Coarse Woody Debris Dynamics in Two Old-Growth Ecosystems Comparing a Deciduous Forest in China and a Conifer Forest in Oregon

Home , Coarse woody debris

([~~ Coarse Woody Debris Dynamics in Two Old-Growth Ecosystems Comparing a deciduous forest in China and a conifer forest in Oregon

Mark E. Hannon and Chen Hua

ead trees are associated with (McKee et al. 1987). many key functions in forest Coarse woody debris Most ecological research has oc- D ecosystems. BecauSethey may curred in mature second-growth for- persist for centuries (Mcfee and Stone has potential to store ests (Spies et al. 1988), where coarse 1966, Triska and Cromack 1980), woody debris is usually less impor- their influence is as long-lasting as that much carbon tant than in old-growth forests. Com- of living trees. During decomposition, parison with other sites indicates that logs and other forms of coarse woody the Andrews and Changbai represent debris (defined as wood pieces more the upper and lower limits of the than ten centimeters in diameter and of wood for fuel) significandy affects importance of coarse woody debris in more than one meter in length) reduce the amount of woody debris. Further- temperate forests (Chen Hua 1989, erosion and affect. soil development, more, woody debris is one of the Harmon et al. 1986). Our objective is store nutrients and water, provide a slowest components of the ecosystem to compare in these two ecosystems source of energy and nutrient Bow, to recover after disturbance (Spies et the amount of coarse woody debris; serve as seedbeds, and provide habitat al. 1988). Therefore, short intervals the processes that affect coarse woody for decomposers and heterotrophs betWeen timber harvests can reduce debris, such as tree mortality and (Franklin et al. 1981, Harmon et al. ecosystem carbon storage in coarse .decay rates; and the role of coarse 1986). In addition, coarse woody de- woody debris even when the living woody. debris in nutrient cycling. To bris has the potential to store a large portion of the ecosystem has recov- assess importance in the global car- amount of carbon in the forest ecosys- ered (Harmon et al. 1990). Con- bon budget, we use these two old- , tern. The role of coarse woody debris versely, allowing debris to accumu- growth ecosystems to estimate the in storing carbon is often overlooked, late woul4 result in more carbon upper and lower limits of coarse with only living plants (Whittaker and being stored in the ecosystem than woody debris mass for undisturbed Likens 1973, Woodwell et. al. 1978) has been predicted by current projec- temperate forests. or soil carbon (Post et. al. 1982, tions, which assume that a steady Schlesinger 1977) being considered. state is reached in less than 100 years Tree mortality Relatively little is known about the (Lugo and Brown 1986). formation and rate of decay of coarse In this .article, we compare the dy- We had expected that tree mortality woody debris or the factors control- namics of coarse woody debris in a rates for Changbai would be higher ling these processes, despite the rele- deciduous old-growth forest system, than for Andrews becausedeciduous vance of this information to the global Changbai Mountain Biosphere Re- species generally have shorter life- carbon cycle. serve in China, and a coniferous old- spans. However, the percentage of Forest management (e.g., removal growth for~t system, H. J. Andrews trees (greater than five cenn.netersin Experiinental Forest in Oregon (Table diameterat breast height)dyingannu- 1). The forest vegetation at Changbai allywas similarbetweenthe two sites: has been studied extensively since 0.3-O.7%/yr for Changbai (Chen Mark E. Harmon is an assistant professor 1979, when the Academia Sinica es- 1989) and 0.5-O.7%/yr for Andrews in the Department of Forest Science, Or- tablished the Changbai Mountain Re- (Franklin et al. 1987). In contrast, egon State University, Corvallis, OR 97331, and Chen Hua is a research assist- search Station of Forest Ecosystems. old-growth deciduous forests in the ant at the Institute of Applied Ecology, The Andrews reserve was established eastern United States have been re- Academia Sinica, Sherigyang, Peoples' Re- in 1948 by the US Forest Service and ported to havea highermortalityrate, public of China. «:>1991 American Insti- has been the site of extensive research 1.19-1.26%/yr (AbreUand Jackson tUteof BiologicalSciences. . on timber and watershed management 1977, Parker et al. 1985). Tropical

