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Dogs may not be inclined to return favors to people, at least when it involves food. 

The result, published July 14 in PLOS ONE, is somewhat surprising since a previous study showed dogs will return favors in the form of food to other dogs. In other studies, dogs helped their owners when the people appeared to be trapped, and canines were able to distinguish between helpful and unhelpful people. So it seems reasonable to think dogs might reciprocate good deeds by humans.

To find out, comparative psychologist Jim McGetrick and colleagues at the University of Veterinary Medicine, Vienna trained pet dogs how to use a button to get food from a nearby dispenser. Each dog was then paired with a human, visible in an adjacent enclosure, who pressed the button to dispense food in the dog’s enclosure. On separate occasions, the dog was also paired with another human who didn’t press the button. When it was the dogs’ turn to offer food to their human partners, the canines were no more likely to press the button to provide food for the helpful human than for the stingy one.

Why didn’t dogs return the humans’ food favors? It may be that they aren’t willing to, or perhaps aren’t able to form this sort of complicated tit-for-tat social contract with humans. Or, there’s another possibility, the study authors note: The dogs simply may not have understood what was being asked of them, which could come down to how the experiment was designed. 

Science News talked to McGetrick about the challenges of testing whether animals like dogs are capable of complex social behaviors. His answers have been edited for clarity and length:

SN: What aspects of the experiment may have influenced why a dog didn’t return the favor for a human?

McGetrick: One possible explanation is the fact that dogs don’t provide humans with food. We feed them all the time, but it’s not something natural that they do. At the same time, dogs have been shown to reciprocate the receipt of food with other dogs [even though] adult dogs also don’t normally provide food to other adult dogs. So, if one applies the argument that this is an unusual setup because dogs don’t provide food to humans, I think one also needs to explain why it would be normal for a dog to provide food to another dog. 

SN: If trading food wasn’t the problem, what else could have been at play?

McGetrick: Another possible explanation for why they didn’t reciprocate is that the setup is very abstract. In a lot of previous reciprocity studies, there were very clear physical mechanisms: You pull a rope which pulls a tray, or a box opens if you press a lever. The dog’s physical connection with the mechanism is very obviously connected to the outcome, so that could be way easier for dogs to understand. In our case, we used the food dispenser where the connection was not that obvious. Having said that, the dogs all learned to press the button and get the food. What they understand about it is another question.

SN: Are there other elements of the experiment that the dogs might not have understood?

McGetrick: I’m not sure that the dogs understood that another individual was helping them. It seemed they certainly saw the human. But even if the dogs look, they might see the human’s face, they might see the human’s hand pressing the button, but they might never register that, “Oh, that’s how I’m getting the food,” or “Oh, the human is doing something for me.” It’s very difficult to know what they understand about the situation.

SN: Do you plan to follow up on any of these possible explanations?

McGetrick: At the moment, we’re running basically the same study but using dogs as the partners [rather than humans]. You can boil our result down to two possibilities. One is that there were methodological issues. Or this is just the answer to the question: Will dogs reciprocate help received from humans? And one way to really answer that is to test them with other dogs with this setup. With the same setup, we should see reciprocity with other dogs. And if we don’t see reciprocity with other dogs as partners, then it would point more towards methodological issues.

SN: How difficult is it to settle on a design for an experiment? 

McGetrick: These are very artificial setups where you’re just trying to get at something real, something that reveals something about nature and reality. And there are maybe 100 of these tiny decisions you make along the way, and so many of them are just intuition. And those minor decisions you make could be the difference between a positive result or a negative result. 

SN: Publishing negative results is somewhat uncommon. Why do you think it’s important?

McGetrick: My feeling is that it’s becoming more common, particularly in the field that I work in. If a study is designed well, structured well and addresses a question, there’s no reason for it not to be published regardless of the result. And it is a big problem if results aren’t published because they’re negative; it hides a lot of important information. The result is the result. You can explain the reasons why you might have gotten that result, but it shouldn’t really matter either way.

Maxwell Ochoo’s first attempt at farming was a dismal failure.

In Ochieng Odiere, a village near the shores of Kenya’s Lake Victoria, “getting a job is a challenge,” the 34-year-old says. To earn some money and help feed his family, he turned to farming. In 2017, he planted watermelon seeds on his 0.7-hectare plot.

Right when the melons were set to burst from their buds and balloon into juicy orbs, a two-month dry spell hit, and Ochoo’s fledgling watermelons withered. He lost around 70,000 Kenyan shillings, or about $650.

Ochoo blamed the region’s loss of tree cover for the long dry spells that had become more common. Unshielded from the sun, the soil baked, he says.

In 2018, Ochoo and some neighbors decided to plant trees on public lands and small farms. With the help of nonprofit groups, the community planted hundreds of trees, turning some of the barren hillsides green. On his own farm, Ochoo now practices alley cropping, in which he plants millet, onions, sweet potatoes and cassava between rows of fruit and other trees.

The trees provide shade and shelter to the crops, and their deeper root systems help the soil retain moisture. A few times a week in the growing season, Ochoo takes papayas, some as big as his head, to market, bringing home the equivalent of about $25 each time.

And the fallen leaves of the new Calliandra trees provide fodder for Ochoo’s five cows. He also discovered that he could grind up the fernlike leaves as a dietary supplement for the tilapia he grows in a small pond. He now spends less on fish food, and the tilapia grow much faster than his neighbors’ fish, he says.

Today, nearly everything Ochoo’s family eats comes from the farm, with plenty left over to sell at market. “Whether during dry spell or rainy season, my land is not bare,” he says, “there’s something that can sustain the family.”

Ochoo’s tree-filled farm represents what many scientists hope will be farming’s future. The present reality, where fields are often cleared of trees to raise livestock or plant row after row of single crops, called monocultures, is running out of room.

About half of all habitable land on Earth is devoted to growing food. More than 30 percent of forests have been cleared worldwide, and another 20 percent degraded, largely to make room for raising livestock and growing crops. By 2050, to feed a growing population, croplands will have to increase by 26 percent, an area the size of India, researchers estimate.

Humans’ collective hunger drives the twin ecological crises of climate change and biodiversity loss. Cutting down trees to make room for crops and livestock releases carbon into the atmosphere and erases the natural habitats that support so many species (SN: 1/30/21, p. 5).

Humankind is in danger of crossing a planetary boundary with unpredictable consequences, says landscape ecologist Tobias Plieninger of Germany’s University of Kassel and University of Göttingen. As land continues to be cleared for agriculture, “there’s high pressure … to shift toward more sustainable land use practices.”

Farmers like Ochoo, who intentionally blend crops, trees and livestock, a practice loosely called agroforestry, offer a more sustainable way forward. Agroforestry may not work in every circumstance, “but it has great potential,” Plieninger says, for working toward food production and conservation goals on the same land.

Integrating trees onto farms may seem like a recipe for lower yields, as trees would replace some crops. But such mixing can actually squeeze more food from a given plot of land than when plants are grown separately, Plieninger says. In Europe, blended farms that grow wheat or sunflowers between rows of wild cherry and walnut trees, for example, can produce up to 40 percent more than monocultures of the same crops for a given area.

Agroforestry was the norm until modern agricultural methods swept the globe, especially after the Industrial Revolution and the rise of chemical fertilizers in the mid-20th century. But small farms in the tropics are still big on trees. Worldwide, about 43 percent of land used for agriculture has at least 10 percent tree cover, according to a 2016 study in Scientific Reports.

Increasing that percentage could have profound and wide-ranging benefits, if done right. “Trees have to be integrated [onto farms] to not create extra problems” for farmers, says Anja Gassner, a senior scientist at World Agroforestry in Bonn, Germany. And the approach looks very different depending on the region and the goals of the people who live there. What Spanish farmers need from their oak-dotted fields where pigs get fat on acorns will be different from what farmers in Ecuador want from their coffee plants growing under the cool shade of tropical inga trees.

