more than 70% of old-growth canopy trees die without exposingbare mineral soil (Spies et al. 1990, Fran-klin and DeBell 1988), so existing shade-tolerant shrubs may dominate.

Prior to timber management, the dis-turbances described above shaped thestructure and dynamics of the forests forseveral thousand years. The disturbancesimposed by timber management deviatefrom natural disturbances to varying de-grees (fig. 2), and these deviations mightinfluence habitat quality for mature-for-est wildlife. Estimating characteristics ofnatural disturbances can facilitate predic-tion of the development of stands thatcontain specific habitat structures.

Ecological Importanceof Disturbance

Size and shape. The abundance ofsome animal species is associated withpatch size (Rosenberg and Raphael1986). An organism may be displaced bydisturbances larger than its home range(the area over which it secures resources),but it might not be displaced if the distur-bance scale is sufficiently small relative tothe home range. Similarly, mature-forestspecies may be more tolerant of frequent

December 1993 33

160I reestacre=i 11

120"

0 4 8 12 16 20 24 28 32 36 40 44+

160

35

30 REMNANT TREE CONTRIBUTION

25

20 --■ OVERSTOM115

10

UNDERSTORil

0 10 20 30 40 50

REMNANTS

Basal area=242 sq. ft./acidVolume=49 MBF/ac.

DgEgilL00 4 8 12 16 20 24 28 32 36 40 44+

1201-

80

40'

Trees/acre=41 0Basal area=290 sq. ft./ac.

A50

Trees/acre=10840 - Basal area=280 sq. ft./ac.

30 r:::

ir!:::

r20

10

: ; : : : „ff, 2,•-• -- - - - - - —0 4 8 12 16 20 24 28 32 36 40 44+

50

40

30

20

10

ir

I

1 A

Trees/acre=281Basal area=134 sq. ft./ac.Volume=29 MBF/ac.

r

zu..:0 4 8 12 16 20 24 28 32 36 40 44+

30

25

20

15

10

5

-

70-YEAR-OLD TREES

♦ TOLERANT REGENERATIQN

0 10 20 30 40 50

185•YEAR-0LD REMNANTS

70-YEAR-OLD TREES

TOLERANT REGENERATION

Figure I. Characteris-tics for time desired fu-ture conditions: (A) aone-story, 100-year-oldDouglas-fir stand withold-growth remnants;(B) a few-storied standwith 2-3 age class de-velopment typical fol-lowing low-intensityfires; and (C) a many-storied stand dominatedby small-size westernhemlock and fir result-ing from canopy-gapdisturbance. The firstrow illustrates the di-ameter distributions fora natural stand. Thelower three rows provideinformation on a man-aged 70-year-old standVertical axis for diame-ter distributions indi-cates trees/acre and hor-izontal axis shows dbbclass in inches. Forfoli-age height profile, verti-cal axis is height inmeters and horizontalaxis shows percent cover.

KEY

111 Douglas-fir

Grand fir

• Hardwoods

C

35

30

25

20

20 30 40 5010

Trees/acre=249Basal area=263 sq. ftdac

4 8 12 16 20 24 28 32 36 40 44+

Trees/acre=156200 Basal area=161 sq. ft./ac

Volume=38 MBF/ac

4 8 12 16 20 24 28 32 36 40 44+

5

disturbances than those that occur oncein many generations. It is likely that spe-cies selecting mature Douglas-fir forestshave persisted in the region by (1) tolerat-ing fine-scale disturbances that lead to en-hanced stand complexity within theirhome ranges (fine-scale creation of snags,logs, or vertical structure); or, followingcoarse-scale disturbances, (2) recoloniz-ing stands of sufficient size that regrowand contain residual trees and deadwood. Recolonization might occur overlong periods of time following large dis-turbances, especially for species with lowdispersal capability such as small mam-mals and amphibians (Harris 1984, p.85). Refugia from coarse-scale distur-bances, such as isolated patches of oldforest, may have allowed some of thesespecies to persist and recolonize followinglarge disturbances such as fire orwindthrow.

The shape of a disturbance can influ-ence the amount of edge and hence themicroclimatic characteristics of the stand(Geiger 1965), so patches with high edge-to-area ratios may influence habitat qual-ity for species sensitive to microclimate(e.g., relative humidity).

