The impact of tree height and distance on crop yields in a temperate short rotation alley cropping agroforestry system: a multi-year study

Abstract Alley cropping agroforestry systems (ACS) integrate rows of trees with rows of crops, creating diverse cropping systems. This study compared the dry matter yields of two winter crops, i.e. winter wheat and winter oilseed rape, and two spring crops, i.e. silage maize and spring barley, in a temperate ACS that integrates rows of short rotation coppice trees with 48 m wide crop alleys with the yields of treeless open cropland as a function of tree height and distance from the tree row. Our study used generalised linear mixed effects models to analyse yield data generated in Wendhausen, northern Germany, from 2016 to 2024. Relative crop yields in the ACS were significantly reduced at a distance of 1 m from tree rows for all crops and at a distance of 4 m for silage maize, suggesting that competitive effects influencing yield are limited to a zone immediately adjacent to the tree rows. Mean relative ACS crop yields were always lower than those at the corresponding distances in the reference crop, except for maize at 24 m. Overall, tree height had a negative effect on the relative crop dry matter yield at 1 m from the tree row. A significant negative effect of increasing tree height on dry matter yield was only detected for spring barley, whereas no effect was observed for silage maize and winter wheat. If possible, poplar harvesting intervals should be adapted to prevent trees from growing too tall.