Fire Intensity Effects on the Understory in Ponderosa Pine Forests

Abstract

The effect of fire intensity on understory vegetation on seral stands of ponderosa pine are presented. Vegetational recovery for 2 burn intensities and unburned sites were compared. The results suggest a change in the understory dominance structure following underburning is related to the amount of duff consumed by the fire and independent of fire line intensity and flame length. A significantly greater proportion of duff was removed on high fire intensity sites (80%) than on low intensity sites (40%). However, the variation in fire line intensity was great, with some overlap. Fire line intensity ranged from 30 to 3,034 kcal/m-s on high intensity sites and from 25 to 194 kcal/m-s on low intensity sites. Flame length ranged from 0.1 to 1.7 m on both high and low intensity sites. Graminoid canopy coverage was lowest on high intensity sites. The reduction was apparently the result of prolonged smoldering of the duff layer. There was no significant difference in coverage among treatments for shrubs or forbs. A significant change in frequency among treatments was noted for 11 of 54 species sampled.