Stable states and thresholds of range condition on North American rangelands: a viewpoint.

Abstract

The concepts of relatively stable multiple states and thresholds or transitions between these states has received little attention in range management until recently. On North American rangelands lower successional stable states occur in sagebrush and other shrub-dominated vegetation types in the Great Basin, the shortgrass steppe, the Southwestern desert grasslands, and communities dominated by annual grasses in California and southern Idaho. Recognition of these stable states and models describing them are needed to develop new concepts about range condition. The model presently used assumes a single stable state (climax) and that the stages of secondary succession on improving rangelands are the reverse of the stages of retrogession. Alternative models presented include the 'cup in ball' analogy, the state-and-transition model, and others. While much theoretical work needs to be done before any of these models can be incorporated into range condition standards, it is important for range managers to recognize that multiple steady states exist for many vegetation types. One assumption of the current range condition model is that a reduction in grazing pressure and an improvement in grazing management will result in range improvement. If a vegetation type is in a stable lower successional state, it normally will not respond to change in grazing or even removal of grazing. Managers must recognize this situation when it occurs so that false expectations of improvement are not fostered.