Genetic diversity affects productivity in early but not late stages of stand development

Recent declines in the genetic diversity of populations have stimulated research on the importance of genetic diversity for the functioning of natural communities. Current studies on this topic are based on the exploration of a limited number of clones and do not allow distinctions to be made between the effects of genetic identity and genetic diversity per se and to evaluate the effects of genetic diversity in genetically diverse communities. Also, most information comes from short-term studies, which are insufficient for evaluating the long-term effects relevant in relatively undisturbed communities of perennial species. We explored the importance of clone diversity vs. clone identity for stand productivity and the changes of the pattern over time. We used 18 clones of a perennial grass, Festuca rubra, to establish a set of communities composed of 1, 6 or 18 clones in two environments and studied the effects of genetic diversity on stand productivity over 3 years. Genetic diversity had a significant effect on stand productivity in the 1st year but not in the 2nd or 3rd year. In most cases, the observed yield was not significantly different from the total expected yield. The biomass of the mixtures never outperformed the biomass of the most productive clone, suggesting that clone identity is an important determinant of total biomass. The results indicate that the effects of genetic diversity on stand productivity may be transient and suggest that the conclusions of short-term studies on diversity effects should be evaluated carefully. They also suggest that individual clones are not complementary and that the properties of the stands are mainly additive results of the properties of the constituent clones. (C) 2008 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.