Plant a tree to save the world on Arbor Day? It's a little more complicated than that.

What can planting a tree do to save the world?

A lot – and at the same time, not enough.

That’s the landscape laid out by a host of experts as the United States reaches its 150th Arbor Day, in a world drastically changed from 1872, when Nebraska newspaper editor J. Sterling Morton first proposed the holiday observed on the last Friday of April.

At a time when trees are more valuable than ever for their ability to reduce the amount of carbon dioxide contributing to a dangerously warming planet, Earth is currently losing its forests at an alarming rate.

A new report from the World Resources Institute, a Washington, D.C.-based nonprofit, analyzed satellite imagery in partnership with the University of Maryland to record global forest loss in 2021. Among its findings:

• The tropics — a region covering Central Mexico to Argentina, as well as much of Africa and Southeast Asia — lost 27.5 million acres of tree cover, equal to about 14 football fields per minute. That released enough carbon dioxide into the atmosphere to match the emissions of India, the world’s third highest greenhouse gas emitter after China and the U.S.

• In the north, the Boreal Forest – vast areas of mostly evergreen trees ringing much of Russia and Canada – also experienced its highest rate of tree loss, driven by the destruction of 16.1 million acres in Russia due to an unprecedented fire season.

• Brazil, where the Amazon rainforest is facing deforestation for agriculture and record-setting wildfires, led all tropical nations by a wide margin in forest loss, with 3.8 million acres. The Democratic Republic of the Congo, Bolivia, Indonesia, and Peru rounded out the top five.

While forest loss in the tropics was down in 2021 from a peak in 2016, it remains higher than yearly averages from a decade ago, a trend that's persisted for four years. That spells trouble for a world committed to stopping deforestation and regrowing lost stretches, according to Frances Seymour, a senior fellow at the institute.

In a landmark meeting last year of the United Nations’ Intergovernmental Panel on Climate Change in Glasgow, Scotland, 141 nations, including the U.S., agreed to “halt and reverse forest loss by 2030,” Seymour noted.

To reach that goal, Seymour added, “Actions are going to have to be dramatic.”

But, hurdles stand in the way. Seymour said deforestation is often pushed by agricultural or economic interests. It will take significant domestic policy commitments from a raft of nations to turn the tide. But at the same time, wealthier countries also need to increase their "green finance" contributions to help developing nations afford and implement more sustainable practices.

"We’re not doing enough to provide incentives to those in a position to stop forest loss,” Seymour said.

At the same time, experts note the clear limitations of planting trees.

In reality, even best case scenarios for the world’s forests result in removing just a fraction of the carbon dioxide from the Earth’s atmosphere needed to keep global warming below critical levels, numerous scientific reports have found.

Discussing the results of the World Resources Institute report with the media this month, Seymour and colleagues noted that large-scale tree planting commitments are a major “greenwashing” concern, in which nations or major companies with significant carbon emissions attempt to offset their footprint by dubious reforestation claims, instead of switching to less-polluting practices.

“We have to dramatically reduce emissions from all sources,” Seymour said. “No one should even think about planting trees instead of reducing emissions from fossil fuels. It’s got to be both, and it’s got to be now.”

The pros and cons of planting trees

Ecology experts note that while planting trees alone won’t solve climate change, it can still provide a host of other benefits, particularly in urban areas.

In 2018, researchers at the University of Louisville launched a study into the potential health and socioeconomic benefits of tree planting. Prior studies have already connected trees and other green spaces to a raft of improvements in everything from cardiovascular disease, to mental health, to increased property values.

But working with the city and other institutions, the new study is planting 10,000 trees systematically, year by year, in eight Louisville neighborhoods. By surveying residents annually and comparing health and quality of life improvements with control neighborhoods not receiving trees, researchers hope for the first time to develop a detailed understanding of how trees can improve lives, and which species provide the most benefit.

“We do not know which trees are good at which places,” said Aruni Bhatnagar, lead researcher and a professor of medicine at Louisville. “Are the benefits because of improved air pollution? Or is it just greener and you feel less anxious? We need to know: What are the underlying mechanisms?”

Erin Axelrod is working on similar questions at a larger scale. A project director for the nonprofit Jonas Philanthropies, Axelrod is overseeing a Trees for Climate Health initiative to plant 10 million trees worldwide by 2025.

But, Axelrod said, the initiative is choosy about which trees it plants and where. A “right tree, right place, right community” philosophy guides the decisions about where, or even whether, to plant.

“We don’t want to disrupt intact ecosystems like grasslands or other native habitats that are already sequestering carbon or providing a multitude of co-benefits,” Axelrod said.

Instead of focusing solely on carbon sequestration or “offsetting emissions,” Jonas Philanthropies also considers the relationship between people and trees. In one example, the nonprofit is supporting an effort in Oakland to plant fruit trees that residents can use to supplement a lack of access to fresh produce. In Appalachia, it is focused on fostering natural regeneration of lands formerly decimated by coal mining and other extractive industries.

In nearly all cases, Axelrod said the organization leans on grassroots organizations and Indigenous people, which have a better track record of planting native species and knowing how to properly manage the land than corporate or government entities. Axelrod said that leads both to better outcomes and more buy-in from communities.

“Conservation historically has been very white-led, and the dominant narrative has been, leave it up to the bureaucratic community,” Axelrod said. “We actually need to be looking at Indigenous-led and person of color-led initiatives.”

Other experts warn that in some cases, a focus on planting trees can actually be harmful.

John Blair, an ecologist at Kansas State University, studies the benefits that grasslands provide. Across much of America’s heartland, vast prairies have been plowed under over centuries to support agriculture.

That’s a problem because grasslands can often be better at mitigating climate change than forests. More so than trees, they store carbon below ground and in deep root systems, so that even when a fire destroys the grass above ground, the carbon stays out of the atmosphere as the grasses regenerate. Grasslands are also often much more resistant to drought and other natural disasters than trees.

“They’re very effective at pumping carbon into the soil and storing it,” Blair said.

Still, conservation groups have paid less attention to grasslands: Just 4% of the country’s original tallgrass prairie ecosystems remain, Blair said, and they remain less protected than many forested areas. Across the world, large scale tree planting operations often target grasslands, threatening the biodiversity of plants and animals while offering little to no climate mitigation benefit.

“Grasslands are one of the least protected major ecosystem on the planet,” Blair said.

The overlooked benefits of grasslands show that world leaders need to move past a focus on trees, said Carla Staver, an ecologist at Yale University whose research focuses on South African savannas.

Many regions of the world can support a variety of ecosystems, Staver said. That means it’s often in the hands of humans to decide what happens to them, and decision-making needs to take into account many factors beyond how much carbon is sequestered on a short-term basis. While research is ongoing, Staver hopes that countries consider available science as they work to implement their 2030 forestation commitments.

“I think we have a good basis for making decisions now,” Staver said.

Yet Staver echoes the warning of other experts: There’s no planting our way out of the climate crisis.

“Unfortunately, there’s no way that nature is going to save us from ourselves,” Staver said. “These carbon sequestration and restoration practices really need to go hand in hand with major emissions reductions.”

This article originally appeared on USA TODAY: Planting trees is good for Earth. Climate change means more is needed.