Physiographical and historical effects on forest vegetation in central New England, USA

Aim Land-use history can be an important determinant of ecosystem characteristics, even in landscapes that outwardly appear natural . In New England, like much of the eastern United States, the natural reforestation of agricultural lands over the past 150 years has created a predominantly forested landscape. Understanding the physiographical and historical factors controlling forest structure and composition is a major challenge to ecologists, conservationists and land managers. Location We studied the forest structure and composition of Petersham, Massachusetts, which is located in the Central Upland physiographical province of New England. Like much of New England, Petersham was largely cleared for agriculture by the mid-1800s, but most of the agricultural fields were abandoned and naturally reforested in the late1800s and early 1900s. The modern landscape is > 90% forested by a mosaic of primary and secondary woodlands. Methods At seventy-four randomly selected 0.04-ha plots, we measured the abundances of all vascular plants in the overstory and understory and nine physiographical and historical variables. Results Species richness was primarily related to landform: species-rich communities occurred in poorly drained basins and species-poor communities occurred on welldrained glacial outwash. Distributions of the sixty-nine most common species were associated with (in order of importance) landform, past land use and elevation. Many species were restricted to specific physiographical conditions, but no species were restricted to specific past land uses. Nine plant associations identified by two-way indicator species analysis were associated with elevation, landform, soil texture and past land use. Ordination by canonical correspondence analysis indicated that the vegetation reflected two principal gradients: a physiographical gradient, defined by landform and soil texture, and a land-use gradient. Main conclusions These analyses suggest the following ranking of factors controlling forest structure and composition in this landscape at this time: landform > agricultural history > elevation > hurricane 1⁄4 fire 1⁄4 logging. Even in this physically heterogenous landscape, land-use history continues to play an important role in shaping forest vegetation 100–150 years after agricultural abandonment and reforestation.