Carbon pools in tree biomass and soils under rotational woodlot systems in Eastern Tanzania

Landscape approaches to carbon (C) accounting in agriculture, forest, and other land uses are being promoted as a win-win option for integrating climate change mitigation with sustainable rural development. However, limited data on the C sequestration potential of agroforestry systems in the semiarid tropics imply that subsistent farmers may not fully benefit from this opportunity. This chapter quantifies C stocks in biomass and soils in semiarid Morogoro, Tanzania to assess the potential of rotational woodlot systems to sequester C in the soil and offset carbon dioxide (CO2) emissions. Carbon levels in native vegetation fallows and forests were used as a reference to evaluate the efficacy of this system to minimize forest degradation and balance CO2 emissions. After a 5 year rotation, wood yield (23-51 Mg C ha-1) was sufficient to meet household demand for fuelwood. Carbon stocks in the highly productive fallows of Acacia crassicarpa A. Cunn. ex Benth., Acacia leptocarpa A. Cunn. ex Benth., and Acacia mangium Willd. (18-26 Mg ha-1) were similar to those in the Miombo forest reserves. Based on C accumulation rates, it would take 4-9 years for these fallows to recover C lost through forest clearance for agricultural expansion, compared to two or three decades for re-growing miombo woodlands. Tree fallows also enriched the soil organic C (16-26 Mg ha-1), in some cases (e.g., A. mangium) close to the reported value for miombo forest soils (28 Mg C ha-1). Overall, this study demonstrates the significant contributions of rotational woodlot systems to reduce forest degradation and offset CO2 emissions through on-farm wood supply. However, policies and programs that consider comprehensive approaches to avoid deforestation are needed to take full advantage of this system for climate change mitigation and adaptation.

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