|De Soyza, Amrita|
|Herrick, Jeffrey - Jeff|
Submitted to: Ecosystem Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/1996
Publication Date: N/A
Interpretive Summary: We are developing indicators that can be used to assess the health of rangelands in the western US. A good sensitive indicator is one that will show a large and easily measured change when the health of a rangeland area is threatened. Good indicators must also be relatively insensitive to natural changes in the amount and type of vegetation present. In desert rangelands cattle congregate near stock watering tanks scattered over the landscape. The heavy disturbance near these watering points results in a deterioration ecosystem health. The disturbance decreases with distance from the watering points until, approximately 1 km away, the land is once again relatively healthy. We collected information on indicators at the watering points and at 3 points beyond, up to a distance of 1 km. Once we identified sensitive indicators we tested these on adjacent healthy (fenced) and unhealthy pastures. Of the indicators we studied, the amount of bare ground, the amount of ground covered by grasses with long life- spans, and the stability (resistance) of soil to erosion were very sensitive to changes in ecosystem health.
Technical Abstract: The sensitivities of 3 indicators of ecosystem health were evaluated at several sites in the Jornada Basin of the Chihuahuan Desert in southern New Mexico. The size of bare patches, proportion of total grass cover contributed by long-lived perennial grasses, and soil stability are interdependent indicators of ecosystem functions related to the retention and use of water and nutrients. Sensitivity tests were chosen using data collected along disturbance gradients and then tested using independent, ungrazed exclosures and adjacent grazed pastures. The mean size of bare soil patches was sensitive to anthropogenic disturbance. When bare soil patch data were transformed using natural logarithms, the skewness of the frequency distribution weighted by mean bare patch size could be used to indicate early disturbance to the ecosystem. The proportion of total vegetation that was long lived also was sensitive to anthropogenic disturbance and appears to be a good indicator of ecosystem degradation. The slake test for soil surface stability was extremely sensitive to disturbance and may serve as an early-warning indicator of soil degradation for the coarse-textured soils that were evaluated.