Rachel Nuwer is a freelance journalist and author based in Brooklyn.
When the 2004 Indian Ocean tsunami slammed into Kapuhenwala, a village on Sri Lanka’s southern coast that is surrounded by a thick tangle of mangrove forest, just two people died. In Wanduruppa, a village less than 20 miles away that had cut down most of its mangroves, nearly 6,000 perished, and the damage was more than 10 times as costly as in Kapuhenwala.
The difference, it turned out, was the trees.
Following the tsunami, news quickly spread about the important role mangroves played in saving lives. Sri Lanka received around $13 million to restore degraded tracts of its coastal forests to protect against future disasters. Sunanda Kodikara, a botanist at the University of Ruhuna, remembers visiting some of the mangrove restoration sites early on to evaluate their progress. When he arrived, however, he was shocked by what he saw. Signs displayed the number of mangrove seedlings planted and the name of the donor, but Kodikara didn’t actually see any plants — only bare mud flats. The trees, he realized, had all died.
Kodikara wanted to know whether the places he visited were isolated failures, or if they represented a more systemic problem. So he and several colleagues surveyed all 23 mangrove restoration projects being carried out across the country. To their surprise, they found that nine of the projects had no surviving plants at all, and only three had survival levels greater than 50%. According to Kodikara, the high rates of failure were primarily because most managers had not bothered to consult with scientific experts. They had planted mangroves in places not suitable for them, and had also simply stuck seedlings in the mud and left.
“It had just become a moneymaking thing,” Kodikara said. “Get some money from a donor and do some planting, then take photos. Nothing beyond that.”
The problems Kodikara and his colleagues uncovered have been repeated with tree-planting projects all over the world. Tree planting in recent years has become tremendously popular — not usually as a means to protect coastlines against tsunamis, but more often as a way for companies, countries and wealthy individuals to show off how green they are or meet carbon offset requirements.
The poor design, maintenance and oversight of so many tree-planting efforts undermine the genuine good that can come of these projects. Worse, too, is the fact that the quick, easy payoff of even unsuccessful tree-planting projects can distract climate mitigation and adaptation efforts away from the more difficult and costly work that must be undertaken to ward off disastrous levels of warming.
If done well, tree planting could help us build a better future. But this will require stronger adherence to scientific evidence and a greater commitment to long-term management than are currently being done in most places. It will also entail being realistic about the limited role that tree planting can actually play in mitigating global warming.
It’s easy to see why trees are appealing as a solution to climate change. They already hold a special place in many people’s hearts: the stuff of childhood memories, of walks in the park and of nature’s beauty and bounty. Simply looking at trees can reduce a person’s stress, lower their blood pressure and improve their mood; exposure to forests can even boost immune systems.
The idea of using trees as a major tool for offsetting emissions took hold in the popular public imagination over the past five to 10 years. “Everyone can understand it,” said Eric Coleman, a social scientist at Florida State University. “It seems like such an easy solution to such an immense problem.”
As the idea of planting trees to combat climate change gained popularity, carbon offset programs were formed to offer polluters the opportunity to purchase credits to make up for their emissions. The credits are calculated based on the amount of greenhouse gases harnessed and stored by individual trees planted or whole sections of forests restored or preserved. In return for these offsets, polluters are permitted a certain amount of emissions that, in theory, are neutralized by their investment in nature. “The logic is pretty simple,” Fangyuan Hua, an ecologist at Peking University in China, told me. “Deforestation is a major source of carbon dioxide contributions to the atmosphere, so reforestation is seen as a reversal of that process.”
Some of these tree-planting programs are hugely ambitious. The Trillion Tree Campaign, for example, aims to plant one trillion trees by 2030, while the Bonn Challenge has set out to restore 1.35 million square miles of degraded and deforested land by the same year. At the 2019 United Nations Climate Action Summit, countries around the world pledged to plant more than 11 billion trees.
The immense popularity of these programs is due in part to trees being hailed as a sort of get-out-of-jail-free card for global warming. Even Donald Trump supported tree planting in his 2020 State of the Union address (while carefully avoiding the words “climate change”), and other Republicans have likewise promoted reforestation while rejecting plans to limit fossil fuel emissions.
By planting trees, Hua said, “heavily polluting industries can get away with saying ‘We’re clean.’” But she and other scientists emphasize that no amount of tree planting will save us from the global devastation of the climate crisis so long as we continue to pump greenhouse gases into the atmosphere at current rates. Even if done well on a large scale, trees can only account for a fraction of the carbon reductions we need to make to keep temperature increases under 2 degrees Celsius. “It’s really impossible to tackle climate change without addressing the main sources of emissions,” Hua said. But that’s not to say tree planting isn’t worth doing, she added. Trees absolutely can play a role — just not a primary role — in mitigating emissions, and they can also bring other benefits. For those gains to be realized, however, tree planting must be thoughtfully planned and maintained over the long term.
Successful tree planting is far more complex, costly and time-consuming than most people assume. “Planting a tree is like having a baby,” said René Zamora-Cristales, a senior forest economist at the World Resources Institute. “If you want to do it right, it requires a long-term commitment.”
