While deforestation garners more attention from environmentalists, fragmentation of forest habitats is of significant concern to ecologists. As forest is fragmented into islands by logging, roads, agriculture, and other disturbances, edge effects alter the structure, microclimate and species composition of the forest patches, usually reducing the overall number of species. Forest specialists are most likely to suffer, losing out to “weedier” generalists and species that can tolerate forest “edge” conditions.
A new study, conducted in the Brazilian Amazon, takes a detailed look at the types of birds that are likely to persist, and even thrive, in forest fragments. Collecting field data on the behavior of forest-dependent bird species, Alexander Lees and Carlos Peres of the University of East Anglia found that species persistence in isolated fragments was strongly linked to their ability to cross gaps consisting of non-forest habitat. The most capable gap-crossers were medium to large-bodied bird species that feed on seeds, fruit, and insects.
A fragment of forest surrounded by cleared areas in the Amazon near Manaus. Image courtesy of Google Earth.
Gap-crossing is strongly influenced by the degree of isolation, a combination of gap width and the vegetation or “matrix” surrounding a forest fragment. The less isolated a patch, the more likely it is to be visited, and perhaps colonized, by bird species.
Armed with this information, Lees and Peres suggest that wide gaps between fragments can be made more hospitable to bird movement by maintaining, establishing, or restoring riparian forest buffers, “stepping-stone” structures like clusters of trees and “living fences”. Such efforts may also facilitate movement by other forest creatures, including mammals and insects.
“Reducing the number and width of forest dividing gaps; maintaining and/or creating forest corridors and increasing matrix permeability through the creation and maintenance of ‘stepping-stone’ structures will maximize the species retention in fragmented tropical forest landscapes,” they write.