Water Relations of Selected Species of Chaparral and Coastal Sage Communities

Water potentials, leaf resistances to water loss, and relative saturation deficits of selected shrub species of chaparral and coastal sage communities were measured each month from June 1973 through May 1974. Measurements were made at coastal and inland sites in southern California, USA with a pressure chamber and a stomatal diffusion porometer, and by floating leaves until saturated. The drought—deciduous Artemisia californica had water potentials < —65 bars by September. The species of evergreen sclerophylls fell into three groups: (1) Arctostaphylos glauca and Ceanothus greggii developed the lowest water potentials (< —65 bars) and showed stomata least responsive to water potential; (2) Rhus ovata, Rhus laurina, and Rhus integrifolia had the highest water potentials (° —25 bars) and stomata most responsive to water potential; and (3) Adenostoma fasciculatum and Heteromeles arbutifolia showed intermediate water potentials and stomatal responses. The coastal and inalnd sites did not differ in water relations within species and genus, although water stress occurred earlier in the summer at the coastal site. At the inland site, soil moisture content and plant water potentials were higher on the south—facing slope, indicating less water stress for species there than on the north—facing slope. Slope differences were not as well defined at the coast.