Study: Integrated global assessment of the natural forest carbon potential (DOI: 10.1038/s41586-023-06723-z)
New research suggests that a realistic estimate of additional global forest carbon-storage potential is approximately 226 gigatonnes of carbon-enough to make a meaningful contribution to slowing climate change.
The study, published today in the journal Nature, highlights the critical importance of forest conservation, restoration and sustainable management in moving toward international climate and biodiversity targets. It involved hundreds of scientists around the world, who stress that this potential can be achieved by incentivizing community-driven efforts to promote biodiversity.
Forest carbon-storage potential has been a highly controversial topic. Four years ago, a study published in the journal Science found that the restoration of forests could capture more than 200 gigatonnes of carbon, which could draw down about 30% of excess anthropogenic carbon from the atmosphere. One gigatonne is equivalent to 1 billion metric tons.
While that research elevated a discussion about the role of nature in fighting climate change, it also raised concerns around the adverse environmental impacts of mass tree plantations, carbon offsetting schemes and greenwashing. While some scientific studies have supported the scale of this finding, others argued that this forest carbon estimate could be up to four or five times too high.
To address this controversial topic, an international team led by the Crowther Lab at ETH Zurich, and including University of Michigan forest ecologist Peter Reich, built an integrated assessment using a comprehensive range of approaches, including vast ground-sourced data and satellite datasets.
Due to ongoing deforestation and degradation, the total amount of carbon stored in forests is about 328 gigatonnes below its natural state. Of course, much of this land is used for extensive human development including urban and agricultural land.
However, outside of those areas, researchers found that forests could capture approximately 226 gigatonnes of carbon in regions with a low human footprint if they were allowed to recover.
Abou 61% of this potential can be achieved by protecting existing forests, so that they can recover to maturity. The remaining 39% can be achieved by reconnecting fragmented forest landscapes through sustainable ecosystem management and restoration.
"Most of the world's forests are highly degraded. In fact, many people have never been in one of the few old-growth forests that remain on Earth," said Lidong Mo, a lead author of the study. "To restore global biodiversity, ending deforestation must be a top priority."
The dataset revealed that biodiversity accounts for about half of global forest productivity. As such, the researchers highlighted that, to achieve the full carbon potential, restoration efforts should include a natural diversity of species. In addition, sustainable agricultural, forestry, and restoration practices that promote biodiversity have the greatest potential for carbon capture.
"Promoting diverse forests will help us maximize their potential to scrub carbon dioxide out of the air and store it in tree trunks and soils," said U-M's Reich, director of the Institute for Global Change Biology at the School for Environment and Sustainability. Reich is a co-author of the new study and was part of its core organizing and writing group.
The study authors stress that responsible restoration is a fundamentally social endeavor. It includes countless actions such as conservation, natural regeneration, rewilding, silviculture, agroforestry and all other community-driven efforts to promote biodiversity. It requires equitable development, driven by policies that prioritize the rights of local communities and Indigenous peoples.
"We need to redefine what restoration means to many people," said Thomas Crowther, senior author of the paper and a professor at ETH Zurich. "Restoration is not about mass tree plantations to offset carbon emissions. Restoration means directing the flow of wealth toward millions of local communities, Indigenous populations and farmers that promote biodiversity across the globe. Only when healthy biodiversity is the preferred choice for local communities will we get long-term carbon capture as a byproduct."
The researchers conclude that ecologically responsible forest restoration does not include the conversion of other ecosystems that would not naturally contain forests.
"Global restoration is not only about trees," said Constantin Zohner, a senior researcher at ETH Zurich. "We have to protect natural biodiversity in all ecosystems including grasslands, peatlands and wetlands that are equally essential for life on Earth."
The new study brings to light the critical importance of natural, diverse forests in contributing to 30% of carbon drawdown potential. However, forests cannot be a substitute for cutting fossil fuel emissions. If emissions continue to rise, the study warns, then ongoing droughts, fires and warming will threaten forests and limit their ability to absorb carbon.
"My biggest fear is that corporations misuse this information as an excuse to avoid cutting fossil fuel emissions. The more we emit, the more we threaten nature and people. There can be no choice between reducing emissions and protecting nature, because we urgently need both. We need nature for climate, and we need climate action for nature," Crowther said.
