tinker and knight 2000 - uwyo.edu

Coarse Woody Debris following Fireand Logging in Wyoming Lodgepole

Pine Forests

Daniel B. Tinker* and Dennis H. Knight

Department of Botany, University of Wyoming, Laramie, Wyoming 82071, USA

ABSTRACTThe accumulation and decomposition of coarsewoody debris (CWD) are processes that affect hab-itat, soil structure and organic matter inputs, andenergy and nutrient flows in forest ecosystems. Nat-ural disturbances such as fires typically producelarge quantities of CWD as trees fall and break,whereas human disturbances such as timber har-vesting remove much of the CWD. Our objectivewas to compare the amount of CWD removed andleft behind after clear-cutting to the amount con-sumed and left behind after natural fires in RockyMountain lodgepole pine. The masses of fallen logs,dead-standing trees, stumps, and root crowns morethan 7.5 cm in diameter were estimated in clear-cutand intact lodgepole pine forests in Wyoming andcompared to estimates made in burned and un-burned stands in Yellowstone National Park (YNP),where no timber harvesting has occurred. Estimatesof downed CWD consumed or converted to char-coal during an intense crown fire were also made inYNP. No significant differences in biomass ofdowned CWD more than 7.5 cm in diameter weredetected between burned stands and those follow-

ing a single clear-cut. However, the total mass ofdowned CWD plus the mass of snags that will be-come CWD was nearly twice as high in burnedstands than in clear-cuts. In YNP, approximately8% of the downed CWD was consumed by fire andan additional 8% was converted to charcoal, for anestimated loss of about 16%. In contrast, approxi-mately four times more wood (70%) was removedby clear-cutting. Considering all CWD more than7.5 cm in diameter that was either still present inthe stand or removed by harvesting, slash treat-ment, or burning, clear-cut stands lost an average of80 Mg ha21 whereas stands that burned gained anaverage of 95 Mg ha21. Some CWD remains as slashand stumps left behind after harvesting, but standssubjected to repeated harvesting will have forestfloor and surface soil characteristics that are beyondthe historic range of variability of naturally devel-oping stands.

Key words: coarse woody debris; lodgepole pine;Pinus contorta; timber harvesting; fire; YellowstoneNational Park; Wyoming; clear-cutting.

INTRODUCTION

Coarse woody debris (CWD) which is present aslogs and snags in most western coniferous forests,plays an important ecological role within theseecosystems. For example, it provides a habitat formany types of organisms in both terrestrial and

aquatic environments (Harvey 1982; Harmon andothers 1986; Franklin and others 1987; Bull andothers 1997). Microbes and fungi, as well asmany insects and other invertebrates, facilitatedecomposition and derive energy and nutrientsfrom rotting logs (Frankland and others 1982).Numerous species of vascular plants, includingsome tree seedlings, establish on CWD, and treeroots commonly grow into decomposing logs onthe forest floor (Grier and others 1981; Harveyand Neuenschwander 1991; Little and others

Received 16 November 1999; Accepted 31 May 2000.*Current address for corresponding author: Department of Geosciences andNatural Resources Management, 207-A Stillwell, Western Carolina Uni-versity, Cullowhee, North Carolina 28723, USA; e-mail: [email protected].

Ecosystems (2000) 3: 472–483DOI: 10.1007/s100210000041 ECOSYSTEMS

© 2000 Springer-Verlag

472

1994; Vogt and others 1995; Jurgensen and oth-ers 1997).

Snags represent a critical habitat for many speciesof cavity-nesting birds (Davis and others 1983; Har-mon and others 1986). Amphibians, reptiles, andmammals rely on many forms of CWD as habitat forcover, feeding, and reproduction (Harmon and oth-ers 1986). CWD is an important source of organicmatter inputs to forest soils (Edmonds 1991), andnitrogen, much of which will become available tovarious organisms, can accumulate in the decom-posing CWD of western coniferous forests (Harvey1982; Fahey and Knight 1986; Hart 1999). Inaquatic systems, CWD is recognized for its effect onthe geomorphic structure within streams and lakes,as well as serving as a habitat for fish and manyaquatic invertebrates (Harmon and others 1986).

The amount of CWD in a forest depends on pro-cesses that affect its accumulation from tree mor-tality and breakage, as well as processes that affectits loss, such as decomposition, burning, and har-vesting. The presence of CWD on a harvested sitesurely affects ecological processes associated withnutrient cycling. In Canadian lodgepole pine for-ests, Wei and others (1997) found that if posthar-vest CWD is left in place, nutrient removal by har-vesting was within the range of nutrient removal bywildfires. In contrast, the complete removal ofCWD from a clear-cut area could result in signifi-cant nutrient losses and a potential reduction inlong-term site productivity. In a study comparingpostharvest slash treatments in clear-cut Wyominglodgepole pine forests, Benson (1982) reported thatburning slash removed approximately 87% of theresidue present following clear-cutting. For thisstudy, we compared the proportion of CWD re-moved by clear-cutting to the proportion consumedby natural fires in Rocky Mountain forests domi-nated by lodgepole pine (Pinus contorta ssp. latifolia[Engelm.ex Wats.] Critchfield). In addition to pro-viding a comparison that is relevant to ecosystemmanagement, our method of estimating theamount of wood consumed by an intense wildfiremay be applicable to other forest types. Naturalforest disturbances typically kill a large number oftrees, which then augment the amount of CWDwhen the trees fall to the ground (Spies and others1988). Most of the live trees killed by intense,stand-replacing fires fall to the forest floor within afew decades (Mitchell and Preisler 1998). Con-versely, human disturbances, such as timber har-vesting, and some forms of postharvest slash treat-ment, such as broadcast burning or pile-and-burn,remove much of the wood that would have becomeCWD (Jurgensen and others 1997). Notably, a large

amount of ‘inherited‘ CWD is present on the forestfloor before the initial harvest. This CWD is a legacyof the trees that were killed during the last stand-replacing fire (Maser and others 1979; Wei andothers 1997) and trees from the present stand thathave died and fallen as a result of natural mortality(Gore and Patterson 1986; Franklin and others1987). This inherited CWD, and therefore totalCWD, would likely decrease with continued de-composition and repeated harvesting.

