The Response of Vegetation to Disturbance in Death Valley National Monument, California

Webb, Robert; Steiger, John; Newman, Evelyn

The response of desert plant assemblages to disturbance was studied in Death Valley National Monument, California. Plant assemblages on debris flows, alluvial terraces, five abandoned townsites, and a pipeline corridor were measured to quantify recovery rates and to develop a model of change in desert vegetation. A review of the literature revealed that little was known about the nature and rate of recovery in disturbed desert ecosystems. Plant succession models are commonly used to describe vegetation dynamics that occur after disturbances. Plant succession refers to sequential, directional changes in the species composition of a plant assemblage that are caused by forces internal and (or) external to the assemblage. The nature of these forces is controversial and dependent upon which model is used; most plant ecologists ascribe them to biological processes. As a result, a common mistaken belief is that plant succession does not occur in deserts because sequential, directional changes have not been consistently observed and measured and the influence of biological processes is assumed to be negligible. Vegetation assemblages occurring on debris flows of different age illustrate sequential, directional changes in the species composition of areas in the Panamint Range dominated by Coleogyne ramosissima. Debris flows were differentiated in age on the basis of the degree of soil development. The species composition changed on debris flows of increasing age, as indicated by increasing soil development, from species with short lifespans oriented to rapid recruitment (for example, Lupin us excubitus) to a mixture of species (for example, Ephedra nevadensis, Lycium andersonii, and Grayia spinosa) to longlived, maintenance-oriented species (for example, Coleogyne). This primary succession sequence, so named because it occurs on a newly created surface, requires thousands of years for the change in dam in ants from short-lived, reproduction-oriented to long-lived, maintenance-oriented species. The recovery of vegetation assemblages at the Skidoo townsite and in the Skidoo pipeline corridor indicates a pattern of vegetation change similar to that measured on the debris flows. These disturbed sites, with recovery periods after abandonment of between 42 and 74 years, were generally colonized by shortlived, reproduction-oriented species (for example, Chrysothamnus viscidiflorus, and perennial grasses) with variable colonization by other species (for example, Grayia, Ephedra, and Coleogyne). The time required for complete recovery of disturbed sites appears to depend on the stage of the predisturbance primary succession. Soil compaction, a possible inhibitor of vegetation establishment, was estimated to require a century for complete amelioration but did not appear to substantively affect the course of recovery.

The Response of Vegetation to Disturbance in Death Valley National Monument, California

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