The alley-cropping systems (ACSs), which integrate parallel tree strips at varying distances on an agricultural field can result, complementarity of resource use, in an increased land-use efficiency. Practitioners’ concerns have been directed towards the productivity of such systems given a reduced area covered by agricultural crops. The land equivalent ratio (LER) serves as a valuable productivity indicator of yield performance and land-use efficiency in ACSs, as it compares the yields achieved in monocultures to those from ACSs. Consequently, the objective of this combined experimental and simulation study was to assess the tree- and crop-yields and to derive the LER and gross energy yield for two temperate ACSs in Germany under different design scenarios, i.e., tree arrangements (lee- or wind-ward) and ratios of tree area to crop area. Both LER and gross energy yields resulted in a convex curve where the maximum values were achieved when either the tree or crop component was dominant (>75% of the land area) and minimum when these components shared similar proportions of land area. The implications of several design scenarios have been discussed in order to improve the decision-making, optimization, and adaptation of the design of ACSs with respect to site-specific characteristics
In Brandenburg, eastern Germany, prospective climate changes imply extreme weather events, increasing annual temperature, and decreasing summer precipitation. Since alley-cropping systems (ACS) have a broad planning horizon, appraising their sustainability and efficiency under changing climate conditions is crucial for forthcoming risk assessments and adaptation scenarios. Consequently, this combined experimental and simulation study investigated the growth vulnerability of poplar clone “Max I” (Populus nigra L. x P. maximowiczii Henry) and black locust (Robinia pseudoacacia L.) short rotation coppices in an ACS established in Brandenburg to a considerable spectrum of weather conditions and long term climate change, from 2015 to the end of 2054. The investigation employed (i) Yield-SAFE, a biophysical, process-based model to simulate the above-ground tree woody biomass and (ii) 100 realisations of the statistical regional climate model STAR 2K. In the most optimistic sequence of events pertaining to air temperature, precipitation, and global radiation, 35% more woody biomass would be achieved by poplar and 43% by black locust in the last period compared to the base period. Alternatively, in the most pessimistic circumstances, 54% less woody biomass would be rendered by poplar and 47% by black locust. Our findings corroborated the tree growth vulnerability to prospective climatic changes, particularly to changes in water availability.