Intensiry. Disturbance intensity influ-ences the amount of organic material de-stroyed or redistributed by the distur-bance (table 1). The residual organicmaterial after disturbance can influencethe direction of succession and the rate ofsubsequent development (Harmon et al.1986). The remaining structures mightdirectly or indirectly provide habitat formature-forest species. Disturbances thatcause gaps in mature and old-growth for-ests also produce snags and logs, and sub-sequent vegetative growth enhances thestand's vertical complexity (Hunter 1990,Spies et al. 1990). Lower numbers andlower frequencies of most mature-forestvertebrates were detected in young, struc-turally diverse, unmanaged stands than inolder unmanaged stands (Ruggiero et al.1991). The large trees and dead woodpresent following coarse-scale distur-bances might persist into the closed-can-opy stage and provide the larger.trees andsnags associated with mature-forest verte-brates. The hypothesis is that the absenceof large trees and dead wood in managedstands would further degrade habitatquality for these species.

Frequency. Disturbance frequency willinfluence species composition and theamount of living and dead organic mate-

December 1993 35

Figure 2. Illustrative comparison of the disturbance effects oftraditional silvicultural systems, natural disturbances, andnew silvicultural approaches.

rial on the site over time (Harmon et al.1986, Spies et al. 1988). Frequent coarse-scale disturbances can delay the onset ofmature forest development or preclude it.Infrequent fine-scale disturbances maydelay the development of multilayeredstands, large snags, and large logs (Spies etal. 1990). Frequency can be characterizedin several ways: disturbance rate per unitarea, percent of a stand disturbed annu-ally, or time between disturbances.

Density and pattern. Disturbance den-sity is the percentage of the stand or land-scape occupied by the type of patch cre-ated by specific disturbances. The densityof disturbances influences the abundanceof structural features produced. For agiven gap size, a stand in which 1% of thestand is in canopy gaps less than 30 yearsold probably will have a less well devel-oped vertical foliage structure and fewerlarge pieces of dead wood than one inwhich 15% is in gaps. The disturbancepattern also might influence habitat qual-ity for species sensitive to habitat contigu-ity. Clumped distributions of fine-scaledisturbances may result in a cumulativedecrease in habitat availability.

Stand Objectives forManaged Forests

No one stand management systemwill precisely match the variability inher-ent in natural stands that resulted from avariety of disturbances. But some of thevariation can be incorporated into man-aged landscapes by using a variety of silvi-cultural systems. The choice of systemwill depend on biological, social, and eco-nomic objectives for the stand and the

landscape and will imitate natural distur-bances to varying degrees. Indeed, exist-ing silvicultural systems with timber ob-jectives reflect the evolutionary regenera-tion and growth strategies of the com-mercially important tree species in aregion. Intensive silviculture for timberproduction, as currently practiced, mightleave less dead wood and fewer noncom-mercial plant species than natural distur-bances (Harmon et al. 1986, Halpern1988, Hansen et al. 1991), so it does notimitate natural disturbances for other for-est resources as well as it does for timber.Even timber yields may decline over sev-eral rotations as a result of net losses ofsoil organic matter (Harmon et al. 1986,Keeves 1966).

This article proposes that a series ofstand condition specifications be devel-oped as target objectives for each stand,including diameter distributions for liv-ing and dead wood in naturally-occurringyoung (40-69), mature (70-200), andold-growth (more than 200-year) stands.The selected unmanaged mature and old-growth stands should support self-sus-taining populations of mature-forest ver-

tebrates. The develop-ment, structure, andcomposition of naturalstands can serve as goalsfor stands managed toproduce habitat for ma-ture-forest wildlife andtimber. The silviculturalgoal would be to providemany of the featuresfound in a natural standduring the developmentof its managed counter-part (figs. I, 3).

Of the many possiblesilvicultural approachesto developing suchstands, four are dis-cussed here—single-story, few-storied, many-storied, and mature-for-

est restoration. The first two approachesimitate coarse-scale disturbances; thethird is patterned after fine-scale naturaldisturbances that might be tolerated bysome mature-forest species; and thefourth develops a young plantation into astand with mature-forest structures. Theobjectives for each stand (targets) arebased on data from the Old-GrowthHabitat Relationships Program, modifiedfor local conditions. The hypotheses to

be tested include whether mature-forestwildlife use these stands.

