Five centuries of changing forest vegetation in the Northeastern United States

Abstract

Maps of physiognomic classes of vegetation in the northeastern United States before European human impact and for the late 20th century, based on pollen data, closely resemble each other, indicating a robust pattern in the face of the novel and extensive disturbances of the last 500 years. On the other hand, species abundances have changed considerably, with today's vegetation having less Fagus L. and Tsuga Carrière and more Betula L., Picea A. Dietr., and Abies Miller. Picea and Castanea Miller increased from 1700 to 1900, but have decreased in this century. The difference between the main physiognomic classes has remained strong, however, with continuously more Picea, Abies and Betula in the north and more Quercus L. and Carya Nutt. in the south, indicating the dominance of climate in regulating the relative abundances of these genera. The vegetational patterning within these broad classes has changed in some places and remained stable in others, suggesting differences in local factors that determine relative species abundances. The influence of slight altitudinal gradients, for example, may influence forest composition only after several generations of trees, while substrate differences may be apparent in the first forest that regenerates after agricultural abandonment or logging. Forests of today, therefore, reflect complex interactions of disturbance and environment, and may be in equilibrium with some but not all features of their current environments.