604 BioScience Vol. 41 No.9 forests also have higher rates of tree Table 1. General site features of Changbai Mountain Biosphere Reserve and H. J. Andrews mortality; Lieberman et al. (1985) Experimental ~orest. found rates of 1.02-2.03%/yr of trees Parameter CbaIigbai Andrews dying in primary moist tropical for- Location ests. Latitude (degrees) 41 N 44N Comparison of tree biomass lost Longitude (degrees) 127E 122W via mortality for the two sites con- Elevation (m) 500-1100 300-1550 firms the premise that deciduous forests produce lesscoarse woody debris Climate Mean annual temperature (0C) 8.5t than do coniferous forests (Harmon 2300t et ale 1986). At Chartgbai, annual Mean annual precipitation (mm) mortality removed from 0.15-0.66 Actual evapotranspiration (mm) 53i:)t Mg. ha-1 . yr:-1in fores~ dominated' by deciduous trees to 1.23 Mg. ha-1 Soil . yr-1 in forestsdominated by Korean Type Brown foresr Typic dystrochreptsS pine, compared with an average of Parent material Volcanic* Volcanics 2.38 Mg. ha-1 . yr-l for Andrews. In pH 5.3-6.5* 5.2-5.85 other areas of the PacificNorthwest, C:N 15-25* 14-235 even higher rates, ranging from 4.54 Trees to 7.0 Mg . ha-1 . yr-1, have betn Dominant species Am mono' Pseudotsuga metlVesi,1 observed (Grier and Logan 1977, Betula costata Thuja plicata Harcombe et ale 1990, Sollins 1982). Pinus koraiensis Tsuga heteTophylla As a first approximation, coarse Tilia amurensis woody debris production appears to Above-ground biomass (Mglha) 206-383'" 492-976" be positively correlated with living Age (years) >160 450 biomass (Harmon et al. 1986) and oem ZhenWen et aI. (1981). should, therefore, increasewith forest tMcKee and Bierlmaier (1987). age aDd/orproductivity. *Chen BoRong et aI. (1981). SBrown and Parsons (1973). It is tempting to assume that most 'wan Zhang et aI. (1980). trees are killed during major distur- 'Dymcss et aI. (1976), Waring and Franklin (1979). bances, but data from Changbai and "'Xu ZhengBan et aI. (1985). the Andrews indicate otherwise. Ty- uGrier and Logan (1977). phoons, such as the one that de- stroyed 10,000 ha of forest in 1986, Changbai, where logs decay rapidly, drews. In examining decomposition causeextensivedisturbance at Chang- rates were 0.027/yr for Tilia and of Abies and Tsuga in the western bai. Givena return interval of 50-100 0.016/yr for PinUs(Chen 1989; Fig- United States, Harmon et ale (1987) years, typhoon-related mortality is ure 1). At Andrews,the decayrate for found an inverserelationshipbetween roughly equal to the mass dying in an Tsug~ was 0.016-0.018/yr and, for decay rate and annual precipitari:<:>o, undistUrbedforest of equivalent size. Pseudotsuga, 0.005-O.010/yr (Gra- perhaps becausethe fungiresix)Dsible At Andrews, the most common cata- ham 1982, Means et ale1986, SoUins for decomposition are obligate aer- strophic disturbance is fire, with a et al. 1987). obes aridexcess.moisturereduces aer- return interval of 500 years. A single The exact cause of differenceSin ation (Griffin1977). fire can add as much as 1000 Mglha decayrate is difficultto assessbecause Fragmentation is another signifi- of coarse woody debris (Agee and rates can be affected by temperature, cant factor in the loss of coarse Huff 1987), although the average is moisture, substrate quality, and size woody debris;.yet its importance in probably closer to 500 Mglha (Spies (Harmon et al. 1986). Pseudotsuga the transfer of organic matter and et al. 1988). In undisturbed