The few recommendations that exist for theamount of CWD that should be left on a site fol-lowing timber harvesting vary widely, from lessthan 10 Mg ha21 in drier Rocky Mountain sitescontaining grand fir (Abies grandis [Dougl. ex D.Don] Lindl.) or ponderosa pine (Pinus ponderosa[Dougl. ex Laws.]) (Graham and others 1994) to125 Mg ha21 for mixed conifer forests of the north-ern Rockies (Reinhardt and others 1991). The de-sired amount of CWD left following harvesting de-pends on habitat type, method of regeneration, andpreharvest levels of soil organic matter and CWD(Brown and See 1981; Jurgensen and others 1997).Given the increasing interest in the use of harvest-ing to mimic natural disturbances (Hammond 1991;Keenan and Kimmins 1993), the differences inCWD and potential CWD biomass in burned andharvested stands should be better understood.

Quantified CWD amounts following fire and log-ging are the net result of how much CWD is pro-duced and eliminated by each process. Estimatingthe amount of CWD removed and created by clear-cutting is relatively straightforward (for example,Brown 1974). On the other hand, comparable esti-mates are more problematic in stands burned byintense wildfires because they require an estimateof the amount of downed CWD that is completelyconsumed and the amount that is converted tocharcoal. Fahnestock and Agee (1983) concludedthat there is no reliable method for verifying thequantity of woody fuels consumed by wildfire. Infact, most studies on wood consumption have beenconducted in prescribed burns or under laboratoryconditions (Kauffman and Martin 1989; Reinhardtand others 1991; Albini and Reinhardt 1995; Calland Albini 1997) that exhibit different thermal dy-namics and behavior than natural fires. Previousestimates of large woody fuels that are burned varywidely, ranging from 4% to 100% of prefireamounts (Brown and others 1985, 1991; Kauffmanand Martin 1989; Reinhardt and others 1991). Oneof the primary objectives of our research was todevelop a method that would produce reasonableestimates of the amount of CWD consumed duringnatural fires.

Coarse Woody Debris in Lodgepole Pine Forests 473

Increasingly, researchers and managers are ex-ploring the idea of using the historic range of vari-ability as a reference to guide the management ofhuman-influenced ecological systems (Swansonand others 1994; Cissel and others 1999; Landresand others 1999). Because of the limited anthropo-genic influence in Yellowstone National Park, oneof the primary areas for this study, we had anopportunity to examine the variability in CWD,which may be used as a reference system for lodge-pole pine forest management. By estimating CWDamounts in stands of various successional stages inYellowstone, we were able to provide baseline in-formation on CWD biomass that may help define arange of variability by which to model managedforest systems.

We compared the mass of CWD after a singleclear-cut timber harvest and a natural fire in lodge-pole pine forests to estimate the net loss or gain ofCWD following each type of each disturbance. Weconsidered CWD to be all downed woody materialmore than 7.5 cm in diameter, including stumpsand woody lateral roots, as well as snags more than7.5 cm in diameter. Mitchell and Preisler (1998)found that 90% of the dead lodgepole pine treeskilled by mountain pine beetles in central Oregonfell within approximately 2 decades. Snags weretherefore included as CWD because they fall andbecome part of the forest floor CWD within a shorttime.

STUDY AREA AND METHODS

Data were collected during 1995–97 from 31stands dominated by lodgepole pine in the Med-icine Bow National Forest (MBNF) in southeast-ern Wyoming (41°N, 106°W) and in YellowstoneNational Park (YNP) in northwestern Wyoming(44°N, 110°W) (Table 1). Because the stands inYNP were essentially undisturbed by human ac-tivity, they provided a unique opportunity to in-vestigate CWD dynamics under natural distur-bance regimes. In contrast, much of the MBNFhas been heavily influenced by timber harvestingfor well over 40 years. Also, many stands thatburn in the MBNF have been altered as well bysalvage logging or firewood gathering, either be-fore or after fires, making accurate estimates ofnatural CWD production difficult.

In YNP, stands burned by crown fires and intensesurface fires were sampled along with unburnedstands (Table 1). Stands that burned in 1988 wereselected based on a burn severity classification donein 1989 as part of an ongoing postfire study ofvegetation and successional dynamics (Turner and

others 1997). Crown fires are those that consumedthe canopy foliage and most small branches andtwigs, as well as most of the forest floor litter. In-tense surface fires are those that did not actuallyburn in the canopy but are nonetheless hot enoughto turn the tree foliage to a reddish-brown color.Unburned and uncut stands of similar age, as theyexisted just before the fires, were located as close toeach burned stand as possible. In addition, a singlestand that burned in 1996 near Pelican Creek inYNP was also sampled for CWD consumption esti-mates. All stands in YNP were located at approxi-mately 2300 m elevation on rhyolitic soils.

In the MBNF, we used eight recent clear-cutstands (harvested in 1991–93; 5–15 ha) and sixuncut and unburned stands ranging in age from 98to 244 years (preharvest age for clear-cuts). Roller-chopping, which leaves the CWD on site, was thepostharvest treatment for all clear-cuts. The soilsare Alfisols (Typic Cryoboralfs), which have devel-oped from Precambrian gneiss and granite, withoccasional Inceptisols (Typic Cryochrepts). Com-mon understory species in our study areas werebuffalo berry (Shepherdia canadensis (L.) Nutt.),grouse whortleberry (Vaccinium scoparium Leibergex Cov.), and common juniper (Juniperus communisL. var. depressa Pursh).

