COMPETITION AND SPACING PATTERNS IN DESERT SHRUBS

SUMMARY (1) Spacing patterns of shrubs were studied on a series of sites in the Mojave and Sonoran Deserts. Both aggregation and regularity in dispersion of individual shrubs were fairly common. Aggregation may result from vegetative reproduction or environmental heterogeneity, and regularity from competition among plants. (2) Small shrubs tend to be clumped, medium-sized ones tend to a random arrangement, and large shrubs tend to a regular pattern. This suggests the increasing importance of competition as the plants grow. (3) Further evidence of interference between plants was provided by the correlations of plant size with the distance to their neighbours. (4) Root systems were extensive enough to abut or overlap each other in the interplant spaces. (5) Most plants tended to have neighbours of the same species rather than other species. (6) None of these results depended on position along the considerable climatic gradients across the Mojave and Sonoran Deserts.