forests, probably decays more slowly than nutrients remains unexplored. Large normal mortality would have added other species because its heartwood pools of wood fragments reside in 1200-2200 Mglha in 500 years. contains fungi-toxic compounds coniferous forest floors (Mcfee and (Schefferand Cowling 1966). Pinus Stone 1966, Sollins et al. 1987). For Decay-rate constants and Tsuga logs of comparable size exattlple, Little and Ohmann (1988) had similar decay rates at the tWo found that decayed wood comprised We used the singleexponential model sites,although Pinuselsewhereis gen- 5-70% of the forest floor in Pseudo- (Olson 1963) to compare the least erally more resistant to decay (Schef- tsuga-Tsuga forests. . and most decay-resistant dominant fer arid Cowling 1966). Meari tem- Although wood fragments ate not species at each site: Tilia amurensis perattire at Changbai (3.9° C) is lost from the ecosystem,they are lost and Pinuskoraiensisat Changbai and considerably less than at AQdrews froin the coarse woody debris pool as Tsuga heterophylla and Pseudotsuga (8.9° C), which should slow mineral- traditionally measured, making the menziesii at the Andrews. As a first ization rates. The higher turnover of analysis of decomposition.of coarse step, we calculated the respiration coarse woody debris at Changbai woody debris complex. The decay and leaching losses from changes in may be due to Changbai receiving rates discussed above overestimate log density (Lambert et al. 1980). At one-third the precipitation of An- the lifespan of coarse woody debris,

October 1991 605 81 r40 Changbai, but projected cover and a mass are more than 12 times greater because the logs at Andrews are 6-1 . LITTER larger. Other old-growth coniferous . II cwo forests store considerably more coarse woody debris than is found at Andrews. In the cool, wet Olympic 4i - . . C20Z National Park, Pseudotsuga-Tsuga forestshave537 Mg/ha coarse wo04y 'C" C >-. :it debris (Agee and Huff 1987). In CIS 2 10 ffi Sequoiadendron and Sequoia forests .e: -tz in California, coarse woody debris ""DZ mass is more than 200 Mglha (Bing- ham and Sawyer 1988, Harmon et al. 0 o C-t 1987). In contrast, Pinus forests have 10 50 only 29-42 Mg/ha of coarse woody :;) rri debris (Fahey 1983, Harmon et al. Go b 1987). CJ) IQ At Changbai, the mass of coarse CJ) 8 40 ::r < I» woody debris is relatively low com- :E '<. . .:J. pared with that of other old-gtowth deciduous forests. In a Fagus-Betula 6 30 . forest in New England, coarse woody debris mass ranged from 30-49 Mg/ha (Gore and Patterson 1986, 4 20 Tritton 1980), and was more than 29 Mg/ha in a Fagus-Betula forest in Tennessee (Harmon et al. 1986). Warmer deciduous forests dominated 2 10 by Quercus or Acer generallycontain lesscoarse woody debris than.do Fa- gus-Betulaforests, although amounts 0 0 of 20-25 Mg/ha have commonlybeen MASS N P Ca K Mg observed (Harmon et al. 1986, Mul- Ier and Yan 1990, Onega and Eick- Figure1. Return of organic matter (Mg. ha-I . yr-I) and selectednutrients (Kg. ha-I meir 1990). . yr-I) to the forestfloor by litter and coarsewoody debris (CWD)at (a) Changbai and (b) Andrews. Coarse woody debris and nutrient cycles unlesswood fragments decomposeat 0.016/yr. This ratio was 0.03/yr in a Nutrient cycleswithin dead wood are a similar rate. Washingtonold-growth Pseudotsuga- stillpoorly understood, but a primary Assuming that the mass of coarse Tsuga forest (SoUins1982). Because role of woody debris may be to stabi- woody debris is in a steady state, the these total rates are approximately lize nutrients after major natural dis- input rate can be used to estimate a twice those calculated from density turbances. During periods of normal decayrate that includesfragmentation changes,it would appear that half the mortality, coarse woody debris adds (Lambert et al. 1980, Sollins 1982). losses from coarse woody debris in fewer nutrients to the forest floor The ratio of input to standing crop PacificNorthwest forestsis