The western Willamette Valley ver-sion of ORGANON (developed fromdata on Oregon State University's [OSU)McDonald Forest) was used to developstand predictions. This model was testedin nearby stands managed under treedensities from 50/acre to 400/acre andages 35-85. ORGANON predicted basalarea, volume, and mortality well in thesestands (pers. commun., D. Hann, Ore-gon State University, Corvallis, 1993).Certain assumptions were made: (1) ex-trapolations of tree growth outside thedata on which ORGANON was based(e.g., tree growth greater than 135 years)would reasonably estimate stand develop-ment; (2) estimates of mortality fromsuppression reasonably reflected snag re-cruitment; (3) the Snag RecruitmentSimulator model (Marcot 1991) wouldprovide a reasonable estimate of snagabundance for dead wood—dependentspecies when the management objectiveis set at 100% of maximum potentialpopulation level for primary cavity-nest-ers (3.7/acre); and (4) no snags were re-tained at initial harvest—that is, all snagsmust be created from green trees or re-cruited through suppression mortality.The latter assumption was a conservativeapproach that meant retaining adequategreen trees for snag replacement to meetcurrent and future dead wood needs, andhence resulted in the greatest impact ontimber volume. The models also includedfour operational assumptions: (1) anynatural advance regeneration that waspresent would be maintained to enhancespecies composition; (2) control of com-peting vegetation might be needed to en-sure regeneration success; (3) retainedgreen trees would be windfirm and havehigh diameter-to-height ratios and deepcrowns to increase postrelease growthrates; and (4) no major blowdown lossoccurred.

The starting points for stand develop-ment predictions were data from a 115-year-old unmanaged stand (site index =121 feet at 50 years for the single-, few-,and many-storied examples) and a 40-year-old plantation (site index = 127 feetfor the mature-forest restoration exam-ple) on the OSU McDonald Forest.Stand exam data from a 20-year-old plan-tation became the basis for regenerationin the single- and few-storied and mature-forest restoration examples, and from nat-

36 Journal of Forestry

effects shortly after natural-disturbance patterns andTable 2. Biological disturbance for two three hypotheticalslivicultural systems that consider both timber removal and mature-forest wildlife habitat

EffectNatural disturbance

Managed standCoarse Fine

Coarse Fine Single-story Few-storied Many-storied

Plant community, stand scaleEarly sera! shrubs andherbs

Shade tolerance of treeregeneration

Wildlife habitat followingdisturbance

Vertical structureEdge effects1Horizontal patchinessForest floor effects

Abundant

Intolerant/tolerant

Low-moderateModerate

Moderate-highLow-moderate

Rare

Tolerant

HighLowHighLow

Abundant

Intolerant

LowHighLow

Moderate

Common-abundant

Intolerant/tolerant

ModerateModerateModerateModerate

Rare

Tolerant/intolerant

HighLowHighHigh

1 Assuming adjacent stands are mature forest

ural regeneration in a partially harvestedstand in the many-storied example. Vol-ume production from single-, few-, andmany-storied stand management throughstand age 70 years (table 3) were com-pared to volume production in the samestand 70 years following clearcutting,planting, and thinning at age 35 and 60;no snags or down logs were created in thelatter stand. Including clearcut harvestand standing volume at age 70, this standproduced 125 mbf/acre.

An adaptation of Morisita's commu-nity similarity index (Brower et al. 1990)allowed comparisons between the diame-ter distribution of target stands and man-aged stands (figs. 1, 3). It was assumedthat diameter distributions would reason-ably represent tree sizes and hence verticalfoliage distribution in the stands. Morisi-ta's index was chosen because it allowscomparison of community structure be-tween two communities with differentdensities of organisms (Brower et al.1990). This index describes the probabil-ity that a woody stem randomly selectedfrom each of two stands would belong tothe same diameter class, relative to theprobability of randomly selecting a pairof woody stems of the same diameterclass from one of the stands. A value of0% meant no similarity between thestands; 100% indicated that the numberof stems in each diameter class was iden-tical for both stands. For instance, naturalmature and old-growth stands were quitesimilar. The average community similar-ity between all possible pairs of six naturalstands (ages 80-300 years) from the OldGrowth Habitat Relationships Program(figs. 1, 3) was 93.2% (SE = 1.42). Aver-age similarity between these naturalstands and the simulated 70-year-old

stand resulting from clearcutting was37% (SE = 4.0). Hence a similaritygreater than 45% (at the 95% confidenceinterval) between managed and targetstands would represent improvementover traditional stand management fortimber production.

