Ecology

Credit: The Aldo Leopold Foundation and University of Wisconsin-Madison Archives

Estella Bergere Leopold was a palaeobotanist whose studies of fossil pollen and spores helped to reconstruct past environments and link them to the present. Her investigations of the Cenozoic era (from 66 million years ago to the present) provided some of the first insights into the evolution of modern plant communities and the factors that governed their development, including the consequences of long-term climate change, mountain building and volcanism. Few researchers before her had traced the rise of present-day ecosystems through time, and her discoveries helped to connect the relatively well-studied ice-age influences on vegetation with deep-time geological processes.Leopold, who has died aged 97, was an ardent conservationist who argued that nature should be cherished and protected. She thought that science should be used in defence of the planet; this is evident in her writings, lectures and political activism.Leopold was born in Madison, Wisconsin, the youngest daughter of conservationist Aldo Leopold and his wife Estella Bergere Leopold. All five Leopold children became esteemed scientists and conservationists in their own right. Her childhood, particularly her time spent at the family cabin, called ‘the Shack’, in central Wisconsin spurred an early interest in ecology. Leopold graduated with a degree in botany from the University of Wisconsin–Madison in 1948 and a master’s degree from the University of California, Berkeley, in 1950. She moved to Yale University in New Haven, Connecticut, to join a new graduate programme in conservation headed by Paul Sears, a pioneer in palynology (pollen analysis), and also to study with mathematical ecologist G. Evelyn Hutchinson and his former student Edward Deevey Jr. Her dissertation focused on the history of New England forests through the analysis of pollen and spores extracted from peat deposits, and palynology became her main research tool.
Current conservation policies risk accelerating biodiversity loss
After graduating from Yale in 1955, Leopold was one of the few women who joined the US Geological Survey in Lakewood, Colorado, as a scientist. By meticulously comparing fossil pollen and spores with modern ones, she reconstructed past floras — innovative and insightful findings at the time. Her early study of the Eniwetok and Bikini atolls in the Pacific Ocean revealed the existence of a tropical rainforest in the south Pacific during the Miocene epoch (23 million to 5 million years ago). She examined Cenozoic plant-fossil sites for evidence of the origins of modern flora. Leopold described the transition from ancient species to newer variants in the Rocky Mountains of western North America, which showed an earlier modernization trend in the middle of the continent than in coastal areas, as a result of greater cooling, seasonality and mountain uplift.Her research in Colorado on the Florissant fossil beds — well-preserved sediments from a 34-million-year-old lake — spurred her to lead a conservation effort in the area. In 1969, the 2,428-hectare Florissant Fossil Beds National Monument was established. Other successful actions included opposing oil-shale development in western Colorado, protesting dam building in the US Grand Canyon and stopping the shipping of highly radioactive materials through waterways that connected the Pacific Northwest region to the Pacific Ocean. Leopold also served on several conservation boards and was president of the Aldo Leopold Foundation, which she founded with her siblings to promote ethical land stewardship.From 1976 to 1982, she directed the Quaternary Research Center at the University of Washington in Seattle and maintained an active research programme there, studying the palaeoecology and palaeoflora of the western United States and comparable settings in China. She officially retired in 2000, but remained active in research until her death.Leopold recognized the power of scientific credentials in environmental activism. Throughout her career, she promoted palaeobotany as a tool for land protection. She argued that the value of a place was partly the result of its ecological history and how environmental events shape it. One of those events is fire. Using ethnographic and palaeoecological studies, Leopold highlighted the importance of Native American burning practices before European settlement for maintaining the health of prairies and woodland; she actively supported deliberate fire management.
