| Intensively managed, short-rotation plantations have been established in the tropics at a rate of about 1.1 million ha yearly since 1980, and increasing agricultural and forest management intensity has been forwarded as a strategy to slow deforestation in the Amazon. The effects of intensive management and multiple rotations on soil structure and function are not known. Assuming that long-term site productivity is controlled by soil organic matter management and maintenance, this research investigated soil organic matter fluxes as indicators of long-term sustainability. The carbon cycling dynamics of Eucalyptus plantation soils were compared to identical, adjacent undisturbed primary forest soils on the Jari plantation in the Brazilian Amazon.; Soil fractionation results have quantified a shift in carbon from labile soil particle-size fractions to less labile fractions in the plantation on the sandy soil, indicating a possible decline in soil quality. Significant differences in the timing and amount of litterfall, microbial biomass, soil respiration rates, decomposition rates, fine root biomass, and soil and air temperatures were found in the plantation systems. This work has provided some insight into differences in factors controlling carbon cycling between native forests and plantations, and these results may indicate a decline in prospects for long-term sustainability of plantation systems on sandy soils. |
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