The way agroforestry is carried out in three very different parts of the world illustrates the promises and challenges of coupling trees and crops.

Made in the shade

If you’re enjoying a morning cup of coffee while reading this, there’s a chance the beans in that brew came from farms practicing agroforestry.

Coffee plants evolved in the understory of Ethiopia’s highland forests; they are well-suited to shade, says Eduardo Somarriba, an agroecologist at the Tropical Agricultural Research and Higher Education Center in Cartago, Costa Rica.

A diverse canopy of native trees can help coffee plants thrive. Certain trees pump nitrogen into the soil, removing the need for intensive fertilizer application, Somarriba says. Native vegetation suppresses weed growth, stabilizes soil and temperature, improves water retention and supports pollinating animals.

But as global thirst for coffee has grown, planting practices have shifted toward shadeless plots filled only with coffee plants that require a steady stream of chemical fertilizers. From 1996 to 2010, the worldwide share of coffee grown under a canopy of diverse trees fell from 43 percent to 24 percent, researchers reported in 2014 in BioScience.

Removing trees is seen as good for increasing yields, though the evidence is mixed. This focus on numbers misses the more diffuse benefits of diversifying farms, Somarriba says, especially small farms, which still produce most of the world’s coffee.

“If coffee prices go down and stay low for five or six years, a small farmer will not be able to make it only from [selling] coffee,” Somarriba says. But adding a mix of trees can build in economic and climate resilience, he says.

Valuable timber trees, like mahogany, can serve as savings accounts, harvested when coffee profits aren’t enough. Mango, Brazil nut or acai trees can supply income, too. But not all places have well-developed markets for these goods, Somarriba says, which presents a challenge to increasing the share of coffee grown under shade.

Some conservationists are trying to boost consumer demand for shade-grown coffee by highlighting how it benefits biodiversity. The Smithsonian Migratory Bird Center, for example, grants a Bird Friendly certification to plantations with ample native tree cover and diversity, a boon for migratory birds. Certified farmers are able to charge a slightly higher price, on average 5 to 15 cents more per pound.

Migratory birds flock to such plantations. “When you’re in a bird-friendly coffee farm, it kind of feels like you’re in the forest,” says Ruth Bennett, an ecologist at the Smithsonian Migratory Bird Center in Washington, D.C. “You hear a lot of bird calls, and it’s a huge diversity of birds, including really sexy tropical species like the turquoise-browed motmot,” she says.

Bird Friendly coffee plantations also appear to be good for mammals. In Mexico, Bird Friendly coffee plantations had more native wildlife, including deer and mice, than other coffee plantations, according to a 2016 study in PLOS ONE.

Ecosystems brimming with diverse species of plants, animals and more make the planet livable by filtering water, cycling nutrients through soils and pollinating crops. While undeveloped forest is clearly best for biodiversity, shade-grown plantations can outshine other land uses. After more than a decade, high-diversity coffee agroforestry systems in southeastern Brazil were ecologically healthier — as measured by tree canopy cover and species richness — than plots set aside for nonagricultural restoration, researchers reported in the September 2020 Restoration Ecology. About 90 percent of the canopy was intact on shaded coffee plots versus about 60 percent for restored forest areas, on average.

Beyond the biodiversity benefits, Bennett says shade-grown coffee just tastes better. Under shade, coffee cherries take longer to develop, which can boost sugar content.

Time to recover

In the Shinyanga region of Tanzania, a return to traditional Indigenous practices, with a dose of modern agroforestry, helped transform what was once the “desert of Tanzania” back into productive savanna woodlands.

The region, about a five-hour drive southeast from the Serengeti, is home to the Sukuma people, traditionally agropastoralists who raised livestock in the hilly grasslands of the region, dotted with acacia and oaklike miombo trees.

But in the 1920s, the landscape began to change. The British colonial government cut back woodlands in a misguided effort to control the tsetse flies that were harming livestock and humans and to plant cash crops like cotton. In the 1960s, forest loss accelerated when the government took ownership of many homesteads. After they lost rights to harvest products from the forest, local Tanzanians had less incentive to conserve the trees.

Within a few decades, the ecosystem had degraded into dry, dusty expanses largely devoid of trees. Food, firewood and water were scarce and local livelihoods suffered, says Lalisa Duguma, a sustainability scientist at World Agroforestry, an international research agency headquarted in Nairobi, Kenya.

By the 1980s, the situation had become so dire that the Tanzanian government intervened. At first, it tried to convince local residents to plant seedlings of fast-growing exotic trees, like eucalyptus, Duguma says. But locals weren’t interested in planting or tending those seedlings. In the face of this setback, experts and officials did something not always done in development projects: They listened.

Listening to locals revealed that an age-old tradition of forming ngitilis could be the foundation for restoration. Roughly translated as “enclosure,” a ngitili cordons off a section of land for a year or two, allowing trees and grasses to recover, and then opening it to provide fodder for grazing animals during the dry season. “By just fencing in degraded land, the process of restoration starts,” Duguma says.

Native seeds and stumps long stunted by grazing or poor soil conditions can begin to grow again, and their numbers can be supplemented with planted trees. Local institutions largely planned and monitored ngitilis, in accordance with traditional practices, often in collaboration with government scientists.

Year by year, the benefits of ngitilis slowly accrued, giving shade and fodder to livestock and wood for energy and building. Maturing trees provided fruits and supported beehives for honey production.

At the start of the restoration in the mid-1980s, there were only 600 hectares of ngitilis in all of the Shinyanga region. After 16 years, more than 300,000 hectares of land was restored. The return of trees in the region may have sequestered more than 20 million metric tons of carbon over 16 years (the equivalent of taking 16.7 million cars off the road for a year), according to a 2005 report by the Tanzanian government and the International Union for the Conservation of Nature. Deeper root systems bolstered soil health, and expanded tree cover cut down on wind and water erosion, halting desertification.

Ngitilis provided benefits equal to $14 per person per month, substantially more than the $8.50 an average person spends in a month in rural Tanzania, the same report noted. Money from communal ngitilis went toward improving housing, Duguma says.

Biodiversity flourished, too. Ngitilis collectively housed over 150 species of trees, shrubs and other plants. With habitat restored, people in the region began to hear the cries of hyenas at night, a welcome return, Duguma says. At least 10 mammalian species came back, including antelope and rabbits, and 145 bird species were recorded within the ngitilis.

There’s an enormous need to scale up this kind of community-driven success across Africa, where roughly 60 percent of agricultural lands are degraded, says Susan Chomba, who led the Regreening Africa initiative before becoming director of Vital Landscapes at the World Resources Institute in Nairobi. Regreening Africa, an ambitious 2017 initiative led by World Agroforestry, hopes to reverse land degradation across 1 million hectares of sub-Saharan Africa by 2022 to improve the lives of people in 500,000 households.

There are many drivers of land degradation, “but the underlying issue is poverty,” Chomba says. If a woman can feed her children only by cutting down a tree to sell firewood, her choice is clear, Chomba says. To offer better options, Regreening Africa hopes to couple agroforestry and sustainable land use practices. The aim is to generate income for local residents while restoring the landscape.

Central to that goal is close collaboration with local people. Some farmers may want to restore water to a region that used to have streams, or people may want shea trees for making profitable shea butter, Chomba says. Tree-planting schemes that come in with preformed ideas of what a region needs, without engaging and listening to the local community, won’t get far, she says.

And land use policies are central to resident buy-in, Chomba says. In Africa, “we are coming from a history of colonialization,” she says. As a result, much of the land that’s forested, or could be restored by farmers, is state owned. Because trees are often state property, it is difficult for locals to profit from the sales of fruits and other tree products.