Address the growing urgency of fungal diseases in crops
In 1969, Estella was named conservationist of the year by the Colorado Wildlife Federation; she received the International Cosmos Prize for contributions to conservation in 2010. But those awards, and numerous others, scarcely do justice to the personal influence that she had on students. I met Estella at the US Geological Survey as an undergraduate student and was overjoyed when she accepted me for graduate studies at the University of Washington. Her unbridled enthusiasm for science and environmental protection was inspiring. Estella had what we students called a ‘1,000-volt look’ whenever an idea piqued her interest — to experience this was electrifying.Estella will be remembered for her important contributions to ecology and for a life-long crusade to protect the land. More than most individuals, her scientific interests were inextricably linked to her environmental activism. She was keenly aware of her family heritage and, like her father, advocated simple outdoor living as a way to learn and appreciate nature. As a woman in a male-dominated field, she maintained a strong sense of humour and fearlessness throughout her career; yet, she also had immense grace and generosity. Estella leaves behind colleagues, former students and environmental activists who treasure her influence and their time with her. More

Fifty years ago this week, Gaura Devi, an ordinary woman from a nondescript village in India, hugged a tree, using her body as a shield to stop the tree from being cut down. Little did she know that this simple act of defiance would be a seminal moment in the history of India and the world. Or that Reni village, where she lived, would come to be recognized as the fountainhead of the Chipko environmental movement.Chipko, in Hindi, means ‘to stick’ or ‘to cling’. In the early 1970s, the Western Himalayan regions of Garhwal and Kumaon, where Reni is situated, were in turmoil. Villagers had been using non-violent methods, including tree hugging, to save their local forests from industrial logging for several months by the time Gaura Devi — and about two dozen women from Reni — showed up on the scene1. But the courage of this small group of women, who stood their ground against loggers who hurled threats and abuses at them, shot the movement to international attention.What followed holds lessons for a planet teetering on the edge of a climate crisis: marginalized communities can succeed in catapulting environmental concerns into the global spotlight through innovative protest tactics. The Chipko movement gave rise to India’s Forest Conservation Act of 1980, the express aim of which is to conserve woodlands. A few years later, a new federal environment ministry was set up to act as a nodal agency for the protection of biodiversity and to safeguard the country’s environment1–3. Even the origin of the term tree hugger — which has since acquired pejorative connotations — can be traced back to the grassroots ecological consciousness that surfaced in India’s villages.
The origins of India’s environment movement
The movement and its aftermath hold sobering lessons, too. Villagers who threatened to cling on to trees were voicing concern not just about the state of the forests, but also about their own lives and livelihoods. Their desire was to exercise greater local control over woodland resources. Women such as Gaura Devi, for instance, had to walk long distances to gather firewood once the forests were denuded1,4.Beginning in the late 1960s, activists who took inspiration from the leader of India’s anti-colonial nationalist campaign, Mohandas Gandhi, had begun to mobilize villagers in the Western Himalayas. Their strategy to improve economic opportunity in the region hinged on the Gandhian vision of bottom-up development. A network of cottage industries and cooperatives began to be set up to market forest products. The government’s competing top-down approach of auctioning forests to big private contractors came as an unwelcome intrusion3,5,6.In essence, what the foot soldiers of Chipko wanted was an acknowledgement of their Indigenous rights to access forest resources that were crucial for their survival. What they got instead was a national law and a ministry populated by a new breed of power brokers — who, in the years to come, would decide at times that habitat preservation is possible only by keeping local communities out.The big debateGarhwal and Kumaon, part of the present-day state of Uttarakhand, were at the heart of independent India’s first big debate on environmental justice and equity for a reason. The terrain is mountainous and most of the land is forested. Lives and livelihoods centre heavily around access to land and water resources. Apart from subsistence agriculture, the main source of income in the region 50 years ago was remittance — money sent home from men who had migrated to cities or joined the armed forces2,4,5.Although daily life was economically precarious for the villagers, the hills also presented them with a fragile environment. In the years preceding the Chipko movement, floods and landslides had wreaked havoc. Some of the villages worst affected lay near forests that had been felled1,5,6.
Three climate policies that the G7 must adopt — for itself and the wider world
The idea of ‘commons’ and ‘sacred forests’ had been an intrinsic part of the cultural ethos of rural India, but the colonial period frayed the bonds that villagers tended to have with their immediate environment. The British Raj’s primary source of income was land revenue. As a result, converting forest or common land into agricultural land by getting rid of existing vegetation was very lucrative1,2.Things did not improve after independence — the Indian government’s fourth five-year plan (1969–74) directed the state forest departments to take control of forests and open lands. This policy resulted in more restrictions to access for the locals, who depended on nearby woodlands to meet their needs for food, fruit, fodder, firewood and other raw materials2,3.The spark that ignited Gaura Devi’s tree-hugging protest came when the provincial government handed over ash trees in the Chamoli district of Garhwal to a private contractor to make sports goods. This disregarded the request put forward by a local artisan’s cooperative, the Dashauli Gram Swarajya Sangh (DGSS, Society for Village Self-Rule), which wanted to use the trees to make agricultural implements1,5.
