Evaluating Physiological Efficiencies of Branching Structure in Low-intensity Tart Cherry and High-density Apple

Branch angle, rotation, and probability of termination have been used to describe the set of all possible branching structures, which can then be evaluated for their weight bearing capacity and light interception (Nikals & Kerchner, 1984, Paleobiology). This model has been updated and adapted to determine the range of generalized branching structures that occur among orchard systems. Pruning experts recommend maintaining 30° to 60^o angles at branching nodes to optimally balance vegetative and reproductive growth. Often ties or weights are used to set these angles within the primary support branches or scaffolds. Does this “optimal angle” occur without such human manipulation in secondary branches? Does the “optimal angle” hold with the increase of management intensity? What effects does this branching angle have on light capture and biomass? Using data from a low intensity tart cherry (Prunus cerasus, mahaleb) and a high-density apple (Malus x domestica) at the Kaysville Experimental Orchard, Utah State University, I establish branching parameters to model the trees’ branching architecture and test how tree growth changes with various human manipulations (i.e. pruning). The model developed from this exercise tests the consequences of various horticultural management strategies on tree fruit physiology in the context of established scaling theory in ecology. It appears that primary branches of low-intensity tart cherry maintain an average of 30^o angles, while terminal branches, which are pruned less, maintain somewhat narrower angles. High-density apples appear to deviate strongly from the low-intensity cherry system and are managed primarily with nearly horizontal lateral branches. The model developed is instrumental in defining branching characteristics of tart cherry trees and will be used to develop high-density tart cherry systems using the high-density apple system as a template. These models are being developed using ecological scaling theory to incorporate plant physiological efficiencies along with the human induced forces inherent in horticulture.