Influence of wildfire and harvest on biomass, carbon pool, and decomposition of large woody debris in forested streams of southern interior British Columbia

Large woody debris (LWD) is an important component in the biogeochemistry cycle of carbon and nutrients in forested stream ecosystems. In-stream LWD volume, biomass and carbon pool were investigated in 19 forested streams in the south central interior of British Columbia. The stream channels were classified into four disturbance categories based upon condition of the adjacent riparian forest. The categories are: (1) riparian forest harvested approximately 10 years ago (HT10), (2) riparian forest harvested approximately 30 years ago (HT30), (3) riparian forest burned by a wildfire approximately 40 years ago (WF), and (4) undisturbed old-growth riparian forest (OF). Streams with riparian forests that were affected by wildfire or were recently harvested were observed to have significantly higher LWD volumes, biomass, and carbon pool as compared to streams flowing through old-growth riparian forests. LWD stocks averaged 376 m(-3) ha(-1) (volume), 112 Mg ha(-1) (biomass), 52 Mg C ha(-1) (carbon) in WF, 258 m(-3) ha(-1), 78 Mg ha(-1) and 36 Mg C ha(-1) in HT10, 180 m(-1) ha(-1), 52 Mg ha(-1) and 23 Mg C ha(-1) in HT30, and 114 m(-3) ha(-1), 37 Mg ha(-1) and 17 Mg C ha(-1) in OF Volume, biomass, and carbon stock were 2.3, 2.0, 2.1, and 1.3, 1.1 and 1.1 times higher in WF and HT10 than in OF, respectively, but LWD loading did not differ significantly between HT30 and OR Major differences were also observed in the state of decay of LWD between the four disturbance categories based upon three decomposition classes. Our study supports the conclusion that harvesting creates a short-term increase in LWD stocks. However, harvesting may greatly reduce LWD loadings over the long-term due to relatively rapid decomposition of LWD due to increased rate of decay, transport, and reduced recruitment from the adjacent riparian forest. In the study streams, the wood density of LWD ranged from 0.273 to 0.427 g cm(-3) depending upon the species and decomposition level. An average decay rate constant of 0.0095 year(-1) was calculated for the LWD based upon wood density. Based upon this decay rate, the time required to loss 50% (t(0.5)) and 95% (t(0.95)) of wood is 74 and 316 years, respectively. (c) 2004 Elsevier B.V. All rights reserved.