Ecology

“In this photo, I’m holding a snake known in Italy as a cervone (Elaphe quatuorlineata). It’s one of 189 that we’ve inspected so far in 2024 in Cocullo, a small town in the Abruzzo region of central Italy.In Cocullo, snakes feature in a spring ritual that dates back at least 2,000 years. At the start of April, snake catchers (known as serpari) capture dozens of snakes in preparation for what’s become Christianized as the procession of St Dominic of Sora. A statue of the saint — who lived in the region and, according to legend, cured many people from snake bites — is then adorned with live snakes and carried through the streets of Cocullo.A project to monitor the health and growth of the snakes has been in place for more than 15 years. I work with Gianpaolo Montinaro, who conceived the project in 2007, to supervise the monitoring on behalf of Italy’s environment ministry. My team, which includes two veterinarians at the University of Bari, acquires biological data and samples and places a microchip in each snake so that it can identified in future. At the end of the ritual, the snakes are released at the exact spot where they were captured.The information collected contributes to scientific publications and strategies on snake conservation — and, from this year, to a project at the Max Planck Institute of Animal Behavior to study animals’ responses to natural disasters. We’d never have been able to collect data on snake populations for so long had it not been for the Cocullo festival. Since 2010, we’ve gathered data on more than 1,500 snakes. This is a genuine example of citizen science, and is all the more impressive given that snakes are widely feared.Outside the snake-festival season, I deal with invasive exotic species, biodiversity-protection policies and endangered species.” More

“In this photo I’m checking my team’s store of stem cells of the fat-tailed dunnart (Sminthopsis crassicaudata), a mouse-like marsupial that is the closest living relative of the thylacine, or Tasmanian tiger (Thylacinus cynocephalus). This mammal was an Australian apex predator, the size of a big dog. It once thrived throughout the continent but went extinct — first on the Australian mainland, and later in Tasmania, where it was hunted for hides and to reduce sheep attacks.The last thylacine, ‘Benjamin’, died in captivity in 1936, on 7 September — a date that is now marked as World Extinction Day.Here at the TIGRR laboratory, our main project is to bring back the thylacine by using gene-editing technology with cells from animals such as the fat-tailed dunnart. To achieve this, we’re trying to produce a complete genome for the species. We sequence DNA from historic specimens, using cells from young thylacines that had been kept for more than 100 years in alcohol preservatives. We compare that DNA with the dunnart genome and work out the gene edits that we would have to make to the dunnart cells to engineer a thylacine.We’re also developing cloning and in vitro fertilization (IVF) techniques for use in marsupials (such techniques are already well established for other mammals).When we restore the genome and thus create a complete thylacine cell, we’ll be able to use cloning, alongside IVF, in dunnarts to create living animals. My motivation is not to create an animal that goes into a zoo. We want to put the thylacine back into the environment, where it can help to address imbalances in the ecosystem.People say we are playing God with our work. But we played God when we wiped out the thylacine. My research is looking at ways to heal lost biodiversity.” More

