A meta-analysis comparing tree growth in monocultures and mixed plantations

Ample evidence has indicated that mixed tree plantations are the most appropriate option for providing a broad range of goods and environmental services, but still debate continues about whether mixed plantations can achieve greater productivity than can monocultures. In this study, a meta-analysis of published studies was performed to synthesize results of growth in mixed plantations and monocultures across differing regions and species. A total of 14 studies representing 46 tree species from tropical and temperate ecosystems were included to test three hypotheses: stand composition affects tree height growth rate; stand composition affects tree diameter growth rate; and presence of nitrogen-fixing tree species in mixed tree plantations affects the diameter growth rate of non-fixing species. It was found that mixed plantations did not have larger height growth rates, but that the diameter growth rate was higher in mixed plantations, with a moderate but statistically significant effect size. Nitrogen-fixing tree species had a positive effect on the diameter growth rate of non-fixing species, with a large and statistically significant effect size. This study suggests that mixing tree species generally increases plantation growth rate. Furthermore, mixed tree plantations can play an important role in satisfying economic needs by shortening rotations yet adding other ecological benefits. Silviculturalists should adopt mixed plantations more widely across degraded landscapes, as well as nitrogen-fixing tree species to maximize positive interactions in mixed plantations. (C) 2007 Elsevier B.V. All rights reserved.