Interior forest is preferred by particular plant and animal species that require a type of habitat isolated from other, non-forest areas. Data to develop this indicator were taken from the National Land Cover Data set (NLCD) and State Highway Administration roads data. Interior forest was defined as forested land cover at least 300 feet from non-forest land cover or from primary, secondary, or county roads (i.e., roads considered large enough to break the canopy). The indicator is expressed as the number of acres of interior forest in the watershed divided by the land acres in the watershed.
Many species are officially listed as rare, threatened, and endangered because of habitat loss. Cutting of old growth forests and development are probably the primary factors responsible for the imperiled status of the Delmarva fox squirrel, which requires a largely closed forest canopy and open understory. The northern goshawk, a state endangered species, nests in mature and old tree habitat. Twenty-one species of birds that breed in coastal Maryland and that require large blocks of interior forest are tracked annually by the U.S. Geological Survey.
Interior forest habitats are relatively rare and easily lost. Interior forest provides one measure for identifying important habitat areas for specific species dependant upon interior conditions. As such, it can help in the identification of forest habitat conservation opportunities on a regional scale. It also suggests to local decision-makers that special care be taken in the land development process to avoid breaking up interior forest areas.