Luis Coloma grew up in Guaranda, Ecuador, a small city in the Andes nestled in a high valley near the Chimborazo volcano. “It was a paradise,” he says. “When I was a kid, the frogs were so abundant it was impossible to ignore them.” Beyond seeing various species living together along the riverbanks, he was elated by their boisterous calls.In secondary school, Coloma paged through field guides and zoology encyclopedias, eager to find frog species that matched the stunning array of colours, shapes and sizes of the ones in his own back garden — but his searches always came up short. “Looking at these animals that didn’t fit the descriptions was fantastic. It was a world of discovery.”Inspired by his childhood obsession with amphibians, Coloma moved to the United States in 1988 to pursue a PhD in systematics and ecology at the University of Kansas in Lawrence. But by the time he returned to Ecuador in the late 1990s, the frogs in the mountains where he grew up had already begun to disappear. “It became clear that there were apocalyptic extinctions happening,” he says. “That was the beginning of my conservation work.”
Want to make a difference? Try working at an environmental non-profit organization
In 2021, Coloma co-authored a paper in PLoS ONE stating that 57% of the amphibian species in Ecuador are endangered or vulnerable because of climate change, habitat loss and disease, particularly that caused by Batrachochytrium dendrobatidis, a chytrid fungus1. But declines in biodiversity extend beyond amphibians. Some scientists argue that Earth is entering a sixth mass-extinction event, the first to be caused entirely by the activities of one species — humans. According to the wildlife charity WWF’s Living Planet Report 2022, since 1970 there has been a 69% decline in the average abundance of nearly 32,000 species populations, with the biggest reductions seen in Latin America and the Caribbean. “It’s heartbreaking,” says Coloma, who is now director of the Jambatu Center for Amphibian Research and Conservation in Quito.Despite the harrowing trends, endangered-species biologists such as Coloma are striving to protect Earth’s biodiversity. But their work with species in danger of extinction brings special challenges — both in handling the organisms and in approaching the daunting odds of success. At times, these efforts can feel like a quixotic battle. Here, endangered-species biologists describe their best strategies for the high-stakes research and how they find reasons for hope.The weight of a wordOne of the major challenges in protecting threatened species is getting them listed as endangered in the first place. Juan Manuel Guayasamín, a biologist at the San Francisco University of Quito, has described 64 amphibian species and 15 reptile species. In 2004, he published a paper describing a new species, the Mache glass frog (Cochranella mache)2. On the basis of his data, he proposed that it should be listed as endangered in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, a comprehensive source that describes the extinction risk for animals, plants and fungi around the world.To get a species listed as endangered, researchers must provide adequate data on population sizes, geographic range and extinction probability, which are challenging metrics to estimate when individuals are hard to find and resources are limited. If scientists cannot estimate population size, Guayasamín recommends evaluating whether the species has a small distribution or a reduced or fragmented habitat. “We have more than 600 species of amphibians in Ecuador. It’s impossible to have a monitoring process for every single species — we don’t have enough people or the funds,” says Guayasamín.But once a species is listed, it can open opportunities for funding and generate broad support. “It’s absolutely worth having species listed as endangered because that’s how you get the public on board with conservation,” says Danya Weber, a conservation biologist and artist in Hilo, Hawaii.

Juan Manuel Guayasamín demonstrates how to handle frogs at a workshop in Colombia.Credit: Pedro Peloso

Biologists often look to national legislation, alongside the IUCN Red List, to protect at-risk species. In 2008, Ecuador became the first country to give nature constitutional rights. It’s still the only country to have such legislation. “It is very unique,” Guayasamín says. “If you can prove that an area at risk has endemic and endangered species, the constitution gives you a lot of strength to take actions to protect it,” such as removing invasive organisms and protecting habitat. Many of the animals described by Guayasamín were key to protecting endangered ecosystems, mostly in the Andes and Chocó ecoregions, under this law.Try to do no harmConservation researchers collect field data on abundance, population trends and threats. They also capture individuals as part of breeding and reintroduction programmes. But their actions can harm not only the species in question, but also the ecosystem. As a result, endangered-species biologists often grapple with the ethical trade-offs between the impacts of interference and the potential consequences of inaction, namely extinction.“My biggest comfort comes when I start my day,” says Dechen Dorji, who grew up in Bhutan and now directs the WWF’s conservation efforts in Asia from his office in Washington DC. “I’m a Buddhist, and one of our common prayers is a simple verse — may all sentient beings be free from all forms of suffering.”During his career at the WWF, Dorji has fought to protect Asian elephants (Elephas maximus), tigers (Panthera tigris) and snow leopards (Panthera uncia), as well as lesser-known species such as the musk deer (Moschus spp.), white-bellied heron (Ardea insignis) and ruddy shelduck (Tadorna ferruginea). Although a better understanding of these animals can improve conservation outcomes, it’s crucial to do research in a way that limits negative impacts, he says. For instance, Dorji and his team have trapped tigers to fit them with GPS tracking collars to study their ecology and movements, but the trapping process can injure the tigers’ limbs. “Humane treatment of tigers, careful planning and continuous monitoring are essential to minimize the risks of injury,” Dorji says.