Single-Storied ApplicationCoarse-scale disturbances such as

patchy fires and slope failures can resultin a primarily even-aged stand with fewresiduals (fig. 1A). Its managed counter-part (table 2), a single-storied stand, rep-resents a slight but important modifica-tion of current clearcuts, which producerelatively uniform stands for timber pro-duction under an even-aged regenerationsystem. The prescription system can bebased on clearcutting, shelterwood, ordeferred rotation (Smith et al. 1989) butreserve green-tree and snag structuresshould be designated.

In this example, two remnant treeslarger than 30 inches dbh were retainedfor each acre, and six snags larger than 25inches dbh at final harvest. Harvest re-sulted in net production of 71 mbf/acre,with an additional 4 mbf/acre retained assnags, logs, and green trees. The regener-ation (265 trees/acre) was 85% Douglas-fir and 15% grand fir (Abies grandis) andhardwoods. At age 45 years, 30% of the8- to 20-inch trees were thinned (3 mbf/acre of timber, 2 mbf/acre allocated tosnags and logs). Standing volume at age70 was predicted to be 49 mbf/acre for atotal timber volume production of 123mbf/acre. Mean annual increment at age70 was similar to the clearcut stand (table3). Similarity between the managed standand the target stand was 63%, while sim-ilarity between the traditional clearcut at

age 70 and the target stand was 46%.Only thinning methods that assumed

uniform spacing of residual trees wereavailable, but variable density plantingand thinning could economically pro-duce a stand of heterogeneous tree sizeswithin an even-aged stand. Thinning fortimber production usually leaves the re-maining trees uniformly spaced with ade-quate room among crowns for continuedvolume growth. Thinnings that are vari-able in intensity within the stand will al-low rapid growth by some trees and re-duced growth or death (snags) by others.

Harvest disturbances in a single-storysystem are more intense and leave fewerlarge trees, snags, and logs, except whenfires have been frequent or intense. Thissystem represents the low end of within-stand natural variation in patch size, can-opy cover, and large live-tree survival.This hypothetical stand might begin toprovide habitat for most species typical ofmature forest after about 70 years.

Few-Storied ApplicationStands with two or three canopy layers

can be created either by regenerating twoor three age classes (Long and Roberts1992), or by regenerating a single ageclass composed of two or three specieswith different growth rates and potentialsizes. The first approach (shelterwoodwith reserves) would apply where existingold stands are being cut and wherewindthrow is not likely. The second ap-proach (mixed-species clearcut) could beapplied in existing young plantations orwhere windthrow and root-rot potentialis high.

Few-storied stands do not fit into tra-ditional concepts of either even-agedstands or uneven-aged stands—Smith

December 1993 37

(1989, p. 17) described these stands as in-termediate. Traditional approaches tocreating balanced uneven-aged standswith more than three age-classes and can-opy layers have used selection regenera-tion methods, in which individual orsmall groups of trees are cut in a mosaicpattern. Such cutting partially imitatesgap disturbances from windfall and smallpatches of insect and disease mortality. Inthe Douglas-fir region, however, groundfires, wind, and other low-intensity,coarse-scale disturbances have createduneven-aged old-growth stands of Dou-glas-fir and western hemlock (fig. IB).Many old-growth stands contain morethan one size class of Douglas-fir withseveral size classes of western hemlock.The diameter distribution in the first di-agram in figure IB probably developedfollowing wind-throw or moderately se-vere wildfires that killed 10%-75% of the

canopy Douglas-firs and western hem-locks (Morrison and Swanson 1990).Relatively even-aged clumps of Douglas-fir or western hemlock became estab-lished beneath the scattered or clumpyoverstory of the canopy survivors.

A regeneration system that partiallyimitates this type of stand would have el-ements of both even-aged and uneven-aged management. Like even-aged sys-tems, disturbance and establishmentwould occur relatively infrequently. Likeuneven-aged systems, more than two ageclasses would be present in the stand.This example retained six trees largerthan 30 inches dbh/acre and created foursnags more than 24 inches dbh/acre atharvest (70 mbf/acre removed as timber,with 5 mbf/acre retained to create snagsand logs). Regeneration (265 trees/acre)was 85% Douglas-fir and 15% grand firand hardwoods. Following creation of 3

