The Role of Competition in Plant Communities in Arid and Semiarid Regions

The importance, and even the existence, of competition among plants in arid ecosystems has often been questioned. An influential statement of Shreve (113) asserted that interspecific competition does not occur in deserts, and Went (145) denied that competition between desert plants occurs at all. Neither provided evidence for his assertions, although Shreve pointed out the diversity of habits and phenologies found among desert species. He may have been responding to the strong emphasis placed on competition by Clements and his followers (e.g. 27). The importance of competition in natural communities has recently been debated (28, 109, 127). These reviews suggested that terrestrial plant communities are among the communities in which competition is relatively important. However, the majority of studies upon which this conclusion is based were made in humid regions. Grime (53) suggested that competition is less important in "high stress" habitats (in which he included dry habitats), but he presented little evidence from true arid or semiarid environments. This paper reviews the available evidence for competition in plant communities in arid and semiarid regions; as is demonstrated, competition certainly occurs in these communities and involves many different species. In several instances it appears to be important in the determination of community structure. Competition may be less frequent in these communities, though not less important on that account. This review also addresses several other questions concerning the role of competition in these communities, including: the role of competition in determining the absence, or presence and abundance, of species in a community, and their spatial arrangement; which