Conservation biologist Danya Weber helps connect people to species through her artwork.Credit: Mahina Choy

To reduce their impacts, Dorji and his colleagues also sample environmental DNA, genetic material shed by organisms that is found in soil, water, faeces and other sources, to non-invasively track the presence of different species in a habitat. “It’s cost effective, accurate and we can detect a whole range of species without causing any harm,” he says.In the Pacific Ocean, Jordan Lerma, a field biologist at Cascadia Research Collective, who is based in Hilo, uses another hands-off approach. As of 2021, the endangered and declining Main Hawaiian Islands population of false killer whales (Pseudorca crassidens) has about 138 individuals. Cascadia researchers want to study their habitat use, abundance, growth, movement patterns and threats. “They are really difficult to find, and once we find them, they don’t want to be around us,” says Lerma. In 2014, to lessen the impacts of boat-based research, Lerma started flying drones over whales and dolphins in Hawaiian waters. Although drones can’t entirely replace hands-on methods, using minimally invasive sampling techniques when possible reduces the number of direct human interactions with animals and provides effective ways to collect biological data.For other researchers, the downsides of studying endangered species in the wild drive them to find alternative ways to protect the animals. Weber started her scientific career in 2016 as a conservation technician at the Kaua‘i Forest Bird Recovery Project, a non-profit organization in Hanapepe, Hawaii, that works to conserve three federally endangered bird species, including the songbirds ‘akikiki (Oreomystis bairdi) and ‘akeke‘e (Loxops caeruleirostris). For the next two years, Weber wandered the forests in search of bird nests to monitor populations and collect eggs for captive breeding. “In Hawaii, we don’t have any native land mammals that walk around in the forest trampling vegetation,” she says. The only large creatures that do so are humans. “When we’re doing conservation work, we’re creating all these little routes for erosion.”
How we packed off the giant pandas from the Smithsonian’s National Zoo
Other protection efforts that involve the use of herbicides to remove invasive plant species can negatively affect native plants and soil microbes, Weber adds. “It’s easy to get laser-focused on the particular endangered species that you’re working with and not take into consideration our impacts on everything else in the area.”In 2017, Weber founded Laulima, a fashion and art store that seeks to connect people with and preserve Hawaii’s native biodiversity through merchandise, including apparel, accessories, stickers and mugs designed by Weber and other artists. “With my artwork, I help people build relationships with these plants and animals they share a home with, since many people will never get the opportunity to visit pristine native forests,” she says. Every product comes with packaging that educates the buyer about the species in the design.“The literal translation of laulima is ‘many hands’,” Weber says. “To protect native species, we need all hands on deck.” Many of Weber’s watercolours and digital illustrations are inspired by species that have political or social relevance. For example, Hawaii’s governor designated 2023 as the year of the kāhuli, so her artwork highlighted these native Hawaiian snails (Achatinella spp.). Weber also raises awareness about endangered Hawaiian monk seals (Monachus schauinslandi), some of which have been killed by humans who mistakenly think the seals are not native and are competing with local fishers for food.For Weber, pursuing a career in conservation art and outreach has been worthwhile. “When I was in the field, it felt like an uphill battle. It’s very hard to see the fruits of your labour. Whereas in outreach, you see people’s mindsets shift. I’ve noticed a lot more teenagers and university-age students getting into careers in conservation.”Banding togetherPerhaps the biggest challenge of endangered-species work is facing the fact that they might soon disappear. “The more you know, the sadder it gets, unfortunately,” says Lerma. And yet, Lerma and others maintain glimmers of hope and continue fighting for protections. For Weber, cracking sarcastic jokes with colleagues about being underfunded and battling invasive species can help to ease the heaviness. Guayasamín leans into his strong sense of moral responsibility: “Many species are in danger because of human activity, so it’s our responsibility to respect nature and address our impacts.”Building collaborations that extend beyond the scientific realm is another way for scientists to find inspiration and camaraderie. In April in Paro, Bhutan, Dorji attended the Sustainable Finance for Tiger Landscapes Conference, which kick-started an effort aiming to raise US$1 billion by 2034 to spend on the conservation of tigers and the landscapes where they live. More than 200 people from around the world attended, including private donors, government leaders and members of financial institutions. “To see that partnership, commitment and sense of urgency was hugely exciting,” says Dorji. “Those kinds of things keep us going.”

