When an edge is created to any natural ecosystem, and the area outside the boundary is a disturbed or unnatural system, the natural ecosystem is seriously affected for some distance in from the edge. In the case of a forest where the adjacent land has been cut, creating an openland/forest boundary, sunlight and wind penetrate to a much greater extent, drying out the interior of the forest close to the edge and encouraging rampant growth of opportunistic species at the edge.
The amount of forest edge of this sort is some orders of magnitude greater now in the United States than when the Europeans first began settling North America. Some native species have opportunistically benefitted from this fact, especially the Brown-headed Cowbird, which is a nest parasite that lays its eggs in the nests of songbirds nesting in forest near the forest boundary. Thus, the more edge in relation to the forest interior, the more cowbirds and the fewer songbirds as a result.
In the case of developed lands juxtaposed to wild lands, problems with invasive exotics often result. Species such as Japanese honeysuckle and multiflora rose have done terrible damage to natural ecosystems.