Large‐area spatially explicit estimates of tropical soil carbon stocks and response to land‐cover change

Studies of tropical soil organic carbon (SOC) response to deforestation present conflicting results, confounding estimates of the regional effects of land‐cover change on carbon storage. We calculated the change in SOC stocks due to deforestation through 1996 for the state of Rondônia, Brazil, in the southwestern Amazon basin. Whereas the net change in SOC for the state as a whole was slightly negative (−0.5% or −5012 Gg), spatially explicit maps suggest dramatic local changes, ranging from −76% to +74%, with outliers as high as +330%. The direction and magnitude of change in SOC following forest clearing is related to original forest soil carbon and pH, which in turn provides a general measure for overall nutrient availability and possible toxicities. When native soil carbon is high, SOC decreases in response to land‐cover conversion from forest to pasture; conversely, low soil carbon and low soil fertility lead to gains in carbon under pasture. Mapping variability, rather than relying on large‐area averages, illustrates why results from individual field sites have been contradictory.