Dorchen Dorji, who grew up in the Himalayan mountains in Bhutan and now oversees the WWF’s conservation efforts in Asia, says collaborating with local community members is essential.Credit: Dechen Dorji/WWF

In January 2023, Lerma founded Nēnē Research and Conservation, an organization that partners with government agencies and community groups to protect the nēnē (Branta sandvicensis), a goose species that is endemic to Hawaii. Nēnē were federally down-listed from endangered to threatened in 2019, thanks to successful conservation efforts that brought the population from 30 individuals in the 1950s up to more than 3,800 in 2022. But the species is still listed as endangered at the state level.Over the past year, Lerma and his team have launched a database in which community members record nēnē sightings, injuries and deaths. Nēnē tend to gather in areas frequented by people, such as golf courses and parks, so they’re easy to find.Lerma’s team used this database, which now has 1,055 contributors and 11,723 sightings, to identify a stretch of road on the Big Island where many nēnē were hit by cars. “We presented that data to the county and got speed tables and raised crosswalks installed. We’re protecting the community and the species. No nēnē have been killed since.”Dorji also emphasizes the importance of collaborating with local and Indigenous communities whose efforts and lands play an essential part in conservation, he says. “We often tell conservation stories from a very utilitarian perspective of how beneficial other species are to humans, but many cultures have their own stories that we need to listen to and respect.”
I took my case to Nepal’s highest court to improve conservation
In many cases, community members uniquely understand the ecology and biology of local flora and fauna. At the Jambatu Center for Amphibian Research and Conservation, Coloma and his colleagues maintain colonies of about 2,600 individuals of 76 amphibian species, including 30 that are close to extinction. He attributes the success of these programmes to two staff members who were born in the jungles of Ecuador. “They are not PhDs. They are people that love these animals and have a specialized understanding of their needs,” he says.In 2016, Coloma heard about the presence of a jambato toad (Atelopus ignescens) from a priest in Angamarca, Ecuador. “The jambato were part of the daily life of the Indigenous people here; they used them as a medicine, and they were part of kids’ games in the Andes,” says Coloma. But the once-abundant species hadn’t been seen since March 1988 and was declared extinct by the IUCN in 2004.When the priest sent Coloma a photo of the toad, which was found by a ten-year-old boy on the child’s family’s farm, Coloma was stunned. “I couldn’t believe it. I lost the faith that I would see these frogs again. It was a dream,” he says. The species was re-listed as critically endangered in 2016. Now, Coloma’s organization is searching for more jambato toads in the wild and breeding them in captivity, with the hopes of reintroducing them in future. “We need to fight for our dreams.” More