Shade is an essential solution for hotter cities
The manner of protest itself was not new. A year earlier, in March 1973, in the nearby village of Mandal, women and men had come together to prevent the felling of trees under the leadership of a local activist, Chandi Prasad Bhatt, who was associated with the DGSS. As word spread, the act of chipko, or embracing a tree, became an andolan — a movement — which united people across social, caste and age groups, with even children participating in many villages1,5.However, the protest in Reni village is now recognized as a seminal moment. Gaura Devi was an ordinary woman. But her extraordinary act continues to stand as a prominent signpost in the evolution of India’s ecological consciousness, even 50 years later.Surprising savioursOn the day the trees near Reni village were to be felled, neither the DGSS members nor the men of the village were present. This was no coincidence, but a deliberate plan by forest department staff, who had organized meetings elsewhere to minimize the possibility of a large-scale protest. However, what they did not account for was the leadership of Gaura Devi, who headed the village’s mahila mandal (women’s group). On being alerted by a young girl who had seen the bus carrying the loggers, Gaura Devi marshalled the women of the village. They put their bodies in front of the axe-wielding men, eventually forcing the loggers to leave1,5.

In Joshimath, India, cracks developed in homes in January 2023 as the town began to sink.Credit: Brijesh Sati/AFP/Getty

What made these village women, whose roles were conventionally restricted to the home, come out in force to protect the trees? The environmental activist Vandana Shiva, adopting an ecofeminist lens, argues that women, especially in rural areas, share close bonds with nature because their daily tasks are entwined with nature7. For the historian Ramachandra Guha, however, although Chipko did see women participating on a scale like never before, it would be simplistic to reduce it to a women’s movement. For Guha, Chipko is a peasant movement centred on the environment, in which both men and women were involved1,5.Chipko is also synonymous with two men: Bhatt and Sunderlal Bahuguna. Both had strong roots in the community, having worked with voluntary organizations based on the Gandhian ideology of non-violence and satyagraha (which loosely translates as ‘truth force’). Through eco-development camps, Bhatt worked tirelessly to raise awareness about the fragility of the region’s environment. Bahuguna’s padayatras (journeys on foot) across India brought Chipko to the attention of people in other parts of the country and across the world. Chipko thus began to spread3,5,6.In the forests of the Western Ghats in the south Indian state of Karnataka, Chipko inspired similar protests called Appiko (meaning ‘cling’ in the local language, Kannada). Internationally, Bahuguna took Chipko to university lecture halls in western Europe, and the simple idea of hugging trees for protection also resonated with activists in Canada and the United States6. In 1987, the movement was awarded the Right Livelihood Award, known as the alternative Nobel prize, for its impact on the conservation of natural resources in India.The afterlifeOver the years, Chipko has been interpreted and reinterpreted by academics and activists. It has been the subject of many books, peer-reviewed papers and popular articles, and is mentioned in the curriculum of Indian schools. Chipko has a prominent place in the discourse on sustainability, too — as an example of the demand for sustainable development at a regional or local level. In March 2018, to commemorate the 45th anniversary of the movement, an iconic photograph of women joining hands around a tree appeared as a Google doodle, highlighting the movement’s international fame.An immediate effect of the 1974 Reni protest was a 15-year moratorium on tree felling4. A slew of laws and regulations for protecting the forest came into effect. Ironically, Chipko, which had set these laws in motion, resulted in local communities losing access to the very forests that met their livelihood and subsistence needs. Little changed in terms of development or employment opportunities for the locals. With forest protection prioritized, even minor development projects, such as village roads or small irrigation channels, were denied permission. At the same time, large infrastructure projects promoted by the government, such as hydroelectric dams, got the go-ahead2.