snags/acre at age 35 years (2 mbf/acre),regeneration was thinned at age 45 yearsto 50 trees/acre (producing 12 mbf/acre)and underplanted with 265 trees/acre(23% Douglas-fir, 77% grand fir). Oneadditional snag/acre was created from the55-year-old trees, and stocking of regen-eration reduced by 70% at age 70. Thepredicted standing volume 70 years afterinitial harvest was 30 mbf/acre, resultingin a predicted net timber volume produc-tion of 112 mbf/acre, plus 8 mbf/acre al-located to trees, snags, and logs (table 3).The mean annual increment for the few-storied stand at age 70 was 15% less thanfor a traditional clearcut. Birch andJohnson (1992) predicted a reduction of15% volume production over 60 yearsusing a similar approach, but they did notconsider retained green trees as potentialvolume for harvest in the future. Pre-dicted similarity between the target standand the managed few-storied stand at age70 was 90%. Similarity between the tar-get stand and a 70-year-old clearcut was27%. This is similar to the approach be-ing taken in some new forestry units(Franklin 1989), except that trees to beretained for specific purposes should bemarked prior to harvest by biologists andsilviculturists, and approved by loggers(to ensure logger safety).

Mortality in the 185-year-old trees(larger than 40 inches dbh) was predictedto be less than 1/acre over 70 years usingORGANON. This mortality would notbe salvaged, resulting in large snags orlogs. Although the model projected standgrowth for only 70 years, about three orfour 70-year-old trees/acre, in addition tothe 185-year-old trees, could be left if thestand was harvested at age 70. The pro-cess of maintaining a 70-year rotation fortimber production in conjunction with anatural rotation of larger trees could pro-vide a long-term multilayered stand sim-ilar to a stand that developed followingnatural disturbance (fig. IB).

Creating a stand of trees with variedgrowth rates might be most applicablewhere windthrow is a concern or wheremanagement is focused on young, uni-form plantations. New stands could beestablished in plantations (similar to sin-gle-story systems) and a mix of slow- andfast-growing species (e.g., Douglas-fir,red alder [Alnus rubraJ, black cottonwood[Populus trichocarpal, and western redce-dar [Thuja plicataJ) planted to produce astand with more than two canopy layers.

Table 3. Predicted growth and harvest from three 115-year-old standsand a 40-year-old stand, McDonald Forest, Benton County, Oregon.

Mean

annual Standing TimberStand

Age increment volume harvest Retention

yrs mbffac/yr mbf/ac Clearcut 115 0.65 75 75 0

35 0.40 6 8 0

45 0.47 13 0 0

55 0.58 24 0 0

70 0.71 35 42 0Total 125 0

Single-story 115 0.65 75 71 4

35 0.47 16 0 0

45 0.60 22 3 2

55 0.67 32 0 0

70 0.77 49 49 0Total 123 6

Few-storied 115 0.65 75 70 5

35 0.49 17 0 2

45 0.60 15 12 0

55 0.60 21 0 1

70 0.60 30 30 0Total 112 8

Many-storied 115 0.65 75 57 18

25 1.20 24 4 2

35 0.97 28 0 0

45 0.87 33 0 0

50 0.82 28 5 2

55 0.78 30 0 0

70 0.73 38 38 0Total 104 22-

Plantation 40 0.50 19 12 2

45 0.49 7 0 1

55 0.51 13 0 0

70 0.66 29 0 2

90 0.78 56 13 0

110 0.85 66 0 2

115 0.85 71 71 0Total 96 7

38 Journal of Forestry

Table 4. Management activities to provide habitat for mature forest wildlife.Habitat characteristic desired Single-story stand Few-storied stand Many-storied standLarge tree size Extend rotation; thin; fertilize Extend rotation; thin; fertilize Large target tree size; low alSnags and logs Reserve at harvest; control Reserve at harvest; control stand Reserve at each cutting cycle

stand density, kill trees density; kill treesVertical complexity Thin; plant mixed species; fer- Thin; plant mixed species Control density and species

tilize when thinningHorizontal patchiness Nonuniform planting; thin Nonuniform planting; thin Nonuniform thinningEdge effects Retain green trees, stand size, Retain green trees, stand size, and Scatter gaps, small gap size

and shape; schedule harvest shape; schedule harvestForest floor Harvest with cable yard or heli- Harvest with cable yard or helicop- Designate skid trails

copter; low intensity site prepa- ter; low intensity site preparationration

Human disturbance Gate roads; infrequent entry Gate roads; infrequent entry Gate roads and skid trails/ 0-factor is a number multiplied by the number of trees/acre in one diameter class to estimate the appropriate number of tree/acre in the next smallest clams:i-lea. class and produce an inverse J-shaped curve. A low 0-factor would have fewer smaller trees and more large ones than a high (;) given the same target treesize. Target tree size is the maximum dbh tree grown for timber production.

