Forest Community Types
Following national guidelines, the Mid-Atlantic Gap Analysis Project (MID-A GAP) developed geographic information system (GIS) data layers that can be used by land managers, environmental planners, and others as tools to assist with a wide variety of natural resources-based projects. The primary purpose of these data was to provide information on the geographic distribution of land cover for the entire study area. The secondary purpose was to provide a variable (vegetation as habitat) for the purposes of mapping vertebrate species habitat associations also known as communities.
Community types for this indicator are defined at the “alliance” level of the National Vegetation Classification System (NVCS). An alliance is a group of plant associations that share a similar architecture and one or more diagnostic species, which are generally the dominants in the primary canopy. Accordingly, forest community types, such as Coastal Plain Beech/Oak Forest or Upland Loblolly Forest are characterized by certain plant and animal species that depend on the particular habitat provided by that forest type.
Portions of eleven Landsat Thematic Mapper (TM) scenes were used in the Mid-Atlantic GAP as the base image for classification. Other spatial data used to facilitate this process included existing land use and cover maps, National Wetlands Inventory (NWI), aerial photos, digital topographic maps, digital orthophoto quadrangles, airborne videography, and ground point sampling.
The GAP data layer is in a grid format, which means the layer is individually valued on a cell-by-cell basis. A simple zonal statistics function summarized the data by 12-digit watershed (a zone). The grid function calculated a majority, minority, median and variety statistic for each zone. The majority is what is mapped here, basically depicting which forest community type dominates in each watershed.
The data developed by the GAP program and mapped here may be used for a variety of coarse (regional) scale landscape analysis and management purposes pertaining to land cover. They provide context for finer-level maps or applications. Appropriate use includes guidance for statewide biological diversity planning or other regional and large area resource planning. For example, when the area occupied by a forest community declines, populations of animals and plants that are highly dependent upon that community type may also decrease.
The maps are also useful for education at all levels for both students and citizens. Finally, the data can assist in assessing environmental impact for large projects such as military activities and for coarse-filter evaluation of potential impacts or benefits of major projects or initiatives on biological diversity, such as utility or transportation corridors, wilderness proposals, open space or recreation proposals.