Positive biodiversity-productivity relationships in forests: climate matters

Abstract

While it is widely acknowledged that forest biodiversity contributes to climate change mitigation through improved carbon sequestration, conversely how climate affects tree species diversity-forest productivity relationships is still poorly understood. We combined the results of long-term experiments where forest mixtures and corresponding monocultures were compared on the same site to estimate the yield of mixed-species stands at a global scale, and its response to climatic factors. We found positive mixture effects on productivity using a meta-analysis of 126 case studies established at 60 sites spread across five continents. Overall, the productivity of mixed-species forests was 15% greater than the average of their component monocultures, and not statistically lower than the productivity of the best component monoculture. Productivity gains in mixed-species stands were not affected by tree age or stand species composition but significantly increased with local precipitation. The results should guide better use of tree species combinations in managed forests and suggest that increased drought severity under climate change might reduce the atmospheric carbon sequestration capacity of natural forests.

Keywords: biodiversity; ecosystem functioning; meta-analysis; overyielding; precipitation.

Figure 1.

Location of the study sites according to global variation in precipitation. Precipitation corresponds to the sum of precipitation in the second winter month, the best correlated variable with PCA₂ coordinates used as moderator in the meta-analyses.

Figure 2.

Effect of precipitation (coordinates on PCA₂) and type of tree species mixture (D, deciduous; E, evergreen) on overyielding in old forests (older than half of the rotation age). The diameter of a bubble is proportionate to the weight (inverse of variance) of the corresponding study in the meta-analyses.