Download the Nature Podcast 3 July 2024 In this episode:00:47 Searching for dark matter in black holesResearchers have been scanning the skies looking for black holes that formed at the very beginning of the Universe — one place where elusive and mysterious dark matter is thought to be located. If these black holes did contain dark matter, they would be especially massive and so researchers would be able to see the bending of light as they pass in front of stars. Such events would be rare, so to find them researchers trawled through a decades-long dataset. However, despite the large number of observations, the researchers didn’t find many examples of these events and none that were long enough to show signs of much dark matter. So, the hunt for enigmatic material goes on.Research Article: Mróz et al.09:42 Research HighlightsHow some comb jellies survive the crushing ocean depths, and how giving cash to mothers in low-income households can boost time and money spent on children.Research Highlight: Deep-sea creatures survive crushing pressures with just the right fatsResearch Highlight: Families given cash with no strings spend more money on kids12:39 A simple, solution to tackle a deadly frog diseaseA simple ‘sauna’ built of bricks and a supermarket-bought greenhouse, can help frogs rid themselves of a devastating fungal disease, new research has shown. Although options to prevent or treat infection are limited, the fungus that causes the disease chytridiomycosis has an achilles heel: it can’t survive at warm temperatures. A team in Australia used this knowledge to their advantage to develop saunas where frogs can warm themselves to clear an infection. Frogs who spent time in these hot environments were able to shake the fungus, and gained some immunity to subsequent infections. Although this research involved only one type of frog, it offers some hope in tackling a deadly disease that has driven multiple species to extinction.Research Article: Waddle et al.News and Views: Mini saunas save endangered frogs from fungal disease20:06 Briefing ChatThis time, we discuss what the upcoming UK election could mean for science, and the return of rock samples from the Moon’s far side.Nature News: UK general election: five reasons it matters for scienceNature News: First ever rocks from the Moon’s far side have landed on EarthSubscribe to Nature Briefing, an unmissable daily round-up of science news, opinion and analysis free in your inbox every weekday.Never miss an episode. Subscribe to the Nature Podcast on Apple Podcasts, Spotify, YouTube Music or your favourite podcast app. An RSS feed for the Nature Podcast is available too. More

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We aim to foster cutting-edge scientific and technological advancements in the field of molecular tissue biology at the single-cell level.
Guangzhou, Guangdong, China
Guangzhou Institutes of Biomedicine and Health(GIBH), Chinese Academy of Sciences More

The frequency at which extreme fires occur around the world has more than doubled during the past two decades, according to an analysis of satellite data1. The trend is driven by the exponential growth of extreme fires across vast portions of Canada, the western United States and Russia, researchers say.The results provide the first solid evidence to support a nagging suspicion that many scientists and others have had as they watch a seemingly endless series of cataclysmic infernos scorch ecosystems and communities: wildfires have increased somehow, and climate change is almost certainly a factor.“It’s the extreme events that we care about the most, and those are the ones that are increasing quite significantly,” says lead author Calum Cunningham, an ecologist at the University of Tasmania in Hobart, Australia. “Surprisingly, this has never been shown at a global scale.”Heating upResearchers have already documented an increase in wildfire activity across the western forests of the United States2, but they have had a harder time pinning down a clear global trend. One confounding factor is that the amount of land burned annually has been declining, in part owing to a steady reduction in fire activity in African grasslands and savannahs.For the current study, published in Nature Ecology and Evolution on 24 June1, Cunningham and his colleagues scoured global satellite data for fire activity. They used infrared records to measure the energy intensity of nearly 31 million daily fire events over two decades, focusing on the most extreme ones — roughly 2,900 events. The researchers calculated that there was a 2.2-fold increase in the frequency of extreme events globally in 2003–23, and a 2.3-fold boost in the average intensity of the top 20 most intense fires each year (see ‘Rising fire intensity’).

Source: Ref. 1

The forests most affected by extreme fires were those in places such as western North America that contain coniferous trees including spruce and pine; they showed an 11.1-fold increase in the number of fires over the study period. Boreal forests at high latitudes in countries such as Canada, the United States and Russia were also significantly affected, showing a 7.3-fold increase in fires.The results aren’t necessarily surprising, says Park Williams, a hydroclimatologist at the University of California, Los Angeles. But they are the first compelling evidence that “extreme fires have grown more extreme”, he adds.Although the study doesn’t directly connect the fire trend to global warming, Cunningham says “there’s almost certainly a significant signal of climate change”. Research has shown3 that rising temperatures are drying out ecosystems — such as coniferous forests — that are naturally prone to fire. This provides fuel that can boost the fires’ size and longevity. The latest study also found that the energy intensity of the fires increased faster during the night-time over the past two decades than during the daytime, which aligns with evidence4 that rising night-time temperatures are contributing to fire risk.The researchers identified extreme fires occurring in several other biomes across the globe, including those in Australia, which experienced unprecedented wildfires in 2019 and 2020, and the Mediterranean. Although they didn’t see clear trends in these regions, Cunningham says that it might be only a matter of time before they emerge as temperatures continue to rise. More

