Random Walks, Fractals and the Origins of Rainforest Diversity

Abstract

Rainforests are legendary because their extreme species richness. In the richest rain forests every second tree on a hectare is a differnt species. As a consequence, most species are rare. Using field data from studies in dfiferent parts of the world, we show that species-rich plots often display a distribution of number of species Ns(I) represented by I individuals with a power-law shape Ns(I)∝I-β with β≈1.5. Power laws are characteristic (but not exclusive) of systems poised close to critical points and this is supported by the analysis of the gap distribution over space in the Barro Colorado Island forest, which has been shown to be fractal. Here we propose a new model of rainforest dynamics which is able to account for a wide set of observations, strongly suggesting that indeed rainforests would be organized close to instability points, showing strongly path-dependent dynamics.