The effect of 50 years of landscape change on species richness and community composition

We analysed a 50-year dataset of avian species observations to determine ho w richness and community composition varied over a period of landscape-scal e environmental change. Our study area, northern lower Michigan, has experi enced substantial land-use and land-cover change over time. Like much of th e northern Midwest, it has shifted from a largely unpopulated, post-logging shrubland to a moderately populated closed-canopy forest. Such changes are generally expected to influence overall richness and community composition . We found that regional richness per year remained virtually unchanged ove r the study period. Year-to-year variation in species number was surprising ly low. Richness totals included vastly different species groups as the com position of the regional bird community changed substantially over time. Ch anges in the types of species present appear to reflect deterministic chang es in habitat. The number of grassland and open-habitat species decreased, for example, while species associated with older forests and urban habitats increased. Our results suggest that habitat changes at the landscape scale do not necessarily lead to changes in the number of species a region can s upport. Such changes, however, do appear to influence the types of species that will occupy a region, and can lead to substantial changes in community composition.