This indicator represents the size of large, unfragmented patches of natural habitat. It identifies minimally disturbed natural areas at least 100 acres in size and greater than 200 meters wide.
Reason for Selection
Large areas of intact natural habitat are favorable for conservation of numerous species, including reptiles and amphibians, birds, and large mammals. The Esri Green Infrastructure data covers the entire United States and has been used in other broad-scale conservation planning efforts, so using this existing data helps align the Blueprint with other conservation efforts and reduce duplication of effort. We chose to use “Core Size (acres)” as the metric for this indicator. Other evaluation attributes included in this index, such as the default “Core Score”, were less suitable because they were calculated using inputs that are duplicative of other indicators.
Esri’s description of the Core Size metric states: “Cores were derived from the 2011 National Land Cover dataset. The ‘natural’ land cover classes were included and all ‘developed’ and ‘agricultural’ classes including crop, hay and pasture lands were excluded. The resulting cores were tested for size and width requirements (at least 100 acres in size and greater than 200 meters) and then converted into unique polygons.”
Input Data
– Esri Green Infrastructure Data: We downloaded this dataset by state from arcgis.com. The Esri Green Infrastructure website provides more information about these data, access to the models utilized to generate them, and additional online applications for green infrastructure planning.
Mapping Steps
1) We created a new feature class by merging all the state-level “Intact Habitat Cores (March 2017)” polygon feature classes that covered the South Atlantic region using the ArcGIS “Merge” tool.
2) We deleted identical polygons from the merged feature class using the ArcGIS “Delete Identical” tool. This removed duplicate polygons that spanned state boundaries and were included in multiple state layers.
3) We converted the polygon to a raster using the ArcGIS “Polygon to Raster” tool using the value field of “Acres”. This resulted in a raster dataset with 30 m cell size with values based on the “Core Size (acres)” field calculated by the ESRI Green Infrastructure Data group.
4) We changed NoData values (pixels not covered by an intact habitat core) to 0.
Final indicator values
The final indicator is continuous, with values ranging from:
High: 445,312 acre core
Low: 0 (not a core or core <100 acres)
Known Issues
– This is based on 2011 NLCD, not the more recent 2016 NLCD. The scripts and input data used to create this layer have been shared by the data creator (Esri). We expect this will help us update this indicator in the future.
– Even small roads serve as hard boundaries for habitat cores. While this makes sense for some species, the effective size of the patch for some more mobile animals is likely underestimated.
– Waterbodies like reservoirs are also considered part of habitat cores, so this layer likely overestimates the effective size of the habitat core for most species.
Disclaimer: Comparing with Older Indicator Versions
There are numerous problems with using South Atlantic indicators for change analysis. Please consult Blueprint staff if you would like to do this (email hilary_morris@fws.gov).
Literature Cited
Esri Green Infrastructure Center, Inc. 2017. Esri Green Infrastructure Data Description. http://www.arcgis.com/sharing/rest/content/items/5561da06127d48a982d6b91929f29666/data
