What is the best tree density?

Question

I want to benefit from the positive effects of trees, but avoid tree-crop competition, what is the best tree density for alley cropping systems? Or would it be better to have trees only in the hedgerows to limit tree-crop competition?

Answer 1

There is no generic answer valid for all pedoclimatic conditions and all tree-crop associations. Another important factor to take into account is also your own priorities (tree growth vs crop yield vs other environemental services). Modelling can help virtually testing different tree densities (and spatial design: within-row and inter-row distances) in a given set of conditions to find the best balance between facilitation (what you call the beneficial effects) and competition between trees and crops. For example, a study commissioned by the French water agency showed that increasing the density of trees along the tree line while increasing the distance between tree lines increased crop yield for a given tree density (but decreased tree yield) and at the same time reduced nitrogen leaching (for some but not all sites)