THE EARLY DEVELOPMENT OF FOREST FRAGMENTATION EFFECTS ON BIRDS

The early development of forest fragmentation effects on forest organi sms is poorly understood partly because most fragmentation studies hav e been done in agricultural or suburban landscapes, long after the ons et of fragmentation. We develop a temporal model of forest fragmentati on effects on densities of forest-breeding birds and provide data from an active industrial forest landscape to test the model. The model an d our empirical data indicate that densities of several forest-dwellin g bird species can increase within a forest stand soon after the onset of fragmentation as a result of displaced individuals packing into re maining habitat. Along with higher densities in the newly formed fragm ents; pairing success in one species, the Ovenbird (Seiurus aurocapill us), was lower in fragments that nonfragments, possible due to behavio ral dysfunction resulting from high densities. Thus, density was inver sely related to productivity. The duration and extent of increased den sities following onset of fragmentation depends on many factors, inclu ding the sensitivity of a species to edge and area effects, the durati on and rate of habitat loss and fragmentation, and the proximity of a forest stand to the disturbance. Incipient forest fragmentation may af fect populations differently from later stages of fragmentation when t he geometry of the landscape has reached a more stable configuration. Our model and data indicate, for reasons unrelated to traditional edge effects, that large tracts of forest can be important because they ar e relatively free from the variety of plant and animal population dyna mics that might take place near new edges, including the encroachment of individuals displaced by habitat loss.