SOILS AND CONIFER FOREST PRODUCTIVITY ON SERPENTINIZED PERIDOTITE OF THE TRINITY OPHIOLITE, CALIFORNIA

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Abstract
The productivity of 22 soils on serpentinized peridotite, as determined by either the Dunning site index (DSI) for mixed conifers or the timber yield index (TYI), is more closely related to the surface (0 to 30 cm) soil Ca/Mg ratio in either ammonium acetate or citrate-dithionite (CD) extracts than to any combination of climatic and physical soil variables or to the Fe, Mn, Cr, Ni, or Co contents in CD extracts. The coefficient of determination of an equation for the TYI as a function of the exchangeable Ca/Mg ratio is 0.87, increasing to 0.93 upon adding a function of the plant-available-water capacity (AWC) in 1 m of soil. Manganese is the only transition element whose content in CD extracts is correlated significantly with the DSI or the TYI, and that correlation appears to be fortuitous. The soil organic carbon content in 0.6 m of soil is a function of productivity, or the TYI (r2 = 0.53). © Williams & Wilkins 1989. All Rights Reserved.