A new study contributed to by Forest Resources researchers right-sizes global reforestation efforts and incorporates their impacts on nearby communities to reduce harm.
From vast tracts of wilderness to city streets and our own backyards, restoring trees has long been recognized as a powerful option for limiting the impacts of global warming – absorbing and storing atmospheric carbon, while also supporting nature’s recovery.
Given the accelerating pace of the climate crisis, however – alongside growing competition with other forms of land-use like agriculture, energy production and infrastructure – experts have debated past studies and critiqued previous estimates about the climate power of reforestation as overly optimistic.
Published in the journal Nature Communications, a new study led by scientists from The Nature Conservancy (TNC) and other leading institutions, including the University of Minnesota Department of Forest Resources, brings fresh perspective to this conversation, by mapping with unprecedented clarity where reforestation can help fight climate change.
Collating insights from 89 previous studies, these new maps show areas least likely to involve trade-offs between reforestation and other urgent priorities like wildlife habitat, food production, and freshwater availability. By combining the latest science with a conservative approach, researchers identified a total available land area of 195 million hectares (Mha) globally – equivalent to around half of the United States.
The drop from previous estimates – about 71-92% less – is due to layers that previous maps haven’t been able to incorporate, because the research was still nascent at the time. It accounts for albedo, for example – how restoring tree cover can, in some locations, actively heat the Earth rather than cool it by affecting how much sunlight is absorbed or reflected. It also excludes native grasslands and other ecosystems where carpeting the land with trees would harm biodiversity and exacerbate fire regimes.
“Our goal for this study was to right-size the estimate of how much reforestation can contribute to climate change, by mapping where trees can actually be planted or regrown with minimum trade-offs and maximum benefits for people and nature,” explains lead author Kurt Fesenmyer, forest spatial data scientist for TNC’s global NCS team.
“We need to ensure the finite funding and policy momentum for reforestation are focused on the locations of greatest opportunity. By adopting a conservative stance that is realistic about the other escalating demands on land-use – as well as what recent science tells us about trade-offs – we hope these maps will bring previous, rather broad-brush estimates of reforestation’s full climate potential into sharper focus for decision-makers. This is something our collaborative Naturebase platform is also helping to achieve,” he adds.
The paper also provides estimates of the impact of policies and land rights on the availability of land for reforestation. UMN Department of Forest Resources Associate Professor Forrest Fleischman and Postdoctoral Associate Pooja Choksi, both coauthors of the study, contributed significantly to the social and economic dimensions of the research.
"Previous studies often failed to address how reforestation could have negative effects on human well-being, especially for poor people living in the remote rural areas often targeted for reforestation. These negative effects are more likely when people lack secure land rights, are highly dependent on natural resources for food and/or fuel, and live in countries where political rights are not respected," says Fleischman.
"Our study points to places where reforestation is most likely to produce win-win outcomes for people and nature, as well as where extra care will need to be taken to ensure that reforestation incorporates local concerns in light of limited land rights, political freedoms, and economic opportunities."
Expanding on the paper’s implications, senior co-author Susan Cook-Patton – a lead reforestation scientist at TNC – says: “As the number of climate-fueled disasters stack up worldwide, it’s increasingly obvious that we can’t waste time on well-meaning but hazily-understood interventions. Make no mistake: Reforestation remains one of the most cost-effective CO2 removal solutions we know of. But we can’t do it everywhere. While there are certainly opportunities to plant and regrow trees beyond what we’ve mapped here, we must fast-track our focus toward the places with greatest benefits and the fewest downsides. This study will help leaders and investors do just that.”
As policymakers plan for a UN Climate COP hosted in the most iconic forest on Earth, this study provides a timely reminder that tree-planting is not a sole solution. Only by restoring – and protecting – forests in lockstep with industrial decarbonization can it make a meaningful difference to bending the curve on climate change back toward safe limits.
Read the full paper in Nature Communications: "Addressing critiques refines global estimates of reforestation potential for climate change mitigation."