Comparison of Current Land Cover Condition to NRCS Ecological Site Descriptions for Box Elder County, Utah
The Southwest Regional Gap Analysis (SWReGAP) land cover map completed in September of 2004 represents current land cover for the southwestern United States. The National Resources Conservation Service (NRCS) soils database (SSURGO) records ecological site descriptions (ESD) for each soil map unit. An ecological site is defined as a distinctive kind of land with specific characteristics that differs from other kinds of land in its ability to produce a distinctive kind and amount of vegetation. Therefore, ESDs are used as a reference land cover state from which state and transition models are developed. A comparison between these two geospatial data sources provides a means to evaluate current land cover state relative to a reference state and to further develop state and transition models for each ESD. A test case covering Box Elder County located in northwestern Utah was used to evaluate the comparability of these two databases. Results show that the SWReGAP land cover map for Box Elder County and SSURGO ESDs for each soil map unit, tend to correlate well with each other. Further analysis within big sagebrush dominated ESDs show approximately 39,000 fewer hectares of sagebrush in the SWReGAP land cover map compared to SSURGO ESD estimates. The majority of this difference in big sagebrush is due to agricultural conversion, followed by conversion to juniper and annual grasses. A current land cover map placed within the context of a reference condition on a site by site basis will allow managers to prioritize restoration activities and to better understand condition and trend.
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