Estimating Conservation Needs for Rangelands Using USDA National Resources Inventory Assessments

Abstract

This study presents (1) the overall concept of assessing non-federal western rangeland soil loss rates at a national scale for determining areas of vulnerability for accelerated soil loss using USDA Natural Resources Conserva- tion Service (NRCS) National Resources Inventory (NRI) data and the Rangeland Hydrology and Erosion Model (RHEM) and (2) the evaluation of a risk-based vulnerability approach as an alternative to the conventional average annual soil loss tolerance (T) for assessment of rangeland sustainability. RHEM was used to estimate runoff and soil loss at the hillslope scale for over 10,000 NRCS NRI sample points in 17 western states on non-federal rangelands. The national average annual soil loss rate on non-federal rangeland is estimated to be 1.4 ton ha -1 year -1 . Nationally, 20% of non- federal rangelands generate more than 50% of the average annual soil loss. Over 29.2 × 10 6 ha (18%) of the non-federal rangelands might benefit from treatment to reduce 1559-1570soil loss to below 2.2 ton ha -1 year -1 . National average an- nual soil loss rates combine areas with low and accelerated soil loss. Evaluating data in this manner can misrepresent the magnitude of the soil loss problem on rangelands. Between 23% and 29% of U.S. non-federal rangelands are vulnerable to accelerated soil loss (≥2.2 ton ha -1 event -1 ) if assessed as a function of vulnerability to a runoff event with a return peri- od of ≥25 years. The NRCS has not evaluated potential soil loss risk in national reports in the past, and adaptation of this technique will allow the USDA and its partners to be proactive in preventing accelerated soil loss on rangelands.