This dataset depicts indices of forest fragmentation within the western
U.S. This dataset can help inform prioritization of landscapes for
conservation through identification of more intact forested areas.
Forest fragmentation was assessed using information derived from the
National Land Cover Dataset (NLCD) and USGS 1:100,000 scale roads.
Within each forested ecoregion in the World Wildlife Fund ecoregions
dataset, landscape units (land units) were defined using U.S. Census
Bureau TIGER highway networks. Land units were blocks of forested land
bounded by highways and were required to be at least 2,000 hectares in
size. Land units smaller than 2,000 hectares or areas within urban
areas were excluded from this analysis. The NLCD dataset was converted
into two categories: forest (including woody wetlands) and nonforest
(including water). USGS roads were converted to 30 meter rasters and
superimposed on the NLCD dataset. All forest patches less than 1
hectare were reclassified to match the surrounding land cover type to
reduce the time required for processing the analysis. The spatial
pattern analysis software tool FRAGSTATS was then used to calculate a
large set of landscape and patch level metrics. The density of all
1:100,000 scale roads (except 4-wheel drive roads) was determined for
each land unit. A subset of these metrics was then extracted to
calculate unweighted ordinal scores; these metrics include road density,
total core area index (percentage of all forest area within a land unit
that is considered core area, based on a 90 meter edge buffer distance),
mean nearest neighbor (average distance in meters from one forest patch
to the nearest forest patch), class area (total amount of forest in
hectares within each land unit), and percentage of landscape (percentage
of land unit composed of forest). These metrics were converted to
ordinal scores using natural breaks (Jenks optimization) with 5 classes.
These ordinal scores were then summed to create an overall fragmentation
index. This dataset represents only a subset of the information
contained in the forest fragmentation database compiled by CBI. Please
contact CBI directly for the full forest fragmentation database. This
dataset is described in detail in: Heilman, G.E. Jr., J.R. Strittholt,
N.C. Slosser, and D.A. DellaSala. 2002. Forest fragmentation of the
conterminous United States: assessing forest intactness through road
density and spatial characteristics. BioScience 52(5): 411-422.