Distribution quantified by microtopography in an assemblage of saxicolous mosses

Microtopography was quantified and related to plant microdistribution in an assemblage of bryophytes on granitic rocks in the inland chaparral of San Diego County, California, U.S.A. The dominant species, Grimmia laevigata, grew mostly on north-, east-, and west-facing surfaces with slope less than 60°. Other bryophytes tended to grow on steep, concave, north- and west-facing surfaces. Occurrence of these latter species was strongly associated with shade, as estimated from microtopography. The relationship of microdistribution to microclimate and ultimately to plant physiology can probably be successfully defined in systems such as this.Nomenclature follows Crum et al. (1973) for bryophytes and Munz (1974) for vascular plants.I thank W. C. Oechel for arranging access to the San Diego State University research area at Echo Valley and to facilities maintained there by the Systems Ecology Research Group; D. Alpert, C. Harkins, C. M. M. Hermida, J. Jacobson, and C. Scheidlinger for assistance with portions of the field work; M. P. Harthill and B. D. Mishler for help with identification of mosses; H. A. Mooney for comments on an earlier draft; and R. E. Cook and N. G. Miller for advice and support in many forms. This work was supported by National Science Foundation Grant DEB-7906428 and by a grant from the William and Alice Hinckley Scholarship Fund.