Existing young, even-aged plantationscould be accelerated toward a multisto-ried condition through precommercialthinning of variable intensity to releasesome trees. Shade-tolerant species (grandfir, western redcedar, western hemlock)could be underplanted to provide addi-tional layers as the stand develops, butthinning both layers may be necessary tomaintain growth in this lower layer (pers.commun., D. Marshall, Oregon StateUniversity, Corvallis, 1992). Thesestands could then be managed as few-sto-ried stands.

Few-storied stands produce greatervariability in vertical structure and treediameter classes than single-story stands.Both types of stands may be smaller insize and more frequently disturbed thansome natural stands that developed fromcoarse-scale disturbances (table I). Cav-ity-nesters typically found in mature for-ests might use these stands within 50years as the crowns close, especially wherelarge trees are close to snags.

Many-Storied ApplicationGroup and single-tree selection sys-

tems designed to produce large tree diam-eters could partially imitate structuresproduced following natural disturbancessuch as individual tree death or gap for-mation. The stands would provide someof the characteristics typical of old-growth stands—large trees, snags, andlogs; many-aged; and many sized (Spiesand Franklin 1988)—but should not beconsidered a replacement for old-growth(Hunter 1989). Lower structural com-plexity and stocking levels are typical fol-lowing cutting in selection systems fortimber because growth is concentrated oncommercial tree species and mortality is

reduced through density management.Producing many-storied stands suitablefor mature-forest wildlife may be possibleon sites where advanced harvesting tech-niques, such as designated skid trails orhelicopter logging, are feasible. Kellogg etal. (1991) found that harvesting a 115-year-old stand using group selection cost5% more than clearcutting with ground-skidding systems and up to 35% morethan clearcutting with cable systems.Modified selection systems should be re-evaluated in light of advances in harvest-ing technology and increasing knowledgeof the ecological importance of fine-scaledisturbances to stand dynamics in Dou-glas-fir/western hemlock forests.

In this example (fig. 1 C), the develop-ment of the 115-year-old stand from Mc-Donald Forest was projected for 70 yearsbased on a 25-year cutting cycle. A com-plete skid trail system could be developedfor the stand prior to the first entry thatwould limit ground impact to less than10% of the stand (Kello K et al. 1991).Volume removal from the first entry waspredicted to be 57 mbf/acre with 3 mbf/acre allocated to snag creation and 15mbf/acre retained as growing stock. Re-generation was 120 trees/acre (13% Dou-glas-fir, 87% grand fir), either planted ornatural, following each entry. Previouslyestablished regeneration was precommer-cially thinned to 509/o-60% of full.stock-ing during each entry, with selection forDouglas-fir and against grand fir. Re-placements for snags, logs, and largegreen trees could be recruited during eachcutting cycle (table 4). Predicted volumeremoval 25 years after initial entry wouldbe 4 mbf/acre, plus 2 mbf/acre as snagsand logs; 50 years after initiating manage-ment, 5 mbf/acre would be removed plus

2 mbf/acre for snags and logs. Standingvolume at age 70 was predicted to be 38mbf/acre; mean annual increment 70years after initiating management waspredicted to be comparable to the tradi-tional clearcut (table 3). If grand fir be-gins to dominate the stand, timber valuemay decline significantly. Similarity be-tween the managed many-storied stand atage 70 and the target stand was 70%.Similarity between the target stand and a70-year-old clearcut was 47%.

Although less cost-effective thanclearcutting, this system could result inlarge logs with high biological and eco-nomic value on a sustained basis whileproducing trees up to 44 inches .dbhwithin a multistoried stand. Managedstands would have fewer large trees andlower woody debris levels than typicalold-growth stands. A dominance shift toshade-tolerant species may necessitatestand reestablishment with Douglas-firusing single- or few-storied approaches.Alternatively, cutting gaps larger thanmost natural canopy gaps in combina-tion with thinning to favor Douglas-firmay allow shade-intolerant species topersist. This system would have highwithin-stand variability in tree size andvertical complexity. Compaction alongdesignated skid trails may have adverseeffects on some burrowing species andon long-term site productivity, but care-fully designed harvesting systems impactless than 10% of the stand (Kellogg et al.1991). Disturbance between entriesshould be minimized. This systemmight provide acceptable habitat formature-forest species such as red treevoles, Douglas squirrels, and pileatedwoodpeckers while allowing regular tim-ber removal.