from frag- than does finelitter at both Changbai indicatesa total decompositionrate of mentation. Direct estimates of frag- and Andrews (Figure 1), primarily 0.039/yr for Tilia and 0.023/yr for mentation in Pseudotsugaand Tsuga due to its lower nutrient content. Pinus at Changbai. The differencebe- logs indicate as. much as 57% of During periods of catastrophic mor- tween rates calculated by density coarse woody debris mass is lost via tality, this lower nutrient content is changesand by input to standing crop fragmen~ation(Graham 1982). offset by the large mass of coarse ratios gives an estimate of the contri- woody debris input. bution of fragmentationto the overall Mass of coarse woody debris An important feature of woody de- mass loss (Lambert et al. 1980). This bris is that nutrients are released at calculation indicates that 30% of the As might be expected from the lower slower rateS than from fine litter mass of coarse woody debris from input and faster decay rates, there is (Chen 1989, Foster and Lang 1982, these speciesis lost via fragmentation. considerably less coarse woody debris Grier 1978, Lambert et al. 1980, 501- The ratio of input to standing crop at Changbai than at Andrews (Tabl~ lins et al. 1987). This slow release for all speciesat Andrews indicates a 2). There are three times the number allows nutrients to be retained within total decomposition rate of 0.011- of logs at Andrews compared with the ecosystem until tree production

606 BioScience Vol. 41 No.9

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Table 2. Mass and nutrient storage in coarse woody debris. from Changbai and Andrews give an Parameter Changbai. Andrewst idea of the range of these conversion Number of piecesper hectare 90-118 346 factors and the mass of coarse woody Projectedarea (%) 1.3-2.0 15.2-2S.4t debris in temperate forests (Figure3). Total mass (Mglha) 7.9-16.2 143*-2155 Although the amount of woody de- Abovegrounddetritus (%) 39-56 74*-815 bris in forests varies with forest age Dead:livetree mass 0.04-0.07 0.20-0.30 and type of management (i.e., slash- Nutrient storage (kglha) and-burn agriculture versus intensive Nitrogen 27-33 199*-298 forestry), it is impossible to take these Phosphorus 3.7-6.3 9.1*-13.6 factors into account without detailed Calcium 33-38 218*-326 land-use data. Our estimates of Potassium 2.7-3.9 30.7*-46 Sodium 1.4-2.8 4.9*-7.4 coarse woody debris mass are, therefore, for undisturbed forests and rep- .Chen (1989). resent a potential maximum. fHarmon et aI. (1986). *So1linset aI. (1987). Coarse woody debris forms from 5Grier and Logan (1977). 39% to 56% of total aboveground detritus (i.e., litter, fine wood, and recovers (Figure 2). Timber harvest that coarse woody debris may release coarse woody debris) in Changbai and salvage after disturbance reduces nutrients faster than is generally sup- and from 74% to 81 % at Andrews. this pool of stable nutrients, but it is posed (SoUins 1982). These percentages appear fairly typi- not clear how this affects the long- cal of what is known from the limited term productivity and stability of eco- Global carbon stores in coarse number of old-growth stands that systems. woody debris have been examined (Agee and Huff Few studies have examined pro- 1987, Grier 1978, Lang and Forman cesses, other than nitrogen fixation, Past efforts at estimating global detri- 1978, Tritton 1980). Based on the that are responsible for net changes in tal storage (including litter, coarse areal extent of temperate deciduous nutrient content of coarse woody de- woody debris, and soil organic mat- and coniferous forests in Whittaker bris (SoUinset aI. 1987). It is tempting ter) have assumed that only a small and Likens (1973) and the mean for- to assume that the processes are the fraction of carbon is stored in coarse est-floor mass presented by Vogt et al. same as in fine litter, but recent re- woody debris (Post et al. 1982, (1986), we estimate that temperate search being conducted