Biscuit Fire, 2002

The 2002 Biscuit Fire in southwest Oregon burned 200,000 hectares, including some soil research plots. After the fire, Forest Service scientists analyzed the soil layers in the plots, and documented an astounding loss of soil carbon and nitrogen, not only from the surface layer of organic matter, but in the mineral soil layers, where a majority of the losses occurred. An inch of soil, about 127 tons per hectare, disappeared, perhaps into the smoke plume, leaving a crust of rocks behind.

The loss of topsoil, carbon, and nitrogen from soil can negatively affect a range of processes, including nutrient retention and water infiltration. In the absence of nitrogen-fixing plants, such losses of nitrogen would require at least a century to be reversed, according to the researchers.

Wildfire may contribute to climate change in the short term, by releasing carbon and nitrous oxide as greenhouse gases and, in the long term, by reducing soil productivity through losses of organic matter and nutrients. With less productive soils, a forest will not grow as quickly nor reabsorb as much carbon as before a burn.

Can. J. For. Res. 38(11): 2771-2783 (2008)