December 1993 39

A

B

Trees/acre = 813

Basal area = 237 sq. ftJac.

0 4 8 12 16 20 24 28 32 36 40 44 44+

300

200

100

0 4 8 12 16 20 24 28 32 36 40 44 44+

Trees/acre = 194

Basal area = 279 sq. ft./ac.

300 Trees/acre = 813Basal area = 237 sq. ftiac.

Volume = 18 MBF/ac.

200

100

0 4 8 12 16 20 24 28 32 36 40 44 44+

80

60

i Trees/acre = 166p ; Basal area = 256 sq. ftiac.

40 F.; Volume = 77 MBF/ac.

20 ....

,;A —,

0 4 8 12 16 20 24 28 32 36 40 44 44+

Figure 3. Diameterdistributions for(A) unmanagedstands at 80 years(top) and 300 years(bottom); and (B)their hypotheticalmanaged counter-parts at 60 years(top) and 120 years(bottom) as pre-dicted by ORGA-NON. Vertical axisindicates treeslacre;horizontal axis isdbh in inches.

KEY

■Douglas-fir

Grand fir

AHardwoods

Plantation RestorationBecause millions of acres of planta-

tions have been created without retentionof large trees, restoration to resemble ma-ture and old-growth stands within someforests should be a high-priority manage-ment goal. In attempting to develop a 40-year-old plantation (319 trees/acre) struc-ture resembling unmanaged young, ma-ture, and old-growth stands, the standwas thinned to 81 trees/acre at age 40, re-moving 12 mbf/acre of timber and allo-cating 2 mbf/acre to snag creation (table3). The stand was planted to 265 trees/acre (28% Douglas-fir, 72% grand fir).

During stand development, snags of asize potentially usable by pileated wood-peckers could be created, so 1 mbf/acrewas allocated at age 45, 2 mbf/acre at age70, and 2 mbf/acre at age 110. Twentyyears after thinning and regeneration,predicted similarity between the planta-tion and an unmanaged, 80-year-oldstand (fig. 3) was 67%. Thinning of thestand at age 90 was simulated by reducingthe density of trees less than 30 inchesdbh by 40% (13 mbf/acre was removed);at this time the predicted similarity be-tween the managed stand and an unman-

aged, mature stand was 91%. At predictedstand development at age 115, predictedsimilarity in diameter distribution be-tween the managed stand and an unman-aged 300-year-old old-growth stand was79%. Standing volume at age 115 waspredicted to be 71 mbf/acre, for a totalproduction of 103 mbf/acre not includingthe allocation CO snags and logs (table 3).Mean annual increment was predicted toincrease from stand age 40 to 120. At age115, either a single- or a few-storied standmanagement approach could be initiated,or the old-forest character of the standcould be maintained using a many-storiedmanagement approach.

Landscapes by DesignWe are inheriting landscapes created

by past disturbances and timber-drivenmanagement objectives on mixed owner-ships that do not consider large-scale hab-itat patterning. Combining a range ofavailable silvicultural systems on thelandscape in a manner that considers sizeand connectedness of mature stands overlandscapes through time would be onestep toward designing forest patterns. Forinstance, harvest of stands within a land-

scape should not excessively fragmentcurrently suitable habitat. Within a "hab-itat management block" for mature-forestspecies, constraints would be needed onthe proportion of the area that would beallowed to consist of other than old-foresthabitat. The amount of old-forest habi-tat, connectivity, and volume removalscould be predicted at the landscape scaleusing a scheduling and network analysisprogram such as SNAP (Sessions and Ses-sions 1992).

The four proposed prescriptionsshould be considered as examples; theywill not apply in all situations nor willthey meet all ecosystem objectives. Silvi-culturists will have to work with wildlifebiologists, forest ecologists, harvestingspecialists, and other resource managersto identify clear objectives for wildlifehabitat and timber; identify existing ex-amples of conditions that meet the ob-jectives; design prescriptions specific tolocal conditions that can attain standobjectives; and plan stand locations tocreate landscape patterns that meet theobjectives.