at Andrews Schlesinger 1977). This assumption, forests contain 16 X 1015g carbon as indicates some differences. For exam- at least for old-growth forests, is a litter. From the range of proportions ple, during the early stages of log mistake. Given the lack of data on the of coarse woody. debris to total decomposition, fungal sporocarps mass of coarse woody debris in vari- aboveground detritus observed for transfer nutrients to the forest floor.1 ous biomes, global carbon storage in Changbai and Andrews, this gives an Thus; in fine litter, fungi immobilize woody debris cannot yet be directly estimate of 10-68 x 1015g carbon as nitrogen, but in coarse woody debris estimated. coarse woody debris. they actively transfer it to the soil. An alternative approach is to calcu- Assessing coarse woody debris as a Another important consideration late a conversion factor from some fraction of total detritus (i.e., litter, in understanding nutrient release better-understood ecosystem compo- coarse woody debris, and soil organic from coarse woody debris is that tree nent, such as above-ground detritus, matter) is difficult given the small boles are composed of several distinct total detritus, or tree biomass. Data number of old-growth forests with substrates. While wood may be 12 slowly releasing nutrients, other parts such as the inner bark (phloem) de- 10 100 z compose and release nutrients at rates 'C" :u >- 8 similar to those of leaf litter. Hence . 80mr- III m an overall pattern of release from .c a. 6 ------60tn dead trees may be a rapid loss of -- -- m '"",------c 10-20% of the nutrients followed by C/J ,, C/J 4 , 4O~ an extended slower rele;1Seof nutri- « , ~ ::E , =r ents. , BIOMASS INCREASE 0 2 , 20~ Finally, the role of fragmentation in m ,, N RELEASE "< 0 I O~ transferring nutrients to fine litter in " I the later stages of woody debris de- , -2 composition is not revealed by pat- o 10 20 30 40 50 60 70 80 90 100 terns of net accumulation. The omis- sion of transfers via fragmentation YEARS from previous calculations suggests Figure 2. Hypothetical releaseof nitrogen from coarse woody debris as compared with rates of biomass accumulation for a Pseudotsuga- Tsuga forest catastrophically dis- turbed by wind. Nitrogen content of coarse woody debris is based on Sollins et al. 1M. E. Harmon, unpublisheddata. (1987). The pattern of forest regrowth is based on Turner and Long (1975).

October 1991 607 ..~ ... . - --.-

total detrital inventories. Changbai, 1015 g carbon. If, however, the frac- (Grier 1978). This range of coarse with 5.8% of total detritus in coarse tion of total detritus is closer to that woody debris to live tree ratios also woody debris, appears to represent for Andrews, then the mass in coarse appears to be typical of tropical for- the low end of the scale. Quercus woody debris is 122 x 1015g carbon. ests. Ratios of 0.04 in a moist (Ed- forests are similar, with 9% of the This latter estimate seems extremely ward and Grubb 1977) and 0.25 in a total detritus in coarse woody debris high, indicating that coarse woody dry tropical forest (Whighamet al. in (Lang and Forman 1978). However, debris to total detrital ratios may be press) have been observed. other deciduous forests such as Fa- an unreliable conversion factor. If ra- Assuming that 80% of the live- gus-Betula of New England have tios for other Pacific Northwest for- plant biomass values for temperate 29% of the total detritus in coarse ests are used, we calculate a maximal forests presented by Whittaker and woody debris (Tritton 1980). More coarse woody debris storage of 28-58 Likens(1973)is above-groundwood, than halfof the total detritus(54%) x 1015g carbon (Grier 1978, Grier et 5-40 X 1015g carbon could be stored at Andrewsis in coarsewoody debris, al. 1981). as coarse woody debris. Becausethe a larger percentage than occurs in Given the lack of information on ratio of liveto dead wood appears to other conifer forests (Fahey 1983, total detrital