Abstract
We investigated the effects of land-use changes on soil carbon storage and soil CO2 flux by comparing soils from mature cloud forest and 31-year-old secondary forest, both in the Santa Elena Forest Reserve, a municipallyowned reserve at an elevation of 1600 to 1700 m near the town of Monteverde, and a clear-cut pasture near the reserve. Soils in the mature forest exhibit only weak horizonation but typically thick A horizons; they also consistently yield the highest carbon contents in the upper 30 cm. Soil CO2 flux was the highest in these soils, but also displayed the highest spatial variability. Secondary forest soils contain substantially less soil carbon than mature forest soils, but more than pasture soils. CO2 flux in the secondary forest soils was more similar to that of the mature forest, but displayed lower spatial variability. The pasture soils contain less soil carbon and produced lower CO2 flux levels than either of the forest soils. The pasture soils typically contain a well-defined coarse sandy layer 10 to 20 cm below the surface that we interpret as a sediment layer deposited across much of the landscape following a widespread erosion event, likely a consequence of the clear-cutting. Soil nitrogen concentrations are more than an order of magnitude lower than soil carbon concentrations, and display no trends between the different landscapes examined. Our preliminary results suggest that reforestation does restore soil carbon to clear-cut landscapes, but returning soil carbon levels to pre-land use levels occurs at a time scale of centuries, rather than decades.
Highlights
Modeling of the anthropogenic climate change anticipated in the coming decades requires a thorough understanding of the carbon cycle, in particular, the various sources and sinks of carbon exchangeable on short time scales
The laboratory analyses of the soil samples from Santa Elena demonstrate that the soil carbon content in all three landscapes has very significant spatial variability, in the upper 10 cm (Table 1, Figure 4(a))
The soil carbon data provide substantive evidence that a great amount of soil carbon is lost during deforestation of cloud forests; at the landscape level, we find that the pasture soils contain 20% less carbon than the mature forest soils in the upper 30 cm
Summary
Modeling of the anthropogenic climate change anticipated in the coming decades requires a thorough understanding of the carbon cycle, in particular, the various sources and sinks of carbon exchangeable on short (decadal) time scales. Studies of carbon cycling recognized the importance of land-use changes, deforestation and afforestation in particular, and attendant fluctuations in above-ground biomass carbon in contributing to fluctuations in the atmospheric reservoir. Mellilo and others [2] estimated that deforestation contributes 23% of the anthropogenic CO2 increase to the atmospheric reservoir, 75% of which is from aboveground biomass, and the remainder from lost soil carbon. A more complete understanding of the rates of change of these carbon stocks will be required to track accurately the changes in the global carbon cycle. Predicting changes in the size of these carbon reservoirs in the future, required for effective modeling of potential climate change, will demand knowledge of OPEN ACCESS
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