The influence of disturbance on tropical rain forest biodiversity: End of a controvers...( These results recently published in Sc...)

These results, recently published in Science, provide better understanding of the dynamics of biodiversity in tropical rain forests. The many species which make up tropical rain forest tree communities show widely differing reactions to environmental factors. This is particularly so with regard to light. Pioneer species, highly heliophile (light-loving or shade-intolerant), establish themselves by taking advantage of canopy light gaps opened up by treefalls. Rapid growth, a feature of these species, enables them rapidly to form a new canopy suitable for more shade-tolerant species to colonize. The non-pioneer heliophiles are the first of these, followed by implantation of progressively more shade-loving trees as the canopy density increases.

The effect of disturbances of various intensities on tree species diversity was measured on forest regeneration. Researchers carried out an inventory of over 17 000 trees on a set of small forest plots, either subjected to different levels of commercial logging, or leaved untouched. Strong disturbances (such as intensive commercial logging), appear to favour pioneer species. If there are very little disturbances (fallen branches or only few and small canopy light gaps), the community is dominated by shade-loving species. Intermediate disturbances (more common or more extensive light gaps in untouched forests, only limited-scale logging) between the two extremes, induce peak diversity owing to the creation of a greater variety of ecological niches, some favourable to heliophilous trees, others better for shade-tolerant species. These results bring partly into question the findings that an American research team published in 1999 after investigations in Panama (2). This is the only other attempt to date to check the intermediate disturbance hypothesis at the same scale of observation. From the study of a 50-ha plot of natural forest, these researchers concluded that disturbance level had no effect on tree species diversit
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Contact: Jean-Franois Molino
molino@mpl.ird.fr
33-04-67 59-39-13
Institut de Recherche Pour le Dveloppement
10-Jan-2002

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