Letters to Nature

Nature 400, 664-667 (12 August 1999) | doi:10.1038/23251; Received 27 November 1998; Accepted 20 May 1999

A general model for the structure and allometry of plant vascular systems

Geoffrey B. West1,2, James H. Brown2,3 & Brian J. Enquist2,3

  1. Theoretical Division, T-8, MS B285, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  2. The Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico 87501, USA
  3. Depatment of Biology, University of New Mexico, Albuquerque, New Mexico 87131 , USA

Correspondence to: Brian J. Enquist2,3 Correspondence and requests for materials should be addressed to B.J.E. (e-mail: Email: benquist@unm.edu).

Vascular plants vary in size by about twelve orders of magnitude, and a single individual sequoia spans nearly this entire range as it grows from a seedling to a mature tree. Size influences nearly all of the structural, functional and ecological characteristics of organisms1,2. Here we present an integrated model for the hydrodynamics, biomechanics and branching geometry of plants, based on the application of a general theory of resource distribution through hierarchical branching networks3 to the case of vascular plants. The model successfully predicts a fractal-like architecture and many known scaling laws, both between and within individual plants, including allometric exponents which are simple multiples of 1/4. We show that conducting tubes must taper and, consequently, that the resistance and fluid flow per tube are independent of the total path length and plant size. This resolves the problem of resistance increasing with length, thereby allowing plants to evolve vertical architectures and explaining why the maximum height of trees is about 100 m. It also explains why the energy use of plants in ecosystems is size independent.