FORTY YEARS OF CHANGE IN THE COMPOSITION OF THE FOREST AT ROBINSON WOODS PRESERVE, BERRIEN COUNTY, MICHIGAN

摘要

Robinson Woods Preserve is a 32.4 ha forest in southwestern Michigan that had been cleared and cropped and then abandoned sometime in the 1920s, at which time secondary succession was initiated. The objective of this study is to describe the current tree species composition and the succes-sional changes that led to it. In 2011 and 2012, the T-square method and the point-centered quarter method were used to determine the current structure and composition of the forest. Data from these methods were compared with similar data from two earlier studies of the same area conducted in 1972 and 1986. Between 1972 and 2011-2012, shade-intolerant trees of Sassafras albidum and Prunus serotina had decreased in importance by 22% and 82%, respectively, while shade-tolerant trees of Fagus grandifolia, Quercus rubra and Acer rubrum had increased by 26,790%, 352% and 21%. respectively. Between 1986 and 2011-2012, the density of most species had declined, except for trees of Fagus grandifolia, whose density had increased by 44%. In addition, trees of S. albidum had been reduced in importance to a subdominant role in the presence of A. rubrum and Q. rubra. Seedling and sapling densities by size class show that most of the canopy trees are reproducing themselves. However, no Ulmus americana and Fraxinus americana trees larger than 45 cm dbh were encountered, the former having been killed by Dutch elm disease and the latter by the emerald ash borer. Over the 90 years since abandonment, a hardwood forest has developed, one in which pioneer tree species have been replaced in part by shade-tolerant trees. Based on these results, it is expected that the future forest will likely become an American beech-sugar maple forest, especially in the absence of periodic fire.