Photo: Kasturi Laxmi Mohit/Unsplash
- Around the world, tree-planting campaigns have become a popular way to mitigate greenhouse gas emissions. But some tree planting efforts are problematic.
- Trees absorb carbon dioxide, but how, where and why a tree is planted matters greatly. Tackling climate change is not as simple as planting some trees and walking away.
- In 2006, the UNEP announced a plan to plant least one billion trees globally by 2007. In 2009, it reported that more than three billion trees had been planted.
- In 2019, researchers at ETH Zurich called restoring Earth’s tree cover the most effective tool to counter the climate crisis – but they later admitted they made a mistake.
- Trees alone can’t actually cancel out the effects of burning fossil fuels, and claiming they can helps corporations skirt actual climate action.
In the heart of Uganda there is a huge, regimented stand of pine trees. This forest is a prime example of “afforestation,” the process of restoring an area deforested by human subsistence activities, like farming. It is also part of the carbon offset business. By planting trees in Uganda, Green Resources, a Norwegian plantation forestry and carbon offset company, can in theory balance out the carbon dioxide emitted by human activity elsewhere. For years, the Swedish Energy Agency (SEA) paid Green Resources to plant the trees and thereby offset some of the agency’s emissions of carbon, a major cause of climate change.
At first, the Green Resources project sounds great. But pine trees don’t normally grow in Uganda, according to the Oakland Institute, a think tank devoted to social and environmental activism. Plantation-style agriculture actually sequesters less carbon, less securely, than naturally generated forests and grasslands. The pine trees aren’t really raised to address the climate crisis, but to be chopped into sawlogs and utility poles. And Green Resources, active in East Africa since 1995, evicted thousands of native Ugandans from the land so it could create the plantation in the first place, according to the Oakland Institute’s 2019 exposé. Following the institute’s report, the SEA suspended and then ended its relationship with Green Resources in 2020, though Green Resources continues to grow trees and gain investors for its pine plantations in East Africa.
Around the world, tree-planting campaigns have become a popular and simple way to mitigate greenhouse gas emissions. But some tree planting efforts, like the Green Resources project in Uganda, are problematic. Many have been based on shaky science hyped by the media and may amount to little more than greenwashing, giving companies cover to continue profiting as they pollute. Trees do absorb carbon dioxide, but how, where and why a tree is planted matters greatly to its climate-mitigating potential. Tackling climate change is not as simple as planting some trees and walking away.
“Who could be against tree planting?” asks Jennifer Skene, natural climate solutions policy manager at the Natural Resources Defense Council. “It seems like such a quaint environmental activity.” Skene has written extensively about the perils of poorly planned reforestation efforts, which can wind up superseding the protection of existing forests. And many planting campaigns are used to justify clearing climate-critical forests elsewhere, she adds.
The idea that we could plant our way out of climate change goes back at least to 1976, when physicist Freeman Dyson suggested in a paper that in the face of planetary warming, we could “plant enough trees and other fast-growing plants to absorb the excess carbon dioxide and bring the annual increase to a halt.” Even then, however, Dyson acknowledged that trees and plants alone likely wouldn’t be enough. The only long-term response to an imminent climate catastrophe would be to “stop burning fossil fuels and convert our civilisation to nuclear or solar-based fuels,” he wrote.
But the idea of using trees as a magic carbon dioxide sponge stuck. In 1989 climate scientist Gregg Marland and his Oak Ridge colleague Thomas Boden testified before the US Senate Committee on Energy and Natural Resources that growing enough trees after cutting down others for fuel could potentially result in net-zero emissions. In 1992 Marland published a paper exploring the idea of sequestering carbon by protecting some forests and harvesting and replanting others.
Then, in November 2006, six months after the climate change documentary An Inconvenient Truth was released, the UN Environment Programme (UNEP) announced its “Plant for the Planet: Billion Tree Campaign,” created in partnership with Kenya’s World Agroforestry Centre. The plan, propelled by activist Wangari Maathai, called for at least one billion trees to be planted globally by 2007. In 2009 UNEP reported that more than three billion trees had been planted since the campaign’s launch, far surpassing its original goal.
In 2011, following Maathai’s death, UNEP found a new face for its cause: a charismatic 13-year-old Bavarian boy named Felix Finkbeiner, who had already adopted UNEP’s catchphrase “Plant-for-the-Planet” as the name of a tree-planting nonprofit he had founded at age nine.
Despite the high-profile nature of these efforts, scientific justification for mass tree planting remained sparse until 2015, when more rigorous defense began appearing in the peer-reviewed literature. That year, a paper published in Nature provided the most complete model of estimated global tree density by using satellite imagery and data from a patchwork of on-the-ground forest surveys. Determining the number of trees currently on the planet was a step toward determining how many more trees could be planted, and to what end. The researchers estimated Earth’s surface was covered with approximately three trillion trees.
The big three-trillion number headlined the paper, press releases and interviews with lead researcher Thomas Crowther, now an ecologist at the Swiss research university ETH Zurich. The paper was discussed across social media and, to date, in more than 300 news stories. Many of those stories highlighted another finding from the paper – that there would be nearly twice as many trees around the world without humans. In response, Finkbeiner and the UNEP increased its initial 2007 goal of planting a billion trees to planting a trillion of them.
