Investigating the effects of planting density and tree size on yield through functional-structural modeling

Abstract

Reducing planting distances is one of the strategies to increase yield in fruit orchards. The yield of an orchard increases with tree density, especially in the case of small tree canopies. However, orchard yield can decrease when trees planted at high densities have a large canopy size. In trees growing in optimal conditions, i.e., without water or nutrient stress, this yield reduction is likely to be the result of competition for light as well as an imbalance between vegetative and fruit growth. Separating these factors and their interactions in the field is not straightforward. Models of carbon acquisition and distribution between organs have been used to simulate and understand some factors affecting yield tree or within the tree. Modeling might help to understand better the effects of tree density and size on orchard yield. We employed a functional-structural tree model to simulate individual organ growth within the canopy as well as tree and orchard yield with different planting distances and tree size. This virtual plant combined sub-models of light interception, photosynthesis, potential relative growth rates of individual organs and inter-organ competition for carbon. Tree canopy architecture measured in the field was used to create several virtual orchard canopies with a range of tree sizes and planting distances. The model simulated growth and yield of individual trees and orchards during one growing season. Virtual experiments showed how different tree densities and sizes affected yield. It increased our understanding of and supported our hypotheses about the effects of planting distances and tree size on orchard yields, which can be useful for designing future field experiments and orchards.