The global south is rich in sustainability lessons that students deserve to hear
The fragility of the landscape has steadily worsened. In February 2021, a catastrophic landslide in Chamoli district caused the death of some 200 people. What made the disaster worse were the multiple hydropower plants situated in the path of the landslides. In January 2023, disaster struck again when the town of Joshimath in Chamoli began sinking. Cracks developed on roads and in homes, and people had to be moved to relief camps. The unplanned development of the town on top of an earthquake-induced subsidence zone was a key reason. But a persistent concern in the region is its intrinsic ecological vulnerability, compounded in recent years by climate change.What is the relevance of Chipko today? According to the United Nations, all of us are living amid the triple planetary crises of climate change, biodiversity collapse and air pollution. Humanity has also transgressed six out of the nine ‘planetary boundaries’ that ensure Earth stays in a safe operating space8. In the context of these monumental concerns, it’s remarkable that Chipko continues to inspire.Social and environmental movements in India are still guided by its spirit. It is a strategy used by non-governmental organizations, activists and citizen groups in their fight against development projects that adversely affect tree cover. Thus, hundreds of Chipko-like movements have bloomed in villages and cities across India, inspired by a simple idea — hugging a tree to save it — and by the courage of village folk.A villager from Chamoli, Dhan Singh Rana, wrote a song describing the life and struggles of Gaura Devi, in which he says, “In this world of injustice, show us your miracle again.”3 As the world careens from one crisis to the next, it is more imperative than ever to rekindle the memory of Gaura Devi. It should inspire us to act to save the planet and contribute to sustainable change, putting aside any misgivings about our own limitations as individuals or communities. More

Giant excavators for use in deep-sea mining must stay parked for now.Credit: Nigel Roddis/Reuters

For more than a week, representatives of nations around the world have been meeting at a session of the International Seabed Authority (ISA) in Kingston, Jamaica. The ISA was established under the UN Convention on the Law of the Sea 30 years ago with the task of protecting the sea bed in international waters — which comprise roughly half of the world’s ocean. The goal of the latest meeting is to write the rules for the commercial mining of metals such as cobalt, manganese and nickel. These are needed in increasing quantities, mainly to power low-carbon technologies, such as battery storage.The meeting is set to end on 29 March, and there’s mounting concern among researchers that the final text is being rushed, not least because some countries including China, India, Japan and South Korea want to press ahead with commercial exploitation of deep-sea minerals. Some in the mining industry would like excavations to begin next year.China dominates the global supply of critical minerals and so far has the most sea-bed exploration licences of any country. These permits do not allow commercial exploitation. One company, meanwhile, The Metals Company, based in Vancouver, Canada, wants to apply for a commercial permit, potentially in late July.
Hypocrisy is threatening the future of the world’s oceans
There is little justification for such haste. Commercial sea-bed mining is not permitted for a reason: too little is known about the deep-sea ecosystem, such as its biodiversity, and its interactions with other ecosystems, and the impact of disturbance from commercial operations. Until we have the results of long-term studies, the giant robotic underwater excavators, drills and pumps that are ready to go must remain parked. Researchers have told Nature that the text is nowhere near ready, and that important due diligence is being circumvented. Outstanding issues need to be resolved, such as what is considered an acceptable level of environmental harm and how much contractors should pay the ISA for the right to extract minerals.Last month, the ISA published the latest draft of its mining regulations text. This ran to 225 pages, and researchers and conservation groups were alarmed to see that, unlike previous drafts, it incorporated proposals that would speed up the process for issuing commercial permits, and it also weakened environmental protections.Worryingly, a few of the changes in the latest text were not identified by square brackets — the practice in international negotiations to highlight wording that has not been agreed on by all parties. Nor were the sources for some changes attributed.Furthermore, in an earlier version of the text, there was a proposal to include measures to protect rare or fragile ecosystems, but this wording is not in the latest draft. Another suggestion was to require that mining applications be decided on within 30 days of their receipt, rather than waiting for the ISA’s twice-yearly meeting — an idea that has support from some in the industry and that does appear in the latest draft.Proposing changes to draft texts is normal in a negotiation, but failing to publicly identify who is proposing them is not. It is damaging to trust and a risk to reaching an outcome in which all parties are happy.Questions are rightly being asked of the leadership of the ISA secretariat, which organizes meetings and is responsible for producing and distributing texts, as well as the leadership of the ISA’s governing council. Nature has reached out to the secretariat with questions, but no response was received by the time this editorial went to press. We urge the ISA to respond, engage and explain.
