For 149 years, Americans have marked Arbor Day on the last Friday in April by planting trees. Now business leaders, politicians, YouTubers and celebrities are calling for the planting of millions, billions or even trillions of trees to slow climate change.
As ecologists who study forest restoration, we know that trees store carbon, provide habitat for animals and plants, prevent erosion and create shade in cities. But as we have explained elsewhere in detail, planting trees is not a silver bullet for solving complex environmental and social problems. And for trees to produce benefits, they need to be planted correctly – which often is not the case.
Tree-planting is not a panacea
It is impossible for humanity to plant its way out of climate change, as some advocates have suggested, although trees are one part of the solution. Scientific assessments show that avoiding the worst consequences of climate change will require governments, businesses and individuals around the globe to make rapid and drastic efforts to reduce greenhouse gas emissions.
Moreover, planting trees in the wrong place can have unintended consequences. For example, planting trees into native grasslands, such as North American prairies or African savannas, can damage these valuable ecosystems.
Planting fast-growing, nonnative trees in arid areas may also reduce water supplies. And some top-down tree-planting programs implemented by international organizations or national governments displace farmers and lead them to clear forests elsewhere.
Large-scale tree-planting initiatives have failed in locations from Sri Lanka to Turkey to Canada. In some places, the tree species were not well suited to local soil and climate conditions. Elsewhere, the trees were not watered or fertilized. In some cases local people removed trees that were planted on their land without permission. And when trees die or are cut down, any carbon they have taken up returns to the atmosphere, negating benefits from planting them.
Karen Holl receives funding from the U.S. National Science Foundation.
Pedro Brancalion receives funding from The São Paulo Research Foundation (FAPESP) and Fundação de Estudos Agrários "Luiz de Queiroz".