The effect of a prescribed burn in southwestern ponderosa pine on organic matter and nutrients in woody debris and forest floor.

After 100 years of fire exclusion, controlled burning in the fall was used as a first step in the reintroduction of periodic burning in a southwestern Pinus ponderosa ecosystem. Organic matter storage in woody debris was decreased 63% from 2325 g/m² to 869 g/m², with a disproportionate (99%) decline in the large, rotten wood. Nutrient storage in the woody debris decreased by 80% for N, 62% for P, 70% for Ca, 71% for Mg, and 74% for K. Forest floor storages were less drastically affected, with organic matter content declining 37% from 3170 g/m² to 1990 g/m² immediately after burning. Nutrient content of the forest floor was not significantly affected by burning due, in part, to the transfer of nutrients from woody debris to the forest floor. By 7 months after burning the forest floor had declined by an additional 440 g/m² of organic matter, most probably from microbial mineralization. Also during this period forest floor storages for all nutrients declined significantly, except K which was unchanged. -from Authors