Modification of the microclimate and water balance through the integration of trees into temperate cropping systems

Abstract

Climate change scenarios predict an increased occurrence of droughts and heatwaves, as well as extreme rainfall events in Central Europe. Alley cropping, which is the inclusion of rows of trees and shrubs in agricultural land, could enhance the resilience of cropping systems, as these systems are expected to positively modify the microclimate and water balance of croplands. This review analyses the effect of alley cropping on the microclimate and water balance, based on the available evidence from temperate alley cropping systems. Within alley cropping systems, the tree rows generate gradients in microclimatic variables, whereby strongest effects are observed in or close to the tree rows. Field-scale studies on light intensity (n=20), wind speed (n=4) and surface runoff (n=3) all reported a reduction compared to sole cropping systems. Effects on air temperature (n=10), relative humidity (n=5) and evapotranspiration (n=6) varied among studies, with the majority reporting a decrease in daytime temperatures (50% of studies), variable effects on relative humidity (60%) and an increase in evapotranspiration (50%) due to higher evapotranspiration by trees. Highest variation among studies was found for soil moisture, with 41% of studies reporting temporal and spatial differences within the system. This variation among studies likely depends on the purpose of the trees (short rotation coppice vs. fruit and/or timber trees) and design of the system. Also site context, such as topography, landscape diversity and climate, could play a role, but these factors are rarely taken into account. Only few studies investigated landscape-scale effects (n=3), such as groundwater recharge and moisture recycling. Future research should investigate the role of site context in the functioning of alley cropping systems and quantify landscape-scale effects. The process understanding gained from those studies will contribute to designing alley cropping systems that enhance the climate change resilience of current central European cropping systems.