Spatio-temporal patterns of large grassland fires in the Intermountain West, U.S.A.

Abstract

The spatial and temporal occurrence of large grassland fires (>2008 ha) in the Intermountain West was examined for the period 1980 through 1995.Results suggest that these fires are largely predictable through space and time.Of the 360 large fires, 339 occurred within eight regions as defined by clustering of fires within physiographic boundaries.These regions were characterized by their abundance of exotic annual grasses and flatter terrain that provided continuous fine-fuel conditions that promoted fire spread.Temporally, the likelihood of a large fire is correlated with summer moisture conditions (Z-index values) in the year preceding that of the fire that are either near-normal or wetter.Conversely, <20% of all the large fires occurred when the previous summer's Z values were below normal.This may be explained by enhanced fine-fuel build-up enabled by mesic conditions, causing increased biomass in the following summer and thus increasing the incidence of large fires.Moisture conditions in the summer in which the large fires occurred appeared to have less influence on the likelihood of those fires.