storage in ecosystems, be more constant than the fraction of Grier 1978). Post et al. (1982) esti- the ratio of coarse woody debris to detritus that is coarse woody debris, mated the storage of litter and soil live tree mass may give a better esti- these estimatesare probably more re- organic matter for temperate forests mate of coarse woody debris mass. liable.Assuminga similarrange holds at 104 X 1015 g carbon. If coarse This ratio is 0.04-0.07 for Changbai for other forested ecosystems,the un- woody debris comprises5.8% of the and 0.2-0.3 for Andrews. In a Fagus- derestimateof global detritus is in the total detritus, as at Changbai, then Betula forest the ratio is 0.20 (Tritton range of from 25-180 X 1015g car- coarse woody debris mass is 6.4 x 1980) and 0.23 in Tsuga-Picea forests bon, or 2-10%. Our final estimate of carbon stores in coarse woody debris is based on the ratio of coarse woody debris production and living tree biomass. The steady-state mass, given these levels of production, can be calculated by dividinginput by the decay rate (Ol- son 1963). At Changbai, mortality . averaged 0.18% of living mass, whereas at Andrews it amounted to 0.55% of the livingmass. This range of living-tree turnover and the biomass valuesfrom Whittaker and Lik- ens (1973)indicatethat coarsewoody debris production could range from 0.25 to 0.76 x 10 g carbon/yr. If decay rates (includingfragmentation) are as high as at Changbai, then a steady-state value of 6-20 x 1015g carbon would result. On the other hand, if decay rates are as low as at Andrews, then a range of 25-76 x 1015 g carbon would be stored by coarse woody debris. Recentstudies of the global carbon cycleindicatethat a terrestrial ecosystem sink of 1.0-2.6 x 1015 g carbon/yr is required to account for observed atmospheric increases (Postet aI. 1990). As organic matter in the soil stores a large fraction of terrestrial carbon, a small increasein storage might account for this sink. How- ever, production of refractory humus substances in soils was estimated to sequester no more than 0.4 x 1015g carbon/yr, an amount consideredtoo low to account for the terrestrial sink (Schlesinger1990). A large Douglas fir snag with green western hemlock seedlings in Olympia National Park. Although, given the data available,

608 BioScience Vol. 41 No.9 140 est Service. This is paper 2620, Forest ...J Research Laboratory, Oregon State ga. 120 University, Corvallis. en a:~ 100 me:: References cited ~~ AbreU, D. B., and M. T. Jackson. 1977. A >-B 80 00 decade of change in an aId-growth beech- 0", maple forest in Indiana. Am. Midi. Nat. 98: 22-32. ~~-- 60 w Agee, J. K., and M. H. Huff. 1987. Fuel suc~ en 40 cession in a western hemlockIDouglas-fir for- ~ est. Can. J. For. Res. 17: 697-704. ° Bingham, B. B., and J. O. Sawyer Jr. 1988. c..> 20 Volume and mass of decaying logs in an upland old-growth redwood forest. Can. J. o For. Res. 18: 1649-1651. Brown, R. P., and R. B. Parsons. 1973. Soil of CWDILITTER CWD/SOM CWDILIVE INPUTIFAST INPUT/SLOW the reference stands-Oregon IBP. USI DECAY DECAY International Biological Program Coniferous Forest Biome Internal Report 128. University of Washington, Seattle. Figure 3. Range of estimates for maximal coarse woody debris carbon stores in Chen Hua. 1989. StUdies on tree mortality and log decomposition of main species in Korean temperate forests~In each case, the range of conversion factors for Changbai and pine deciduous mixed forest. Master's disser- Andrews was usedto derive estimates.Decay rates of 0.039/yr and 0.01lyr were used tation, InstitUte of Applied Ecology, Aca- to calculatethe input/fastdecayand input/slowdecay.The horizontal lineindicatessoil demia Sinica, Shengyang, Peoples' Republic organic matter (SOM)stores of temperate forests (Post et aI. 1982). of China. Cheng BaRong, Xu GuangShan, Ding Gui- Fang, and Zhang YuHua. 