Stress Effects on Bird-Species Diversity within Mature Forest Ecosystems

Abstract

Two beech-maple forests, one virgin (control) and one selectively cut (experimental), were analyzed in detail for man-made stress effects upon tree-avian community structural relationships. Vegetation analyses revealed that Hueston Woods, a virgin beech-maple forest in southwestern Ohio, was stratified into two distinct canopy layers, whereas Lewis Woods, a previously thinned beech-maple forest in Ecentral Indiana, contained four distinct canopy strata. Although sugar maple (Acer saccharum) and American beech (Fagus grandifolia) were most abundant in both community types, they were truly dominant in terms of importance values in Hueston Woods. Lewis Woods had a more heterogeneous vegetational structure and greater absolute density, species diversity (H'), species richness (D) and species evenness (e) values than Hueston Woods. Lewis Woods resembled an earlier seral stage of ecological succession. This supports the hypothesis that species diversity is less in a climax community than in preclimax conditions. Avian analyses revealed significant differences (p < .05) for the resident evenness (apportionment) values between the two study areas. This difference was consistent through the 10-week (25 April-3 July 1973) observation period. Although Hueston Woods contained 38 resident species within a 15-acre (6.1 ha) study plot as compared to 32 species for Lewis Woods, evenness values were slightly greater for Lewis Woods. These findings support the concept of birds representing an equilibrium taxon in terms of the evenness component of species diversity. This study presents strong evidence that birds do tend to depict and to respond to the overall structure of a major plant community. It is suggested that resident bird populations be considered as indicator taxa when attempting to measure and evaluate the impact of man-made stress on total ecosystems.