For one thing, you can’t just stick a sapling in the ground, walk away and assume it will survive. Trees need to be cared for during their first few years of life, sometimes with water, fertilizer, weeding and protection from herbivores. Tree planting programs rarely include long-term management plans, however — an oversight that has contributed to the failure of large, well-funded initiatives in countries ranging from India and Turkey to Canada and the Philippines.
In India, the government started planting trees around 50 years ago throughout Himachal Pradesh, first as an effort to combat deforestation and more recently as a means of improving the country’s carbon budget. Local communities may or may not be involved in making decisions about planting trees on their land, and in some cases, officials from the forest department simply show up and announce an upcoming tree planting day that everyone is required to participate in.
Coleman attended one of these events near the town of Dharamshala: “You go out into a field, they have all these saplings lined up in lories, and — at least at the one I went to — all the guys from the village and forest service sit around and watch a bunch of women plant trees.”
At pretty much all of these sites, after the trees are in the ground, the forestry service officials do not bother with any follow-up care, Coleman added. And because the trees weren’t something the community wanted in the first place, no one living nearby usually cares for them, either.
In 2021, Coleman and his colleagues used satellite imagery to reveal that India’s tree-planting initiatives have not increased the overall proportion of forest cover, but that they have shifted the composition of trees growing there away from broadleaf varieties toward quick-growing pines. They also found through field interviews that tree planting has detracted from people’s livelihoods because the species favored by the government are not those preferred by local people for fuel and fodder. Decades of expensive tree planting had been a waste, Coleman and his colleagues concluded. “Because officials are motivated by policy quotas, there are incentives to care about how many trees are planted,” he said, “rather than the right trees in the right places that are then cared for.”
Which trees are being planted where is at least as thorny a problem as long-term care. Evergreen conifers are dark and tall, so they absorb more sunlight than shrubs, grass or snow. If conifers are planted on landscapes that were previously more reflective, they will actually increase local warming and contribute to climate change. Planting non-native species can likewise backfire. South Africa, for example, introduced Australian acacias in the 19th and 20th centuries for timber and dune stabilization. But the trees spread, displacing native flora and fauna and lowering the water table. South Africa now spends millions of dollars annually on acacia clearing.
Tree-planting efforts are best suited for degraded land that was previously forested, but sometimes land not suitable for trees is targeted for “reforestation.” One of the most alarming examples are projects in Africa’s natural grasslands, nearly 400,000 square miles of which are marked for “restoration” by 2030. Adding trees to iconic savannah landscapes in the Serengeti and elsewhere could damage those ecosystems and probably would not provide long-term carbon storage either. Wildfires regularly blaze across the areas where these projects are proposed, and savannah elephants have a habit of eating and knocking over trees.
Some supposedly green tree-planting programs are commercial monoculture plantations, which lead to little if any long-term carbon storage because the trees are quickly harvested, often for wood pellets or pulp for goods like toilet paper. When tree-based products decompose or are processed or burned, their stored carbon is released back into the atmosphere as carbon dioxide or, worse, as methane.
Even when people attempt ideal restoration initiatives — returning native trees to degraded habitats where they once had thrived — they still tend to underestimate the amount of time it will take for those trees, or the forest ecosystem as a whole, to reach full carbon-storing capacity. In 2016, for example, scientists in Uganda’s Kibale National Park compared preserved sections of old-growth forest with degraded areas that had been replanted in 1995 with native seedlings. In 18 years, the restored tracts of forest had reached the equivalent of just 12% of the virgin forest’s aboveground growth. Another 96 years would be needed for the replanted areas to match those of the old-growth forest, the researchers calculated. That timeline is typical: According to the Intergovernmental Panel on Climate Change, full recovery for most felled forests takes centuries.
Over that much time, as the climate warms, ecosystems will be transformed. Trees planted today in habitats suitable for them may find themselves in the midst of a very different environment in a matter of decades. Rain patterns are changing, driving up temperatures and increasing the risk of fires, droughts, hurricanes and other events that can damage or kill large numbers of trees. Even with the most careful planning and care, a razed forest replanted today has an uncertain future — and thus an uncertain capacity to store carbon — in the long term.
There are numerous entities that exist to verify and set standards for carbon offset programs, including the American Carbon Registry, the Climate Action Reserve and the Verified Carbon Standard. But their rules are not watertight, and neither is the oversight meant to ensure that they are being followed. “They’re just not as rigorous as they could be,” said Deborah Lawrence, an environmental scientist at the University of Virginia.
Troubling evidence indicates that even the most celebrated programs can fall well short of their intended goals. According to a 2019 analysis conducted by Barbara Haya at the University of California, Berkeley, nearly all of the projects in California’s cap-and-trade program — a centerpiece of the state’s plans to cut greenhouse gas emissions — overestimate the number of credits generated, She found that approximately 80 million tons of carbon dioxide, or a third of the total cuts that California’s cap-and-trade program was expected to achieve in the coming decade, were wrongfully credited. One primary problem was that reductions in timber harvesting at accredited project sites likely caused timber harvesting to occur elsewhere to meet demand. In some cases, landowners were also being paid for trees they had no intention of harvesting anyway, meaning there was no net reduction in emissions.
