The allometry of the weight of fruit on trees and shrubs in Barbados

Branch sampling of branch diameter and fruit crop on 22 species of Barbadian trees and shrubs provided sufficient data to build regressions between plant size and fruit crop weight. Orchard plants bear much more fruit than wild, feral or garden plants of similar size, but this difference disappears in multiple regression of fruit crop weight (F in g, fresh mass) on branch or stem diameter (D in cm) and individual fruit weight (W in g): F=22D^1.2 W^0.57. This explains 89% of the variation in F and successfully predicts crop weight for wild tropical and temperate trees and shrubs, but underestimated the crops on commercial, temperate, fruit trees by an order of magnitude. Comparisons of crop weight for feral, wild, and garden plants (F_f) using a simple regression F_f=47D^1.9 show that crop weight is a minor load relative to branch weight for larger branches. Although fruit crops represent a declining proportion of total plant weight as plants become larger, the crops become larger relative to leaf and twig weight and in this sense, reproductive investment increases in larger plants. Finally, our equations, combined with the self-thinning rule, suggest that stands of large species of fruit plants produce more fruit per unit of land area than stands of small ones.