“If I’m planting a tree that will take years to grow, and I’m not guaranteed ownership of that tree or land, what’s my incentive for investing in it?” Chomba asks. “Restoration efforts must be coupled with ensuring land rights.”

The U.S. breadbasket

In the United States, thoughts of agriculture likely conjure images of Iowa’s endless cornfields or massive hog farms. While industrialized monoculture is the norm among big players, small-scale farmers are more able to incorporate trees into their fields, or bring crops into the forests.

According to the U.S. Department of Agriculture’s 2017 Census of Agriculture, of the approximately 2 million farms in the United States, only 1.5 percent report practicing some form of agroforestry. This percentage is likely an underestimate, but experts say it reveals how much room there is to grow.

Agroforestry practices vary across the United States. In the Midwest, trees serve as windbreaks for crops and line creeks to minimize fertilizer runoff. In cattle country, ranchers plant honey locust trees in their pastures to provide shade during the summer and nutrient-rich pods that feed animals. Forest farming, where nontimber crops such as wild mushrooms or ginseng are grown within a managed or wild forest, is becoming more popular across the eastern states.

Agroforestry is all about breaking down the wall between agricultural lands and woodlands and blending them together, says John Munsell, a forest management researcher at Virginia Tech in Blacksburg. “It’s a way of thinking creatively across a landscape,” he says. Often, small-scale farmers are more game for trying.

Anna Plattner and Justin Wexler have had to get creative to support their farm in New York’s Hudson Valley. The 38-hectare farm grows heirloom plants used by the Mohican and Munsee peoples indigenous to the region. The farm also incorporates traditional agroforestry methods, Wexler says. Rows of pawpaw and persimmon trees are staggered between native varieties of corn, beans and squash. The farm also grows more obscure foods, including hopniss, a legume that was a staple for some Native American tribes before Europeans arrived.

Wexler says he hopes that focusing on foods of Indigenous peoples can help others learn about the history and culture of the area. Demand for these unfamiliar crops isn’t high, so in addition to selling to wholesalers and restaurants, this year, Plattner and Wexler debuted monthly “wild harvest boxes” — a sort of local Blue Apron for native produce. The boxes come stuffed with snippets of history about the foods and recipe ideas. “Every plant has its own story to tell,” Plattner says.

Small farms may be more willing to embrace agroforestry, but to meet the looming challenges of climate change and biodiversity loss, large farms need to as well.

In the United States, “there is huge potential to scale up agroforestry,” says agroecologist Sarah Lovell, director of the Center for Agroforestry at the University of Missouri in Columbia.

For Lovell, step one involves identifying marginal areas on farms where trees could be planted with minimal disruption to the status quo, such as along creeks. Putting trees around waterways can reduce flooding and erosion, improve water quality and house wildlife, Lovell says. In the “true breadbasket of the Midwest,” she estimates, only 2 to 5 percent of such areas are currently making use of trees.

Eventually, she says she would like to see a drastic scaling up of alley cropping, with lines of fruit or nut trees fully integrated into fields. The need to move fruit and nut production east, away from increasingly drought-stricken California, may provide an extra push for bringing more trees onto monoculture farms, Lovell says.

But corn and soybean fields dominate much of U.S. agricultural land. These lucrative crops serve as raw materials for everything from biodiesel to high fructose corn syrup. To convince farmers to replace some of those crops with trees, the fruits of those trees will have to become more mainstream. The Savanna Institute, an agroforestry nonprofit in Madison, Wis., is focused on expanding the market for chestnuts and hazelnuts.

“We call them corn and soybean on trees,” says Savanna Institute ecologist Kevin Wolz. Chestnuts are about 90 percent starch, like corn; hazelnuts are 75 percent oil and protein, like soybeans, Wolz says. Researchers at the institute are working out just how these tree products could replace corn and soy as raw materials in production pipelines, with rows of nut trees breaking up monoculture fields. “We think these could be the next commodity crops that the Midwest can produce,” Wolz says.

Whether we’ll be drinking soda sweetened with chestnut syrup anytime soon remains to be seen. But to transform agriculture from a climate change problem to a solution, Wolz says such bold and imaginative thinking is essential.

Agroforestry isn’t a silver bullet for addressing climate change, the biodiversity crisis or food insecurity, Wolz says. But when applied with place and people in mind, he says it can be a Swiss Army knife.

Climate change is helping Atlantic hurricanes pack more of a punch, making them rainier, intensifying them faster and helping the storms linger longer even after landfall. But a new statistical analysis of historical records and satellite data suggests that there aren’t actually more Atlantic hurricanes now than there were roughly 150 years ago, researchers report July 13 in Nature Communications.

The record-breaking number of Atlantic hurricanes in 2020, a whopping 30 named storms, led to intense speculation over whether and how climate change was involved (SN: 12/21/20). It’s a question that scientists continue to grapple with, says Gabriel Vecchi, a climate scientist at Princeton University. “What is the impact of global warming — past impact and also our future impact — on the number and intensity of hurricanes and tropical storms?”

Satellite records over the last 30 years allow us to say “with little ambiguity how many hurricanes, and how many major hurricanes [Category 3 and above] there were each year,” Vecchi says. Those data clearly show that the number, intensity and speed of intensification of hurricanes has increased over that time span.

But “there are a lot of things that have happened over the last 30 years” that can influence that trend, he adds. “Global warming is one of them.” Decreasing aerosol pollution is another (SN: 11/21/19). The amount of soot and sulfate particles and dust over the Atlantic Ocean was much higher in the mid-20th century than now; by blocking and scattering sunlight, those particles temporarily cooled the planet enough to counteract greenhouse gas warming. That cooling is also thought to have helped temporarily suppress hurricane activity in the Atlantic.  

To get a longer-term perspective on trends in Atlantic storms, Vecchi and colleagues examined a dataset of hurricane observations from the U.S. National Oceanic and Atmospheric Administration that stretches from 1851 to 2019. It includes old-school observations by unlucky souls who directly observed the tempests as well as remote sensing data from the modern satellite era.

Storm count

The National Oceanic and Atmospheric Administration’s record of hurricane observations in the Atlantic Ocean begins in 1851. To adjust for changes in observational practices from 1851 to 2019, researchers developed a statistical method to estimate the number of storms that went unobserved in pre-satellite years. Then, the team took successive 15-year averages of the annual estimated counts (blue line, with error margins shaded in blue) to determine whether a trend exists over time. The adjusted count suggests no clear trend in hurricane frequency over roughly the last 150 years.

Frequency of Atlantic hurricanes, 1851–2019

How to directly compare those different types of observations to get an accurate trend was a challenge. Satellites, for example, can see every storm, but earlier observations will count only the storms that people directly experienced. So the researchers took a probabilistic approach to fill in likely gaps in the older record, assuming, for example, that modern storm tracks are representative of pre-satellite storm tracks to account for storms that would have stayed out at sea and unseen. The team found no clear increase in the number of storms in the Atlantic over that 168-year time frame. One possible reason for this, the researchers say, is a rebound from the aerosol pollution–induced lull in storms that may be obscuring some of the greenhouse gas signal in the data.  

More surprisingly — even to Vecchi, he says — the data also seem to show no significant increase in hurricane intensity over that time. That’s despite “scientific consistency between theories and models indicating that the typical intensity of hurricanes is more likely to increase as the planet warms,” Vecchi says. But this conclusion is heavily caveated — and the study also doesn’t provide evidence against the hypothesis that global warming “has acted and will act to intensify hurricane activity,” he adds.

Climate scientists were already familiar with the possibility that storm frequency might not have increased much in the last 150 or so years — or over much longer timescales. The link between number of storms and warming has long been uncertain, as the changing climate also produces complex shifts in atmospheric patterns that could take the hurricane trend in either direction. The Intergovernmental Panel on Climate Change noted in a 2012 report that there is “low confidence” that tropical cyclone activity has increased in the long term.

