Wildfire Impacts On Wood Decomposition in Two Western Forests.

Organic matter (OM) decomposition is an important factor in assessing the impact of land management on soil carbon (C) cycling and C sequestration (pools). Due to past fire exclusion practices and recent drought conditions in western North America, the number of large, high intensity fires has increased in the last decade.  Consequently, there has been much interest on the effects such fires have on soil organic matter pools and the decomposition of new and residual OM after the fires. While most decomposition studies after fire have concentrated on surface leaf litter, much less is known on mineral soil.  As part of a comprehensive study on the impact of wild and prescribed fire on soil physical, chemical and biological properties in western North American forests, we used “standard” wood stakes as an “index” of fire effect on organic matter decomposition across a range of forest types and mineral soil conditions.  Our study sites were located on the Gallatin and Bitterroot National Forests in MT.  Each forest has unique soil and climatic characteristics.  As expected, there are differences in wood decomposition between the burned and unburned stands.  We evaluate both pine (Pinus taeda) and aspen (Populus tremuloides) decomposition in the mineral soil and on the soil surface.  For the pine stakes in the mineral soil we could find no statistically significant differences in belowground decomposition among the two forests.  We will discuss both aspen and pine decomposition rates.  Our data will help elucidate the changes large-scale wildfires have on soil organic matter, decomposition, and the potential for forest sites to recover.