COS 93-3
Tropical forest size structure: Dominance of the suppressed
Tropical forests are beautiful places with amazing amounts of diversity. Despite this complexity, these forests are remarkably consistent in the size distribution of trees. Across the globe, tropical forests follow a tight power-law distribution with very similar exponents. Such a consistent and clear pattern warrants an explanation, and that explanation is likely to provide an understanding of basic governing processes of these forests. We investigate the generation and stability of this pattern with 30 years of data from 50 hectares of a tropical forest in Panama. With insights from the data, we build a stochastic model capable of regenerating the power law. With a few simplifications we derive an analytical version of the stochastic model, revealing a new and specific hypothesis for the pattern generation.
Results/Conclusions
Through model analysis we find that this power law could be generated through a self-thinning process. The bulk of the distribution is made up of those trees that are shaded and left in the understory by trees recovering from disturbance. The slope of the diameter, abundance relationship – the strikingly similar phenomenon across tropical forests - is governed by only by the scaling exponent of tree crown area with diameter, a likely physically constrained parameter. This finding has the potential to explain the consistency of the relationship across tropical forests and has implications for the differences in forest dynamics between temperate and tropical forests as well.