These types of problems are not unique to California. A 2020 investigation carried out by Bloomberg, for example, revealed that GreenTrees, a company that claims to be “the largest U.S.reforestation project” — and whose customers included United Airlines, Walt Disney Co., Shell, Microsoft, Bank of America and more — regularly sold carbon credits for trees that were already planted and that landowners had no plans to cut down, or that were already planned to be planted anyway.
In the worst cases, people have cut down existing trees only to replant new ones so they can reap monetary rewards. In 2018, the Mexican government launched a $3.4 billion reforestation program intended to help meet climate goals and combat poverty by paying people to plant trees for fruit or timber. As Bloomberg reported, the program wound up incentivizing land owners to cut down tracts of jungle so they could plant fruit or timber species for reimbursement. In 2019 alone, Mexico lost an area of jungle almost the size of New York City because of the program’s perverse incentives, Bloomberg reported.
In April this year, researchers likewise found that large-scale government tree-planting initiatives in China inadvertently caused the loss of some natural ecosystems. Grain for Green, a prominent $66 billion tree-planting program, was launched in 1999 to incentivize people to plant trees on marginal cropland on sloped terrain to stop erosion, flooding and mudslides. Though the project increased tree cover in China by 32% and reduced erosion by 45%, it and similar ones also destroyed up to 600 square miles of China’s wetlands from 2000 to 2016 because the newly planted trees changed water dynamics. Without adjustments, the researchers warn that China could lose more than 10% of wetland areas in some nature reserves.
Additionally, Hua and her colleagues have found that even though Grain for Green technically increased the percentage of tree cover in China, most of the trees planted were in plantations with a single or a few species, and sometimes non-native ones. Meanwhile, the country’s native forest “has effectively been displaced,” Hua said — direct loss in some areas, as well as indirect loss because tree plantations took up land that otherwise could have been restored into native forests.
No one really knows how effective tree-planting projects have been overall — there’s no global database or comprehensive tracking effort. “The stuff we do know seems to suggest that, at best, it’s mixed,” Coleman said. “Some places have been effective, and some places haven’t.”
Awareness is increasing that tree planting entails more than just sticking a sapling in the ground and walking away, and scientific studies are starting to illuminate what works and what doesn’t. In March, for example, Hua and her colleagues analyzed data from 264 studies of tree plantations and native forests in 53 countries, scrutinizing the relative performance of those two types of landscapes on carbon storage, soil erosion control, water provisioning, biodiversity conservation and timber production. Native forests outperformed plantations on all fronts except timber production. The more biodiverse a forest, researchers are coming to understand, the better it tends to be at providing all other environmental services, including carbon sequestration and storage.
“We’re beginning to realize that the capacity of ecosystems to absorb carbon may be intimately linked to how robust and stable the system is,” Hua said. “The more diverse the tree cover is, the more effective it is at capturing carbon.”
Including local people in reforestation efforts is also critical. Local partners can make or break any conservation initiative, be it a single planted tree, a major restoration project or the protection of an entire old-growth forest. If a project aligns with their interests — they are getting fairly compensated for the use of their land, for example, or the trees bring some benefit such as fruit, ecotourism or timber — then they can often be counted on as environmental stewards.
Ultimately, the best way to maximize the many benefits that forests naturally provide, including carbon sequestration, would be to protect existing, well-functioning ecosystems, especially old-growth ones. Globally, we currently lose an area of tropical rainforest about the size of New Mexico every year. “We cannot talk about restoration without talking about trying to maintain what we already have,” Zamora-Cristales said. “Otherwise, it’s like putting trash in front of you while cleaning behind you.”
In some cases, paying to preserve threatened forests can be the most effective opportunity for carbon offset initiatives. A paper published in May in Nature Sustainability found, for example, that 58% of threatened forests in Southeast Asia could be protected as financially viable carbon projects. In 2019, Norway committed to paying Gabon $150 million to keep its rainforests intact.
When forests have been degraded, in some cases, simply leaving the land alone and letting trees naturally regenerate from seed banks left in the soil is better than intensive restoration work. This is known as passive regrowth, and it can be much less expensive and lead to a more diverse composition of species on restored land. The forests of the eastern United States, for example, were heavily logged in the 18th and 19th centuries, but large areas have since naturally grown back without a concerted restoration effort. “You don’t have to plant a tree for it to grow,” said Karen Holl, an environmental scientist at the University of California, Santa Cruz.
Deliberate interventions will still be needed to restore the most heavily degraded ecosystems, though. And for better or worse, tree-planting efforts are here to stay. Reducing corruption, mismanagement and wasted time and money tied to these projects will depend on reinforcing the scientific research on how to maximize the benefits for people and the planet, and then using those lessons to strengthen existing protocols. Stricter measures will also be required to ensure that efforts on the ground actually adhere to the rules, and prohibit polluters from being able to simply buy their way out of curbing emissions.