Estimates of CWD Biomass

Twenty-five 15.2-m (50-ft) transects were used ineach stand for estimating CWD biomass with theplanar intercept method (Brown 1974). Thismethod only requires that logs be classified assound or rotten, but instead we classified each loginto one of five decay classes using the classificationof Maser and others (1979). Decay class I logs aresound and still have bark, branches, and twigs. Atthe other end of the decay gradient, highly-decayedclass V logs are elliptical in cross section and arepartially buried in the forest floor.

In addition, two or three 20 3 20 m plots wereestablished in each stand. All downed CWD morethan 7.5 cm in diameter, root crowns more than 7.5cm in diameter, seedlings (less than 1 m tall), andstanding-live and-dead trees more than 7.5 cm indiameter were mapped in each plot. From thesemaps, stand density, percent cover, and biomass ofstanding trees (live and dead) and stumps werecalculated using allometric equations developed byPearson and others (1984) in the Medicine BowNational Forest. The equations provide estimates ofthe biomass of tree root crowns, boles, branches,and foliage using individual tree basal area. Wheretree boles had been removed or separated from thestump, either through clear-cutting, fire, or natural

474 D. B. Tinker and D. H. Knight

treefall, stumps were included as root crown bio-mass (which provides a conservative estimate oftotal live biomass, since lateral woody roots and fineroots are not included). In burned stands, stumpswere included in estimates of total live- and dead-standing biomass. Within each stand, 10 of thelargest trees were cored using an increment borer,and cores were subsequently mounted on boardsand sanded. Annual rings were counted to estimatethe age of the stand. Two-tailed t tests were per-formed on biomass data to test for significant dif-ferences between mean values of biomass estimatesof clear-cut vs burned, unburned vs uncut, clear-cut vs uncut, and crown fires vs surface fires, withan alpha level of 0.05.

Estimates of CWD Conversion to Charcoaland Consumption

Our CWD consumption estimates were made dur-ing 1997 in a single stand near Pelican Creek thatburned in YNP during the summer of 1996. CWDconsumed by fire or converted to charcoal was to-taled from (a) the amount of CWD converted tocharcoal that is still present and measurable, and (b)measurements of logs completely consumed by thefire. We attempted to include estimates of the bio-mass of logs partially consumed by the fire, which,when it occurs, typically creates cupped depressionson the log surface. However, our methods for thisestimate proved inaccurate (Tinker 1999), so data

Table 1. Characteristics of Stands Sampled in Yellowstone National Park (YNP) and the Medicine BowNational Forest (MBNF)

Stand Name Treatment Elevation (m) Trees/haa Est. Age (y)

YNP (17)Hllp0un Unburned 2204 950 27Hllp1un Unburned 2292 725 61CClp1un Unburned 2280 2725 103CClp2un Unburned 2216 975 173Fsunb Unburned 2377 1387 193Lewis Falls Unburned 2438 1194 —Flsb Surface fire 2304 2087 106Fssb Surface fire 2371 912 251Hltsb Surface fire 2423 525 262Mallard Surface fire 2286 933 185Flcrown Crown fire 2310 587 150Hltcrown Crown fire 2423 775 189Fscrown Crown fire 2384 500 242Lewis Canyon Crown fire 2387 683 208Pelican Creek Crown fire 2420 983 —Arrow Double burn 2362 733 12Cascade Double burn 2432 367 35

MBNF (14)95-01 Uncut 2646 1233 10896-01 Uncut 2758 667 24496-02 Uncut 2734 1075 23096-03 Uncut 2755 1683 23396-04 Uncut 2621 2367 13197-01 Uncut 2743 800 98cc1 Clear-cut 2667 983 273cc2 Clear-cut 2646 283 —cc3 Clear-cut 2737 1567 222cc4 Clear-cut 2725 700 222cc5 Clear-cut 2627 1667 112cc6 Clear-cut 2649 850 240cc7 Clear-cut 2743 825 238cc8 Clear-cut 2743 1000 104

aDensity prior to either fire or clear-cutting.


for paratially consumed CWD are not included inour results. This and other potential sources of errorare discussed below.

CWD converted to charcoal. Our approach to esti-mating the amount of CWD converted to charcoal isbased on Newton’s formula for the volume of atapered cylinder (Harmon and Sexton 1996):

V 5 L ~ Ab 1 4 Am 1 At!/6 (1)

where V is the volume, L is log length, and Ab, Am,and At are the cross-sectional areas of the base,middle, and top of the log, respectively. The maxi-mum diameters at the middle and at each end weremeasured using tree calipers on each of 50 downedlogs that had fallen to the ground and had beencharred or subsequently partially burned in 1996.This calculation provided diameters of the log, in-cluding the burned charcoal exterior. Each log wasthen cut at the three points of measurement usinga chainsaw, and diameter measurements were re-peated on the inner, unburned portion of the wood.These two sets of measurements provided the vol-umes of two tapered cones—one larger cone thatincluded the charcoal and one smaller cone thatwas the unburned portion of the log. The differencebetween the two cone volumes is an estimate ofcharcoal volume, which was converted to mass us-ing density values for the five different decay classesof lodgepole pine from Harmon and Sexton (1996).Estimates of this type are based on the assumptionthat logs have been uniformly charred around theircircumference. There is variability in charcoal deptharound some logs, but our observations in the fieldcorroborate the assumption of relatively even char-ring. Still, some diameter reduction of charred logscould have occurred before the remaining charcoalwas formed, and our measurements must be con-sidered as underestimates.

