Factors affecting vegetation on a serpentine soil: II. Chemical composition of foliage and soil

Abstract

does not appear. First page follows. Introduction Serpentine soils have a unique combination of chemical characteristics that affect the vegetation found on them. Species growing on these soils are usually subjected to low concentrations of Ca, high concentrations of Mg, occasionally toxic levels of Ni, Cr, and Co, and deficiencies of Mo (proctor and (Woodell, 1975). N, P, K, and S deficiencies are known to be of importance on some serpentine soils (Jones, Williams, and Ruckman, 1977). Several workers have demonstrated that different species, and even different races of a species, growing on the same soil will differ in their elemental composition (Collander, 1941); (Lyon et al. 1971); (Shewry and Peterson, 1975); (Johnston and Proctor, 1977). These differences may reflect differences in mechanisms of adaptation to these soils (especially in the case of such inhospitable soils as serpentine soils), although they do not reveal what the mechanisms are or even what concentrations are optimum. Optimum concentrations of these elements need to be defined for each species. Experimental work, where the growth medium is varied under controlled conditions, is necessary to accurately define these optima (Walker, Walker, and Ashworth, 1955); (Marrsand Proctor, 1976). Nevertheless, the abundance and vigor of species in the field may prove to be related to soil and leaf concentrations of important elements. These relations might supply some information about optimum concentrations where experiment is impractical or where information is desired to help select species for further experimentation. Four species dominate in the study area: Cupressus sagentii, Quercus durata, Arctostaphylos viscida, and Adenostoma fasciculatum. Cupressus sargentii and Q. durata are considered to be serpentine endemics (McMillan, 1956). Arctostaphylos viscida occurs both on and off serpentine in the Sierra Nevada, but is restricted to it in the Coast Range of California, U.S.A., where this study took place (J. Major, personal communication). Althought Adenostoma fasciculatum is very widespread in chaparral in California, serpentine ecotypes may occur. Arctostaphylos viscida and Q. durata were the most widespread species in our study area. Sites containing C. sargentii had significantly lower concentrations of Ca in the soil than sites containing Adenostoma fasciculatum (Part I). Arctostaphylos viscida was more abundant where C. sargentii occurred, and Q. durata was more abundant where Adenostoma fasciculatum occurred. This paper examines differences in the concentration of elements in the four species. To improve understanding of the adaptive strategies of these species, it also correlates their abundance and size with nutrient concentrations in leaf and soil. Methods Forty sample stands were selected randomly from about 280 ha within the watersheds of Cedar and Pocock creeks (California, U.S.A.; latitude 38°47? N, longitude 122° 22? W). Within each stand, three transects, each 15 m long and 7.5 m apart, were laid out parallel to each other and to the contour of the slope in spring and summer, 1975,