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Percent Change in Forest Land Area, 1982 - 1992

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Description

This shaded polygon map shows the percent change in the amount of non-Federal forest land area from 1982 to 1992 within each 8-digit hydrologic unit, using 1982 as a base year. The percentages are presented in five categories based on the following divisions: an increase of more than 25%, an increase of 5% to 25%, little change (less than 5% change), a decrease of 5% to 25%, and a decrease of over 25%. Data are not collected on Federal lands, areas with 95% or more federal land are shaded out. Areas with less than 5% non-Federal forest land are also excluded from the analysis.

Cautions for this Product:
This map does not include National Forests, or other Federally owned forest land. Areas with small amounts of forest land may have very high rates of change. This map is best used in conjunction with a map showing percent non- Federal area in forest land. Data are not available for Alaska or the Pacific Basin. Data for Puerto Rico and the U.S. Virgin Islands are aggregated by 6-digit hydrologic unit.



Sources

Source: National Resources Inventory, 1997
Distributor: USDA-NRCS-RIAD
Reliability:
NRI sample data are generally reliable at the 95% confidence interval for state and certain broad substate area analyses. Generally, analyses that aggregate data points by smaller geographic areas and/or more specific criteria result in fewer data points for each aggregation and therefore less reliable estimates. NRI maps reflect national patterns rather than site- specific information.


Layers

Aggregate Layer: 8 Digit Hydrologic Unit Areas with Federal Land
Other Layers Displayed: Rivers, States


Definitions

Federal land:
A land ownership class designating land that is owned by the Federal Government. It does not include, for example, trust lands administered by the Bureau of Indian Affairs nor Tennessee Valley Authority (TVA) land. No data are collected for any year that land is in this ownership. [NRI-97]

Forest land:
A Land Cover/Use that is at least 10 percent stocked by single stemmed forest trees of any size which will be at least 4 meters (13 feet) tall at maturity. When viewed vertically, canopy cover is 25 percent or greater. Also included are areas bearing evidence of natural regeneration of tree cover (cutover forest or abandoned farmland) and not currently developed for nonforest use. For classification as forest land, an area must be at least one acre and 100 feet wide. [NRI-97]

Hydrologic units:
A hierarchical system developed by the U.S. Geological Survey that divides the United States and the Caribbean into 21 major regions, 222 subregions, 352 accounting units, and further subdivided into 2,150 cataloging units that delineate river basins having drainage areas usually greater than 700 square miles. [USGS]


Product Information

Product ID: 5875
Production Date: 1/12/01
Product Type: Map


For additional information contact the Resources Inventory and Assessment Division. Please include the Product ID you are inquiring about. nri@wdc.usda.gov or 1400 Independence Avenue SW - P.O. Box 2890 - Washington D.C. 20013. If you use our analysis products, please be aware of our disclaimer.