Logs completely consumed by fire. We used twotypes of evidence to estimate the volume of CWDthat is completely combusted: log shadows and logtrenches. Log shadows are linear, tapered, light graypatches on the otherwise blackened soil surface;they are apparently created by the high tempera-tures of glowing combustion on logs in close prox-imity to the forest floor and the accompanying ox-idation of surficial organic matter (Figure 1a). Logtrenches are elongated, concave depressions in theforest floor that were occupied by decayed logs(decay classes 3–5) prior to the fire, but where thelogs were completely consumed (Figure 1b). Logshadows and trenches were mapped separatelyfrom the unburned CWD within the 20 3 20 mplots, and the maps were overlaid with digital maps

of the unburned CWD using the ARC/INFO Geo-graphic Information System (ESRI Inc. 1995). Inmost cases, the overlays associated the shadows andtrenches with unburned portions of logs of identi-fiable size and decay classes. The associations wereused to estimate the probable dimensions and decaystage of the logs prior to the fire.

The dimensions of missing logs in log trenchesnot associated with adjacent unburned logs wereestimated from regression models we developedduring this study in unburned forests in YNP, whichuse trench width to predict log diameter (Table 2).We determined that almost all logs that burned andformed trenches were of decay classes IV and V,which are elliptical rather than round in cross sec-

Figure 1. Photographs taken immediately after the Pel-ican Creek fire in Yellowstone National Park in Augustand September 1996, showing log trenches (A) and logshadows (B). The size of the light-colored area (logshadow) on the forest floor is indicative of the amount ofwood that was consumed. Similarly, the cupped depres-sion (log trench) shows where a decaying log once occu-pied the forest floor before being consumed by the fire.Note the unburned woody lateral root from a lodgepolepine that had grown into the decaying log, suggestingthat the log was a source of water and nutrients for thegrowing root.


tion. The estimated volumes of each elliptical logand bulk densities for each decay class were multi-plied by wood density values for the appropriatedecay class (Harmon and Sexton 1996) to calculatethe biomass of the logs that had occupied thetrenches.

The application of this log shadow/log trenchmethod provides a conservative estimate, becausesome of the consumed CWD more than 7.5 cm indiameter does not leave any obvious trace of itsexistence. However, at the present time, there is noalternative for studies of natural fire. Notably, thismethod cannot be applied beyond 1 year after a firebecause most of the log shadows disappear and thelog trenches are less conspicuous.

Logs partially consumed by fire. To account for theCWD lost through partial burning of logs, we at-tempted to estimate pre- and postfire log biomassby applying a repeated measure design using theplanar intercept method twice along the sametransects. Other studies have used this procedurefor the same purpose in prescribed burns (Kauff-man and Martin 1989; Brown and others 1991).Postfire biomass was first estimated along transectsusing the planar intercept method. To estimate pre-fire biomass, each log was cut in half at the pointalong the log where the postfire measurement wastaken, and the maximum radius that was exposedby the cross-sectional cut was recorded. The maxi-mum radius was then doubled to provide a prefirediameter of each log, which was used to calculateprefire biomass. The difference between pre- andpostfire estimates would provide an estimate of theCWD consumed by partial burning of logs.

However, using this method, we found small andnonsignificant differences between pre- and post-fire biomass estimates. We therefore concluded thatthe planar intercept method is not appropriate forestimating the amount of biomass lost through par-tial burning of logs. These estimates are not in-cluded in our analysis. Because neither CWD con-

sumption by partial burning nor partialconsumption of snags or stumps was estimated, ourvalues represent a conservative estimate of the ac-tual amount of CWD consumed by fire.

Estimates of Net Loss or Gain ofCWD Biomass

CWD biomass measurements, together with esti-mates of the amount of CWD removed by harvest-ing and consumed or converted to charcoal by fire,were used to calculate the losses and gains of CWDduring natural fires and clear-cut timber harvesting.In burned stands, live trees killed but not consumedby fire were considered a potential source of CWD.In clear-cuts, live trees removed by harvesting rep-resented a loss of potential CWD. Estimates of pre-harvest live-tree biomass in clear-cuts, which rep-resents the loss of potential CWD, were made fromindividual stump basal areas using the allometricequations of Pearson and others (1984). Posthar-vest slash more than 7.5 cm in diameter, along withstumps left after bole removal, were consideredCWD in clear-cuts.

RESULTSUncut and unburned stands. Comparisons be-

tween uncut stands in the MBNF and unburnedstands in YNP were performed to detect any re-gional differences that might affect subsequentcomparisons. No significant differences for any sizeclasses of CWD were observed between the twosites (P . 0.3) (Figure 2).

Clear-cut and burned stands. No significant differ-ences between any size class of downed CWD morethan 7.5 cm in diameter or total downed CWD(CWD plus fine woody debris more than 7.5 cm indiameter) were found when comparing clear-cut toburned stands; (P . 0.2) (Figure 3). However, asexpected, there was significantly more CWD in theform of snags in burned stands. If the snags are

Table 2. Regression Models Developed during this Study in Unburned Stands in Yellowstone NationalPark (YNP) for Predicting Log Diameters from Trench Widths

DecayClassa Regression Model R2

III (n 5 30) D1 5 1.00(TW) 1 3.64 0.72IV (n 5 30) D1 5 1.01(TW) 1 1.06 0.93V (n 5 30) D1 5 0.87(TW) 1 2.96 0.89

D1, predicted log diameter; TW, trench widthaBecause decay class I and II logs do not form trenches, no regression models are included for them.


included, there is more than double the biomass ofCWD more than 7.5 cm in diameter in burnedstands than in clear-cut stands (P , 0.05) (Figure3). In contrast, clear-cut stands had five times morefine woody debris less than 7.5 cm in diameter thanburned stands (P , 0.05; 20.6 and 4.5 Mg ha21,respectively).

Clear-cut and uncut stands. There were no signif-icant differences in CWD of any size class between

clear-cut and uncut stands (P . 0.05) (Figure 4).However, clear-cuts contained almost three timesthe amount of fine woody debris (less than 7.5 cmin diameter) and more than double the amount ofstump biomass than uncut stands (P , 0.05).

