Hi-sAFe: A 3D Agroforestry Model for Integrating Dynamic Tree–Crop Interactions

Abstract

Agroforestry, the intentional integration of trees with crops and/or livestock, can lead to multiple economic and ecological benefits compared to trees and crops/livestock grown separately. Field experimentation has been the primary approach to understanding the tree–crop interactions inherent in agroforestry. However, the number of field experiments has been limited by slow tree maturation and difficulty in obtaining consistent funding. Models have the potential to overcome these hurdles and rapidly advance understanding of agroforestry systems. Hi-sAFe is a mechanistic, biophysical model designed to explore the interactions within agroforestry systems that mix trees with crops. The model couples the pre-existing STICS crop model to a new tree model that includes several plasticity mechanisms responsive to tree–tree and tree–crop competition for light, water, and nitrogen. Monoculture crop and tree systems can also be simulated, enabling calculation of the land equivalent ratio. The model’s 3D and spatially explicit form is key for accurately representing many competition and facilitation processes. Hi-sAFe is a novel tool for exploring agroforestry designs (e.g., tree spacing, crop type, tree row orientation), management strategies (e.g., thinning, branch pruning, root pruning, fertilization, irrigation), and responses to environmental variation (e.g., latitude, climate change, soil depth, soil structure and fertility, fluctuating water table). By improving our understanding of the complex interactions within agroforestry systems, Hi-sAFe can ultimately facilitate adoption of agroforestry as a sustainable land-use practice.

Nutrient acquisition strategies in agroforestry systems

“…However, modification of the available soil volume for trees was suggested to increase black walnut (Juglans nigra) rooting density in the smaller soil volume and subsequently increased the allelopathic juglone in the tree rows (Jose and Gillespie 1998), with potential impacts on other species in non-excluded areas. Pruning has also been shown to modify the depth at which trees in agroforestry systems acquire nutrients (Rowe et al 2006), and is now being included in important process-based agroforestry models that estimate root architecture in 3-dimensions (Dupraz et al 2019) However, we note that active suppression of direct competition between tree and crop roots may also be circumventing other important sources of complementarity and facilitation within common rooting zones that are a function of root-root interactions.…”

“…Uptake potential is derived from the summed crop and tree components capacity for uptake as indicated by their root length and nutrient concentration in soil, and the nutrient demands of the crop and tree components as indicated by plant biomass. More recent advancements in the Hi-sAFe model, parameterized for temperate agroforests with deciduous trees, account for vertical and horizontal N acquisition patterns of trees in agroforests through 3-dimensional voxels that can include some key nutrient acquisition parameters such as fine root lifespan and specific root length as well as fraction of colonized roots (Dupraz et al 2019). These tree structure and acquisition patterns then impact the crop component, including inputs of additional N from senesced tree roots, although the belowground processes modelled (e.g.…”

Simulating the effects of water limitation on plant biomass using a 3D functional–structural plant model of shoot and root driven by soil hydraulics

“…Postma and Lynch 2012), while other models specifically designed for intercropping (e.g. Dupraz et al 2019) may consider light environment and soil resources (e.g. water and nitrogen) but be designed to work on very different scales.…”

Oil Palm Agroforestry Can Achieve Economic and Environmental Gains as Indicated by Multifunctional Land Equivalent Ratios

“…However, long-term experiments require a lot of time, labour, funds and persistence. Three-dimensional models of all above-and belowground interactions in resource capture are in development but are not yet easy to parameterize and use (Dupraz et al, 2019). Hence, this study relied on a well-established tree-soil-crop interaction model called Water, Nutrient and Light Capture in Agroforestry System (WaNuLCAS) (van Noordwijk and Lusiana, 1999;van Noordwijk et al, 2011) and the Biofuel Emission Reduction Estimator Scheme (BERES) (van Noordwijk et al, 2013).…”