In 2019, Crowther and a team of researchers at ETH Zurich published a follow-up study in Science stating that restoring Earth’s tree cover was the most effective tool we had to counter the climate crisis. The researchers mapped where trees can grow and in what densities—subtracting known areas of existing forest, cities, and agricultural land – and then calculated the potential carbon storage of planting additional trees using estimates from existing forests.
They concluded that planting more than a half trillion trees could sequester “a considerable proportion of the global anthropogenic carbon burden,” some 205 gigatonnes, over several decades. According to NASA, that would be a reduction of approximately 25 percent of current atmospheric carbon levels, “enough to negate about 20 years of human-produced carbon emissions at the current rate, or about half of all carbon emitted by humans since 1960.” The story was picked up by more than 400 news outlets worldwide.
But many scientists quickly raised concerns about the analysis. Several groups of experts, including Gregg Marland, published comments in Science asserting that the paper miscalculated trees’ capacity for carbon storage and neglected to address such nuanced effects as the impact on grasslands and wetlands and whether the trees would be protected once planted. According to one group of scientists, the new study overestimated trees’ potential to capture carbon by a factor of five.
Crowther and his team eventually acknowledged a “considerable” margin of error and retreated from the claim in the original paper that tree restoration was “the most effective solution” to climate change. “That was incorrect,” read the correction in Science.
Despite the backpedaling, Crowther is listed on Plant-for-the-Planet’s website as its chief scientific adviser. He is currently working with Finkbeiner – now a PhD student in the Crowther Lab – on an experiment studying how soil restoration impacts tree planting on a privately purchased plot on Mexico’s Yucatán Peninsula.
Overstating the climate benefits of planting trees can hamper real solutions to climate change. Trees alone can’t actually cancel out the effects of burning fossil fuels, but claiming they can helps corporations skirt actual climate action while pouring money into tree-planting projects that may do more harm than good.
“The way offsets are conceived gives the idea that they are a solution to the climate crisis when really, they are a way to enable the fossil fuel sector,” says Skene from the NRDC. “Offsetting is not a substitute for cutting our greenhouse gas emissions by drastically reducing our reliance on fossil fuels.” What’s more, monitoring and maintenance are nonexistent for many tree planting projects, says Skene. If trees are not planted in the right place at the right time and cared for after planting, they can die and sequester no carbon at all.
“You can’t plant away climate change,” says Karen Holl, who runs a restoration ecology lab at the University of California, Santa Cruz.
Finkbeiner, on the other hand, stands by the importance of trees. While he says he does not expect tree planting and forest restoration to solve the climate crisis, he thinks it is too late to rely only on reduced emissions. “We are really at an all-of-the-above point in the climate crisis,” he says.
Today, Plant-for-the-Planet runs an online tree-planting and forest-restoration platform where individuals and groups post planting initiatives and solicit donations. The organisation says it vets all initiatives on its site and requires them to meet rigorous standards set by the International Union for Conservation of Nature. Despite all the money going into myriad projects, whether the projects actually sequester carbon is difficult to say. An investigation by German news source Die Zeit found that Plant-for-the-Planet’s primary replanting project in Mexico had little to show for all its effort and that the fates of the planted trees was unclear.
And yet, equating trees planted to carbon sequestered has become a staple of many tree-planting campaigns and seems to be a big business. The world’s top tree buyers today include the cloud-computing company Salesforce, which has bankrolled the planting of nearly 44 million trees, as well as German retail chains REWE and dm-drogerie markt and Staples Europe, each with over one million trees purchased as part of the Plant-for-the-Planet campaign.
To counter greenwashing and overinflated carbon sequestration promises, scientists like Holl are focused on reforestation policies and practices that meet people’s needs while conserving Earth’s diverse ecosystems. These practices are not a magic solution to the climate crisis but can play a role in sequestering carbon, bolstering ecosystems, and supporting local people.
A frequently consulted reforestation expert, Holl collaborated with Pedro Brancalion, coordinator of the Laboratory of Tropical Forestry at the University of São Paulo in Brazil, to identify best practices as well as weak spots in campaigns that involve growing and protecting trees. They’ve found a lack of planning commonly leads to issues like reduced water yield in arid regions, destruction of grasslands, the spread of invasive species, social conflicts, more forest clearing (ironically), and displaced farmers and lost livelihoods.
While good planning can help avoid these issues, the best way to add trees to an ecosystem may not involve active planting at all. Instead, protecting existing forests and allowing forest ecosystems to recover on their own may be the best approach. When a project’s main goal is to restore forest area, allowing trees to grow naturally without intervention may lead to the success of a greater number of trees and more carbon storage overall compared with planting, says Holl. And the cost of promoting natural regeneration is often also much lower than the cost of planting. Allowing trees to grow naturally has other benefits as well, including improved biodiversity. Biodiversity benefits are not a given for plantation-style forests run by companies like Green Resources.
“Campaigns would do better if they planned for trees’ permanence and scaled up their quality rather than focus on the quantity of trees put in the ground,” says Holl. “We need to focus on growing
trees, not planting them, and doing so for the right reasons.”