Loss and fragmentation of natural areas and its effect on connectivity

Assessing effects of land use on landscape connectivity: loss and fragmentation of western U.S. forests

 Theobald, David M., Kevin R. Crooks, and John B. Norman

 Ecological Applications, 21:2445–2458.

The accent of this paper is on US, but what is described is of relevance worldwide. The methodology described can be readily modified to examine connectivity for other habitats/ecological systems and for other geographic areas

Loss and fragmentation of natural areas is a big concern for conservation scientists and land managers worldwide. Deleterious effects of land-use change are adversely affecting connectivity and conservation of biodiversity.

The authors of this paper say there is an urgent need to develop practical approaches to identify where important lands are for landscape connectivity (i.e., linkages), where land use constrains connectivity, and which linkages are most important to maintain network-wide connectivity extents. Their effort was to develop an approach that provides comprehensive, quantitative estimates of the effects of land-use change on landscape connectivity and illustrate its use on a broad, regional expanse of the western United States.

The researchers quantified loss of habitat and landscape connectivity for western-forested systems due to land uses associated with residential development, roads, and highway traffic. They examined how these land-use changes likely increase the resistance to movement of forest species in non-forested land cover types and reduce the connectivity among forested habitat patches. They applied a graph-theoretic approach that incorporates ecological aspects within a geographic representation of a network.

The researchers found that roughly one-quarter of the forested lands in the western United States were integral to a network of forested patches. Of course, the lands outside of patches remain critical for habitat and overall connectivity. Using remotely sensed land cover data (ca. 2000), they found 1.7 million km² of forested lands. They estimate that land uses associated with residential development, roads, and highway traffic have caused roughly a 4.5% loss in area (20 000 km²) of these forested patches. Continued expansion of residential land is likely to reduce forested patches by another 1.2% by 2030. They also identified linkages among forest patches that are critical for landscape connectivity. 

The researchers emphasize that their approach can be readily modified to examine connectivity for other habitats/ecological systems and for other geographic areas, as well as to address more specific requirements for particular conservation planning applications