Post Fire Forest Floor Fire Severity Index Relationships with Soil Mercury Pools.

Fire is a disturbance that has important implications on mercury dynamics.  Although we know fire leads to combustion of forest floor and soil organic matter and losses of mercury from soil, little research has assessed how fire severity influences post-fire mercury pools. If we can relate fire severity indices with changes in soil mercury pools, fire severity can be used as a surrogate to evaluate mercury emissions post fire.  We used forest floor fire severity indices both aggregated at the plot scale and individual measurements at the subplot scale where soils were sampled, to assess our ability to predict mercury emissions with the index. The Pagami Creek Fire occurred in the fall of 2011 in northern Minnesota.  We sampled forest floor and 0-10, and 10-20 cm mineral soil depth directly after fire and again after one growing season. During the first sampling we compare fire severity indices and soil mercury aggregated at the plot scale.  During the second sampling we assessed forest floor fire severity and measured soil mercury at the subplot scale.  Our initial results indicate that aggregating at the plot scale does not differentiate among forest floor fire severity categories.  Differences in mercury pools where only found between burned and unburned plots.  We anticipate that assessing forest floor fire severity at the subplot scale and relating it directly to the soil samples taken at that scale will explain more of variability in the relationship between forest floor fire severity and post fire mercury pools.