Natural disturbances strongly influence the species composition and diversity of old-growth forests through the creation of canopy openings and the addition of dead woody material. These structural features are less frequent in second-growth forests. A large-scale field experiment was established in the Flambeau River State Forest, northern WI, to test if artificial disturbances created in second-growth forests would have a similar effect relative to what is expected in old growth. The creation of canopy openings nearly 400 m2 in size, could promote the increased presence of birds that prefer low lying vegetation, warmer and drier environments, and/or greater open areas for flying. Our objective in this project was to compare bird species diversity within created canopy openings (n=5) and untreated, relatively closed-canopy conditions (n=5). We conducted bird point counts for 5 minutes within each location. This process was carried out over three separate days, within one week, at varying times during the dawn chorus. We analyzed differences in presence/absence, species richness, and diversity between the two canopy conditions using Simpson’s index and a 2-sample t-test on mean counts per species.
Results/Conclusions
The findings of this study indicate no apparent difference in the avian composition patterns of gap and control plots. We observed no statistically significant difference in the mean counts of Red-eyed Vireo, Hermit Thrush, and the Eastern Wood-Pewee (all p values > .05), some frequently observed species, all of which have a preference for hardwood forest clearings and shrubbery. However, these bird species were seen in fairly similar amounts in both conditions. (Simpsons Index: Gap= 4.412 Control= 4.477). Further analysis will analyze the effect of sapling density and Canopy openness on the lack of variation between these conditions.
Based on our limited sampling, we observed that while the established conditions created a change in forest structure, they were not to the degree needed to stimulate an avian response in these habitat-specific species.