Geologic evidence of Atlantic storm frequency, which can go back over 1,000 years, also suggests that hurricane frequency does tend to wax and wane every few decades, says Elizabeth Wallace, a paleotempestologist at Rice University in Houston (SN: 10/22/17).

Wallace hunts for hurricane records in deep underwater caverns called blue holes: As a storm passes over an island beach or the barely submerged shallows, winds and waves pick up sand that then can get dumped into these caverns, forming telltale sediment deposits. Her data, she says, also suggest that “the past 150 years hasn’t been exceptional [in storm frequency], compared to the past.”

But, Wallace notes, these deposits don’t reveal anything about whether climate change is producing more intense hurricanes. And modern observational data on changes in hurricane intensity is muddled by its own uncertainties, particularly the fact that the satellite record just isn’t that long. Still, “I liked that the study says it doesn’t necessarily provide evidence against the hypothesis” that higher sea-surface temperatures would increase hurricane intensity by adding more energy to the storm, she says.

Kerry Emanuel, an atmospheric scientist at MIT, says the idea that storm numbers haven’t increased isn’t surprising, given the longstanding uncertainty over how global warming might alter that. But “one reservation I have about the new paper is the implication that no significant trends in Atlantic hurricane metrics [going back to 1851] implies no effect of global warming on these storms,” he says. Looking for such a long-term trend isn’t actually that meaningful, he says, as scientists wouldn’t expect to see any global warming-related hurricane trends become apparent until about the 1970s anyway, as warming has ramped up.

Regardless of whether there are more of these storms, there’s no question that modern hurricanes have become more deadly in many ways, Vecchi says. There’s evidence that global warming has already been increasing the amount of rain from some storms, such as Hurricane Harvey in 2017, which led to widespread, devastating flooding (SN: 9/28/18). And, Vecchi says, “sea level will rise over the coming century … so [increasing] storm surge is one big hazard from hurricanes.”

Between a death and a burial was hardly the best time to show up in a remote village in Madagascar to make a pitch for forest protection. Bad timing, however, turned out to be the easy problem.

This forest was the first one that botanist Armand Randrianasolo had tried to protect. He’s the first native of Madagascar to become a Ph.D. taxonomist at Missouri Botanical Garden, or MBG, in St. Louis. So he was picked to join a 2002 scouting trip to choose a conservation site.

Other groups had already come into the country and protected swaths of green, focusing on “big forests; big, big, big!” Randrianasolo says. Preferably forests with lots of big-eyed, fluffy lemurs to tug heartstrings elsewhere in the world.

The Missouri group, however, planned to go small and to focus on the island’s plants, legendary among botanists but less likely to be loved as a stuffed cuddly. The team zeroed in on fragments of humid forest that thrive on sand along the eastern coast. “Nobody was working on it,” he says.

As the people of the Agnalazaha forest were mourning a member of their close-knit community, Randrianasolo decided to pay his respects: “I wanted to show that I’m still Malagasy,” he says. He had grown up in a seaside community to the north.

The village was filling up with visiting relatives and acquaintances, a great chance to talk with many people in the region. The deputy mayor conceded that after a morning visit to the bereaved, Randrianasolo and MBG’s Chris Birkinshaw could speak in the afternoon with anyone wishing to gather at the roofed marketplace.

The two scientists didn’t get the reception they’d hoped for. Their pitch to help the villagers conserve their forest while still serving people’s needs met protests from the crowd: “You’re lying!”

The community was still upset about a different forest that outside conservationists had protected. The villagers had assumed they would still be able to take trees for lumber, harvest their medicinal plants or sell other bits from the forest during cash emergencies. They were wrong. That place was now off-limits. People caught doing any of the normal things a forest community does would be considered poachers. When MBG proposed conserving yet more land, residents weren’t about to get tricked again. “This is the only forest we have left,” they told the scientists.

Finding some way out of such clashes to save existing forests has become crucial for fighting climate change. Between 2001 and 2019, the planet’s forests trapped an estimated 7.6 billion metric tons of carbon dioxide a year, an international team reported in Nature Climate Change in March. That rough accounting suggests trees may capture about one and a half times the annual emissions of the United States, one of the largest global emitters.

Planting trees by the millions and trillions is basking in round-the-world enthusiasm right now. Yet saving the forests we already have ranks higher in priority and in payoff, say a variety of scientists.

How to preserve forests may be a harder question than why. Success takes strong legal protections with full government support. It also takes a village, literally. A forest’s most intimate neighbors must wholeheartedly want it saved, one generation after another. That theme repeats in places as different as rural Madagascar and suburban New Jersey.

Forest loss down

Destruction of the world’s natural forests continues, though rates have been slowing. The target of two international agreements — to halve the previous decade’s rate by 2020 — has not been met.

Source: FAO, 2020

Overlooked and underprotected

First a word about trees themselves. Of course, trees capture carbon and fight climate change. But trees are much more than useful wooden objects that happen to be leafy, self-manufacturing and great shade for picnics.

“Plant blindness,” as it has been called, reduces trees and other photosynthetic organisms to background, lamented botanist Sandra Knapp in a 2019 article in the journal Plants, People, Planet. For instance, show people a picture with a squirrel in a forest. They’ll likely say something like “cute squirrel.” Not “nice-size beech tree, and is that a young black oak with a cute squirrel on it?”

This tunnel vision also excludes invertebrates, argues Knapp, of the Natural History Museum in London, complicating efforts to save nature. These half-seen forests, natural plus human-planted, now cover close to a third of the planet’s land, according to the 2020 version of The State of the World’s Forests report from the United Nation’s Food and Agriculture Organization. Yet a calculation based on the report’s numbers says that over the last 10 years, net tree cover vanished at an average rate of about 12,990 hectares — a bit more than the area of San Francisco — every day.

This is an improvement over the previous decades, the report notes. In the 1990s, deforestation, on average, destroyed about 1.75 San Francisco equivalents of forest every day.

Trees were the planet’s skyscrapers, many rising to great heights, hundreds of millions of years before humans began piling stone upon stone to build their own. Trees reach their stature by growing and then killing their innermost core of tissue. The still-living outer rim of the tree uses its ever-increasing inner ghost architecture as plumbing pipes that can function as long as several human lifetimes. And tree sex lives, oh my. Plants invented “steamy but not touchy” long before the Victorian novel — much flowering, perfuming and maybe green yearning, all without direct contact of reproductive organs. Just a dusting of pollen wafted on a breeze or delivered by a bee.

To achieve the all-important goal of cutting global emissions, saving the natural forests already in the ground must be a priority, 14 scientists from around the world wrote in the April Global Change Biology. “Protect existing forests first,” coauthor Kate Hardwick of Kew Gardens in London said during a virtual conference on reforestation in February. That priority also gives the planet’s magnificent biodiversity a better chance at surviving. Trees can store a lot of carbon in racing to the sky. And size and age matter because trees add carbon over so much of their architecture, says ecologist David Mildrexler with Eastern Oregon Legacy Lands at the Wallowology Natural History Discovery Center in Joseph. Trees don’t just start new growth at twigs tipped with unfurling baby leaves. Inside the branches, the trunk and big roots, an actively growing sheath surrounds the inner ghost plumbing. Each season, this whole sheath adds a layer of carbon-capturing tissue from root to crown.

“Imagine you’re standing in front of a really big tree — one that’s so big you can’t even wrap your arms all the way around, and you look up the trunk,” Mildrexler says. Compare that sky-touching vision to the area covered in a year’s growth of some sapling, maybe three fingers thick and human height. “The difference is, of course, just huge,” he says.

