Appendix A. Land Cover Classification System

Our analysis of land use and land cover change over the 1973–2000 study period is based on classifications of land cover for five dates. The classification system consists of the following 11 general land cover classes:

• Water
• Developed
• Mechanically disturbed
• Mining
• Barren
• Forests
• Grassland/Shrubland
• Agriculture
• Wetland
• Non-mechanically disturbed
• Ice and snow

Two primary factors affected the design of our classification system. The first factor was recognizing that the use of moderate-resolution imagery (Landsat Thematic Mapper (TM) and Multispectral Scanner (MSS)) would necessitate a land cover classification system that was fairly general in order to achieve high interpretation accuracy and consistency. Our ability to identify and map land cover would be limited by the technical specifications of the Landsat MSS, TM, and Enhanced Thematic Mapper (ETM) sensors and by the local and regional landscape characteristics that affect the form and contrast visible in satellite imagery. This would be especially true when interpreting Landsat MSS data. The second factor involved choosing classes that captured the land cover changes of interest. Since we were interested in land use change with cover serving as a surrogate for land use, we decided to use the Anderson Level I classes (Anderson and others, 1976) because they were designed as use surrogates. However, we selectively modified the Anderson system by adding two disturbance categories (i.e., mechanically disturbed (human-induced) and non-mechanically disturbed (natural)). The following definitions describe each class:

Water – Areas persistently covered with water, such as streams, canals, lakes, reservoirs, bays, or oceans.

Developed – Areas of intensive use with much of the land covered with structures or anthropogenic impervious surfaces (e.g., high-density residential, commercial, industrial, roads, etc.) or less intensive uses where the land cover matrix includes both vegetation and structures (e.g., low-density residential, recreational facilities, cemeteries, parking lots, utility corridors, etc.), including any land functionally related to urban or built-up environments (e.g., parks, golf courses, etc.).

Mechanically disturbed – Land in an altered and often unvegetated state that, due to disturbances by mechanical means, is in transition from one cover type to another. Mechanical disturbances include forest clear-cutting, earthmoving, scraping, chaining, reservoir drawdown, and other similar human-induced changes.

Mining – Areas with extractive mining activities that have a significant surface expression. This includes (to the extent that these features can be detected) mining buildings, quarry pits, overburden, leach, evaporative, tailings, or other related components.

Barren – Land comprised of soils, sand, or rocks where less than 10 percent of the area is vegetated. Barren lands are usually naturally occurring.

Forest – Tree-covered land where the tree cover density is greater than 10 percent. Note that cleared forest land (i.e., clear-cuts) is mapped according to current cover (e.g., mechanically disturbed or grassland/shrubland).

Grassland/Shrubland – Land predominately covered with grasses, forbs, or shrubs. The vegetated cover must comprise at least 10 percent of the area.

Agriculture – Land in either a vegetated or an unvegetated state used for the production of food and fiber. This includes cultivated and uncultivated croplands, hay lands, pasture, orchards, vineyards, and confined livestock operations. Note that forest plantations are considered forests regardless of the use of the wood products.

Wetland – Land where water saturation is the determining factor in soil characteristics, vegetation types, and animal communities. Wetlands usually contain both water and vegetated cover.

Non-mechanically disturbed – Land in an altered and often unvegetated state that, due to disturbances by non-mechanical means, is in transition from one cover type to another. Non-mechanical disturbances are caused by fire, wind, floods, animals, and other similar phenomena.

Ice and Snow – Land where the accumulation of snow and ice does not completely melt during the summer period (e.g., alpine glaciers and snowfields).