Abstract

Terrestrial stocks of soil carbon (C) are an important part of the global C budget, and are considered in the Kyoto Protocol. However, there have been few studies in forested regions over the influence of land-use changes on volcanic soils (Andisols) and its simulation through models. The objective of this study was to determine the influence of native forest, pine plantation, and pasture on the C content and organic matter quality in an Andisol of the Chilean Patagonia, and to simulate the effects using the CO2FIX model. The model was calibrated to each land-use area, and C content was determined in lenga (Nothofagus pumilio) and pine (Pinus ponderosa) trees using previously derived allometric equations, and in pasture by direct measurement. The C content was measured in soils (0-100-cm depth) (Typic Hapludands; Umbric Andosols), and the light (>212 µm), intermediate (212-53 µm), and heavy (<53 µm) fractions of organic matter (0-40-cm depth) which have progressively lower labilities. Total C (vegetation+soil) in the lenga forest was greater than in the pine plantation or pasture, but the C content in soil was greater in the pasture than in the other areas. Over all sites, there was more C in the light fraction than in the intermediate and heavy fractions at 0-5-cm depth, but C content was greater in the heavy fraction with increasing soil depths. However, the quality of soil organic matter was better in the lenga forest compared with the other sites, as indicated by higher ratios of light fraction C between 0-20- and 20-40-cm depths. CO2FIX adequately simulated the C contents in the vegetation, and recalibration for slower degradation rates of soluble organic compounds in Andisols provided better approximation of C content in soil, but overestimated the content of labile C.