Big trees may not be common, but they make an outsize difference in trapping carbon, Mildrexler and colleagues have found. In six Pacific Northwest national forests, only about 3 percent of all the trees in the study, including ponderosa pines, western larches and three other major species, reached full-arm-hug size (at least 53.3 centimeters in diameter). Yet this 3 percent of trees stored 42 percent of the aboveground carbon there, the team reported in 2020 in Frontiers in Forests and Global Change. An earlier study, with 48 sites worldwide and more than 5 million tree trunks, found that the largest 1 percent of trees store about 50 percent of the aboveground carbon-filled biomass.

Plant paradise

The island nation of Madagascar was an irresistible place for the Missouri Botanical Garden to start trying to conserve forests. Off the east coast of Africa, the island stretches more than the distance from Savannah, Ga., to Toronto, and holds more than 12,000 named species of trees, other flowering plants and ferns. Madagascar “is absolute nirvana,” says MBG botanist James S. Miller, who has spent decades exploring the island’s flora.

Just consider the rarities. Of the eight known species of baobab trees, which raise a fat trunk to a cartoonishly spindly tuft of little branches on top, six are native to Madagascar. Miller considers some 90 percent of the island’s plants as natives unique to the country. “It wrecks you” for botanizing elsewhere, Miller says.

He was rooting for his MBG colleagues Randrianasolo and Birkinshaw in their foray to Madagascar’s Agnalazaha forest. Several months after getting roasted as liars by residents, the two got word that the skeptics had decided to give protection a chance after all.

The Agnalazaha residents wanted to make sure, however, that the Missouri group realized the solemnity of their promise. Randrianasolo had to return to the island for a ceremony of calling the ancestors as witnesses to the new partnership and marking the occasion with the sacrifice of a cow. A pact with generations of deceased residents may be an unusual form of legal involvement, but it carried weight. Randrianasolo bought the cow.

Randrianasolo looked for ways to be helpful. MBG worked on improving the village’s rice yields, and supplied starter batches of vegetable seeds for expanding home gardens. The MBG staff helped the forest residents apply for conservation funds from the Malagasy government. A new tree nursery gave villagers an alternative to cutting timber in the forest. The nursery also meant some jobs for local people, which further improved relationships.

The MBG staff now works with Malagasy communities to preserve forests at 11 sites dotted in various ecosystems in Madagascar. Says Randrianasolo: “You have to be patient.”

Today, 19 years after his first visit among the mourners, Agnalazaha still stands.

Saving forests is not a simple matter of just meeting basic needs of people living nearby, says political scientist Nadia Rabesahala Horning of Middlebury College in Vermont, who published The Politics of Deforestation in Africa in 2018. Her Ph.D. work, starting in the late 1990s, took her to four remote forests in her native Madagascar. The villagers around each forest followed different rules for harvesting timber, finding places to graze livestock and collecting medicinal plants.

Three of the forests shrank, two of them rapidly, over the decade. One, called Analavelona, however, barely showed any change in the aerial views Horning used to look for fraying forests.

The people living around Analavelona revered it as a sacred place where their ancestors dwelled. Living villagers made offerings before entering, and cut only one kind of tree, which they used for coffins.

Since then, Horning’s research in Tanzania and Uganda has convinced her that forest conservation can happen only under very specific conditions, she says. The local community must be able to trust that the government won’t let some commercial interest or a political heavyweight slip through loopholes to exploit a forest that its everyday neighbors can’t touch. And local people must be able to meet their own needs too, including the spiritual ones.

A different kind of essential

Another constellation of old forests, on the other side of the world, sports some less-than-obvious similarities. Ecologist Joan Maloof launched the Old-Growth Forest Network in 2011 to encourage people to save the remaining scraps of U.S. old-growth forests. Her bold idea: to permanently protect one patch of old forest in each of the more than 2,000 counties in the United States where forests can grow.

She calls for strong legal measures, such as conservation easements that prevent logging, but also recognizes the need to convey the emotional power of communing with nature. One of the early green spots she and colleagues campaigned for was not old growth, but it had become one of the few left unlogged where she lived on Maryland’s Eastern Shore.

She heard about Buddhist monks in Thailand who had ordained trees as monks because loggers revered the monks, so the trees were protected. A month after the 9/11 terrorist attacks, she was inspired to turn the Maryland forest into a place to remember the victims. By putting each victim’s name on a metal tag and tying it to a tree, she and other volunteers created a memorial with close to 3,000 trees. The local planning commission, she suspected, would feel awkward about approving timber cutting from that particular stand. She wasn’t party to their private deliberations, but the forest still stands.

As of Earth Day 2021, the network had about 125 forests around the country that should stay forests in perpetuity. Their stories vary widely, but are full of local history and political maneuvering.

 In southern New Jersey, Joshua Saddler, an escaped enslaved man from Maryland, acquired part of a small forest in the mid-1880s and bequeathed it to his wife with the stipulation that it not be logged. His section was logged anyway, and the rest of the original old forest was about to meet the same fate. In 1973, high school student Doug Hefty wrote more than 80 pages on the forest’s value — and delivered it to the developer. In this case, life delivered a genuine Hollywood ending. The developer relented, and scaled back the project, stopping across the street from the woods.

In 1999, however, developers once again eyed the forest, says Janet Goehner-Jacobs, who heads the Saddler’s Woods Conservation Association. It took four years, but now, she and the forests’ other fans have a conservation easement forbidding commercial development or logging, giving the next generation better tools to protect the forest.

Goehner-Jacobs had just moved to the area and fallen in love with that 10-hectare patch of green in the midst of apartment buildings and strip malls. When she first happened upon the forest and found the old-growth section, “I just instinctively knew I was seeing something very different.”

Trees are symbols of hope, life and transformation. They’re also increasingly touted as a straightforward, relatively inexpensive, ready-for-prime-time solution to climate change.

When it comes to removing human-caused emissions of the greenhouse gas carbon dioxide from Earth’s atmosphere, trees are a big help. Through photosynthesis, trees pull the gas out of the air to help grow their leaves, branches and roots. Forest soils can also sequester vast reservoirs of carbon.

Earth holds, by one estimate, as many as 3 trillion trees. Enthusiasm is growing among governments, businesses and individuals for ambitious projects to plant billions, even a trillion more. Such massive tree-planting projects, advocates say, could do two important things: help offset current emissions and also draw out CO₂ emissions that have lingered in the atmosphere for decades or longer.

Even in the politically divided United States, large-scale tree-planting projects have broad bipartisan support, according to a spring 2020 poll by the Pew Research Center. And over the last decade, a diverse garden of tree-centric proposals — from planting new seedlings to promoting natural regrowth of degraded forests to blending trees with crops and pasturelands — has sprouted across the international political landscape.

Trees “are having a bit of a moment right now,” says Joe Fargione, an ecologist with The Nature Conservancy who is based in Minneapolis. It helps that everybody likes trees. “There’s no anti-tree lobby. [Trees] have lots of benefits for people. Not only do they store carbon, they help provide clean air, prevent soil erosion, shade and shelter homes to reduce energy costs and give people a sense of well-being.”

Conservationists are understandably eager to harness this enthusiasm to combat climate change. “We’re tapping into the zeitgeist,” says Justin Adams, executive director of the Tropical Forest Alliance at the World Economic Forum, an international nongovernmental organization based in Geneva. In January 2020, the World Economic Forum launched the One Trillion Trees Initiative, a global movement to grow, restore and conserve trees around the planet. One trillion is also the target for other organizations that coordinate global forestation projects, such as Plant-for-the-Planet’s Trillion Tree Campaign and Trillion Trees, a partnership of the World Wildlife Fund, the Wildlife Conservation Society and other conservation groups.

A carbon-containing system

Forests store carbon aboveground and below. That carbon returns to the atmosphere by microbial activity in the soil, or when trees are cut down and die.

