Species diversity independent of age structure
The high biodiversity of tropical rainforests is probably much less related to a diverse age structure of the stands than previously assumed.
In a global comparison of equatorial primeval forests, those test areas with the smallest overall age structure showed the greatest variety of tree species. According to Richard Condit from the American Smithsonian Tropical Research Institute and his colleagues, this would invalidate the theory according to which the number of species is largely determined by the coexistence of a wide variety of fast and slow-growing plants of different ages.
Although demographic variations may support the coexistence of different species, they do not explain the differences observed by the scientists between the lowest and highest species numbers of the test areas. The comparison of places like Mudumalai in India with only 73 tree species or the Malaysian Sarawak with more than 1160 species each on fifty hectares showed that the respective annual mortality of all seedlings is the lowest in the various locations. As a result, there is a rather regular growth of uniform age groups whose diversity is controlled by other factors.
