Edaphic Climax Pattern of the Pygmy Forest Region of California

The dwarfed conifer forests occurring on the coastal terraces of Mendocino County, California, are oligotrophic communities containing edaphic endemics as dominants. Species distributions and community characteristics are traced along a gradient in podzolization of the soils from these pygmy conifer stands on highly weathered terrace spodosols, to redwood stands on weakly developed slope spodsols. Vegetation stature, canopy closure, species richness, litter biomass and pH generally decrease along the gradient as podzolization and nutrient impoverishment increase, whereas soil organic matter and available water capacity tend to be highest at the gradient extremes. Analyses of pygmy forest soils show low levels of macro— and micro—nutrients, and high levels of exchangeable aluminum. When ordinations of stands based on vegetational data are compared with rankings based on environmental data, changes in pH of the soil A horizon are found to correlate most highly with vegetation changes. Nutrient loss and acidification, initiated by varying rates of soil weathering in the pygmy forest region, may be aggravated, in the case of pygmy forest soils, by a series of feedback effects, including solubilization of possibly toxic amounts of aluminum by low pH, which may contribute to the observed plant stunting and shrinking pools of nutrients in the biomass. A ranking of stands along a soil nutrient gradient, based on field observations and presence data for species, correlated successively less strongly with ordinations computed by similarity—projection, Bray—Curtis method, importance—projection, principal components analysis, and factor analysis. Although these ordinations were expected to produce distortions in the interstand relations due to the modal and even polymodal nature of species response curves and to the presence of species not spanning the range of the data set, additional distortions due to variability in sample data were also highlighted.