Vegetation Zonation in a Vernal Marsh on the Santa Rosa Plateau of Riverside County, California

Abstract

A series of four vernal marshes, ranging in size from 2 to 30 acres, occurs on the top of the lava-capped Mesa de Colorado of Rancho California, approximately 5 miles west of Murrieta, on the Santa Rosa Plateau. The marshes are located less than a mile west of the Santa Rosa Ranch head- quarters as indicated on the vegetation map of a florula of the Santa Rosa Plateau ( Lathrop and Thorne, 1968, Fig. 2). The location of the marshes is also shown in aerial photographs of a floristic survey of the marshes ( Thorne and Lathrop, 1969, Figs. 1, 2). Brief descriptions of the soils, underlying rock strata, rainfall, seasonal appearance, zonation, etc. of the marshes are also included in the previous article. Additional plant species appearing in the marshes following the survey listed above were reported in a subsequent article ( Thorne and Lathrop, 1970). To the previous floristic knowledge of this unusual habitat, the authors propose to add quantitative measurements of the vegetation. Field work was conducted at the vernal marsh sites by one or both of the authors twice weekly between February 14 and July 8, 1974. The nomenclature of plant species encountered in measurements at the sample sites ( TABLE lA- E) largely follows that of Munz ( 197 4) , and the species are listed, along with their habitat or habitats, in the vernal marsh articles cited previously. METHODS