Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/1997
Publication Date: N/A
Interpretive Summary: Indicators of ecosystem health are most useful if they can be used to diagnose a deterioration of ecosystem health before the problem becomes impossible to reverse or even halt. We have developed several such early- warning indicators based on factors that promote wind- and water-driven erosion of resources from the soil. Erosion occurs mainly in areas where the soil is not protected from wind and rain, therefore, the amount and size of bare soil is a very important indicator. Other good indicators include the amount soil surface covered by grasses and the proportion of these grasses that have long life-spans, the amount of surface covered by plants that are able to spread vegetatively, and an index based on the surface covered by plants that are preferred as forage by livestock. The soil-type and other characteristics of a site may also affect how well these indicators work and, therefore, this information is essential in order to interpret the results of applying indicators to any ecosystem.
Technical Abstract: Perennial grasslands that dominated the southwestern US during the past 10,000 years have been desertified to varying extents. Desertification is a temporal phenomenon, defined as a change in the scale of the spatial distribution of resources. We report here on several indicators of desertification using bare patch indices as surrogates for direct measures of desertification. A bare patch index based on canopy cover, which is relevant for precipitation and wind driven erosion, is not equivalent to another bare patch index based on soil surface measurements, which indicates overland water flow driven erosion. Percent grass cover, percent long-lived grass cover, percent cover of vegetative reproducers and a relative preference index all yielded sensitive indicators of desertification. The usefulness of some indicators, such as organic litter, is dependent upon recent environmental history. Other indicators, such as percent cover due to species resistant to grazing, appear not to b sensitive to desertification and need further development. Range site type may also be important in determining indicator responses, where some indicators were sensitive to range site while others were not. Overall, we have identified several sensitive indicators of desertification based on vegetational characteristics in varied range sites in the northern Chihuahuan Desert.