The Role of Charcoal in Nutrient Cycling Following Prescribed Fires.

Over a century of fire prevention and suppression in the western United States has led to overstocked and diseased forests with increased fuel loading and vertical continuity of fuels, thus increasing the risk of severe and stand-replacing wildfire. Mechanical thinning followed by pile burning is a commonly used technique to reduce fuel loads. Charcoal, a product of pile burning, can have major impacts on nutrient dynamics within forest soils. Specifically, charcoal-rich environments have been shown to enhance nitrogen cycling. In this study incubations of soil amended with varying amounts of charcoal (0.5, 1, 2.5, and 5% by weight) were conducted to assess the importance of charcoal in microbial activity and nitrogen cycling in forest soils in Little Valley, approximately 30 km south of Reno, Nevada. Carbon respiration and potential nitrification rate, proxies for microbial activity and size of the nitrifying microbial community respectively, were monitored over a two month period. In general, microbial respiration and potential nitrification were highest at 2.5% charcoal additions.  Also, microbial respiration rates decreased but potential nitrification rates increased over time across most treatments. Polyphenol sorption onto charcoal-amended soil was also analyzed and showed that extractable polyphenol concentrations decreased with increasing amounts of charcoal which may partly explain patterns in potential nitrification rates. Prescribed fire is a powerful tool at the disposal of forest managers and can be used to increase forest health and productivity. Managing prescribed fires for increased charcoal production can benefit soil microbial activity but may stimulate nitrogen losses through increased nitrate production.