Global spatial assessment of potential for new peri-urban forests to combat climate change

Forests hold and remove vast quantities of carbon dioxide from the atmosphere. Given the challenges of reducing emissions quickly enough and the stakes involved, planting new trees is therefore crucial in the broader battle against climate change. Accordingly, the proposal from the G20 summit of November 2021, to fight the climate crisis by planting 1 trillion trees by 2030, has been accepted, elevating tree restoration as an emissions-reduction strategy. At the same time, increasing urbanization has rendered more and more forested areas to the periphery of cities. Here we show that, globally, between 141 and 322 Mha are potentially available for tree restoration in such peri-urban areas. New forests around cities could provide crucial ecosystem services, improving air quality, mitigating temperatures, reducing heat islands and removing greenhouse gases as well as other pollution from the atmosphere. We constructed a 500-m-resolution global map of the peri-urban areas suitable for tree restoration. We found that these areas may host between 241 and 106 billion trees, depending on different land-availability scenarios, and between 101 and 34 billion trees when excluding areas that currently serve as croplands. Almost 80% of such trees could be hosted in just 20 countries. Although forest restoration activities such as tree planting cannot replace reducing carbon emissions, incrementing peri-urban forests can play a crucial role in the fight against climate change. Our results and the maps we constructed may help decision-makers to come to more informed decisions about where to focus reforestation efforts.