Revisiting the Deciduous Forests of Eastern North America

the dominant land cover in the eastern United States, extending from New England to Florida and westward to the prairies of the Great Plains (Greeley 1925). Native American communities had certainly influenced forest composition and structure, though the magnitude and extent of their influence are subject to continuing debate (Russell 1983). It was in the 18th and 19th centuries, however, that an unprecedented modification of the forests of the eastern United States took place. Forests were cleared extensively for agriculture, timber production, fuelwood, and urban expansion (Whitney 1994), such that forest cover reached its nadir in the early 20th century. According to US Census records, of the total acreage of land in farms in the eastern United States, less than 10 percent was reported as nonpastured woodland in 1930 (Geospatial and Statistical Data Center 2004). Now this area east of the 100th meridian is nearly 40 percent forest cover (USGS/USFS 2002). So although forest cover has increased dramatically in parts of the eastern United States over the last century, most forest land is successional, and quite distinct from old-growth forests. Biotic communities are shaped by the interaction of three templates: the physical environment (climate, soils), biotic interactions (competition, predation), and disturbances (fire, windthrow). Over the past 300 years, human activity in the eastern United States has altered all of these templates, resulting in forests that are not only much younger but in many cases dramatically different from the presettlement forest in terms of composition and structure. Numerous studies have detailed the biological consequences of anthropogenic change to the physical environment, including climatic warming (McNulty and Aber 2001), acid rain and other changes in atmospheric chemistry (Driscoll et al. 2001), and altered hydrologic regimes (Magilligan and Stamp 1997, Cowell and Dyer 2002). Biotic interactions have been altered by the introduction of a large and growing number of exotic species that compete with native species, as well as an expanding list of host-specific insects, fungi, and pathogens that may cause significant mortality to particular species within a forest (Rossman 2001), much as the chestnut blight (Cryphonectria parasitica) did in the early 20th century. Disturbance regimes have also been altered, decreasing the rate of some disturbances and introducing novel ones. Anthropogenic changes may include the exclusion of natural disturbances—fire, for example— resulting in a decrease in disturbance-adapted species such as pines (Cowell 1998, Radeloff et al. 1999). The introduction of novel disturbances may have even more wide-reaching and dramatic effects. Agricultural clearing, for instance, followed by abandonment and forest regeneration, tends to favor shade-intolerant species, such as the fast-growing tulip poplar (Liriodendron tulipifera) or red maple (Acer rubrum; Dyer