A global meta-analysis of the impacts of tree plantations on biodiversity

Aim Planted forests are becoming increasingly common world-wide for a variety of reasons, including water conservation and carbon sequestration, although the effects of tree plantations on biodiversity are unclear with respect to whether planted ecosystems are "green deserts" or valuable habitats for biodiversity. Location Global. Time period 1980-2020. Taxa studied Flora, fauna and microorganisms. Methods By conducting a meta-analysis of 361 observations from 138 sites world-wide, we explored the global patterns and associated drivers of biodiversity responding to tree plantations by comparing biodiversity levels in plantations and adjacent habitats (primary or secondary forests). Results Overall, the biodiversity (species richness) and abundance across multitrophic levels in tree plantations were lower than those in primary forests, reached similar values to secondary succession, but varied with plantation and management regimes. Specifically, the biodiversity across multitrophic levels in reforestation was higher than that in afforestation; the biodiversity in mixed, native species and unmanaged plantations was higher than that in monoculture, exotic species and managed plantations. The diversity of vertebrates, invertebrates and plants in reforestation was lower than that in primary forests, whereas belowground biodiversity in reforestation showed no difference from primary forests. Invertebrate diversity in reforestation was lower than that in secondary succession, whereas plant diversity was higher than that in secondary succession. Moreover, the biodiversity in reforestation increased with reforestation age. Furthermore, structural equation models showed that aboveground faunal diversity in reforestation was driven by canopy coverage and plant diversity and that reforestation affected belowground biodiversity mainly by changing soil organic carbon. Main conclusions Our findings suggest that reforestation by planting mixed native species will be more beneficial to biodiversity. We reveal that biodiversity in intensively managed plantations is significantly lower than that in restoration-oriented plantations. We highlight that primary forests are not replaceable, but that planted forests might be a reliable way to restore biodiversity rapidly.