Ecological consequences of habitat fragmentation: Implications for landscape architecture and planning

Habitat loss and isolation associated with land conversion for human activities constitute the most serious threat to the Earth's biological diversity. The study of habitat fragmentation provides an important link between the concepts and principles of landscape ecology and the practice of landscape architecture and planning. Here I review ecological literature to examine current understanding of the ecological consequences of habitat fragmentation, and briefly suggest ways in which the results of these studies may guide decision-making by landscape architects and planners. Two theoretical developments in ecology have informed studies of habitat fragmentation and have provided testable hypotheses for empirical studies: island biogeography theory and metapopulation dynamics. Ecologists have examined the influences of habitat fragment size, shape, degree of isolation, context, and habitat quality or heterogeneity on plant and animal population persistence, community composition, and ecosystem processes. Disruption of continuous habitat usually results in an increase in the length of the boundary between fragments and their surrounding habitats. Newly created edges experience shifts in microclimatic characteristics, which may significantly alter the native plant and animal communities present. The size of a habitat fragment markedly influences the ecological processes occurring therein, largely due to the changes induced by these habitat edges. In general, species richness declines as fragment area decreases. Vegetated corridors may facilitate the movement of plants and animals among habitat fragments, however, more information is needed regarding the efficacy of corridors in reducing species loss from fragmented habitats. Fragments with highly irregular, convoluted boundaries will likely have greater exchange of nutrients, materials, and organisms with adjacent habitats than will those with less convoluted boundaries. Adjacent habitat types, land management regimes, and intensity of human activities influence boundary permeability and thus flow among habitat fragments. Large fragments are likely to be more heterogeneous than small fragments; they contain a greater variety of soil types, greater topographic variation, and a greater number of habitat types. An integrated view of the spatial characteristics of habitat fragments and their ecological consequences improves our ability to predict the outcomes of, and to design, particular patterns of land conversion.