Modeling seasonal branch carbon dynamics in pistachio as a function of crop load

•A branch carbon budget model was developed to study bearing pattern in pistachio.•spring growth relies on resource remobilization.•Embryo growth in July and August can deplete all the C assimilated by the branch.•A branch was not able to sustain energetically more than 28 fruits.•In-season dynamics of competition for C may limit productivity in pistachio.