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Habitat Fragmentation • Habitat fragmentation is the seperation of a landscape into various landuses (e.g, development, agriculture, etc.), resulting in numerous small, disjunct habitat patches left for use by wildlife. • As the name implies, it describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat) • Fragmentation eliminates habitat for those species requiring large unbroken blocks of habitat • This disconnection of natural habitat amplifies the negative effects of decreasing total habitat area Causes of Fragmentation • • • • • • • Urbanization Agriculture Transportation Deforestation Resource Extraction Flood control and hydroelectric dams Oil and gas pipelines Edge Effects • 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. • Air temperature, soil moisture, light intensity and levels of photosynthetically active radiation (PAR) all change at edges. Edge Effects • The effect of having more edge habitat and less interior space is that edge species increase and interior species decrease Other Impacts • Fragmentation eliminates habitat for those species requiring large unbroken blocks of habitat (e.g., bobcats and grizzly bears, deer). • Additionally, the small habitat patches resulting from fragmentation often do not provide the food and cover resources for many species that do attempt to use them • This can result in an increased risk of death by predation, if the animal has to venture beyond the cover of the patch to find new food resources, or starvation. • Leaving the safely on interior spaces forces many sepcies into open spaces where the are more easily preyed apon • Once habitat is fragmented there is an island effect whereby species extirpated due to predation or disease are unlikely to be naturally reintroduced to the area Degree of Fragmentation • Large patches are typically considered more important than smaller ones because they tend to include more viable populations of native plants and animals, including species dependent on interior habitat • However, small patches can also be important conservation targets because they may contain unique or rare habitat types or species or may act as stepping stones. Small patches may also provide sufficient habitat for species that don’t have large area requirements. Size Matters!! • Larger patches have more interior habitat, while smaller patches have less or no interior habitat. Size Matters!! • Populations are typically more stable and sustainable and less susceptible to local extinction in large patches than small patches. Size Matters!! • A large patch often contains greater habitat and species diversity than a small patch. More importantly, large patches are more likely to maintain native species in good quality habitat, whether or not greater diversity naturally occurs or not. Staying Connected • Species movement among habitat patches can be facilitated through the protection of discrete spatial features such as stepping stones and linkages or through surrounding matrix lands that allow movement among patches • Proximity and location of patches and the specific behavior and life histories of the target species are also factors in determining species movement among habitat patches Staying Connected • Interconnectedness is an important feature of networks, as it facilitates species movement among patches. • Small interconnected patches provide cover, resting, and foraging habitats for animals en route to larger habitat patches. • However, a network that is designed for connectivity but ignores other principles may have too much linear habitat and edge. Time to “Shape” up • Irregularly shaped parcels have more edge habitat and edge species and less interior habitat and interior species than round shaped parcels. • Also, irregularly shaped patches have greater interaction with the surrounding habitat matrix, increasing chances for negative interactions such as habitat degradation from adjacent land use or other disturbances. Time to “Shape” up • Linear shaped patches, including corridors and riparian buffers, contains little or no interior habitat, while blocks of habitat in a rounder shape has more interior habitat. © 2003 Defenders of Wildlife. All rights reserved. What is a “Buffer” • • • • • A buffer is essentially a ring of protective habitat that surrounds an natural area. It provides a gradual transitional zone from one ecosystem to another (ecotone) minimizing negative edge effects that are often associated with habitat fragmentation The creation of a buffer zone will reduce animal contact with unfriendly land use. Buffer zones are used to protect natural or restored areas from pollutants such as nutrients, pesticides and sediments, and from physical impacts such as encroachment. The desired width of a buffer zone is dependant upon topography, adjacent land use, and the home ranges of the animals present. Corridors • A Corridor is a natural or artificial connection between two pieces of fragmented habitat • corridors facilitate everyday home range movements, seasonal and breeding migrations, dispersal, and range shifts in response to environmental and climatic changes • Corridors connecting fragments of isolated habitat provide a safe passageway allowing for immigration and emigration of animals aiding gene flow and decreasing the chance of local extinction events