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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of a Site Conservation Rating System in Southeastern Arizona

Authors
item Watters, S - UNIV. OF ARIZ.
item Weltz, Mark
item Smith, L - UNIV. OF ARIZ.

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 1996
Publication Date: N/A

Interpretive Summary: The objective of this study was to develop a method to evaluate the apparent health and sustainability of rangeland ecosystems. Two methods were developed and tested in this study. Both methods use the Site Conservation Threshold concept proposed by the Society for Range Management. The Site Conservation Threshold is the point when accelerated soil erosion occurs and the long-term health and stability of the ecosystem are at risk. A rating system based on observable land-surface characteristics was developed. The observer compares the study area to a photographic chart from a known reference areas to classify the area in one of five classes: one (maximum erosion) to five (no erosion). The second method used the Water Erosion Prediction Project (WEPP) model. The WEPP model predicted sediment yield was compared to soil loss tolerance value (T) to establish relationships between soil loss and land-surface characteristics. The results from the rating system was highly correlated to the WEPP model. Four indices of apparent health were determined: standing biomass >750 (kg/ha), basal cover >8%, average distance between perennial plants <15( cm), and the area with no rooted perennial plant <13%. If any one of these conditions were met then the area was considered healthy with minimal indication that accelerated erosion would reduce the long term sustainability of the ecosystem.

Technical Abstract: The objectives of this study were to develop methods to identify a Site Conservation Threshold, the point at which accelerated erosion occurs. Sixteen study areas were chosen to represent a wide range of land-surface characteristics to determine the health of a semi-arid desert grassland. A Site Stability Rating based on observable vegetation and soil-surface characteristics was developed. The observer compares the study area to a photographic chart from a known reference area to classify the area in one of five classes (one: maximum erosion to five: no erosion). Site Stability was estimated for 100 quadrats per study area. The Water Erosion Prediction Project (WEPP) model was used as an objective index of soil stability to assess the degree of site protection. The soil loss tolerance value (T) was used with the sediment yield predicted by the WEPP model to establish a threshold value of site stability. The subjective rating method was highly correlated to the WEPP model results. Four indices of apparent health were established: standing biomass > 750 (kg/ha), basal cover > 8 %, average distance to the nearest perennial plant <15 (cm), and frequency area with no rooted perennial plant (13%). If any one of these conditions were met then the area was considered healthy with minimal indication that accelerated erosion would reduce the long term sustainability of the ecosystem.

Last Modified: 10/22/2014
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