Edges: The Good and the Bad
NY Birders Conservation Column
John Confer, Conservation Committee
Published in the January 2008 issue of NY Birders
Modern conservation has set the preservation of contiguous forests and prevention of forest fragmentation as a paradigm for habitat management. Yet, older wildlife management emphasized the value of edge for biodiversity and my research on habitat management for Golden-winged Warblers restored shrublands and created forest edge. These seeming conflicts can be reconciled if we consider some details.
Fragmentation of forests in regions with considerable agriculture leads to a major loss of wildlife in the remaining forest. Agricultural lands support high densities of predators, such as Blue Jays and crows, raccoons and feral cats, and of the Brown-headed Cowbird, the nest parasite. In addition to the loss of the forest itself, nesting success can decline to near zero as these predators and nest parasites venture several hundred feet into a forest from a forest-agriculture edge.
In extensively forested landscapes, removal of trees and creation of new edges do not attract feral cats or high numbers of jays, crows or cowbirds. Clear cutting is often followed by growth of viburnum and dogwood with berries that are used by black bear for fat deposition and successful hibernation while the growth of annual and perennial herbs provides seeds and insects that enhance the growth of young Wild Turkey.
I have directed the restoration of small patches of shrubland in the middle of extensive forests. In Sterling Forest State Park this has apparently increased the density of forest nesting species in the adjacent forest, increased the diversity of species by attracting grassland species that were absent, and has supported the return of nesting Golden-winged Warblers.
The different effects of a forest edge on forest
species depend on the surrounding landscape. In
urban and agricultural landscapes, forest edges
usually are a disaster for species remaining in the
forest. In forested landscapes, a timber harvest
that leaves some canopy trees or creates shrublands
will increase biodiversity by supporting the
declining guild of shrubland species and may
benefit many avian and non-avian species in the
remaining forest. More information about forest fragmentation
is available on the website of the Cornell
Lab of Ornithology.