Tongass National Forest, Cover Type, 2013 (Clipped to Select Ranger Districts)

The original CoverType Dataset was clipped by the four Ranger Districts of interest:  Thorne Bay, Craig, Wrangell, and Petersburg.

Below is the information from the original dataset:
CoverType is a photo-interpreted delineation of the Tongass National Forest by land type and timber cover type. Classification of lands was done sequentially: 1) land and water identified; 2) forested and non-forested areas were identified; 3) forested areas were classified by forest type and forest productivity; and 4) productive forest lands were further characterized by volume class, tree size, species composition. The original classifications were based on photo-interpretation of 1:15840 aerial photographs in 1978. The minimum map unit size is approximately 10 acres, though the average area for forested polygons is 60 acres. Additionally, CoverType is updated for new stands created through natural events or management activity. The data has also been corrected for errors, as found, that occurred during the attributing and digitizing of the original classification data.

Overview: 
The dataset differentiates between 'forested' and 'non-forested' areas. 'Non-forested' land has either never supported forests, or are lands formerly forested where forest use is precluded by development for other uses. 'Forested' land is defined as land with at least 10 percent stocked by forest trees of any size or formerly having had such tree cover, and not currently developed for non-forest land. 'Forested' lands are further classified as either 'productive' or 'non-productive'. 'Productive' land is producing or capable of producing crops of industrial wood. This includes areas suitable for management to grow crops of industrial wood generally of a site quality capable of producing in excess of 20 cubic feet per acre of annual growth. This includes land capable of producing at least 8,000 board feet per acre. Permanently inoperable or non-stockable areas are excluded because they are not suitable for silviculture management. Conversely, non-stocked areas which are stockable and otherwise meet this definition are included. 'Unproductive' forest are all forested lands not included in the productive forest land classification. The productive forest areas are classified according to species (FTYPE), stand size class (SSIZEC), and volume class (VOLC). The FTYPE names are derived from the species or group of species with the plurality of basal area in sawtimber stands and number of stems in all other stands. In the field, forest stands are divided into size classes (SSIZEC) based on tree diameters and age. These broad classes can be fairly well recognized on aerial photos from the texture of the stand, height of the trees and diameter and shape of crowns. Stand size class is determined by the plurality of space occupied by all trees. Basal area is used as the basis for estimating plurality of space occupied by sawtimber trees and numbers of trees for poletimber and seedling-sapling tree sizes. Volume class (VOLC) was determined by using aerial stand volume tables for Western hemlock and Sitka spruce based on stand height and crown closure. While volume class information is included in the coverage, a direct correlation between forest structure (as exhibited by stand height and crown closure) and timber volume has not been established.