SOURCE: MINNESOTA BOARD OF WATER AND SOIL RESOURCES 2019; images: T. Tibbitts

Yet, as global eagerness for adding more trees grows, some scientists are urging caution. Before moving forward, they say, such massive tree projects must address a range of scientific, political, social and economic concerns. Poorly designed projects that don’t address these issues could do more harm than good, the researchers say, wasting money as well as political and public goodwill. The concerns are myriad: There’s too much focus on numbers of seedlings planted, and too little time spent on how to keep the trees alive in the long term, or in working with local communities. And there’s not enough emphasis on how different types of forests sequester very different amounts of carbon. There’s too much talk about trees, and not enough about other carbon-storing ecosystems.

“There’s a real feeling that … forests and trees are just the idea we can use to get political support” for many, perhaps more complicated, types of landscape restoration initiatives, says Joseph Veldman, an ecologist at Texas A&M University in College Station. But that can lead to all kinds of problems, he adds. “For me, the devil is in the details.”

The root of the problem

The pace of climate change is accelerating into the realm of emergency, scientists say. Over the last 200 years, human-caused emissions of greenhouse gases, including CO₂ and methane, have raised the average temperature of the planet by about 1 degree Celsius (SN: 12/22/18 & 1/5/19, p. 18).

The litany of impacts of this heating is familiar by now. Earth’s poles are rapidly shedding ice, which raises sea levels; the oceans are heating up, threatening fish and food security. Tropical storms are becoming rainier and lingering longer, and out of control wildfires are blazing from the Arctic to Australia (SN: 12/19/20 & 1/2/21, p. 32).

The world’s oceans and land-based ecosystems, such as forests, absorb about half of the carbon emissions from fossil fuel burning and other industrial activities. The rest goes into the atmosphere. So “the majority of the solution to climate change will need to come from reducing our emissions,” Fargione says. To meet climate targets set by the 2015 Paris Agreement, much deeper and more painful cuts in emissions than nations have pledged so far will be needed in the next 10 years.

But increasingly, scientists warn that reducing emissions alone won’t be enough to bring Earth’s thermostat back down. “We really do need an all-hands-on-deck approach,” Fargione says. Specifically, researchers are investigating ways to actively remove that carbon, known as negative emissions technologies. Many of these approaches, such as removing CO₂ directly from the air and converting it into fuel, are still being developed.

But trees are a ready kind of negative emissions “technology,” and many researchers see them as the first line of defense. In its January 2020 report, “CarbonShot,” the World Resources Institute, a global nonprofit research organization, suggested that large and immediate investments in reforestation within the United States will be key for the country to have any hope of reaching carbon neutrality — in which ongoing carbon emissions are balanced by carbon withdrawals — by 2050. The report called for the U.S. government to invest $4 billion a year through 2030 to support tree restoration projects across the United States. Those efforts would be a bridge to a future of, hopefully, more technologies that can pull large amounts of carbon out of the atmosphere.

The numbers game

Earth’s forests absorb, on average, 16 billion metric tons of CO₂ annually, researchers reported in the March Nature Climate Change. But human activity can turn forests into sources of carbon: Thanks to land clearing, wildfires and the burning of wood products, forests also emit an estimated 8.1 billion tons of the gas back to the atmosphere.

That leaves a net amount of 7.6 billion tons of CO₂ absorbed by forests per year — roughly a fifth of the 36 billion tons of CO₂ emitted by humans in 2019. Deforestation and forest degradation are rapidly shifting the balance. Forests in Southeast Asia now emit more carbon than they absorb due to clearing for plantations and uncontrolled fires. The Amazon’s forests may flip from carbon sponge to carbon source by 2050, researchers say (SN Online: 1/10/20). The priority for slowing climate change, many agree, should be saving the trees we have.

Forests in flux

While global forests were a net carbon sink of about 7.6 gigatons of carbon dioxide per year from 2001 to 2019, forests in areas such as Southeast Asia and parts of the Amazon began releasing more carbon than they store.
Tap map to enlarge

Net annual average contribution of carbon dioxide from Earth’s forests, 2001–2019

Just how many more trees might be mustered for the fight is unclear, however. In 2019, Thomas Crowther, an ecologist at ETH Zurich, and his team estimated in Science that around the globe, there are 900 million hectares of land — an area about the size of the United States — available for planting new forests and reviving old ones (SN: 8/17/19, p. 5). That land could hold over a trillion more trees, the team claimed, which could trap about 206 billion tons of carbon over a century.

That study, led by Jean-Francois Bastin, then a postdoc in Crowther’s lab, was sweeping, ambitious and hopeful. Its findings spread like wildfire through media, conservationist and political circles. “We were in New York during Climate Week [2019], and everybody’s talking about this paper,” Adams recalls. “It had just popped into people’s consciousness, this unbelievable technology solution called the tree.”

To channel that enthusiasm, the One Trillion Trees Initiative incorporated the study’s findings into its mission statement, and countless other tree-planting efforts have cited the report.

But critics say the study is deeply flawed, and that its accounting — of potential trees, of potential carbon uptake — is not only sloppy, but dangerous. In 2019, Science published five separate responses outlining numerous concerns. For example, the study’s criteria for “available” land for tree planting were too broad, and the carbon accounting was inaccurate because it assumes that new tree canopy cover equals new carbon storage. Savannas and natural grasslands may have relatively few trees, critics noted, but these regions already hold plenty of carbon in their soils. When that carbon is accounted for, the carbon uptake benefit from planting trees drops to perhaps a fifth of the original estimate.

There’s also the question of how forests themselves can affect the climate. Adding trees to snow-covered regions, for example, could increase the absorption of solar radiation, possibly leading to warming.

“Their numbers are just so far from anything reasonable,” Veldman says. And focusing on the number of trees planted also sets up another problem, he adds — an incentive structure that is prone to corruption. “Once you set up the incentive system, behaviors change to basically play that game.”

Adams acknowledges these concerns. But, the One Trillion Trees Initiative isn’t really focused on “the specifics of the math,” he says, whether it’s the number of trees or the exact amount of carbon sequestered. The goal is to create a powerful climate movement to “motivate a community behind a big goal and a big vision,” he says. “It could give us a fighting chance to get restoration right.”

Other nonprofit conservation groups, like the World Resources Institute and The Nature Conservancy, are trying to walk a similar line in their advocacy. But some scientists are skeptical that governments and policy makers tasked with implementing massive forest restoration programs will take note of such nuances.

“I study how government bureaucracy works,” says Forrest Fleischman, who researches forest and environmental policy at the University of Minnesota in St. Paul. Policy makers, he says, are “going to see ‘forest restoration,’ and that means planting rows of trees. That’s what they know how to do.”

Counting carbon

How much carbon a forest can draw from the atmosphere depends on how you define “forest.” There’s reforestation — restoring trees to regions where they used to be — and afforestation — planting new trees where they haven’t historically been. Reforestation can mean new planting, including crop trees; allowing forests to regrow naturally on lands previously cleared for agriculture or other purposes; or blending tree cover with croplands or grazing areas.

In the past, the carbon uptake potential of letting forests regrow naturally was underestimated by 32 percent, on average — and by as much as 53 percent in tropical forests, according to a 2020 study in Nature. Now, scientists are calling for more attention to this forestation strategy.

If it’s just a matter of what’s best for the climate, natural forest regrowth offers the biggest bang for the buck, says Simon Lewis, a forest ecologist at University College London. Single-tree commercial crop plantations, on the other hand, may meet the technical definition of a “forest” — a certain concentration of trees in a given area — but factor in land clearing to plant the crop and frequent harvesting of the trees, and such plantations can actually release more carbon than they sequester.