Crown fires and surface fires. No significant differ-ences in any size classes of CWD were observedbetween stands that were subjected to crown firesand those that were burned by intense surface fires(P . 0.10 for all size classes). The biomass of snagswas not statistically different among the two burnintensifies (P . 0.10). In fact, tree mortality was100% in both types of fire.

CWD converted to charcoal or completely consumed.The amount of CWD of all decay classes convertedto charcoal during the Pelican Creek fire in 1996was estimated to be at least 6.4 Mg ha21 (around8% of CWD present in the stand). Charcoal thick-ness was relatively consistent for decay classes I–IV(Table 3). Conversion of decay class V CWD tocharcoal could not be estimated because of the dif-ficulty we encountered in locating and obtainingintact cross sections. Analysis of log shadow and logtrench evidence indicated that downed CWD wasreduced by at least 6.4 Mg ha21 (around 8%) dur-ing the 1996 Pelican Creek fire. Decay class V ac-counted for only 10% of the biomass loss estimatedfrom log shadows but 44% of the biomass lossestimated from log trenches. Three-fourths of thelog trenches had been occupied by class V logs(Table 4). When both losses are added, 12.8 Mgha21 of downed CWD were consumed or convertedto charcoal by the Pelican Creek fire (around 16%of the total).

Figure 2. Biomass of uncut stands (MBNF, cross-hatched bars; n 5 6) and unburned stands (YNP, solidbars; n 5 6). Total Downed Wood 5 total downed woodof all sizes; Total CWD (more than 7.5 cm in diameter) 5total downed wood 1 stumps 1 snags (all more than 7.5cm in diameter); Total CWD (all sizes) 5 total CWD of allsizes 1 stumps 1 snags; Total Biomass 5 total CWD of allsizes 1 live trees (including boles, branches and leaves).Error bars are 6 1 SE.

Figure 3. Biomass of clear-cut stands (MBNF, hatchedbars) and burned stands (YNP, solid bars). Total DW 5total downed wood of all sizes; Total CWD 5 totaldowned wood of all sizes 1 stumps 1 snags. Stumps andsnags are both more than 7.5 cm in diameter. Error barsare 6 1 SE. Asterisks indicate significant differences be-tween clear-cut and burned stands. Stump biomass ishigher in clear-cuts than in burned stands only becausebolewood removal creates stumps during timber harvest.

Figure 4. Biomass of clear-cut stands (MBNF, hatchedbars) and uncut stands (YNP, solid bars). Total DW 5 totaldowned wood of all sizes; Total CWD 5 total downedwood of all sizes 1 stumps 1 snags. Stumps and snags areboth more than 7.5 cm in diameter. Error bars are 6 1 SE.Asterisks indicate significant differences between clear-cut and uncut stands.


Net loss or gain of CWD biomass. Clear-cut har-vesting resulted in an average net wood loss of 83Mg ha21 (137 Mg ha21 removed as live trees minus54 Mg ha21 gained from downed CWD) (Figure 5).In contrast, assuming an approximate 16% reduc-tion in CWD by consumption and conversion tocharcoal, as calculated above, lodgepole pine standsthat burn still would have an average net CWDincrease of 99.2 Mg ha21 after all snags fall (112 Mgha21 gained minus 12.8 Mg ha21 burned) (Figure5). Clear-cutting removes almost 11 times as muchwood biomass as a natural fire (137 Mg ha21 re-moved by clear-cutting divided by 12.8 Mg ha21

removed by CWD consumption) (Figure 5).

DISCUSSION

The range of our CWD biomass estimates is broad(29–284 Mg ha21), but it is consistent with CWDestimates from other studies in Rocky Mountainand Pacific Northwest coniferous forests (Table 5).Although both clear-cutting and natural fires createCWD, our data show that clear-cutting removes47–116 Mg ha21 (mean, 83) more potential CWD(live trees) than is added by downed CWD left on

Table 3. Coarse Woody Debris (CWD) Biomass (Mg ha21) Converted to Charcoal by Decay Class duringthe 1996 Pelican Creek Fire, Based on Data from 50 Logs

DecayClass

OuterConeBiomass

InnerConeBiomass

BiomassLoss

PercentLoss

I 0.35 0.32 0.02 7.1II 4.3 4.0 0.3 7.7III 2.5 2.3 0.2 7.7IV 0.15 0.14 0.01 7.6V no data no data no data no dataAll 7.3 6.7 0.5 7.6

Table 4. Coarse Woody Debris (CWD) Consumed during the 1996 Pelican Creek Fire, Estimated Using100 Postfire Log Shadows and 27 Log Trenches

Decay Class

Log Shadows Log Trenches

Number (%)Biomass(Mg ha21) (%) Number (%)

Biomass(Mg ha21) (%)

I — — — —II 15 (15) 0.6 (16) — —III 50 (50) 2.2 (56) 3 (12.5) 1.1 (44)IV 27 (27) 0.7 (18) 3 (12.5) 0.3 (12)V 8 (8) 0.4 (10) 21 (75) 1.1 (44)

Total 100 (100) 3.9 (100) 27 (100) 2.5 (100)

Figure 5. Average CWD biomass (Mg ha21) gained (graybars) and lost (black bars), and the net gain or loss (cross-hatched bars) for all clear-cut stands (MBNF) and burnedstands (YNP). In clear-cuts, gain is from postharvest slashand loss is from removal of live tree boles. In burnedstands, gain is from fire-killed trees and loss is from woodconsumption and conversion to charcoal. Error barsare 6 1 SE. There is no error bar for the loss category forburns because this estimate is from a single stand.


the site (Figure 5). Repeated timber harvesting thatleaves amounts of CWD similar to those we mea-sured will result in an overall decline in CWD overtime. If a stand is subjected to regular, repeatedharvesting, the inherited CWD that decomposeswill not be replaced, since most of the bolewood isremoved during each harvest event (Spies and oth-ers 1988; Harmon and others 1990, 1996; Wei andothers 1997). The effects of this decline on biolog-ical diversity, nutrient cycling, and soil develop-ment should be considered when making decisionsabout sustainable forest management.

