Fragmentation of Continental United States Forests

Characterizing wildfire regimes in the United States

“…3A) observed at Bailey's ecoregion division level suggests that the ratio of the number of large to small wildfires decreases from east to west across the conterminous U.S. Controls on the wildfire regime (e.g., climate and fuels) vary temporally, spatially, and at different scales (3), so it is difficult to attribute specific causes to this east-to-west gradient. For example, the observed reduced contribution of large wildfires to total burned area (i.e., ␤ large) in eastern ecoregion divisions may be due to greater human population densities that increase forest fragmentation compared with western ecoregions (40). Alternatively, the observed gradient may have natural drivers, with climate and vegetation producing conditions more conducive to large wildfires in some ecoregions compared with others.…”

“…It has been suggested (20) that increased landscape heterogeneity decreases disturbance (e.g., wildfire) spread. Historic anthropogenic forest clearance, resulting in forests fragmented by agricultural and urban land cover, has increased the heterogeneity of eastern landscapes (40). This may have reduced the relative number of large to small fires in the east compared to the west.…”

“…This may have reduced the relative number of large to small fires in the east compared to the west. In western landscapes, forests have also become fragmented, but via replacement by shrublands and grasslands (40) that are more conducive to wildfire spread than the agricultural and urban land covers that have fragmented eastern forests.…”

Land fragmentation under rapid urbanization: A cross-site analysis of Southwestern cities

“…To measure land fragmentation, we employ the National Land Cover Database (NLCD) for 1992 and 2001, compiled from Landsat Thematic Mapper (TM) images, which provides seamless coverage for all sites (Homer et al 2004). NLCD was the first nationwide initiative that provided consistent land-cover inventory for the US and it has been widely used in studying urbanization (Vogelmann et al 1998) and landscape fragmentation (Heilman et al 2009;Riitters et al 2002). The dataset does have limitations for land fragmentation analyses, especially in detecting peri-urban and exurban development (see for example Irwin and Bockstael 2007;Ward et al 2000).…”

“…To analyze urban growth patterns and their spatial heterogeneity, we weighed the benefits of using a full coverage moving windows analysis (Riitters et al 2002) and a transect analysis (Luck and Wu 2002;Yu and Ng 2007). The transect methodology was selected due to the linear form of many of the sites and our wish to detect directionality of urbanization patterns.…”