Fire Intensity Effects on the Understory in Ponderosa Pine Forests

Abstract

The effect of fire intensity on understory vegetation on serri 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 foilowhrg 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 kcai/m-s on high intensity sites and from 25 to 194 kcai/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. Prescribed burning can be an effective tool in managing seral stands of ponderosa pine (Pinusponderosa). Fire may be used to reduce fuel loading, thin thickets of saplings, create mineral seedbed for seed germination, remove shade tolerant trees from the understory, prune the lower branches from trees, and reduce needle litter on the soil surface (Biswell et al. 1973). Prescribed burning can also be an effective tool for understory vegetation management. Herbaceous yields are dependent on the percent tree overstory canopy closure and the amount of accumulated litter (Wright 1978). Different intensity fires may be used to manipulate the total tree canopy and litter depth. The effect fire intensity may have on understory development has not been previously studied. The objective of this study was to evaluate the effect of fire intensity on early vegetational development in ponderosa pine communities of the Douglas-fir/ ninebark (Pseudotsuga menriesiij Physocarpus