As an example, consider how these ap-proaches might be distributed on a land-

40 Journal of Forestry

scape to meet a management objective ofmaintaining mature-forest species whileallowing some timber removal. Becauseground-skidding is generally limited toslopes less than 35%, areas with suchslopes that are known to support mature-forest species could be managed by pro-ducing many-storied stands to maintainthese species and provide connectivityamong other stands. Single- and few-sto-ried stands could be used on steep side-slopes. Few-storied stands might be mostappropriate on steep slopes adjacent to ri-parian buffer strips because they wouldprovide at least a low contiguous canopycover and a source of large logs for the ri-parian system. Restoration could be ap-plied to young plantations.

The resulting landscape would be amosaic of many-storied stands inter-spersed with single- and few-storiedstands in various stages of development.Managers would have to be committed todesigning the landscape to meet the needsof mature-forest species over time. Oncestand and landscape conditions sup-ported populations of species associatedwith old forests, stand conditions couldbe prolonged by using selection systemsthat create many-storied stands. Indeed,this progression from coarse-scale distur-bance (single- and few-storied stands) tofine-scale disturbance (many-storiedstands) is typical of natural developmentof mature and old-growth forests (Spies etal. 1990). Decisions regarding use ofcoarse-scale disturbances in managedstands should be based on landscape ob-jectives. Further, silviculturists must beaware that natural disturbances (e.g., rootrots, fire, wind) will continue to alterstand structure in managed stands.

Unless a landscape had been cut to thepoint that further harvest would exces-sively fragment the area, volume removals(though low) would continue until theareas became fully managed; then timberproduction would increase (Gagliuso andMcComb 1992). Volume removalswould be lower and species mix may dif-fer from stands managed solely for timberproduction. The level of removals will de-pend on site quality, species composition,desired structures, current structure, rela-tive value placed on wildlife by landown-ers, and legislative mandates.

Hypothesis TestingForest management is entering an era

of ecosystem management. New ap-

proaches are often being implementedfaster than research can provide informa-tion on impact and effectiveness. All ofthe approaches illustrated in this articleare based on ecological concepts thatneed to be tested with long-term studies.A deductive approach to hypothesis test-ing should be used to assess (1) the likeli-hood that predicted stand developmentwill be achieved, including disturbance aswell as suppression mortality and changesin species composition; (2) economic fea-sibility of the systems; and (3) responsesof mature-forest wildlife to silviculturalsystems (Romesburg 1981).

Research is being conducted in east-central Coastal Range stands in Oregonto examine the growth of residual and re-generated trees, harvesting costs, sitepreparation costs and effectiveness, wild-life population responses, and estheticvalues associated with similar treatments(Brunson and Shelby 1992). However,experiments must be conducted at bothstand and landscape scales. Stand-levelstudies can provide information on re-generation and residual tree responses,harvesting system approaches and costs,and responses of species with small homeranges. Large manipulations (thousandsof acres) should be the basis for testingspecies responses to treatments, especiallyfor species with large home ranges.

Traditional divisions between re-search and management must be mini-mized for experiments to succeed. Re-searchers must work with managers toachieve stand and landscape patterns thatmeet the goals for both experimental de-signs and multiple-use management.Managers must appreciate the impor-tance of replicated experimental designs.Although Bayesian statistics may be nec-essary approaches to understandinglarge-scale processes (Reckhow 1990),cause-and-effect relationships could beassessed using a repeated measures exper-imental design (Gurevitch and Chester1986) at the landscape scale. Replicatedstudies of habitat and wildlife wouldhave to occur on large scale. DCAs couldserve as control areas, with manipula-tions occurring on landscapes pairedwith DCA controls to provide a basis forcomparing species and community re-sponses to changes. Although DCAs al-ready contain many second-growthstands, animal responses to developinghabitat conditions in DCAs withoutsubsequent management could be corn-

pared to responses to habitat develop-ment outside DCAs in areas managedusing techniques discussed in this article.

Monitoring correct implementationand prescription effectiveness will be crit-ical to give managers the flexibility to al-ter approaches over time in an adaptivemanagement approach. Adaptive man-agement will allow managers to incorpo-rate monitoring results into new prescrip-tions, thereby increasing the likelihood ofreaching their objectives. Mil

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ABOUT THE AUTHORS

William C. McComb is professor and wild-life biologist, and William H. Emminghamis associate professor and silviculturist, De-partment of Forest Science, Oregon StateUniversity, Peavy Hall 154, Corvallis97331-7501; Thomas A. Spies is researchforester and forest ecologist, USDA ForestService, Pacific Northwest Research Station,Corvallis.

42 Journal of Forestry