Many questions arise that are difficult to answer.For example, considering that lodgepole pine oftengrow on nutrient-poor sites in the Rocky Moun-tains, and considering that their roots often growinto decomposing logs, will tree growth decline asthe amount of CWD declines? Also, does the pres-ence of decomposing CWD on the soil surface havea significant effect on the structure and chemistry ofthe underlying mineral soil?

Unburned stands in YNP and unharvested standsin the MBNF had similar amounts of CWD (Figure2). However, burned stands contained more thantwice the amount of CWD more than 7.5 cm indiameter than clear-cut stands (Figures 2 and 6),largely due to the removal of live trees in harvestedstands and the presence of snags in burned stands.

Wei and others (1997) found three to five timesmore CWD in lodgepole pine stands that burnedthan in those that were clear-cut, although theirmeasurements did not account for consumption ofCWD by fire. The snags killed by crown or intense

Table 5. Comparison of Coarse Woody Debris (CWD) (more than 7.5 cm in Diameter) BiomassEstimates in Western Coniferous Forests

Study Location Forest TypeCWD Biomass(Mg ha21) Reference

Cascade Mountains,Washington, USA

Abies amabilis 147–809 Grier and others 1981

Olympic National Park,Washington, USA

Picea sitchensis/Tsugaheterophylla

120–161 Graham and Cromack 1982

MBNF, Wyoming, USA Pinus contorta 123–180 Pearson and others 1984Sequoia National Park,

California, USAVarious mixedconifers

29–400 Harmon and others 1987

British Columbia, Canada Pinus contorta 156–392 Comeau and Kimmins 1989Rocky Mountain National

Park, Colorado, USAPicea engelmannii/Abieslasiocarpa

123 Arthur and Fahey 1990

British Columbia, Canada Pinus contorta 118 Blackwell and others 1992British Columbia, Canada Pinus contorta 52–141 Wei and others 1997MBNF and YNP,

Wyoming, USAPinus contorta(undisturbed)

29–121 Present study

YNP, Wyoming, USA Pinus contorta (burnedin 1988)


MBNF, Wyoming, USA Pinus contorta (clear-cut in 1991–93)


MBNF, Medecine Bow National Forest; YNP, Yellowstone National Park

Figure 6. Biomass of total CWD (stumps including rootcrowns, total downed wood less than 7.5 cm and morethan 7.5 cm in diameter, and snags) in undisturbedstands, clear-cut stands, and burned stands (all burn se-verities) of lodgepole pine forests in Wyoming. Values tothe right of each category are the percentage of totalCWD.


surface fires are an important source of CWD dur-ing early stand development (Figures 5, 6) (Harmonand others 1986) unless the stand should reburnduring early development, when additional CWDcould be consumed. Spies and others (1988) foundthat CWD accumulation was highest in very youngand very old Douglas fir stands, suggesting that firesthat burn such stands could result in a greater lossof CWD than those that burn mid-successionalstands with less CWD.

The similarity in CWD between stands burned bycrown fires and stands burned by intense surfacefires was not surprising. Intense surface fires createsufficient heat to kill most or all of the trees inlodgepole pine stands, as happens during crownfires. Notably, both surface fires and timber harvest-ing with roller-chopping consume less fine fuelsthan do crown fires.

Estimating the amount of CWD completely con-sumed or converted to charcoal by natural fire waschallenging. Examinations of cross sections ofburned logs during the initial stages of our studyrevealed a thin charcoal shell surrounding an oth-erwise unburned log, suggesting that far less CWDwas consumed during natural fires than we hadpreviously thought. Our estimate of 16% of CWDconsumed or converted to charcoal is less than thatof Reinhardt and others (1991), who found that30%–39% of all CWD more than 7.5 cm in diam-eter was consumed by prescribed fire in mixed co-nifer stands in northern Idaho. Brown and others(1991) estimated that woody fuel consumption inprescribed burns, also in Idaho, ranged from 12% to65% (mean, 33%), which encompasses our esti-mate.

Using data from prescribed fires and subjectiveestimates, Fahnestock and Agee (1983) estimatedthat the amount of snag and CWD biomass con-sumed by fire was 20% during fires of moderateintensity and 30% during high-intensity fires.However, it seems unlikely that the spatial andthermal dynamics of a prescribed burn would becomparable to an intense forest fire, which burnsthrough a stand more rapidly. Hall (1991) foundthat high-intensity fires consumed 23% less largewoody fuels than moderate-intensity fires underotherwise similar conditions, apparently due to theshorter duration of high-intensity fires, which typ-ically do not reduce fuel moisture to the same de-gree as moderate-intensity fires.

Of course, CWD consumption by fire will varyseasonally and annually, depending on tempera-ture, precipitation, and fuel moisture content, andour estimates do not account for this variability.When Brown and others (1985) summarized data

from three previous studies of fuel consumption,they found that large woody fuels were reduced by25%–40% when fuel moisture was near 30%, butthey were reduced by 80%–100% when fuel mois-ture was only 10%. The variability between esti-mates of wood consumption suggests that addi-tional research is required to gain a betterunderstanding of the reduction of woody fuels bynatural fires.

Complete estimates of CWD consumption requiremeasurements of all woody components of thestanding-dead trees and forest floor. Therefore, ourdata provide underestimates of the wood burnedduring a fire because no measurements were madeof the losses from partially burned logs, or of com-plete or partial consumption of stumps and prefiredead-standing trees. Our field observations suggestthat these additional losses would be small com-pared to downed CWD. Data from unburned standsindicated that there is around 50% less wood in theform of snags and stumps than in downed CWD.Therefore, even if a proportion similar to that ofdowned CWD was consumed from snags andstumps, the additional amount consumed would bearound 8%, for a total of around 24% wood con-sumption. Most of the partial burning of snags anddowned CWD occurs when two pieces of wood arein contact—for example, when a log is lying at thebase of a snag. We consistently noticed an apparentloss of CWD in areas where the close proximity oftwo logs created an environment conducive toglowing combustion, a condition that surely in-creases with CWD biomass. Albini and Reinhardt(1995) suggested that large woody material nor-mally does not burn if the only source of heat is itsown combustion, a condition that is common fordowned CWD in natural fires.

