Many northeastern North American forests are undergoing a shift from Quercus-Carya domination to increasing amounts of Acer rubrum and other species. Although this shift in species composition and its cause, fire suppression since European colonization, are well understood the structure of these transitioning forests requires more study.
Newly developed metabolic theory does a good job of predicting many demographic characteristics of forest stands and thus provides a good tool to assess these transitioning forests. Here we examine two such demographic characteristics, stem diameter distribution and average distance to a nearest neighbor in the same size class for individuals, in an 18-ha transitioning Quercus-Carya forest plot in the ES George Reserve in Pinckney Michigan.
Results/Conclusions
This forest displays deviations from the patterns expected based on metabolic theory and from observations of other forests. This theory suggests a power law distribution of stem diameters. Here we find a systemic deviation with too many large-to-medium size stems (~30 cm to 60cm DBH), which are predominately Q. alba, Q. rubra, C. cordiformis, C. ovate and C. glabra individuals. When these are removed the remaining stems fit a power law with scaling exponent -2.4, in line with what is seen in other transitional forests. Additionally we find systematic deviation from the linear relationship predicted between size class and distance between nearest neighbors of individuals within that size class. Again the large Quercus and Carya are responsible for this deviation, causing the ~30cm to 60cm size classes to be closer to each other than expected by the metabolic theory. When these species are excluded the linear relationship is recovered. In effect we have a 'regular' forest with a number of large Quercus and Carya packed in at a much higher density than expected.