Mean Patch Size

The Indicator

The fragmentation of Maryland’s forests is having an adverse effect on many of Maryland’s wildlife species. As residential and other development spreads across the landscape, the spatial configuration of the remaining forests changes, and in most cases the tendency is towards smaller and more isolated forested tracts, or “patches.” This in turn impacts habitat available to species dependent upon larger forested tracts and the “interior” conditions these tracts often contain. This indicator looks at the mean size of forest patches within a watershed as defined by the National Land Cover Data set (NLCD), expressed in acres.

As forest patch size decreases, and as patches of habitat become more isolated, population sizes of species dependant upon contiguous blocks of forest, especially of rare species, may decline below the threshold needed to maintain genetic variance, withstand oscillations and meet social requirements like breeding and migration.

In addition, to some extent the sustainability of the forest resource land base is linked to the size of forested patches and tracts. For example, private forestry activities (both industrial and non-industrial) are more likely to be commercially viable in regions with an intact, relatively unfragmented resource base.

Indicator Use

Watersheds with large forest patches should be the focus of land conservation initiatives aimed at maintaining the integrity of these patches, and protecting the connectivity of forest resources in the region. For those watersheds with smaller forest patches, opportunities may exist to increase habitat and habitat connectivity by examining gaps in forest cover within existing patches, as well as expanding forest cover along the external edges of existing patches.

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