Despite the fact that several experiments have been conducted to explore the biodiversity-productivity relationship in synthesized and natural plant communities, the results obtained were contradictory and no clear consensus has been reached. Recent experiments that surveyed mature natural plant communities have investigated this relationship across enviro nmental gradients, where biotic and/or abiotic factors are correlated with the observed diversity and productivity levels. We studied the effect of plant diversity on ecosystem productivity in agriculturally managed (managed at a low intensity with moderate level of disturbance) and natural (no history of management) grasslands at a within-site scale in order to minimize the confounding effect of environmental factors. We tested the effects of two diversity measures (species richness and species evenness) on productivity within- and across-sites scale. Our results indicated that this relationship was different between the natural and the managed grasslands and varied according to the diversity measure. Species richness only poorly explained the variation in productivity for the managed grasslands, while the variations in system productivity were better explained by species evenness. Interestingly, our results from the natural low productive, species poor grassland are in agreement with the results obtained from the recent experiments that artificially manipulated diversity levels and found an asymptotic increase in productivity along with increasing species richness. Our results provide additional evidence of the complex behavior that measures of species diversity that combine several aspects of diversity such as species evenness, species identity as well as the interactions among the species may be better determinants of the response of the ecosystem to b
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