Floristics and avian community structure: Implications for regional changes in eastern forest composition

Because many forest stands are increasingly dominated by maple (Acer spp.) in eastern North America, there will likely be a relative scarcity of mature oak (Quercus spp.) forests within the next several decades. In an effort to understand how avian communities may be affected by a regional change in forest composition from oak to maple dominance, we compared bird communities in both oak- and maple-dominated forest stands in three seasons (winter, spring, and fall). In 1998 and 1999, birds were surveyed and habitat characteristics were measured in six mature forest woodlots in central Pennsylvania. Total abundance of birds was greater within oak- than maple-dominated stands in all seasons, whereas species richness was greater in oak stands only in the spring. Resident species, long-distance migrants, woodpeckers, bark-gleaners, and 11 individual species were more abundant within oak than maple stands in at least one season. Differences in avian community structure between oak and maple stands were greatest in the fall when oaks produced hard mast and in the spring when insectivorous birds gleaned arthropods from tree substrates. This pattern was consistent with our expectations based on mast characteristics and tree physiognomy of maples and oaks as well as the diet and foraging behavior of birds. Our results suggest that a regional change from oak- to maple-dominated forests may strongly affect avian community structure and populations of some common bird species associated with eastern deciduous forests.