Response of Two Semiarid Grasslands to a Second Fire Application

Abstract

Prescribed fire was used in two semiarid grasslands to reduce shrub cover, promote grass production, and reduce erosional loss that represents a potential non-point-source of sediment to degrade water quality. This study measured transported soil sediment, dynamics in soil surface microtopography, cover of the woody shrub, grass, and bare ground cover classes, and soil fertility measured by nitrogen-mineralization potentials for the respective cover classes over a 9-year period during which 2 fires occurred. In general, the effects of two drought periods were equal to or greater than the effects of fire on the measured parameters. Following the second fire at the grama grass-dominated site, the number of live junipers was significantly lowered (P < 0.001). Fire consumed grass and shrub cover, which created the potential for greater transport of sediment and loss in soil surface elevation. Soil fertility under shrubs was significantly higher than soil fertility under grasses in both grassland sites before and after the first fire; however, that highly significant pattern was not present after the second fire for about 2 years at both sites. This suggests that the reestablishment of a natural fire frequency would likely dampen the well-documented pattern of greater soil fertility under shrub islands relative to grass islands. Repeat use of prescribed fire may keep shrub cover in check and promote fundamental changes in soil processes within semiarid grasslands, but its value must be weighed against the increased potential for erosion following fire.