Norway’s approval of sea-bed mining undermines efforts to protect the ocean
It is possible that the benefits to low-carbon technologies outweigh the risks of deep-sea mining if these are mitigated. But some 25 countries are calling for a moratorium on the practice, at least until the science is better understood. The European Parliament also backs a moratorium. This is also the official view of the High Level Panel for a Sustainable Ocean Economy, a group of 18 countries that pledged to not undertake commercial deep-sea mining in their national waters — despite founding member Norway’s decision to open up applications for commercial licences, which the European Parliament has criticized.The UN Convention on Migratory Species is urging that its member states should neither encourage nor engage in deep-sea mining “until sufficient and robust scientific information has been obtained to ensure that deep-seabed mineral exploitation activities do not cause harmful effects to migratory species, their prey and their ecosystems”.The ISA and its member states should exercise care, make their decisions on a consensus of evidence and be transparent in doing so, because transparency is foundational to the success of international relations. The deep seas are the least explored parts of the planet; we should not allow for their loss before we even understand their complexities. More

It was a call from a reporter that first made ecologist Jason Hoeksema think things had gone too far. The journalist was asking questions about the wood wide web — the idea that trees communicate with each other through an underground fungal network — that seemed to go well beyond what Hoeksema considered to be the facts.Hoeksema discovered that his colleague, Melanie Jones, was becoming restive as well: her peers, she says, “had been squirming for a while and feeling uncomfortable with how the message had morphed in the public literature”. Then, a third academic, mycorrhizal ecologist Justine Karst, took the lead. She thought speaking out about the lack of evidence for the wood wide web had become an ethical obligation: “Our job as scientists is to present the truth, as close as we can get to it”.Their concerns lay predominantly with a depiction of the forest put forward by Suzanne Simard, a forest ecologist at the University of British Columbia in Vancouver, in her popular work. Her book Finding the Mother Tree, for example, was published in 2021 and swiftly became a bestseller. In it she drew on decades of her own and others’ research to portray forests as cooperating communities. She said that trees help each other out by dispatching resources and warning signals through fungal networks in the soil — and that more mature individuals, which she calls mother trees, sometimes prioritize related trees over others.The idea has enchanted the public, appearing in bestselling books, films and television series. It has inspired environmental campaigners, ecology students and researchers in fields including philosophy, urban planning and electronic music. Simard’s ideas have also led to recommendations on forest management in North America.
It takes a wood to raise a tree: a memoir
But in the ecology community there is a groundswell of unease with the way in which the ideas are being presented in popular forums. Last year, Karst, at the University of Alberta in Edmonton, Canada; Hoeksema, at the University of Mississippi in Oxford; and Jones, at the University of British Columbia in Kelowna, Canada, challenged Simard’s ideas in a review1, digesting the evidence and suggesting that some of Simard’s descriptions of the wood wide web in popular communications had “overlooked uncertainty” and were “disconnected from evidence”. They were later joined by other researchers, including around 30 forest and fungal scientists, who published a separate paper that questioned the scientific credibility2 of two popular books about forests — one of them Simard’s — saying that some of the claims in her book “do not correctly reflect, and even contradict, the data”. The article warns of “the perils of plant personification”, saying that the desire to humanize plant life “may eventually harm rather than help the commendable cause of preserving forests”. Another review of the evidence appeared in May last year3.Simard, however, disagrees with these characterizations of her work and is steadfast about the scientific support for her idea that trees cooperate through underground fungal networks. “They’re reductionist scientists,” she says when asked about criticism of her work. “They’ve missed the forest for the trees.” She is concerned that the debate over the details of the theory diminishes her larger goal of forest protection and renewal. “The criticisms are a distraction, to be honest, from what’s happening in our ecosystems.”Robert Kosak, dean of the faculty of forestry at the University of British Columbia, supports Simard and calls her “a world-renowned scientist, a strong advocate for science-based environmental solutions, an amazing communicator, mentor, and teacher, and a wonderful colleague”.The dispute offers a window into how scientific ideas take shape and spread in popular culture — and raises questions about what the responsibilities of scientists are as they communicate their ideas more widely.Conversation starterIn her book, Simard tells of an idyllic childhood, with summers spent in the ancient forests of British Columbia. While an undergraduate, she worked at a forestry company, witnessing clear-cut logging at first hand. The experience set the course of her career. On graduating, she took a government forest-service post, and joined the University of British Columbia in 2002. She still works there, running a research programme called the Mother Tree Project, which develops sustainable forest-renewal practices.One of Simard’s earliest papers appeared in Nature4 in 1997, describing evidence that carbon could travel underground between trees of different species, and suggesting that this could be through an underground fungal network. Nature put the paper on its cover and dubbed the idea the wood wide web — a term that quickly caught on and is now widely used to describe the idea (Nature’s news team is editorially independent of its journal team).Tree leaves turn sunshine and carbon dioxide into sugars, and some of this flows to their roots and into mycorrhizal fungi, which grow into the root tip and donate water and nutrients in return. There was already evidence, from a laboratory study5, that carbon can move through the tendrils of the fungi that link seedling roots together. But Simard’s approach, a controlled experiment in clear-cut forest, was “groundbreaking”, says David Johnson, who studies the ecology of soil microbes at the University of Manchester, UK.