1981. The main we are unable to estimate the amount soil groups and their properties of the natU- cates that previous amounts of ral reserve on north slope of Changbai of carbon that might be sequestered detrital carbon may have been under- Mountain. Res. For. Ecosyst. 2: 196-204. by coarse woody debris, it is likely to estimated by 5-75%. From the data Chi ZhenWen, Zhang FengShen, and Li be a large quantity. Our analysis at hand, the contribution of coarse Xiao Yan. 1981. The primary study of water- shows that, by excluding coarse woody debris to global detrital stor- heat conditions of forest ecosystem on the northern slope of Changbai Mountain. Res. woody debris, previous studies have age cannot be determined with cer- For. Ecosyst. 2: 167-178. substantially and systematically un- tainty, but given the current pattern Dyrness, C. T., J. F. Franklin. and W. H. Moir. derestima,ted detrital carbon. Our es- of forest regrowth in temperate for- 1976. A preliminary classmcation of forest timates are for maximal storage; the ests, a large fraction of the currently communities in the central portion of the actual storage is lower because forest western Cascades in Oregon. Coniferous hypothesized terrestrial sink could be Forest Biome Bulletin 4, University of Wash- harvest and land clearing remove sub- associated with coarse woody debris ington, Seattle. stantial amounts of coarse woody de- accumulation. This large range of un- Edwards, P. J., and P. J. Grubb. 1977. StUdies bris. certainty will not be resolved until the of mineral cycling in a montane rain forest in When allowed to regrow, however, dynamics and stores of coarse woody New Guinea. J. Ecol. 65: 943-969. Fahey, T. J. 1983. Nutrient dynamics of above- forests begin to accumulate carbon in debris are considered in a wider range ground detritus in lodgepole pine (Pinus con- both living and dead wood. Succes- of biomes. torta ssp. latifolia) ecosystems, southeastern sional studies of coarse woody debris Wyoming. Ecol. Mongr. 53: 51-72. stores (Gore and Patterson 1986, Acknowledgments Foster, J. R., and G. E. Lang. 1982. Decompo- Spies et al. 1988, Tritton 1980) and sition of red spruce and balsam fir boles in the White Mountains of New Hampshire. input rates (Harcombe et al. 1990, We gratefully thank Xu ZhengBan, Can. J. For. Res. 12: 617-626. Tritton 1980) indicate that stores of Zhao Sidong, Dai HongCai, Wan Franldin,J. F., K. CromackJr., W. Denison, A. coarse woody debris reach a steady Zhang, Yan Fazhu, Zhan Sujuan, McKee, C. Maser, J. Sedell, F. Swanson, and state decades to centuries after living Zhan Dilan, Gao Zhiqing, SuJai, Yin G. Juday. 1981. Ecological characteristics of wood. Thus models of forest recovery Xiaodong, Geng Xiaoyuan, Shao old-growth Douglas-fir forests. USDA Forest Service General Technical Report PNW-118, that exclude dead wood may not ac- Guaofan, ChengBorong,and the staff Portland, OR. count for a substantial amount of of Changbai Mountain ResearchSta- Franklin, J. F., H. H. Shugart, and M. E. carbon that is being absorbed by re- tion of Forest Ecosystem, Academia Harmon. 1987. Tree death as an ecological coverin.g forests in the later stages of Sinica for their help. We also thank process.BioScience37: 550-556. succeSSIOn. Gore, J. A., and W. A. Patterson III. 1986. Philip Sollinsfor sharing information Mass of downed wood in northern hard- on nutrient stores at AndrewsExper- wood forests in New Hampshire: potential Conclusions imental Forest. The researchwas sup- effects in forest management. Can. J. For. ported by grants from the National Res. 16: 335-339. A comparison of coarse woody debris Science Foundation (BSR8516590, Graham, R. L 1982. Biomass dynamics of dead Douglas-firand westernhemlockboles dynamics and mass in two old- BSR-8514325, BSR-8918643), Man in mid-elevation forests of the Cascade growth temperate forests in the Pa- and Biosphere Program, and Pacific Range.Ph.D.dissertation,OregonStateUni- cific Northwest and in China indi- Northwest Research Station US For- versity,Corvallis.

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