Effects of wildfire on structure and function of boreal forest ecosystems

The effect of wildfire on the structure and function of boreal forests is a key issue for understanding the boreal forest role in the climate system and global carbon (C) cycle. The objectives of this dissertation were to (1) quantify the effects of wildfire on C distribution and net primary production (NPP) for the Dahurian larch (Larix gmelinii Rupr.) forest ecosystems in northeastern China; (2) quantify sources and magnitude of error for biomass estimates from allometry models for boreal forests in central Canada; (3) measure and model CO₂ fluxes from coarse woody debris (R_CWD) and soil surface (R_S) in a black spruce ( Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada; and (4) examine changes in structure and C distribution in the fire chronsequence. I used field measurements, laboratory experiments, and statistical modeling to address these objectives during the period of 1998–2002.; Wildfire strongly affected C cycling in boreal forest ecosystems by direct C release from biomass combustion and indirect effects on thermal and hydrological regimes, ecosystem structure and function during post-fire succession. The direct C emission from the 1987 wildfire in northeastern China was estimated to comprise 0.6–1.3% of that year's global C emission from biomass burning. Wildfire removed vegetation, produced a large amount of coarse woody debris (CWD), increased soil temperature and resource availability, and hence increased microbial activity (R_CWD and R_S), accelerated vegetation reestablishment and C accumulation. The R_CWD varied from 6.3 to 22.7 kg Ct−1 CWD year−1 depending upon temperature, water content, and decay status of the black spruce CWD; R_S ranged from 146 to 413 g C m−2 year−1 across the black spruce fire chronosequences on contrasting soil drainages; the mean annual aboveground C accumulation rates varied from 10 to 75 g C m−2 year−1 . Species diversity was greatest in the younger stands, but by 71 years after wildfire black spruce comprised more than 83% of the overstory C content.; I also demonstrated that forest types, fire regime, biotic and abiotic interactions, stand age, and soil drainage must be considered when developing C budgets for boreal forest ecosystems.