Comparing the carbon accounting between different restoration projects becomes particularly important in the framework of international climate targets and challenges. For example, the 2011 Bonn Challenge is a global project aimed at restoring 350 million hectares by 2030. As of 2020, 61 nations had pledged to restore a total of 210 million hectares of their lands. The potential carbon impact of the stated pledges, however, varies widely depending on the specific restoration plans.

Levels of protection

The Bonn Challenge aims to globally reforest 350 million hectares of land. Allowing all to regrow naturally would sequester 42 gigatons of carbon by 2100. Pledges of 43 tropical and subtropical nations that joined by 2019 — a mix of plantations and natural regrowth — would sequester 16 gigatons of carbon. If some of the land is later converted to biofuel plantations, sequestration is 3 gigatons. With only plantations, carbon storage is 1 gigaton.

Amount of carbon sequestered by 2100 in four Bonn Challenge scenarios

SOURCE: S.L. LEWIS ET AL/NATURE 2019; graphs: T. Tibbitts

In a 2019 study in Nature, Lewis and his colleagues estimated that if all 350 million hectares were allowed to regrow natural forest, those lands would sequester about 42 billion metric tons (gigatons in chart above) of carbon by 2100. Conversely, if the land were to be filled with single-tree commercial crop plantations, carbon storage drops to about 1 billion metric tons. And right now, plantations make up a majority of the restoration plans submitted under the Bonn Challenge.

Striking the right balance between offering incentives to landowners to participate while also placing certain restrictions remains a tricky and long-standing challenge, not just for combating the climate emergency but also for trying to preserve biodiversity (SN: 8/1/20, p. 18). Since 1974, Chile, for example, has been encouraging private landowners to plant trees through subsidies. But landowners are allowed to use these subsidies to replace native forestlands with profitable plantations. As a result, Chile’s new plantings not only didn’t increase carbon storage, they also accelerated biodiversity losses, researchers reported in the September 2020 Nature Sustainability.

The reality is that plantations are a necessary part of initiatives like the Bonn Challenge, because they make landscape restoration economically viable for many nations, Lewis says. “Plantations can play a part, and so can agroforestry as well as areas of more natural forest,” he says. “It’s important to remember that landscapes provide a whole host of services and products to people who live there.”

But he and others advocate for increasing the proportion of forestation that is naturally regenerated. “I’d like to see more attention on that,” says Robin Chazdon, a forest ecologist affiliated with the University of the Sunshine Coast in Australia as well as with the World Resources Institute. Naturally regenerated forests could be allowed to grow in buffer regions between farms, creating connecting green corridors that could also help preserve biodiversity, she says. And “it’s certainly a lot less expensive to let nature do the work,” Chazdon says.

Indeed, massive tree-planting projects may also be stymied by pipeline and workforce issues. Take seeds: In the United States, nurseries produce about 1.3 billion seedlings per year, Fargione and colleagues calculated in a study reported February 4 in Frontiers in Forests and Global Change. To support a massive tree-planting initiative, U.S. nurseries would need to at least double that number.

A tree-planting report card

From China to Turkey, countries around the world have launched enthusiastic national tree-planting efforts. And many of them have become cautionary tales.

China kicked off a campaign in 1978 to push back the encroaching Gobi Desert, which has become the fastest-growing desert on Earth due to a combination of mass deforestation and overgrazing, exacerbated by high winds that drive erosion. China’s Three-North Shelter Forest Program, nicknamed the Great Green Wall, aims to plant a band of trees stretching 4,500 kilometers across the northern part of the country. The campaign has involved millions of seeds dropped from airplanes and millions more seedlings planted by hand. But a 2011 analysis suggested that up to 85 percent of the plantings had failed because the nonnative species chosen couldn’t survive in the arid environments they were plopped into.

More recently, Turkey launched its own reforestation effort. On November 11, 2019, National Forestation Day, volunteers across the country planted 11 million trees at more than 2,000 sites. In Turkey’s Çorum province, 303,150 saplings were planted in a single hour, setting a new world record.

Within three months, however, up to 90 percent of the new saplings inspected by Turkey’s agriculture and forestry trade union were dead, according to the union’s president, Şükrü Durmuş, speaking to the Guardian (Turkey’s minister of agriculture and forestry denied that this was true). The saplings, Durmuş said, died due to a combination of insufficient water and because they were planted at the wrong time of year, and not by experts.

Some smaller-scale efforts also appear to be failing, though less spectacularly. Tree planting has been ongoing for decades in the Kangra district of Himachal Pradesh in northern India, says Eric Coleman, a political scientist at Florida State University in Tallahassee, who’s been studying the outcomes. The aim is to increase the density of the local forests and provide additional forest benefits for communities nearby, such as wood for fuel and fodder for grazing animals. How much money was spent isn’t known, Coleman says, because there aren’t records of how much was paid for seeds. “But I imagine it was in the millions and millions of dollars.”

Coleman and his colleagues analyzed satellite images and interviewed members of the local communities. They found that the tree planting had very little impact one way or the other. Forest density didn’t change much, and the surveys suggested that few households were gaining benefits from the planted forests, such as gathering wood for fuel, grazing animals or collecting fodder.

But massive tree-planting efforts don’t have to fail. “It’s easy to point to examples of large-scale reforestation efforts that weren’t using the right tree stock, or adequately trained workforces, or didn’t have enough investment in … postplanting treatments and care,” Fargione says. “We … need to learn from those efforts.”

Speak for the trees

Forester Lalisa Duguma of World Agroforestry in Nairobi, Kenya, and colleagues explored some of the reasons for the very high failure rates of these projects in a working paper in 2020. “Every year there are billions of dollars invested [in tree planting], but forest cover is not increasing,” Duguma says. “Where are those resources going?”

Trees can buy time for tech testing

If done right, planting trees might give researchers time to develop some of these carbon-capture technologies.

Bioenergy with carbon capture and sequestration

Plant biomass is used to produce electricity, fuel or heat. Any CO₂ released is captured and stored.

Direct air capture

Chemical processes that capture CO₂ from ambient air and concentrate it, so that it can be injected into a storage reservoir.

Carbon mineralization

Through chemical reactions, CO₂ from the atmosphere becomestrapped in existing rock.

Geologic sequestration

CO₂ is captured and injected into deep underground formations.

images: T. Tibbitts

In 2019, Duguma raised this question at the World Congress on Agroforestry in Montpellier, France. He asked the audience of scientists and conservationists: “How many of you have ever planted a tree seedling?” To those who raised their hands, he asked, “Have they grown?”

Some respondents acknowledged that they weren’t sure. “Very good! That’s what I wanted,” he told them. “We invest a lot in tree plantings, but we are not sure what happens after that.”

It comes down to a deceptively simple but “really fundamental” point, Duguma says. “The narrative has to change — from tree planting to tree growing.”

The good news is that this point has begun to percolate through the conservationist world, he says. To have any hope of success, restoration projects need to consider the best times of year to plant seeds, which seeds to plant and where, who will care for the seedlings as they grow into trees, how that growth will be monitored, and how to balance the economic and environmental needs of people in developing countries where the trees might be planted.

“That is where we need to capture the voice of the people,” Duguma says. “From the beginning.”

Even as the enthusiasm for tree planting takes root in the policy world, there’s a growing awareness among researchers and conservationists that local community engagement must be built into these plans; it’s indispensable to their success.

“It will be almost impossible to meet these targets we all care so much about unless small farmers and communities benefit more from trees,” as David Kaimowitz of the United Nations’ Food and Agriculture Organization wrote March 19 in a blog post for the London-based nonprofit International Institute for Environment and Development.

For one thing, farmers and villagers managing the land need incentives to care for the plantings and that includes having clear rights to the trees’ benefits, such as food or thatching or grazing. “People who have insecure land tenure don’t plant trees,” Fleischman says.