Although our calculations of CWD consumptionare underestimates, we have attempted to accountfor both additions and removals from burning andclear-cut harvesting. As noted by Fahnestock andAgee (1983), additional work is needed to developmethods for estimating the amount of CWD con-sumed during natural fires. For now, measure-ments of CWD from natural stand conditions, bothburned and unburned, provide the best data avail-able for estimating the historic range of variabilityfor CWD, which may be used as a managementguideline for the amount of CWD that should bepresent on a given site. Our CWD data from YNPprovide important baseline information that can beused as such a guide. In addition, our informationon the amount of CWD left after clear-cutting pro-vides managers with a look at how closely thispractice does (or does not) resemble naturally de-


veloping stands with respect to CWD amounts. Per-haps if more CWD was left on clear-cut sites, de-veloping stands would more closely resembleconditions that are created by natural fires. How-ever, simulation modeling is required to estimatethe long-term effects of different fire and harvestregimes on CWD amount, distribution, anddynamics.

ACKNOWLEDGMENTS

This work was supported by grants from the Uni-versity of Wyoming/National Park Service ResearchCenter and the US Department of Agriculture (NRI96-35101-3244). David Melkonian, Kristofer M.Johnson, Sharon Stewart, Donna Ehle, and SallyTinker assisted in the field and in the laboratory.Michael M. Sanders, David Carr, and Carol Tolbertof the Laramie District of the Medicine Bow/RouttNational Forest were helpful throughout the study,as were David Phillips and Kathleen O’Leary of theSouth Ranger District of Yellowstone National Park.We also thank Don Despain, Larry C. Munn, Wil-liam H. Romme, George F. Vance, and Anna Krzy-szowska-Waitkus for sharing their insights regard-ing our methodology, wood consumption, andlodgepole pine forest ecology. David Foster, LucyTyrell, and an anonymous reviewer provided help-ful comments on an earlier draft of the manuscript.

REFERENCES

Albini FA, Reinhardt ED. 1995. Modeling ignition and burningrate of large woody natural fuels. Int J Wildland Fire 5(2):81–91.

Arthur MA, Fahey TJ. 1990. Mass and nutrient content of de-caying boles in an Engelmann spruce–subalpine fir forest,Rocky Mountain National Park, Colorado. Can J For Res 20:730–7.

Benson RE. 1982. Management consequences of alternative har-vesting and residue treatment practices—lodgepole pine.USDA Forest Service general technical report INT-132. Inter-mountain Forest and Range Experiment Station. 58 p.

Blackwell B, Feller MC, Trowbidge R. 1992. Conversion of denselodgepole pine stands in west-central British Columbia intoyoung lodgepole pine plantations using prescribed fire. 1. Bio-mass consumption during burning treatments. Can J For Res22:572–81.

Brown JK. 1974. Handbook for inventorying downed woodymaterial. USDA Forest Service general technical report INT-16. Intermountain Forest and Range Experimental Station,Ogden, UT.

Brown JK, Marsden MA, Ryan KC, Reinhardt ED. 1985. Predict-ing duff and woody fuel consumed by prescribed fire in thenorthern Rocky Mountains. USDA Forest Service researchpaper INT-337. Intermountain Forest and Range ExperimentalStation, Ogden, UT.

Brown JK, Reinhardt ED, Fischer WC. 1991. Predicting duff andwoody fuel consumption in northern Idaho prescribed fires.For Sci 37:1550–66.

Brown JK, See TE. 1981. Downed dead woody fuel and biomassin the northern Rocky Mountains. USDA Forest Service gen-eral technical report INT-117. 19 p.

Bull EL, Parks CG, Torgersen TR. 1997. Trees and logs importantto wildlife in the interior Columbia River Basin. USDA ForestService PNW-GTR-391. Pacific Northwest Research Station,Portland, OR.

Call PT, Albini FA. 1997. Aerial and surface fuel consumption incrown fires. Int J Wildland Fire 7(3):259–64.

Cissel JH, Swanson FJ, Weisberg PJ. 1999. Landscape manage-ment using historical fire regimes: Blue River, Oregon. EcolAppl 9:1217–31.

Comeau PG, Kimmins JP. 1989. Above- and below-ground bio-mass and production of lodgepole pine on sites with differingsoil moisture regimes. Can J For Res 19:447–54.

Davis JW, Goodwin GA, Ockenfels RA. 1983. Snag habitat man-agement. USDA Forest Service general technical report RM-99.

Edmonds RL. 1991. Organic matter decomposition in westernUnited States forests. In: Harvey AE, Neuenschwander LF,editors. Proceedings—management and productivity of west-ern-montane forest soils. USDA Forest Service general tech-nical report INT-280. p 118–28.

ESRI Inc. 1995. Understanding GIS: the ARC/INFO method.Redlands (CA): Environmental Systems Research Institute.

Fahey TJ, Knight DH. 1986. The lodgepole pine ecosystem. Bio-Science. 36:610–17.

Fahnestock GR, Agee JK. 1983. Biomass consumption andsmoke production by prehistoric and modern forest fires inwestern Washington. J For 81:653–7.

Frankland JC, Hedger JN, Swift MJ. 1982. Decomposer basidio-mycetes: their biology and ecology. London: Cambridge Uni-versity Press.

Franklin JF, Shugart HH, Harmon ME. 1987. Tree death as anecological process. BioScience 37:550–6.

