Fire Impact on Groundlayer Flora in a Sand Forest 1990-1994

Abstract

-Groundlayer response to prescribed fire was monitored in a central Illinois sand forest between 1990 and 1994. The first of three annual fires resulted in a significant increase in richness and cover of herbaceous species, and a minor decrease in woody cover. Successive fires maintained or slightly increased herb richness and cover, but did not change woody cover. Before burning, the forest understory was dominated by dense shrubs (7489% cover) over a sparse herb layer (4-18% cover). After the first fire, herb cover increased over fourfold to 48-57%, and to 65-66% after the second fire. Fire nonsignificantly reduced woody cover by some 20%, primarily due to a reduction in Parthenocissus quinquefolia (Virginia creeper), but did not affect frequency of woody vegetation. Species richness increased over 50% after the first fire, from 6.2-7.0/M2 to 9.8-10.8/M2, due to the increased frequency of herbaceous, and especially annual, species. Most of the postfire increase in herbaceous cover was due to Eupatorium rugosum (white snakeroot), which increased from 3X higher than preburn levels. The alien biennial Alliaria petiolata was maintained in a reduced condition by repeated fires, but in the absence of fire doubled in cover every 2 yr, from 4.6% in 1990 to 8.6% in 1992 to 17.0% in 1994.