Scientists can measure the carbon-storage capacity of various types of soil.Credit: Patrice Latron/Eurelios/Look at Sciences/Science Photo Library

When it comes to carbon, humanity has two pressing problems. First, there’s too much of it in the atmosphere. The atmospheric concentration of carbon dioxide has increased by about 50% since the start of the industrial age, from 280 parts per million to nearly 420 parts per million in 2023 (see go.nature.com/2j4heej). Much of that comes from the combustion of fossil fuels, but agriculture is a major contributor. Each year, around 13.7 billion tonnes of CO2 or equivalent greenhouse gases is released into the atmosphere by agricultural processes, with more than one-quarter of global greenhouse-gas emissions arising from food production1.The second carbon problem is that there isn’t enough of it in the soil. Soil carbon has been drastically depleted around the world, thanks to intensive farming practices that have been developed to feed the growing population. One estimate suggests that around 133 billion tonnes of carbon — about 8% of total organic soil carbon — has been lost from the top 2 metres of soil since the advent of agriculture some 12,000 years ago. Around one-third of that loss has occurred since the Industrial Revolution in the 1800s2.This imbalance means that agriculture has an ace up its sleeve: although it’s currently a carbon source, it also has the potential to be a carbon sink, which could alter the planet’s climate-change trajectory (see ‘Green horizons’). It’s not only possible, but it’s relatively easy to recharge soil organic carbon stocks by supporting and enhancing the natural processes that draw and convert CO2 into soil carbon.

Source: FAOSTAT for 2021 and model projections for future years

The latest Intergovernmental Panel on Climate Change (IPCC) synthesis report3 puts carbon sequestration in agriculture as one of the highest potential contributions to reducing net emissions. At around 3.5 gigatonnes of CO2 or its equivalent greenhouse gases per year, this is greater than the emissions from the entire European Union in 2022 — exceeded only by a conversion of current energy supplies to solar or wind energy, or reduced destruction of natural ecosystems. The challenge is to ensure that this happens fast enough, and at a low enough cost, for it to make a substantial contribution to achieving global net-zero carbon emissions by 2050.The agricultural techniques that can help to increase soil carbon sequestration aren’t necessarily complex. But with the looming deadline of net-zero carbon emissions by 2050, as set by the Paris climate agreement, the pressure is on scientists to identify the most efficient, effective and rapidly scalable methods for soil carbon sequestration and how these can help to achieve the dual goals of mitigating climate change and improving soil health.Carbon farmingSoil organic carbon is the result of the CO2 that plants have extracted from the atmosphere and incorporated into their structure, especially root systems, being used to nourish other living organisms in the soil.
Nature Spotlight: Agricultural sciences
“Before soil carbon was even a thing from a climate-change perspective, people were promoting the increase of organic matter in the soil to improve its fertility, to improve water-holding capacity and resilience to droughts, and to prevent erosion,” says Peter Smith, a soil scientist at the University of Aberdeen, UK, and science director of Scotland’s ClimateXChange centre in Edinburgh, UK. “Nobody disagrees that increasing the amount of soil organic matter is a good thing,” Smith says.The good news is that increasing soil carbon isn’t high tech. Evolution has already done most of the hard work by giving plants the ability to extract CO2 from the atmosphere through photosynthesis, turning it into carbohydrates and oxygen. The plants assimilate that carbon into their cells and tissues, which eventually become integrated into the soil when the plant sheds matter in the form of leaves, branches, flowers or fruit, or when it is consumed by other organisms, or when the plant dies and decomposes.The biggest barrier to this process is humans and the bad habits that we have developed to squeeze better short-term yields out of soil. One of these is tilling, particularly the deep ploughing that is commonly used to prepare the soil for planting. “A century ago, one of the things that made the prairie regions across the globe so fertile is that when we tilled them, the organic matter degraded and that released tremendous amounts of nutrients and produced bountiful crops,” says David Burton, a soil scientist at Dalhousie University in Halifax, Canada. That process breaks up the soil, including the root systems of the crops and grasses, causing the release of CO2 into the atmosphere. Tilling also destroys the structure of the soil and increases the risk of erosion by wind or water, which can in turn cause more CO2 to be released.

