## Abstract

Summary: The West, Brown, Enquist (WBE) model derives symmetrically self-similar branching to predict metabolic scaling from hydraulic conductance, K, (a metabolism proxy) and tree mass (or volume, V). The original prediction was K∝V^{0.75}. We ask whether trees differ from WBE symmetry and if it matters for plant function and scaling. We measure tree branching and model how architecture influences K, V, mechanical stability, light interception and metabolic scaling. We quantified branching architecture by measuring the path fraction, P_{f}: mean/maximum trunk-to-twig pathlength. WBE symmetry produces the maximum, P_{f} = 1.0. We explored tree morphospace using a probability-based numerical model constrained only by biomechanical principles. Real tree P_{f} ranged from 0.930 (nearly symmetric) to 0.357 (very asymmetric). At each modeled tree size, a reduction in P_{f} led to: increased K; decreased V; increased mechanical stability; and decreased light absorption. When P_{f} was ontogenetically constant, strong asymmetry only slightly steepened metabolic scaling. The P_{f} ontogeny of real trees, however, was 'U' shaped, resulting in size-dependent metabolic scaling that exceeded 0.75 in small trees before falling below 0.65. Architectural diversity appears to matter considerably for whole-tree hydraulics, mechanics, photosynthesis and potentially metabolic scaling. Optimal architectures likely exist that maximize carbon gain per structural investment.

Original language | English (US) |
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Pages (from-to) | 217-229 |

Number of pages | 13 |

Journal | New Phytologist |

Volume | 201 |

Issue number | 1 |

DOIs | |

State | Published - Jan 2014 |

## Keywords

- Branching symmetry
- Euler buckling
- Hydraulic architecture
- Light interception
- Metabolic scaling theory
- Plant allometry
- West Brown and Enquist

## ASJC Scopus subject areas

- Physiology
- Plant Science