Andy Marshall, a biologist, yanks on the steering wheel of a battered Nissan station wagon and swings it off a track in the Kilombero Valley of southern Tanzania. Rain from the night before has left hubcap-deep puddles across the road. Mr. Marshall downshifts, swerves onto a recently harvested field of sugar cane, and parks on the furrows. The Nissan shudders for an instant before going quiet.
The biologist – a researcher on the staffs of the University of the Sunshine Coast in Queensland, Australia and the University of York in England – and three Tanzanian villagers slog a short distance through dirt clods and stubble toward a tall leafy wall of deep green: the Magombera Forest. Cradled at the base of the Udzungwa Mountains, the Magombera is one of the most biologically diverse habitats in Africa. Many large mammals, birds, and reptiles inhabit the emerald woods, including elephants, waterbucks, buffaloes, bush pigs, wart hogs, aardvarks, porcupines, and three monkey species. Marshall himself has discovered a new species of chameleon here: the Kinyongia magomberae. An unusual mixture of East African trees normally not found together shade the forest floor. The canopy towers 100 feet above the ground.
Until recently, the Magombera carpeted about six square miles of mostly flat land in the valley. But in the past three decades, half of the forest plain has been cleared, primarily for farming. The jungle that remains has been seriously degraded – selectively logged for construction timber – leaving gaping holes in the high, green canopy.
Marshall wants to patch Magombera’s wounds. The unnatural holes in the forest’s fabric lessen the trees’ capacity to soak up and store carbon dioxide, the gas that’s warming the planet and turning the weather chaotic. Forest gaps also reduce the jungle’s suitability for some of its rare wildlife. If only he can cure this small woodland’s ills, Marshall says, his method might then revive millions more acres of unhealthy forest around the world – and perhaps make a significant contribution to slowing global warming. There’s “huge potential,” he says. He needs only one simple tool: a sharp machete.
Marshall’s method of stemming greenhouse gases – by pruning excessive undergrowth that prevents forests from flourishing – is one of a slew of quixotic ideas being worked on by scientists and researchers around the world to help solve what could be the dominant issue of the next 100 years.
While most of the attention in curbing global warming focuses on lowering emissions, many people are trying to solve the problem from the other side – by preserving the “lungs of the Earth” that absorb and sequester harmful gases. Though some of the initiatives may be more notional than forest-ready, experts believe it will ultimately take a host of different approaches to avert worsening superstorms and to keep rising seas from coursing through coastal cities from Miami to Ho Chi Minh City, Vietnam.
Every year humans disgorge 36 billion metric tons of carbon dioxide – almost enough to fill up all of the Great Lakes – out of tailpipes and smokestacks. Fortunately, only about half of this planet-insulating gas stays in the atmosphere. Otherwise, Earth would be warming at an even faster rate. Ocean water and vegetation on land absorb the other half, in equal parts. Forests alone soak up one-quarter of the torrent of CO2 that people pump into the air. “We are talking about a free 25 percent emissions reduction,” says Scott Denning, a climate scientist at Colorado State University in Fort Collins. “It’s awesome.”
Preserving the health of forests is one of the best ways to slow global warming, says Professor Denning, especially in the band of productive tropical jungle that encircles the globe from the Amazon to Central Africa, through Southeast Asia and Indonesia. But humans are doing the opposite. They’re clearing these forests at a furious clip. In the thousands of years since humans discovered fire and invented agriculture and axes, people have chopped down, burned off, and cleared away a third of the woods that once carpeted the earth. The world has lost a forested area twice the size of the United States. After accelerating for centuries, the rate of forest loss has slowed slightly in recent decades. Still, every year loggers and farmers cut down a West Virginia-size area, almost all in tropical South America, Africa, and Asia.
In 2014, diplomats from 36 countries, including the US, many European nations, and Japan, signed the New York Declaration on Forests, an agreement intended to halt deforestation by 2030. They pledged to restore and reforest 865 million acres – an area larger than India – as well. That is a monumental logistical challenge. “2030 is only 12 years away,” says Stephen Elliott, a biologist at Thailand’s Chiang Mai University. Mr. Elliott, director of his university’s Forest Restoration Research Unit, is among the hundreds of scientists and policymakers around the world looking for ways to renew the vitality of land degraded by wholesale and selective logging, and protect the endangered woods that remain.
The world hears about advances in driverless car technology every day, and Elliott says the same autonomous navigation techniques might someday help to achieve the ambitious objectives of the New York Declaration. “I don’t think we can do an area the size of India by 2030 manually,” he says.
By “manually,” Elliott means how people restore forests today. He says that in Thailand, and in most other tropical countries, forest crews work with tools and apply techniques that would be familiar to their ancestors, “using Iron Age hoes and Stone Age baskets.” Sturdy farmworkers haul heavy hampers of nursery-raised saplings into clearings. They insert root balls into shallow holes cut through unyielding soil mats.
Such backbreaking work is expensive, even where labor is cheap. It’s slow, too. Farmers and ranchers already occupy the most accessible, easily worked parcels – flat areas near roads. Politically and economically, these plots are not open for reforestation. Roads don’t go where most of the available land is. Steep slopes, untamed rivers, and other obstacles also hinder access, multiplying the difficulty and expense.
Reforestation is “the only agricultural and horticultural activity that hasn’t been automated,” Elliott says. In 2015, he set out to change that, with help from autonomous drones. He invited an interdisciplinary group of 80 scientists and engineers from around the world to meet up in northern Thailand where he studies reforestation methods.
They bantered and brainstormed for four days about how drone squadrons might reconnoiter over restoration plots, pluck seed-laden fruit from treetops, shoot those seeds into the soil, and care for the seedlings that later emerged. Freewheeling discussions on how aerial robots could cut down fruit with mini chain saws, ferry this harvest in nets, and ward off rodents with urine-soaked cat litter, lived up to a conference slogan: “The craziest ideas are best.” “It was the best fun I’ve ever had,” says Elliott.
Many researchers are withholding judgment about the potential for drone restoration of forests, though. Robin Chazdon, a biologist at the University of Connecticut in Storrs, says Elliott’s idea for robotic weeding “raised my eyebrows a bit.” Professor Chazdon edited a 2016 paper in the journal Biotropica where Elliott laid out his ideas. “There are a lot of issues that remain to be worked out,” she says. Not the least of these is how to induce air-dropped seeds to germinate and how to repel seed-hungry herbivores.
Other ways to preserve the carbon sequestering ability of forests focus on preventing the trees from being cut down to begin with. This isn’t easy, either. Any attempt to silence chain saws and the thwack of axes must answer to a litany of powerful interests craving new land and fresh wood. Farmers want more acreage for crops. Ranchers want new pastures. Developers want lots to build on. And both timber companies and small-scale loggers want lumber.
Farmers in the Hoima and northern Kibaale districts in western Uganda are clearing trees – mostly for subsistence farming and to sell wood for timber and fuel – faster than almost anywhere else on Earth. In 2011, Seema Jayachandran, an economics professor at Northwestern University in Evanston, Ill., began an unusual investigation: how to entice small landowners in Uganda into protecting land, not clearing it.
With collaborators in the US, Belgium, and the Netherlands, Professor Jayachandran recruited 1,099 Ugandan families for a study of whether modest cash rewards could sway them. Her results, published last July in the journal Science, has attracted worldwide attention from forest restoration experts.