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| Background: The carbon stored in vegetation varies across tropical landscapes due to a complex mix of climatic
and edaphic variables, as well as direct human interventions such as deforestation and forest degradation. Mapping
and monitoring this variation is essential if policy developments such as REDD+ (Reducing Emissions from
Deforestation and Forest Degradation) are to be known to have succeeded or failed.
Results: We produce a map of carbon storage across the watershed of the Tanzanian Eastern Arc Mountains (33.9
million ha) using 1,611 forest inventory plots, and correlations with associated climate, soil and disturbance data. As
expected, tropical forest stores more carbon per hectare (182 Mg C ha-1) than woody savanna (51 Mg C ha-1). However,
woody savanna is the largest aggregate carbon store, with 0.49 Pg C over 9.6 million ha. We estimate the whole
landscape stores 1.3 Pg C, significantly higher than most previous estimates for the region. The 95% Confidence
Interval for this method (0.9 to 3.2 Pg C) is larger than simpler look-up table methods (1.5 to 1.6 Pg C), suggesting
simpler methods may underestimate uncertainty. Using a small number of inventory plots with two censuses (n = 43)
to assess changes in carbon storage, and applying the same mapping procedures, we found that carbon storage in the
tree-dominated ecosystems has decreased, though not significantly, at a mean rate of 1.47 Mg C ha-1 yr-1 (c. 2% of the
stocks of carbon per year).
Conclusions: The most influential variables on carbon storage in the region are anthropogenic, particularly historical
logging, as noted by the largest coefficient of explanatory variable on the response variable. Of the non-anthropogenic
factors, a negative correlation with air temperature and a positive correlation with water availability dominate, having
smaller p-values than historical logging but also smaller influence. High carbon storage is typically found far from the
commercial capital, in locations with a low monthly temperature range, without a strong dry season, and in areas
that have not suffered from historical logging. The results imply that policy interventions could retain carbon
stored in vegetation and likely successfully slow or reverse carbon emissions | |
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