Knowledge Bank

Forest Gardens are a sustainable agroforestry farming practice implemented in regions around the world experiencing varying climate regimes. They utilize multiple canopy layers, the lower canopy being crops, and the other canopies being a combination of trees, shrubs, or other vegetation types. Forest Gardens are motivated by the goals of increasing ecosystem carbon sequestration, and alleviating heat and moisture stress through modulated microclimates. However, the extent to which ecosystem functions, including plant water use, carbon sequestration, and crop yield, could benefit from the implementation of Forest Gardens has not been quantified. The success of Forest Gardens also depends on sustainable irrigation strategies to optimize management goals, which requires mechanistic quantification. Here, focusing on a typical Forest Garden located in Senegal, I used in situ collected meteorological and soil moisture conditions to characterize microclimates in multi-layer canopies. The dataset was used to force an ecohydrological model to simulate soil evaporation loss, plant water use, and plant carbon sequestration under varying microclimate conditions. Specifically, I implemented two canopy structures, one with single canopy layer representing a traditional farm set up and the other with dual canopy layers representing the structure of a typical Forest Garden. I tested the impacts of dual canopy structure on ecosystem water consumption, carbon uptake and water use efficiency. Different water use strategies of trees and crops were also evaluated by modulating plant hydraulic traits. The results show that a dual-layer canopy structure of Forest Gardens alleviates the heat and atmospheric moisture stress for plants and reduces soil evaporation loss. As a result, Forest Gardens offer higher ecosystem water use efficiency, stronger carbon sink. The crop yield also likely exceeds that of traditional farms when provided with sufficient irrigation, especially for crops with an aggressive water use strategy. Nevertheless, when irrigation supply is limited, aggressive water using plants in Forest Gardens likely suffer stomatal closure, thereby restricting carbon uptake and increasing the risk of plant mortality. The findings provide support for the benefit of Forest Gardens on increasing carbon sequestration and reducing water loss. Due to tradeoffs among ecosystem functions, optimal and plant water use and irrigation strategies irrigation should be identified based on specific objectives and priorities among multiple objectives. Further in situ measurements are required to assess model uncertainties to provide robust scientific support for sustainable agroforestry management.