Native forests regenerated to increase carbon sequestration can often sustain higher biodiversity (see S. Lewis et al. Nature 568, 25–28; 2019), but planting non-native species should not be categorically excluded. Even the use of exotic clones and monocultures is sometimes justified.

Non-native trees can be more resistant to introduced pathogens (see, for example, P. Woodcock et al. Forestry 91, 1–16; 2017). They grow uniformly and yield timber, paper and other products. In harsh urban environments in northern Europe, they can also be more resilient and provide better ecosystem services than can native trees (H. Sjöman et al. Urban Forestry Urban Greening 18, 237–241; 2016). And shrubs and grasses could be better than tree plantations in arid regions.

Given the scale of the environmental challenge, researchers, policymakers, non-governmental organizations and the private sector must work together around the world to produce evidence-based recommendations for future tree-planting projects.