Dominance and Suppression, Size-Dependent Growth and Self-Thinning in a Natural Impatiens Capensis Population

Abstract

(1) The development of biomass frequency distributions and mortality patterns was investigated in a dense, self-thinning, natural stand of Impatiens capensis. Densitydependent growth and mortality were also investigated by repeatedly censusing marked individuals in plots at natural and experimentally reduced densities. Morphological measurements permitted estimates of plant size and mean relative growth rate to be made for each individual. (2) At natural density, size distributions became more hierarchical as the plants grew, while in the thinned plots there was no such increase; size distributions therefore became significantly more hierarchical in the control plots than in the thinned plots. (3) In the control plots, the relative growth rate of individuals was positively correlated with initial plant size and many of the smaller plants had negative growth rates. In contrast, in the thinned plots, relative growth rate was negatively correlated with plant size and all the plants had positive growth rates. (4) Survivorship was significantly lower in the control plots than in the experimentally thinned plots. Individual longevity increased with plant size in both treatments, but the relationship was much stronger at natural density. (5) These results indicate that dominance and suppression influence size-hierarchy development in dense, natural Impatiens capensis populations. Small, suppressed plants lose biomass through leaf abcission and senesce more rapidly than large plants during selfthinning.