Changing tropical forest dynamics and their effects on canopy geometry and tropical forest biodiversity

Abstract

Risks to forest canopies are the result of risks to the trees that comprise them. Whether a canopy degrades depends on the relative rates of recruitment, growth, reproduction, and mortality among trees within the forest, and assessing that risk means studying how those dynamics are affected by environmental changes. We focus here on (1) the recent changes in the dynamics of tropical forest trees, particularly in Amazonia, as evidenced by long-term forest inventories, (2) the potential drivers of these changing dynamics, (3) how the changing dynamics may be altering the physical structure of forest canopies, and (4) how such changes in canopy structure might influence tropical forest biodiversity. We review evidence that in Amazonia, and likely elsewhere, tropical forest turnover has increased over recent decades (i.e., that the mean time a stem, or a unit of basal area, or unit of biomass, remains within a forest, has decreased), concomitant with an acceleration of tree recruitment, growth, and mortality. We suggest that this is increasing the physical heterogeneity of tropical forest canopies, as more and larger treefall gaps are formed (and filled in faster), and that these changes will have consequences for tropical forest biodiversity, dynamics, and function that demand.