Agricultural practices such as ploughing release carbon dioxide into the atmosphere.Credit: Jonas Gratzer/LightRocket/Getty

Therefore, one way to potentially keep that carbon in the soil is to reduce or eliminate tilling in what’s called no-till or zero-till agriculture. Instead of turning over large amounts of soil to plant seeds or seedlings, farmers use equipment that creates either a narrow channel or a hole into which the seed or seedling can be planted. The residue of the previous season’s crop — stubble, stalks and stems, for example — is left in the soil and on the surface. The idea is that this reduces the disturbance of the soil structure and leaves more of the soil organic carbon in place.Although carbon sequestration through no-till is promising, the evidence is mixed. Research suggests that the amount of soil carbon sequestered with no-till farming varies with climate and soil type. One analysis found evidence that the greatest increase in soil carbon with no-till agriculture occurred in warmer and wetter climates rather than in cooler and drier climates4. However, less tilling does mean less fuel consumption — because farmers don’t have to plough as often and as deep — and therefore lower emissions. For example, the use of low-till farming in the United States is estimated to have saved the equivalent of around 3,500 million litres of diesel annually, enough to offset the annual CO2 emissions of around 1.7 million cars5.Another method to increase the retention of soil carbon is to grow cover crops alongside the main crop, instead of manually pulling up or poisoning weeds that appear. This keeps the root structure and its soil carbon contribution intact and in place. A study of two Australian vineyards found that allowing grasses to grow in between the rows of grape vines was associated with a nearly 23% increase in soil organic carbon over a 5-year period compared with the conventional method of using herbicide to control grass growth6. The practice is gaining momentum in North American vineyards , and it is already well established in European ones, where cover crops such as clover and barley have been shown to improve soil carbon levels while reducing weeds7.There is also a growing interest in the carbon sequestration potential of adding inorganic, or mineral carbon, to agricultural soils through a process called enhanced weathering. This involves adding ground-up silicate rock, such as basalt, to the soil. The minerals in the rock dust — mainly magnesium and calcium — interact chemically with CO2 in the atmosphere to form carbonates, which remain in the soil in a solid form or dissolve and gradually drain out to the ocean through the water table8.A four-year study, which was published in February, of the US corn-belt region found that applying crushed basalt to maize (corn) and soya bean fields was associated with sequestration of an extra 10 tonnes of CO2 per hectare per year, while also increasing crop yields by 12–16%9. “It’s one of the most intensively managed areas of agricultural land in the world, so if it works there, then you’ve got kind of instant scalability,” says study co-author David Beerling, a biogeochemist and director of the Leverhulme Centre for Climate Change Mitigation at the University of Sheffield, UK.Deforestation is another major contributor to agricultural sector carbon emissions, particularly in cattle farming10, in which forests are bulldozed to create pastures for animals. Agroforestry — the integration of trees into farming systems — is one way to mitigate this problem. Growing trees and shrubs among crops and pastures not only increases carbon sequestration in the soil and the tree biomass, but also provides further benefits including wind-breaks and shade for cattle. Agroforestry is well established in many parts of the world, including in tropical areas where trees provide shade for crops such as coffee beans.As promising as soil carbon sequestration looks on paper, it has a limit, says Smith. “If we’re chucking it all up from geological sources, the biological sinks aren’t enough to suck up all that carbon,” he says. It’s also finite — there is a limit to how much carbon an area of land can sequester. The question is: what is that limit?Measure, monetise, incentivizeSoil scientist Rattan Lal, director of the Lal Carbon Center at Ohio State University in Columbus, says that if the world switches to non-fossil-fuel sources of energy, it will be possible to achieve a long-term positive soil carbon budget in which more carbon is absorbed by agriculture than is generated by it. “By 2100, the [carbon] sink capacity of the land is about 150 to 160 gigatonnes of carbon, and another of the same amount for trees,” Lal says. That amounts to around two gigatonnes of carbon per year that could be sequestered in soils. Other studies suggest that number could be as high as 4–5 gigatonnes of carbon per year11. Given global emissions now sit at around 35 gigatonnes per year, this is a substantial proportion12.Even at the lower estimate, if the entirety of that atmospheric carbon removal is realized, Lal’s research suggests it could reduce global atmospheric concentrations of CO2 by around 157 parts per million13, which would completely remove all the extra CO2 emitted since the start of the Industrial Revolution. “Agriculture could be a part of the solution,” he says.

