Soil organic matter, mitigation of and adaptation to climate change in cocoa-based agroforestry systems

Summary

Belowground roles of agroforestry in climate change mitigation (C storage) and adaptation (reduced vulnerability to drought) are less obvious than easy-to-measure aspects aboveground. Documentation on these roles is lacking. We quantified the organic C concentration (C_org) and soil physical properties in a mountainous landscape in Sulawesi (Indonesia) for five land cover types: secondary forest (SF), multistrata cocoa-based agroforestry (CAF) aged 4-5 years (CAF4), 10-12 years (CAF10), 17-34 years (CAF17), and multistrata (mixed fruit and timber) agroforest (MAF45) aged 45-68 years. With four replicate plots per cover type, we measured five pools of C-stock according to IPCC guidelines, soil bulk density (BD), macro porosity (MP), hydraulic conductivity (K_s), and available water capacity of the soil (AWC). The highest C-stock, in SF, was around 320 Mg ha^-1, the lowest, 74 Mg ha^-1, was in CAF4, with the older agroforestry systems being intermediate with 120 to 150 Mg ha^-1. Soil compaction after forest conversion led to increased BD and reduced MP, Ks, and AWC. Older agroforestry partly recovered buffering: AWC per m of rooted soil profile increased by 5.7 mm per unit (g kg-1) increase of C_org. The restored AWC can support about a week's worth of evapotranspiration without rain, assisting in climate change adaptation.