Effects of Roads on Habitat

Roads fragment habitat and create habitat edges, favoring species that use edges. Edge-dwelling species generally are not threatened, however, because the human-dominated environment has provided ample habitat for them. Road building introduces new edge habitat in the forest. The continuity of the road system also creates a corridor by which edge-dwelling species of birds and animals can penetrate the previously closed environment of continuous forest cover. Species diversity can increase, and increased habitat for edge-dwelling species can be created.

Roads and their adjacent environment qualify as a distinct habitat and have various species, population, and landscape-scale effects (Baker and Knight 2000, Dawson 1991, van der Zande and others 1980). Some research has attempted to describe habitat modifications caused by roads, but most of this work is species and site specific (Lyon 1983). Surveys of songbirds in two National Forests of northern Minnesota found 24 species of birds more abundant along roads than away from them (Hanowski and Niemi 1995). Close to half these species were associated with edges, including birds like crows (Corvus brachyrhynchos) and blue jays (Cyanocitta cristata) that use roads as corridors to find food. Turkey hens (Megapodiidae) in North Carolina nested near closed and gated logging roads and used them extensively in all stages of brood development (Davis 1992). One study showed that habitat in the road-side right-of-way supports a greater diversity of small mammals than do adjacent habitats (Adams and Geis 1983), but this finding may not apply to forest roads with only narrow cuts and fills on either side.

The similarity between forest roads and transmission-line rights-of-way may be important in assessing the contribution of roads to habitat. Studies have shown that wide transmission-line corridors support grassland bird communities of species not found in the forest, and narrow corridors produce the least change from forest bird communities (Anderson and others 1977). The same study notes that increasing edge diversity of birds, for instance, may negatively affect abundance of interior species (see Roads and Biological Invasions).

See also:  Roads and Fragmentation