Soil scientist Rattan Lal at Ohio State University in Columbus says that a switch to non-fossil fuels should make it possible for more carbon to be absorbed by agriculture than is generated by it.Credit: The Ohio State University

However, the soil-science community is divided over whether sequestering carbon in soils could be part of the climate-change remedy, says Alex McBratney , a soil scientist and director of the Sydney Institute of Agriculture at the University of Sydney, Australia. Even today, there are some people who think it’s simply too difficult because of the challenge of measurement.Soil carbon content varies a lot geographically, even over short distances, so getting a reasonably accurate measurement at a point in time means taking lots of samples — and that can add up financially. Soil carbon also fluctuates naturally, depending on weather conditions and other factors. And the change in soil carbon levels over time might also be small relative to the overall amount of carbon in the soil, which makes it harder to record a significant change.Soil carbon levels also change slowly. “We would say, as a rule of thumb, that it probably takes of the order of five years to show observable differences … that you can detect against the background of this natural variation,” McBratney says. Combined with variability, this makes it challenging to show that extra soil carbon has been sequestered, especially in a cost-effective manner.Cultivating changeDespite the uncertainties of soil carbon sequestration, it is a hot topic when it comes to emission reductions. Governments have leapt enthusiastically, and sometimes prematurely, into capitalizing on the possibility of buying and selling carbon credits from agriculture. These are credits earned from reducing carbon emissions that can be used to offset carbon emissions from other sources or sectors — a win-win situation, given the added benefits of improving soil health.Marit Kragt, an agriculture and resource economist at the University of Western Australia in Perth, became interested in soil carbon sequestration shortly after the Australian government introduced the Carbon Farming Initiative act in 2011. Her concerns were that the policy had been formulated with little scientific or economic data on, for example, the best practices for sequestering soil carbon, the impact of climate, the cost to farmers and whether soil carbon sequestration would truly increase overall soil carbon.This cost-benefit analysis will be crucial to overcoming the sociocultural barriers to change. There is resistance to changing farming practices, particularly when the advice to do so comes from scientists or policymakers, says Kragt. “Sociocultural change is actually really important in any society, but is often forgotten,” she says. “When you have a group of people advocating for something and they’re not part of the farming community or trusted peers, there is push back.”However, Kragt says that most farmers who implement carbon-positive farming techniques don’t do it for the credits. “I think most people that have taken up carbon farming practices will have done so because they wanted to regenerate their environment,” she says. Many farmers are also concerned about climate change because they can see the impact on their livelihoods. “They have seen the bushfires, droughts and extreme heat that’s affecting their harvests, so they know that something needs to change.” More