Limits to adaptation: Agroforestry buffers but does not offset climate change impacts on maize yields in Dodoma, Tanzania

Abstract Agricultural productivity in the semi-arid region of central Tanzania is low and projected to further decrease due to climate change, exacerbating the already high levels of food insecurity among the rural population. Agroforestry is actively promoted in the region as an adaptation strategy due to its multiple biophysical and socio-economic benefits, but whether it can buffer future climate change impacts on maize yields has not yet been quantified. Previous modelling studies in central Tanzania focused either on maize monocropping or on agroforestry under current climate. Moreover, it remains unclear whether yield gains from agroforestry constitute genuine adaptation. Here, we show for the first time how a comprehensive evaluation framework can be used to disaggregate projected yield changes into four distinct indicators: climate change impact, agroforestry impact, agroforestry adaptation effect, and climate change impact with adaptation. The Agricultural Production Systems Simulator was used to simulate maize yields at six sites in Dodoma under current climate conditions and under a low- and a high-emission scenario (shared socio-economic pathways 1-2.6 and 5-8.5) for two periods centred on 2030 (2016–2045) and 2050 (2036–2065). Above-ground agroforestry effects were represented by 10% and 20% shading, associated temperature reductions, and tree litter input. Without adaptation, climate change is projected to reduce maize yields by 23–33%. Agroforestry increased yields under all climate conditions, and the agroforestry adaptation effect grew towards 2050, with 20% shade being most effective. However, the climate change impact with adaptation shows that agroforestry buffers but does not offset yield losses: under the high-emission scenario, yields remained below the baseline at both shade levels, with losses increasing towards 2050. These results demonstrate both the potential and the limits of agroforestry as an adaptation strategy in semi-arid Tanzania.