Appendix C Ecological Subregions of the United States

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Glossary of selected terms

Included are definitions of selected terms that may not be commonly known to the user of this document. This abbreviated glossary does not include the many, specialized terms used to describe taxa of geologic and soil classifications. Some of the more general geology and soil terms are defined in the glossary of the table that supplements the map of ecoregions and subregions of the U.S. For other definitions the user is directed to references such as Bates and Jackson (1980) for geologic terms and Soil Survey Staff (1992) for soil terminology.

ALLUVIUM---A general term for clay, silt, sand, gravel, or similar unconsolidated detrital material deposited during comparatively recent geologic time by a stream or other body of running water as a sorted or semisorted sediment in the bed of the stream. (Bates and Jackson 1980.)

CIRQUE---A deep steep-walled half-bowl-like recess or hollow situated high on the side of a mountain and commonly a thte head of a glacial valley, and produced by the erosive activity of a mountain glacier. (Bates and Jackson 1980.)

COLD-DECIDUOUS BROADLEAF---Woody angiosperms with wide, flat leaves (e.g., paper birch) that are shed by plants during the dormant season (that portion of the year when frosts occur).

COLLUVIUM---A general term applied to any loose, heterogeneous, and incoherent mass of soil material and/or rock fragments deposited by rainwash, sheetwash, or slow continuous downslope creep, usually collecting at the base of gentle slopes or hillsides. (Bates and Jackson 1980.)

CUESTA---A hill or ridge with a gentle slope on one side and a steep slope on the other; formed by uplifted rock outcrop consisting of strata having different restances to erosion. (Bates and Jackson 1980.)

DIVISION---An ecological unit in the ecoregion planning and analysis scale of the National Hierarchical Framework corresponding to subdivisions of a Domain that have the same regional climate. (ECOMAP 1993.)

DOMAIN---An ecological unit in the ecoregion planning and analysis scale of the National Hierarchical Framework corresponding to subcontinental divisions of broad climatic similarity that are affected by latitude and global atmospheric conditions. (ECOMAP 1993.)

DRUMLIN---An elongated hill or ridge of glacial drift.

DRY---A classification of climate based on the K\"oppen System for regions where evaporation exceeds precipitation. (Bailey 1980.)

ECOREGION---A scale of planning and analysis in the National Hierarchical Framework that has broad applicability for modeling and sampling, strategic planning and assessment, and international planning. Ecoregions include Domain, Division, and Province ecological units.

ECOSYSTEM---A complete interacting system of organisms and their environment. (FSM 2060.)

FLOODPLAIN---The surface or strip of relatively smooth land adjacent to a river channel, constructed by the present riven in its existing regimen and covered with water when the river overflows its banks. (Bates and Jackson 1980.)

LIFE ZONES---A classification of macroclimatic conditions based on temperature and precipitation that has been widely applied in tropical environments to delineate zones dominated by vegetative communities of characteristic physiognomy and composition. (Holdridge 1967.)

MARINE AND ESTUARINE PROVINCE---Regionalizations at the System level of the wetland classification system developed by Cowardin and others (1979) consisting of the open ocean overlying the continental shelf and adjacent areas of coastlines that are influenced by tidal activity.

MORAINE---A mound, ridge, or other distinct accumulation of unsorted, unstratified glacial drift, predominantly till, deposited chiefly by direct action of glacier ice, in a variety of topographic landforms that are independent of control by the surface on which the drift lies. (Bates and Jackson 1980.)

NEEDLE-LEAVED EVERGREEN---Woody gymnosperms with green, needle-shaped, or scale-like leaves (e.g., black spruce) that are retained by plants throughout the year. (Cowardin and others 1979.)

PLANT ASSOCIATION---A potential natural plant community of definite floristic composition and uniform appearance. (FSM 2060.)

PLANT COMMUNITY---A group of one or more populations of plants in a common spatial arrangement. (FSM 2060)

PLAYA--- A term used in the southwestern U.S. for a dry, vegetation-free, flat area at the lowest part of an undrained desert basin, underlain by stratified clay, silt, or sand, and commonly by soluble salts. (Bates and Jackson 1980.)

POLAR---A classification of climate based on the K\"oppen System for regions where the warmest month is colder than 50oF (10oC). (Bailey 1980.)

POTENTIAL NATURAL COMMUNITY---The biotic community that would be established if all successional sequences of its ecosystem were completed without additional human-caused disturbance under present environmental conditions. Grazing by native fauna, natural disturbances, such as drought, floods, fire, insects, and disease, are inherent in the development of potential natural communities which may include naturalized exotic species. (FSM 2060.)

POTENTIAL NATURAL VEGETATION---The vegetation that would exist today if man were removed from the scene and if the plant succession after his removal were telescoped into a single moment. The time compression eliminates the effects of future climatic fluctuations, while the effects of man's earlier activities are permitted to stand. The maps and descriptions of potential natural vegetation developed by K\"uchler (1964) for the 48 conterminous States are among the most widely used.

POTHOLE---A shallow depression, generally less than 10 acres in area, occurring between dunes on a prairie, often containing an intermittent pond or marsh and serving as a nesting place for waterfowl. (Bates and Jackson 1980.)

PROVINCE---An ecological unit in the ecoregion planning and analysis scale of the National Hierarchical Framework corresponding to subdivisions of a Division that conform to climatic subzones controlled mainly by continental weather patterns. (ECOMAP 1993.)

REGIONALIZATION---A mapping procedure in which a set of criteria are used to subdivide the earth's surface into smaller, more homogeneous units that display spatial patterns related to ecosystem structure, composition, and function. (ECOMAP 1993.)

SCALE---The degree of resolution at which ecological processes, structures, and changes across space and time are observed and measured. (ECOMAP 1993.)

SECTION---An ecological unit in the subregion planning and analysis scale of the National Hierarchical Framework corresponding to subdivisions of a Province having broad areas of similar geomorphic process, stratigraphy, geologic origin, drainage networks, topography, and regional climate. Such areas are often inferred by relating geologic maps to potential natural vegetation groupings as mapped by K\"uchler (1964). (ECOMAP 1993.)

SUBENVELOP---The general altitude of the drainage network that portrays differences in stream gradient from one geomorphic unit to another.

SUBREGION---A scale of planning and analysis in the National Hierarchical Framework that has applicability for strategic, multi-forest, statewide, and multi-agency analysis and assessment. Subregions include Section and Subsection ecological units.

SUBSECTION---An ecological unit in the subregion planning and analysis scale of the National Hierarchical Framework corresponding to subdivisions of a Section into areas with similar surficial geology, lithology, geomorphic process, soil groups, subregional climate, and potential natural communities. (ECOMAP 1993.)

SUBTROPICAL---A classification of climate based on the K\"oppen System for regions where there are eight months or more warmer than 50oF (10oC) and the coolest month is warmer than 32oF (0oC) but colder than 65oF (18oC). (Bailey 1980.)

TEMPERATE---A classification of climate based on the K\"oppen System for regions where there are four to eight months warmer than 50oF (10oC) and the coldest month is cooler than 32oF (0oC). (Bailey 1980.)

TROPICAL---A classification of climate based on the K\"oppen System for regions where the coolest month is warmer than 65oF (18oC) (Bailey 1980).

TUNDRA---A classification of climate based on the K\"oppen System for regions where the warmest month is colder than 50oF (10oC) but warmer than 32oF (0oC). (Bailey 1980.)

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