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

Abstract

[1] 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 (À0.5% or À5012 Gg), spatially explicit maps suggest dramatic local changes, ranging from À76% 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.

Changes in soil organic carbon of terrestrial ecosystems in China: A mini-review

“…The monitoring sites would exponentially increase for an improvement in the precision [102]. To reduce uncertainties in the estimates of SOC change, measurements should be made at a sufficient number of sites, allowing for upscaling of these site-specific measurements to a finite area [24,103]. Unfortunately, the measurements of SOC in woodland and shrubland in the 2000s are rather deficient in China, which inevitably introduces errors into measurement-based estimates.…”

Estimates of fire emissions from an active deforestation region in the southern Amazon based on satellite data and biogeochemical modelling

“…Although our results show that in these areas fire emissions may provide a reasonable proxy for carbon losses from deforestation over short timescales if emissions from non-deforestation fires (7%) are subtracted, over longer timescales emissions could be substantially higher than those from fires only due to ongoing soil respiration (Fearnside and Barbosa, 1998). In areas with low soil carbon density, however, conversion from forest to pasture may actually increase soil carbon stocks (Holmes et al, 2006) and more detailed spatial-specific modelling is needed to fully understand the contribution of soil carbon dynamics following deforestation. We aim to include this in future DECAF versions.…”

“…In addition, the monthly time step of our model results will be suitable for use in atmospheric transport models, facilitating a comparison with atmospheric measurements providing top-down constraints on the bottom-up modelled emissions. Emissions from ongoing soil respiration can be large and are more difficult to validate than fire emissions, partly due to large spatial variability (Holmes et al, 2006), and should be an area of intense future research to allow for reliable estimates of deforestation carbon emissions. For estimates of overall net flux from deforestation over decadal time scales, carbon uptake from regrowth as well as initial fire and respiration emissions need to be included.…”

Optimising carbon sequestration in arid and semiarid rangelands

“…Potential biomass defined by remnant vegetation was most probably underestimated, due to almost ubiquitous forest degradation and because farmers usually deforest the mostproductive land first (Pressey et al, 1996;Holmes et al, 2006). The strongest effects of this selective process were near major rivers, and in the arid west where there was woody biomass attrition without broad-scale deforestation.…”