Branch Thinning and the Large-Scale, Self-Similar Structure of Trees.

Branch Thinning and the Large-Scale, Self-Similar Structure of Trees.
Am Nat. 2018 Jul;192(1):E37-E47
Authors: Hellström L, Carlsson L, Falster DS, Westoby M, Brännström Å
Abstract
Branch formation in trees has an inherent tendency toward exponential growth, but exponential growth in the number of branches cannot continue indefinitely. It has been suggested that trees balance this tendency toward expansion by also losing branches grown in previous growth cycles. Here, we present a model for branch formation and branch loss during ontogeny that builds on the phenomenological assumption of a branch carrying capacity. The model allows us to derive approximate analytical expressions for the number of tips on a branch, the distribution of growth modules within a branch, and the rate and size distribution of tree wood litter produced. Although limited availability of data makes empirical corroboration challenging, we show that our model can fit field observations of red maple (Acer rubrum) and note that the age distribution of discarded branches predicted by our model is qualitatively similar to an empirically observed distribution of dead and abscised branches of balsam poplar (Populus balsamifera). By showing how a simple phenomenological assumption-that the number of branches a tree can maintain is limited-leads directly to predictions on branching structure and the rate and size distribution of branch loss, these results potentiall...

Source: The American Naturalist - June 15, 2018 Category: Biology Authors: Hellström L, Carlsson L, Falster DS, Westoby M, Brännström Å Tags: Am Nat Source Type: research