Effects of postsettlement human activities on forest composition in the north-eastern United States:: a comparative approach

Aim This study compares human impacts and forest ecosystem response across geographical regions. Such a comparison allows us to evaluate the relationship between regional changes in forest composition and regional patterns of human activity. Location Four study areas in the north-eastern USA were investigated, two of which were dominated by oak-pine forests at the time of European settlement (Central Massachusetts, MA; Pike County, PA), and two of which were dominated by beech and hemlock (South Berkshire, MA; Wayne County, PA). Methods Trees recorded in early land survey records were compiled and compared with data on modern forest composition obtained from recent forest inventories. To assess the similarity of the four regions with regard to species composition, Euclidean Distances (ED) were calculated between the colonial and modern forest composition for each of the four regions. Information about the history of human impacts in the four study regions was used to interpret the changes in forest composition. Results General changes in forest composition through the historical period include a decline in beech, hemlock and chestnut, and an increase in maple and birch. Changes in pine and oak were minor by comparison. Supraregional human impacts are generally linked with supraregional trends in species composition, whereas regional patterns of land use caused regional patterns of change in species composition. Main conclusions These results suggest that human activities do not necessarily lead to more similar species composition between regions, especially if these activities show clear spatial patterns at about the same resolution that species composition is evaluated. Comparing species-specific changes in forest composition with species-specific human activities on the same spatial scale is crucial in order to evaluate human impacts on ecosystems and to make more robust generalizations about the temporal dynamics of landscapes.