Gore JA, Patterson WA III. 1986. Mass of downed wood innorthern hardwood forests in New Hampshire: potential ef-fects of forest management. Can J For Res 16:335–9.

Graham RL, Cromack K Jr. 1982. Mass, nutrient content, anddecay rate of dead boles in rain forests of Olympic NationalPark. Can J For Res 12:511–21.

Graham RT, Harvey AE, Jurgensen MF, Jain TB, Tonn JR, Page-Dumroese DS. 1994. Managing coarse woody debris in forestsof the Rocky Mountains. USDA Forest Service research paperINT-RP-477.

Grier CC, Vogt KA, Keyes MR, Edmonds RL. 1981. Biomassdistribution and above- and below-ground production inyoung and mature Abies amabilis zone ecosystems of theWashington Cascades. Can J For Res 11:155–67.

Hall JN. 1991. Comparison of fuel consumption between highintensity and moderate intensity fires in logging slash. North-west Sci 65:158–65.

Hammond H. 1991. Seeing the forest among the trees: the casefor holistic forest use. Vancouver: Polestar Press.

Harmon ME, Cromack K Jr, Smith BG. 1987. Coarse woodydebris in mixed-conifer forests, Sequoia National Park, Cali-fornia. Can J For Res 17:1265–72.

Harmon ME, Ferrell WK, Franklin JF. 1990. Effects on carbonstorage of conversion of old-growth forests to young forests.Science 247:699–702.

Harmon ME, Franklin JF, Swanson FJ, Sollins P, Gregory SV,


Lattin JD, Anderson NH, Cline SP, Aumen NG, Sedel JR,Liendaemper GW, Cromack K Jr, Cummins KW. 1986. Ecol-ogy of coarse woody debris in temperate ecosystems. Adv EcolRes 15:133–302.

Harmon ME, Garman SL, Ferrell WK. 1996. Modelling the his-torical patterns of tree utilization in the Pacific Northwest:carbon sequestration implications. Ecol Appl 6:641–52.

Harmon ME, Sexton J. 1996. Guidelines for measurements ofwoody detritus in forest ecosystems. Publication no. 20. USLTER Network Office. Seattle: University of Washington. 73 p

Hart SC. 1999. Nitrogen transformations in fallen tree boles andmineral soil of an old-growth forest. Ecology 80:1385–94.

Harvey AE. 1982. The importance of residual organic debris insite preparation and amelioration for reforestation. In: HarveyAE, Neuenschwander LF, editors. Proceedings—managementand productivity of western-montane forest soils. USDA ForestService general technical report INT-280.

Harvey AE, Neuenschwander LF, editors. 1991. Proceedings—management and productivity of western-montane forestsoils. USDA Forest Service general technical report INT-280.

Jurgensen MF, Harvey AE, Graham RT, Page-Dumroese DS,Tonn JR, Larsen MJ, Jain TB. 1997. Impacts of timber har-vesting on soil organic matter, nitrogen, productivity, andhealth of inland northwest forests. For Sci 43:234–51.

Kauffman JB, Martin RE. 1989. Fire behavior, fuel consumption,and forest-floor changes following prescribed understory firesin Sierra Nevada mixed conifer forests. Can J For Res 19:455–62.

Keenan RJ, Kimmins JP. 1993. The ecological effects of clearcut-ting. Environ Rev 1:121–44.

Landres PB, Morgan P, Swanson FJ. 1999. Overview of the useof natural variability concepts in managing ecological systems.Ecol Appl 9:1179–88.

Little RL, Peterson DL, Conquest LL. 1994. Regeneration ofsubalpine fir (Abies lasiocarpa) following fire: effects of climateand other factors. Can J For Res 24:934–44.

Maser C, Anderson RG, Cromack K. Jr, Williams JT, Martin RE.

1979. Dead and down woody material. In: Thomas JW, editor.Wildlife habitats in managed forests: the Blue Mountains ofOregon and Washington. USDA Forest Service agriculturalhandbook no. 553. p 78–85.

Mitchell RG, Preisler HK. 1998. Fall rate of lodgepole pine killedby the mountain pine beetle in central Oregon. WesternJ Appl For 13:23–6.

Pearson JA, Fahey TJ, Knight DH. 1984. Biomass and leaf area incontrasting lodgepole pine forests. Can J For Res 14:259–65.

Reinhardt ED, Brown JK, Fischer WC, Graham RT. 1991. Woodyfuel and duff consumption by prescribed fire in northernIdaho mixed conifer logging slash. USDA Forest Service re-search paper INT-443.22 p.

Spies TA, Franklin JF, Thomas TB. 1988. Coarse woody debris inDouglas-fir forests of western Oregon and Washington. Ecol-ogy 69:1689–702.

Swanson FJ, Jones JA, Wallin DO, Cissel JH. 1994. Naturalvariability implications for ecosystem management. In: JensenME, Bourgeron PS, editors. Eastside forest ecosystem healthassessment, volume 2. Ecosystem management: principles andapplications. US Forest Service general technical report PNW-GTR-318. Pacific Northwest Research Station, Portland, OR. p89–106.

Tinker DB. 1999. Coarse woody debris in Wyoming lodgepolepine forests [Dissertation]. Laramie (WY): University of Wyo-ming.

Turner MG, Romme WH, Gardner RH, Hargrove WW. 1997.Effects of fire size and pattern on early postfire succession insubalpine forests of Yellowstone National Park, Wyoming.Ecol Monog 67:411–33.

Vogt KA, Vogt DJ, Asbjornsen H, Dahlgren RA. 1995. Roots,nutrients and their relationship to spatial patterns. PlantSoil168–9:113–23.

Wei X, Kimmins JP, Peel K, Steen O. 1997. Mass and nutrientsin woody debris in harvested and wildfire-killed lodgepolepine forests in the central interior of British Columbia. Can JFor Res 27:148–55.


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