Ecosystems (2000) 3: 472–483 DOI: 10.1007/s100210000041 ECOSYSTEMS © 2000 Springer-Verlag Coarse Woody Debris following Fire and Logging in Wyoming Lodgepole Pine Forests Daniel B. Tinker* and Dennis H. Knight Department of Botany, University of Wyoming, Laramie, Wyoming 82071, USA ABSTRACT The accumulation and decomposition of coarse ing a single clear-cut. However, the total mass of woody debris (CWD) are processes that affect hab- downed CWD plus the mass of snags that will be- itat, soil structure and organic matter inputs, and come CWD was nearly twice as high in burned energy and nutrient flows in forest ecosystems. Nat- stands than in clear-cuts. In YNP, approximately ural disturbances such as fires typically produce 8% of the downed CWD was consumed by fire and large quantities of CWD as trees fall and break, an additional 8% was converted to charcoal, for an whereas human disturbances such as timber har- estimated loss of about 16%. In contrast, approxi- vesting remove much of the CWD. Our objective mately four times more wood (70%) was removed was to compare the amount of CWD removed and by clear-cutting. Considering all CWD more than left behind after clear-cutting to the amount con- 7.5 cm in diameter that was either still present in sumed and left behind after natural fires in Rocky the stand or removed by harvesting, slash treat- Mountain lodgepole pine. The masses of fallen logs, ment, or burning, clear-cut stands lost an average of dead-standing trees, stumps, and root crowns more 80 Mg haϪ1 whereas stands that burned gained an than 7.5 cm in diameter were estimated in clear-cut average of 95 Mg haϪ1. Some CWD remains as slash and intact lodgepole pine forests in Wyoming and and stumps left behind after harvesting, but stands compared to estimates made in burned and un- subjected to repeated harvesting will have forest burned stands in Yellowstone National Park (YNP), floor and surface soil characteristics that are beyond where no timber harvesting has occurred. Estimates the historic range of variability of naturally devel- of downed CWD consumed or converted to char- oping stands. coal during an intense crown fire were also made in YNP. No significant differences in biomass of Key words: coarse woody debris; lodgepole pine; downed CWD more than 7.5 cm in diameter were Pinus contorta; timber harvesting; fire; Yellowstone detected between burned stands and those follow- National Park; Wyoming; clear-cutting. INTRODUCTION aquatic environments (Harvey 1982; Harmon and others 1986; Franklin and others 1987; Bull and Coarse woody debris (CWD) which is present as others 1997). Microbes and fungi, as well as logs and snags in most western coniferous forests, many insects and other invertebrates, facilitate plays an important ecological role within these decomposition and derive energy and nutrients ecosystems. For example, it provides a habitat for from rotting logs (Frankland and others 1982). many types of organisms in both terrestrial and Numerous species of vascular plants, including some tree seedlings, establish on CWD, and tree Received 16 November 1999; Accepted 31 May 2000. roots commonly grow into decomposing logs on *Current address for corresponding author: Department of Geosciences and Natural Resources Management, 207-A Stillwell, Western Carolina Uni- the forest floor (Grier and others 1981; Harvey versity, Cullowhee, North Carolina 28723, USA; e-mail: [email protected]. and Neuenschwander 1991; Little and others 472 Coarse Woody Debris in Lodgepole Pine Forests 473 1994; Vogt and others 1995; Jurgensen and oth- amount of ‘inherited‘ CWD is present on the forest ers 1997). floor before the initial harvest. This CWD is a legacy Snags represent a critical habitat for many species of the trees that were killed during the last stand- of cavity-nesting birds (Davis and others 1983; Har- replacing fire (Maser and others 1979; Wei and mon and others 1986). Amphibians, reptiles, and others 1997) and trees from the present stand that mammals rely on many forms of CWD as habitat for have died and fallen as a result of natural mortality cover, feeding, and reproduction (Harmon and oth- (Gore and Patterson 1986; Franklin and others ers 1986). CWD is an important source of organic 1987). This inherited CWD, and therefore total matter inputs to forest soils (Edmonds 1991), and CWD, would likely decrease with continued de- nitrogen, much of which will become available to composition and repeated harvesting. various organisms, can accumulate in the decom- The few recommendations that exist for the posing CWD of western coniferous forests (Harvey amount of CWD that should be left on a site fol- 1982; Fahey and Knight 1986; Hart 1999). In lowing timber harvesting vary widely, from less aquatic systems, CWD is recognized for its effect on than 10 Mg haϪ1 in drier Rocky Mountain sites the geomorphic structure within streams and lakes, containing grand fir (Abies grandis [Dougl. ex D. as well as serving as a habitat for fish and many Don] Lindl.) or ponderosa pine (Pinus ponderosa aquatic invertebrates (Harmon and others 1986). [Dougl. ex Laws.]) (Graham and others 1994) to The amount of CWD in a forest depends on pro- 125 Mg haϪ1 for mixed conifer forests of the north- cesses that affect its accumulation from tree mor- ern Rockies (Reinhardt and others 1991). The de- tality and breakage, as well as processes that affect sired amount of CWD left following harvesting de- its loss, such as decomposition, burning, and har- pends on habitat type, method of regeneration, and vesting. The presence of CWD on a harvested site preharvest levels of soil organic matter and CWD surely affects ecological processes associated with (Brown and See 1981; Jurgensen and others 1997). nutrient cycling. In Canadian lodgepole pine for- Given the increasing interest in the use of harvest- ests, Wei and others (1997) found that if posthar- ing to mimic natural disturbances (Hammond 1991; vest CWD is left in place, nutrient removal by har- Keenan and Kimmins 1993), the differences in vesting was within the range of nutrient removal by CWD and potential CWD biomass in burned and wildfires. In contrast, the complete removal of harvested stands should be better understood. CWD from a clear-cut area could result in signifi- Quantified CWD amounts following fire and log- cant nutrient losses and a potential reduction in ging are the net result of how much CWD is pro- long-term site productivity. In a study comparing duced and eliminated by each process. Estimating postharvest slash treatments in clear-cut Wyoming the amount of CWD removed and created by clear- lodgepole pine forests, Benson (1982) reported that cutting is relatively straightforward (for example, burning slash removed approximately 87% of the Brown 1974). On the other hand, comparable esti- residue present following clear-cutting. For this mates are more problematic in stands burned by study, we compared the proportion of CWD re- intense wildfires because they require an estimate moved by clear-cutting to the proportion consumed of the amount of downed CWD that is completely by natural fires in Rocky Mountain forests domi- consumed and the amount that is converted to nated by lodgepole pine (Pinus contorta ssp. latifolia charcoal. Fahnestock and Agee (1983) concluded [Engelm.ex Wats.] Critchfield). In addition to pro- that there is no reliable method for verifying the viding a comparison that is relevant to ecosystem quantity of woody fuels consumed by wildfire. In management, our method of estimating the fact, most studies on wood consumption have been amount of wood consumed by an intense wildfire conducted in prescribed burns or under laboratory may be applicable to other forest types. Natural conditions (Kauffman and Martin 1989; Reinhardt forest disturbances typically kill a large number of and others 1991; Albini and Reinhardt 1995; Call trees, which then augment the amount of CWD and Albini 1997) that exhibit different thermal dy- when the trees fall to the ground (Spies and others namics and behavior than natural fires. Previous 1988). Most of the live trees killed by intense, estimates of large woody fuels that are burned vary stand-replacing fires fall to the forest floor within a widely, ranging from 4% to 100% of prefire few decades (Mitchell and Preisler 1998). Con- amounts (Brown and others 1985, 1991; Kauffman versely, human disturbances, such as timber har- and Martin 1989; Reinhardt and others 1991). One vesting, and some forms of postharvest slash treat- of the primary objectives of our research was to ment, such as broadcast burning or pile-and-burn, develop a method that would produce reasonable remove much of the wood that would have become estimates of the amount of CWD consumed during CWD (Jurgensen and others 1997). Notably, a large natural fires. 474 D. B. Tinker and D. H. Knight Increasingly, researchers and managers are ex- others 1997). Crown fires are those that consumed ploring the idea of using the historic range of vari- the canopy foliage and most small branches and ability as a reference to guide the management of twigs, as well as most of the forest floor litter. In- human-influenced ecological systems (Swanson tense surface fires are those that did not actually and others 1994; Cissel and others 1999; Landres burn in the canopy but are nonetheless hot enough and others 1999). Because of the limited anthropo- to turn the tree foliage to a reddish-brown color. genic influence in Yellowstone National Park, one Unburned and uncut stands of similar age, as they of the primary areas for this study, we had an existed just before the fires, were located as close to opportunity to examine the variability in CWD, each burned stand as possible. In addition, a single which may be used as a reference system for lodge- stand that burned in 1996 near Pelican Creek in pole pine forest management.