Effects of routine disturbance on forest structure and composition along the edge of an urban forest on a college campus

Background/Question/Methods

With the increase in urban development, forest fragments are becoming more prevalent. Previous research has shown that the edge between a forest and a non-forest environment affects tree species richness and community structure up to five meters within the forest. Trees on the edge are generally younger, have a smaller DBH (diameter at breast height), and the tree community has a greater species richness than compared to the community within the forest. An urban, fragmented oak-hickory-maple forest is located on the Meredith College campus, Raleigh, NC. A 1-ha plot with 100 10m x 10m subplots was established in 2007 to initiate a long-term project supporting undergraduate research. The meadow is cut and maintained regularly up to the forest edge for utility access to adjacent electrical lines. We identified, tagged, and measured all of the trees with a DBH ≥ 5 cm in this permanent plot, and compared the DBH and species composition of the tree community along the 100 m gradient from the forest edge.

Results/Conclusions

For all parameters, we found that there was a significant difference between the subplots within 10 m of the edge and all other interior subplots. We found that the trees in the inner subplots had a larger average DBH than those located along the edge of the forest and the interior subplots had a higher total stand basal area. There was greater species richness and stem density along the edge of the forest compared to the interior subplots of the forest. As expected, we also found that there was a negative linear relationship between DBH and stem density for all subplots. Our results confirm trends found in previous studies that tree size is lower and species richness is higher along forest edges than the interior, and community structure parameters (stand density and basal area) also differ between forest edges and the interior. However, our findings suggest that community species composition is not necessarily impacted by continual, local disturbance along forest edges. We believe the maintenance of the meadow along the forest edge explains our observed differences in forest structure and species richness, but species composition may be determined by the disturbance of larger-scale ecological processes such as species distributions, seed dispersal, and microhabitat affiliations.