Deviation from symmetrically self-similar branching in trees predicts altered hydraulics, mechanics, light interception and metabolic scaling
Article first published online: 17 SEP 2013
© 2013 The Authors. New Phytologist © 2013 New Phytologist Trust
Volume 201, Issue 1, pages 217–229, January 2014
How to Cite
Smith, D. D., Sperry, J. S., Enquist, B. J., Savage, V. M., McCulloh, K. A. and Bentley, L. P. (2014), Deviation from symmetrically self-similar branching in trees predicts altered hydraulics, mechanics, light interception and metabolic scaling. New Phytologist, 201: 217–229. doi: 10.1111/nph.12487
- Issue published online: 26 NOV 2013
- Article first published online: 17 SEP 2013
- Manuscript Accepted: 8 AUG 2013
- Manuscript Received: 1 MAY 2013
- NSF. Grant Number: IBN-0743148
- ATB. Grant Number: 0742800
- branching symmetry;
- Euler buckling;
- hydraulic architecture;
- light interception;
- metabolic scaling theory;
- plant allometry;
- West Brown and Enquist
- 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∝V0.75. 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, Pf: mean/maximum trunk-to-twig pathlength. WBE symmetry produces the maximum, Pf = 1.0. We explored tree morphospace using a probability-based numerical model constrained only by biomechanical principles.
- Real tree Pf ranged from 0.930 (nearly symmetric) to 0.357 (very asymmetric). At each modeled tree size, a reduction in Pf led to: increased K; decreased V; increased mechanical stability; and decreased light absorption. When Pf was ontogenetically constant, strong asymmetry only slightly steepened metabolic scaling. The Pf 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.