The effect of successional age on bird species composition in northern lower Michigan and testing the intermediate disturbance hypothesis for bird and tree diversity

Abstract

The purpose of this study was to determine the effects of forest succession on bird species composition and to test the intermediate disturbance hypothesis. We surveyed three forest plots – an early successional logging plot, a mid successional aspen plot, and a mature hardwood forest, in lower Northern Michigan where forests follow succession from aspen and beech to hardwood and pine. At each site we determined tree species, diameter at breast height, and distance from the point of our point-quarter center method along two transects. We also conducted bird surveys along the same transects, using the line transect method, and recorded all birds heard or seen. The red-eyed vireo and eastern wood-pewee were the most prevalent bird species at each of our three sites. Our comparisons of variables (tree density, H’, richness, and ground cover) between each forest plot were significant, indicating differences due to successional stages. Bird richness followed the predictions of the intermediate disturbance hypothesis, being highest in the mid successional plot. Our results for bird and tree diversity were entirely opposite the intermediate disturbance hypothesis, being lowest in the mid-successional plot. We found one significant positive correlation between bird species diversity and tree density. This result leads us to believe that the density of trees has the greatest effect on bird populations. We can conclude that each forest plot is at a different successional stage, and that bird richness is affected more by density of trees than the type, size, or understory composition.