Sheltered by trees – long-term yield dynamics in temperate alley cropping agroforestry with changing water availability

As warm season droughts increase in frequency due to climate change, causing severe yield losses especially among cereal crops, European agriculture is in dire need of adaptation. While agroforestry is widely regarded as a key adaptation measure, little is known on how yield performance is influenced by changing water availability. Therefore, we assessed the yield dynamics of five winter crops (winter wheat, triticale, winter barley, winter pea, and rapeseed) during seven growing seasons (2012 to 2023) in a well-established (since 2008) alley cropping agroforestry trial site in Southwestern Germany. The trial integrates three different agroforestry practices in a randomized block design: i) willow short-rotation coppice, ii) walnut trees for nut production, and iii) diverse hedgerows. The relationship between crop yield and climatic water balance was analysed using a linear mixed-model. In this unique long-term comparison, we demonstrate that individual alley cropping practices exhibited distinct yield patterns with increased distance to tree rows. In contrast to the willow short rotation coppice, walnut and hedgerows did not evoke significant winter crop yield declines in their close proximity. While in the walnut plots yields did not significantly vary at all with distance to tree rows, yields adjacent to hedge rows declined significantly towards the alley center. Moreover, inter-annual variation in water availability significantly influenced yield distribution across these distances. While yield response to changing climatic water balance varied with aspect, the tree rows overall contributed to stabilizing crop yields under fluctuating water availability as yields did not vary significantly close to trees. Our results underline the potential of agroforestry to sustain yields in the face of increasingly variable water availability. Therefore, substantiating the contribution of alley cropping agroforestry to resilient farming systems facing increasingly variable weather conditions, informing planning, policy support and agroforestry practice at advancing climate resilient agroforestry in temperate regions.