The effects of fire on Sonoran Desert plant communities

The effects of fire on Sonoran Desert plant communities were determined by analyzing the influence of anthropogenic and climatic factors on fire regimes and measuring the responses of plants on a time-since-fire (tsf) gradient.; An upward trend in the number of fires has occurred during the past 45 years in the Sonoran Desert; however, there was not a significant (P < 0.05) trend in hectares burned. The positive trend in number of fires was consistent with an increase in the population of Maricopa County and an increase in traffic along major Sonoran Desert highways in the Tonto National Forest. The number of hectares burned did not change with increased winter, summer, spring, fall or total annual precipitation. However, the number of fires and hectares burned increased with increased precipitation from two and three consecutive winters' precipitation. Traffic and three consecutive winters' precipitation had the strongest coefficients in predicting the number of fires in the Sonoran Desert, yielding the model: y (number of fires) = −49.166 + .0066x₁ (traffic) + .148x₂ (three consecutive winters' precipitation). The best prediction model for hectares burned (y) was: y = −2335.606 + 9.137x (three consecutive winters' precipitation).; Overall plant density decreased as canopy cover increased on a tsf gradient. Native species most impacted by fire were saguaro (Carnegiea gigantea ) and foothill paloverde (Cercidium microphyllum). Foothill paloverde appeared to have recovered, with respect to density and canopy cover, in the years after the Siphon Fire (15–20 tsf). Repeated fires in the Bush Highway study plots have caused an increase in density for purple three-awn (Aristida purpurea) and desert senna ( Cassia armada) and a decrease in native species such as saguaro, foothill paloverde, white ratany (Krameria grayi), wolfberry (Lycium spp.), and creosote bush (Larrea tridentada). No difference in production of red brome (Bromus rubens) was found between burned and control plots during the spring of 1998.