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
Contact: Jean-Franois Molino
Institut de Recherche Pour le Dveloppement