Abstract
A dynamic model for growth and mortality of individual plants in a stand was developed, based on the process of canopy photosynthesis, and assuming an allometric relationship between plant height and weight, i.e. allocation growth pattern of plant height and stem diameter. Functions G(t, x), for the mean growth rate of individuals of size x at time t, and M(t,x), for the mortality rate of individuals of size x at time t, were developed from this model and used in simulations. The dynamics of size structure were simulated, combining the continuity equation model, a simple version of the diffusion model, with these functions. Simulations reproduced several well-documented phenomena: (1) size variability in terms of coefficient of variation and skewness of plant weight increases at first with stand development and then stabilises or decreases with an onset of intensive self-thinning; (2) during the course of self-thinning, there is a power relationship between density and biomass per unit ground area, irrespective of the initial density and of the allocation-growth pattern in terms of the allometric parameter relating plant height and weight. The following were further shown by simulation: (a) competition between individuals in a crowded stand is never completely one-sided but always asymmetrically two-sided, even though competition is only for light; (b) plants of ‘height-growth’ type exhibit a greater asymmetry in competition than plants of ‘diameter-growth’ type, (c) the effect of competition on the growth of individuals in a crowded stand converges to a stationary state, even when the stand structure still changes greatly. All of these theoretical results can explain recent empirical results obtained from several natural plant communities. Finally, a new, general functional form for G(t, x) in a crowded stand is proposed based on these theoretical results, instead of a priori or empirical growth and competition functions.
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Claims 6
Claim · model-written summary
The model reproduced an initial increase in plant weight size variability followed by stabilization or decline with intensive self-thinning.
Verbatim
e0“size variability in terms of coefficient of variation and skewness of plant weight increases at first with stand development and then stabilises or decreases with an onset of intensive self-thinning”
Claim · model-written summary
During self-thinning, simulated stand density and biomass per ground area followed a power relationship irrespective of initial density or allocation pattern.
Verbatim
e0“there is a power relationship between density and biomass per unit ground area, irrespective of the initial density and of the allocation-growth pattern”
t0“Plant Populations”
Claim · model-written summary
Simulated light competition in a crowded stand was asymmetrically two-sided.
Verbatim
e0“competition between individuals in a crowded stand is never completely one-sided but always asymmetrically two-sided, even though competition is only for light”
t0“Plant Populations”
Claim · model-written summary
Height-growth type plants showed greater competitive asymmetry than diameter-growth type plants.
Verbatim
e0“plants of ‘height-growth’ type exhibit a greater asymmetry in competition than plants of ‘diameter-growth’ type”
Claim · model-written summary
The simulated effect of competition on individual growth converged to a stationary state even while stand structure changed greatly.
Verbatim
e0“the effect of competition on the growth of individuals in a crowded stand converges to a stationary state, even when the stand structure still changes greatly”
t0“Plant Populations”
Claim · model-written summary
The authors proposed a new general functional form for growth rate G(t, x) in crowded stands.
Verbatim
e0“a new, general functional form for G(t, x) in a crowded stand is proposed”
t0“Plant Populations”