The effects of interspecific competition on the distribution of northern hardwood forest tree species on a landscape level.

Abstract

Across the landscape of the northern Lower Peninsula of Michigan many tree species coexist and have similar abundance patterns. In some cases a positive correlation might reflect similar resource requirements in an ecosystem that provides these resources. In other cases, tree species abundances negatively coexist on the landscape level. This negative co-occurrence may be caused by variation in resource availability throughout a habitat and each species having different resource needs, or it may be caused by interspecific competition due to shared limiting resources. Across the landscape of UMBS, we found a significant positive abundance correlation between hop hornbeam (Ostrya virginiana) and white ash (Fraxinus americana). Also, we found a significant negative correlation between sugar maple (Acer saccharum) and red maple (Acer rubrum) (p<0.05), and sugar maple and bigtooth aspen (P. grandidentata) (p<0.05). In order to test if competition is the most important driving force for the landscape patterns, we tested for abundance correlation on a local level, one-hectare plot. By bringing this study to the local level we were able to alleviate a large variance in abiotic factors which could influence tree distribution patterns within the study area. The test for competition was done by measuring the basal area of 30 target red maple, 30 target bigtooth aspen, and 30 target white ash trees and the surrounding species within 5 meters, as estimated using diameter at breast height (DBH). We found a significant positive correlation between red maple and sugar maple and red maple and beech (P<0.05), and no significant correlation between hop hornbeam and white ash. Because of these positive local level correlations, we suggest that competition is not the driving force for landscape level patterns among these trees and that abiotic factors might be the largest influence.