Responses of the Herb Layer to the Gap Dynamics of a Mature Beech-Maple Forest

Abstract

Responses to gap formation and canopy redevelopment are inferred from comparison of the herb layers of young (1-2 year), mid (5-7) and old (12-15) gaps and areas of intact canopy in Hueston Woods, a mature beech-maple forest in southwestern Ohio. Gap formation did not alter spring environmental conditions, but produced increases in solar radiation and soil moisture in summer after canopy closure. These environmental factors decreased as tree cover increased with gap age. Herb species richness was largely unaffected by gap dynamics; however, total herb cover increased with gap formation and decreased with canopy redevelopment. High herb cover resulted primarily from increases in Impatiens pallida and Pilea pumila in the young gaps and Osmorhiza claytoni in mid-aged gaps. In general, herb species that increased were spring/summer or summer species, i.e., species in leaf after canopy closure when there were environmental differences among the gap classes and the closed-canopy area. Annuals exhibited the greatest increases in young gaps and perennials in mid-aged gaps. Spring species, i.e., those in leaf only as late as canopy closure, generally were either unaffected by gaps or decreased. We hypothesize that species that increase may be important in maintaining soil nutrients in gaps and that gaps may be important in maintaining the potential of these species to increase after disturbance.