Rainforest dynamics: the need for new paradigms

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Abstract

A desire to understand the maintenance of the very high species-richness of tropical lowland rain forest provides the setting for this paper. It is widely accepted that both niche-differentiation and chance effects among ecologically very similar species play an important part in maintaining richness. The purpose of the paper is to provide an improved background of ideas on rainforest dynamics, against which to consider differentiation in the regeneration niche, and against which to plan management and conservation. Paradigms deemed to need review are the following: the all-importance of canopy gaps, the existence of a spectrum of tolerance in which the relative positions of species are not dependent on size of individual, the association of large seed size with shade tolerance, the idea that soil seed banks are composed of species demanding sizeable canopy gaps, and the all-importance of shade as opposed to competition for water or mineral nutrients in limiting regeneration. Recent evidence bearing on these ideas is reviewed briefly, and an alternative set of paradigms is offered.