SOIL DEVELOPMENT ALONG AN ELEVATIONAL TRANSECT IN THE WESTERN SIERRA-NEVADA, CALIFORNIA

Soil development along an elevational transect on the western slopes o f the central Sierra Nevada was investigated to assess the effects of climate on soil properties and processes, The transect of seven soils formed in granitic residuum spans elevations from 198 to 2865 m with m ean annual temperature and precipitation differences of 13 degrees C ( 3.9-16.7) and 94 cm (33-127), respectively. Soil pH decreased by about two units and base saturation decreased from 90 to 10% with increasin g elevation. Concentrations of organic C in the solum increased with e levation, with the largest single increase occurring between the oak w oodland (5-6 kg C/m(2)) and mixed-conifer sites (10-15 kg C/m(2)). Cla y mineralogy showed a general trend of desilication and hydroxy-Al int erlayering of 2:1 layer silicates with increasing elevation, The degre e of chemical weathering, based on clay and secondary Fe oxide concent rations in the solum, showed a maximum (clay = 536 kg/m(2) and Fe oxid es = 24 kg/m(2)) at mid-elevations having intermediate levels of preci pitation and temperature. While some soil properties show a continuous progression (e.g., organic carbon, base saturation, clay mineralogy) with elevation, other properties (e.g., pH, soil color, clay and secon dary Fe oxide concentrations) show a pronounced change (threshold-type step) over a short distance at about 1600 m. The explanation for the abrupt nature of this shift is not known; however, it coincides with t he approximate elevation of the present-day average effective winter s now-line. (C) 1997 Elsevier Science B.V.