When it comes to forest soil, wildfires pack...( For decades scientists and resource ...)

For decades, scientists and resource managers have known that wildfires affect forest soils, evidenced, in part, by the erosion that often occurs after a fire kills vegetation and disrupts soil structure. But, the lack of detailed knowledge of forest soils before they are burned by wildfire has hampered efforts to understand fire's effects on soil fertility and forest ecology.

A new study led by the Pacific Northwest (PNW) Research Station addresses this critical information gap and represents the first direct evidence of the toll wildfire can take on forest soil layers. It draws on data from the 2002 Biscuit Fire, which scorched some 500,000 acres in southwest Oregon, including half of a pre-existing study's experimental plots, which had been studied extensively before the fire. The result was a serendipitous and unprecedented opportunity to directly examine how wildfire changes soil by sampling soils before and after a wildfire. The study appears in the November issue of the Canadian Journal of Forest Research.

"Losing our experiment in the fire was hard, but the opportunity to better understand fire as a dominant ecosystem process has been very exciting," said Bernard Bormann, a research forest ecologist with PNW Research Station and the study's lead investigator. "This study, covering over 300 acres, provided nearly 400 soil sampling points as well as extensive tree and understory plots to use in our analysis."

Bormannalong with study co-author and Western Washington University professor Peter Homann and colleagues from the PNW Research Station and Oregon State Universityconducted chemical analyses on soil samples collected before and after the fire. They found that the combustion of the organic layer at the soil's surface, including woody debris, caused intense, 1,300 F-plus temperatures, which, in turn, displaced considerable amounts of carbon and nitrogen from the underlying mineral soil layer and left mostly as
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