© 2005 Heron Publishing—Victoria, Canada
DESPOT, a process-based tree growth model that allocates carbon to maximize carbon gain
Thomas N. Buckley (1, 2, 3) and David W. Roberts (4)
1. Environmental Biology Group and CRC for Greenhouse Accounting, Research School of Biological Sciences, The Australian National
University, Canberra, ACT 2601, Australia / 2. Biology Department, Utah State University, Logan, UT 84322, USA / 3. Corresponding author (tom_buckley@alumni.jmu.edu) / 4. Ecology Department, 310 Lewis Hall, Montana State University, Bozeman, MT 59717, USA / Received March 15, 2005; accepted July 28, 2005; published online November 8, 2005
Summary
We present a new model of tree growth, DESPOT (Deducing Emergent Structure and Physiology Of Trees), in which carbon (C) allocation
is adjusted in each time step to maximize whole-tree net C gain in the next time step. Carbon gain, respiration and the acquisition
and transport of substitutable photosynthetic resources (nitrogen, water and light) are modeled on a process basis. The current
form of DESPOT simulates a uniform, monospecific, self-thinning stand. This paper describes DESPOT and its general behavior
in comparison to published data, and presents an evaluation of the sensitivity of its qualitative predictions by Monte Carlo
parameter sensitivity analysis. DESPOT predicts determinate height growth and steady stand-level net primary productivity
(NPP), but slow declines in aboveground NPP and leaf area index. Monte Carlo analysis, wherein the model was run repeatedly
with randomly different parameter sets, revealed that many parameter sets do not lead to sustainable NPP. Of those that do
lead to sustainable growth, the ratios at maturity of net to gross primary productivity and of leaf area to sapwood area are
highly conserved.
Keywords:
C allocation, forest productivity, optimality, photosynthesis, tree height, water relations.
