Microclimate and Pedogenic Implications in a 50-Year-Old Chaparral and Pine Biosequence

Abstract

Vegetation, which is generally considered a co-variable controlled by climate in studies of pedogenesis, can itself alter the balance of soil-forming processes by modifying the microclimate. The chaparral and pine biosequence at the San Dimas Experimental Forest (SDEF) in southern California offers an opportunity to determine the effect of individual species on soil microclimate and related soil properties. Soil temperature and moisture were monitored under pure stands of Coulter pine (Pinus coulteri B. Don), chamise (Adenostoma fasciculatum Hook. and Arn.), and scrub oak (Quercus dumosa Nutt.). Despite the appreciable differences in soil morphology that have evolved under pine compared with oak, the microclimates created by the dense canopies and thick litter layers (7–10 cm) of these two vegetation types were similar. Average monthly soil temperatures within the top 65 cm ranged from about 8 to 20°C under pine and 7 to 18°C under oak. Average monthly water contents ranged from 8 to 32% (by volume) under pine and 6 to 32% under oak. In contrast, average monthly soil temperatures within the top 65 cm under chamise ranged from 6 to 23°C and average monthly water contents were 6 to 36%. Diurnal variation in soil surface temperature under chamise was much more pronounced than under oak and pine because of the relatively open canopy and thin litter layer. Microclimate created by chamise may play an important role in the decomposition rate of litter, but appears to have little influence on soil processes occurring within the mineral soil. Soil macrofaunal communities appear to have a greater effect than microclimate in causing the divergent soil morphologies under oak and pine.