Trees are an important tool to counter climate change: They capture carbon dioxide, improve biodiversity and increase groundwater. Adding a trillion trees could scrub out two-thirds of all emissions, according to scientists, and that's why everyone from the World Economic Forum to YouTube influencers have launched large planting programs. There's just one problem: The success rate of typical programs is often dismal. Many end up with no trees surviving to maturity.

After years of experiments, John Leary believes he has found the magic ingredient to boost results: local people.

Leary is the executive director of Trees for the Future (TFF), a nonprofit group founded in 1989 and based in Silver Springs, Maryland. The first few million trees Leary and his team planted were aimed at reforestation, providing carbon offsets or wildlife conservation zones. But less than 5% of the trees survived without local supervision.

That led them to the Forest Garden Approach, which trains farmers to use trees as a means of improving the productivity of degraded lands. Now TFF can plant each tree for as little as 10 cents while quadrupling the earnings of locals and boosting tree survival rates. Instead of releasing carbon through using techniques like slash and burn, the farmers growing the forest gardens are capturing more than 230 tons of carbon dioxide per acre over a 20-year period.

The Forest Garden Approach looks to first make poor farmers richer, rather than focusing on the number of trees planted. It's a lesson Leary took from his previous role as a volunteer for the Peace Corps, the U.S. program aimed at promoting economic and social development abroad. "You need to get local people involved and design any project such that it also benefits the local community," he said.

So far, Leary and his team have worked with farmers to build 10,000 forest gardens, which is estimated to sequester 2.4 million tons of carbon dioxide over a 20-year period-that's like taking 25,000 cars off U.S. roads. Projects so far have focused almost exclusively in Africa, with major projects in Senegal, Kenya and Tanzania. TFF typically targets a distressed region in a poor country. Leary's team recruits 100 or more farmers interested in improving their farms and then provides training.

In the four-year program, TFF provides educational resources tailored to their local needs and ongoing support, along with seeds and saplings. Farmers are taught how to build a "living fence"-that is, planting trees all along the edges of the farmland. The green wall keeps grazing animals (and neighbors) from plundering the farm. The trees also help retain more water in the soil.

By the end of the program, each acre of farmland can boast of as many as 1,500 trees, with many bearing produce that can be eaten or sold.

One of the most common reasons lands degrade is because farmers grow the wrong kind of crop, and so Leary helps them recognize what will flourish.

"In most countries, there tends to be one major cash crop that has destroyed the countryside," Leary said. "It's peanuts in Senegal and maize in Kenya and Tanzania."

He teaches farmers to move away from monoculture. They also become adept at making their own fertilizers. The upshot is that the farmers have something to sell every month of the year. That results in an increase of income and consumption of more nutritious food in their diets.

"It's clear that the major solution to climate change has to be reduction in fossil-fuel emissions," said Dominick Spracklen, professor of biosphere-atmosphere interactions at England's University of Leeds, who hasn't worked with TFF. "But we will also need negative emissions, and tree planting is the main way we can get there… it's really important that local people are involved in any tree-planting program."

In the 12 months to July 2019, Leary's group built nearly 6,000 forest gardens containing 11 million trees. The nonprofit's budget has grown, too. Annual contributions to TFF have doubled to $5 million last year from $2.5 million in 2017, and Leary expects to raise as much as $8 million in 2020.

While Leary's attention will continue to be on African countries, TFF has built an app that any farmer in the world (who can read English and French) can use to learn the steps needed to build a forest garden. Leary has seen a large number of downloads in India, Australia and Zambia. "Anyone with a little bit of experience in gardening or forestry can pick up what we do pretty easily," Leary said.

This is article was written by Akshat Rathi, a reporter for Bloomberg.