Fleischman and others outlined many of the potential social and economic pitfalls of large-scale tree-planting projects last November in BioScience. Those lessons boil down to this, Fleischman says: “You need to know something about the place … the political dynamics, the social dynamics.… It’s going to be very different in different parts of the world.”

The old cliché — think globally, act locally — may offer the best path forward for conservationists and researchers trying to balance so many different needs and still address climate change.

“There are a host of sociologically and biologically informed approaches to conservation and restoration that … have virtually nothing to do with tree planting,” Veldman says. “An effective global restoration agenda needs to encompass the diversity of Earth’s ecosystems and the people who use them.”

Sea otters’ secret to staying warm isn’t in thick stores of blubber. It’s in their muscles.

Leaks in the energy-generating parts of muscle cells help otters maintain a resting metabolism three times as fast as predicted for a creature their size, researchers report in the July 9 Science. The find shows how otters meet the challenge of staying warm at sea — and could apply to other marine mammals, too.

“This could be a game changer in terms of how we think about the evolution of all marine mammals, not just sea otters,” says Terrie Williams, an ecophysiologist at the University of California, Santa Cruz, who was not involved in the study. To dwell in cold oceans, mammals must have developed ways to regulate their body temperature amid the chill. “To me, this is probably one of the clearest pieces of evidence saying, ‘Here’s how they did it,’” Williams says.

Other marine mammals have high metabolisms to cope with cold water, too, but they also often rely on large bodies and blubber to stay toasty (SN: 12/14/18). Sea otters are lean and compact, the smallest mammals in the ocean, bobbing like furry barrels on waves. And the insulating properties of sea otters’ fur — the densest on the planet — can’t fully protect them from losing too much heat. Water transfers heat 23 times as efficiently as air, and small bodies with less surface area lose heat faster, even when covered in fluff.

“Being a small-bodied marine mammal in cold waters presents a real thermal challenge,” says Traver Wright, a comparative physiologist at Texas A&M University in College Station. Scientists already knew sea otters rely on an extreme metabolism to maintain, on average, a 37° Celsius body temperature, eating 25 percent of their body mass in food every day (SN: 6/13/14). But researchers didn’t understand the cellular origins of “that revved-up metabolism for heat generation,” Wright says.

Wright and colleagues searched for the heat source in otters’ muscles. Skeletal muscle makes up 40 to 50 percent of most mammals’ body mass, so it affects the whole body’s metabolism. The team collected tissue from 21 captive and wild sea otters, ranging from babies to adults. Then, using a device called a respirometer, researchers measured otter muscle cells’ respiratory capacity in different states of oxygen flow compared with other animals — including humans, Iditarod sled dogs and elephant seals. The rate of oxygen flow offers an indirect measurement of cells’ heat production.

Leaks in mitochondria — the energy-generating part of cells — generate extra heat and cause sea otters’ extreme metabolism, the researchers found. Metabolism describes how food gets converted into energy in cells. Mitochondria pump protons across their inner membrane to store energy that can be used to power the cell. But if those protons leak back over the membrane before being used for work, that energy is lost as heat. Because these leaks increase the amount of energy lost as heat, otters need to eat more food to make up for that lost energy, revving up their metabolism. 

Other mammals — including extremely small mice with high metabolisms — can also generate heat this way. But sea otters are much better at it: These leaks account for about 40 percent of otters’ muscle cells’ total respiratory capacity, higher than any known mammal. Producing heat this way helps the animals stay comfortable in 0° C Pacific waters. “That message is loud and clear, and just brilliant,” Williams says.

Sea otters’ high leak capacity “is not necessarily what they’re running all the time,” Wright says, but probably can be activated when otters need to generate more warmth. Scientists don’t yet know how otters’ cells turn this process on and off.

Baby otters don’t yet have the muscle mass to stay warm through these leaks, but their muscle cells generate heat at adult rates, the researchers found, showing that leak begins early. Finding similar leak capacities in wild and captive otters of different ages suggests that these leaks are the “driving force” behind otters’ metabolism, Wright says.

It’s not yet clear if otters inherit this trait or develop it with exposure to cold water. “We don’t know if this is inherent,” Wright says, “or if this is something that quickly comes on after birth as a means of generating heat on demand.”

Finding the cellular source of sea otters’ souped-up metabolism could help scientists better understand how other marine mammals cope with frigid water. And it could lead to new insights into how the ancestors of these creatures first evolved to live and thrive in the seas.

Jupiter may have formed in a shadow that kept the planet’s birthplace colder than Pluto. The frigid temperature could explain the giant world’s unusual abundance of certain gases, a new study suggests.

Jupiter consists mostly of hydrogen and helium, which were the most common elements in the planet-spawning disk that spun around the newborn sun. Other elements that were gases near Jupiter’s birthplace became part of the planet, too, but in only the same proportions as they existed in the protoplanetary disk (SN: 6/12/17).

Astronomers think the sun’s composition of elements largely reflects that of the protoplanetary disk, so Jupiter’s should resemble that solar makeup — at least for elements that were gases. But nitrogen, argon, krypton and xenon are about three times as common on Jupiter, relative to hydrogen, as they are on the sun.

“This is the main puzzle of Jupiter’s atmosphere,” says Kazumasa Ohno, a planetary scientist at the University of California, Santa Cruz. Where did those extra elements come from?

If Jupiter was born at its current distance from the sun, the temperature of the planet’s birthplace would have been around 60 kelvins, or –213˚ Celsius. In the protoplanetary disk, those elements should be gases at that temperature. But they would freeze solid below about 30 kelvins, or –243˚ C. It’s easier for a planet to accrete solids than gases. So if Jupiter somehow arose in a much colder environment than its current home, the planet could have acquired solid objects laden with those extra elements as ice.

For this reason, in 2019 two different research teams independently made the radical suggestion that Jupiter had originated in the deep freeze beyond the current orbits of Neptune and Pluto, then spiraled inward toward the sun.

Now Ohno and astronomer Takahiro Ueda of the National Astronomical Observatory of Japan propose a different idea: Jupiter formed where it is, but a pileup of dust in between the planet’s orbit and the sun blocked sunlight, casting a long shadow that cooled Jupiter’s birthplace. The frosty temperature made nitrogen, argon, krypton and xenon freeze solid and become a greater part of the planet, the scientists suggest in a study in the July Astronomy & Astrophysics.

The dust that cast the shadow came from rocky objects closer to the sun that collided and shattered. Farther from the sun, where the protoplanetary disk was colder, water froze, giving rise to objects that resembled snowballs. When those snowballs collided, they were more likely to stick together than shatter and thus didn’t cast much of a shadow, the researchers say.

“I think it’s a clever fix of something that might have been difficult to rectify otherwise,” says Alex Cridland, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.

Cridland was one of the scientists who had suggested that Jupiter formed beyond Neptune and Pluto. But that theory, he says, means Jupiter had to move much closer to the sun after birth. The new scenario avoids that complication.

How to test the new idea? “Saturn might hold the key,” Ohno says. Saturn is nearly twice as far from the sun as Jupiter is, and the scientists calculate that the dust shadow that chilled Jupiter’s birthplace barely reached Saturn’s. If so, that means Saturn arose in a warmer region and so should not have acquired nitrogen, argon, krypton or xenon ice. In contrast, if the two gas giants really formed in the cold beyond the present orbits of Neptune and Pluto, then Saturn should have lots of those elements, like Jupiter.

Thanks to the Galileo probe, which dove into the Jovian atmosphere in 1995, astronomers know these abundances for Jupiter. What’s needed, the researchers say, is a similar mission to Saturn. Unfortunately, while orbiting Saturn, the Cassini spacecraft (SN: 8/23/17) measured only an uncertain level of nitrogen in the Ringed Planet’s atmosphere and detected no argon, krypton or xenon, so Saturn doesn’t yet constrain where the two gas giants arose.