Forest ecologist Suzanne Simard’s 1997 study looked at carbon transfer between Douglas fir (Pseudotsuga menziesii) and paper birch trees (Betula papyrifera, pictured).Credit: Steve Gettle/Nature Picture Library

She planted pairs of seedlings — one paper birch (Betula papyrifera) and one Douglas fir (Pseudotsuga menziesii) — close to one another. She shaded the Douglas fir to prevent it from manufacturing sugars. Then she bathed the air surrounding each seedling with traceable, labelled carbon dioxide. She found carbon in sugars made by the birch in the needles of the shaded Douglas fir. Smaller quantities of sugars from the fir were found in the birch.A third seedling in each group — western red cedar (Thuja plicata) — which is not colonized by the same types of mycorrhizal fungi, absorbed less carbon than did the other seedlings. The results, the authors concluded4, suggest that carbon transfer between birch and Douglas fir “is primarily through the direct hyphal pathway”. That is, there could be an active fungal pipeline connecting the roots of both trees.Over the years, Simard and other researchers developed in published work the idea that there could be a common mycorrhizal network in the forest soil, connecting many trees of the same and different species.About a decade ago, Simard began to take the idea further, and into the media. In a short film called Mother Trees Connect the Forest, she said of forest trees: “These plants are really not individuals in the sense that Darwin thought they were individuals competing for survival of the fittest. In fact, they’re interacting with each other, trying to help each other survive.”In 2016, in a TED talk that has had more than 5.6 million views, she portrayed forest trees as “not just competitors” — competition being foundational to the understanding of how ecosystems work — “but as cooperators”. Her 1997 experiment, she said, had revealed evidence for a “massive underground communications network”. Her later work, she added in the TED talk, found that some bigger, older “mother trees”, as she called them, are particularly well connected. They nurture their young — preferentially sending them carbon and making space for them in their root systems. What’s more, “when mother trees are injured or dying, they also send messages of wisdom on to the next generation of seedlings.”Then came her book — a memoir and detailed account of her work. It has been praised for its vivid and personal depiction of the scientific life.The book concludes that to escape environmental devastation, humans should adopt attitudes to nature that are similar to those of Indigenous people. “This begins by recognizing that trees and plants have agency,” she writes.Simard has worked to change forestry practices in North America in line with her ideas, for example by sparing the oldest trees during clear-cutting so that they can provide an infrastructure for the next generation of planted trees.Challenging ideasBut academics were increasingly concerned that the ideas and the publicity that they were attracting had moved beyond what was warranted by the scientific evidence.The disquiet came to a head when the 2023 scientific review1 was published. The authors, Hoeksema, Jones and Karst, have all collaborated scientifically with Simard in the past; Jones was an author of the 1997 paper. The review considers the evidence for popular claims made about the wood wide web.
‘We are killing this ecosystem’: the scientists tracking the Amazon’s fading health
Their review has drawn praise for its scholarship. It is “the gold standard of how one should tackle a contentious and important field”, says James Cahill, who studies plant behaviour at the University of Alberta.Simard takes the opposite view: the paper, she says, fails to see the bigger picture, and its prominence is “an injustice to the whole world”.The review laid out what the authors regard as the three key claims underlying the popular idea of the ‘mother tree’: that networks of different fungi linking the roots of different trees — known as common mycorrhizal networks (CMNs) — are widespread in forests; that resources pass through such networks, benefiting seedlings; and that mature trees preferentially send resources along the networks to their kin. The scientists concluded that the first two are insufficiently supported by the scientific evidence, and that the last “has no peer-reviewed, published evidence”.Some elements of the wood-wide-web idea are not in dispute, they say. For instance, mycorrhizal fungi can latch onto multiple roots of the same plant; one species of fungus can connect with the roots of different species of plant; and mycelia — a cobweb of fungal tendrils — can spread over large distances.But evidence for a CMN in trees — one in which an individual fungus links the roots of the same or different tree species — is patchy, the review authors say. There are well-documented CMNs that link certain plants together: some orchids use CMNs to connect with trees, for instance, so that the orchids can feed on tree sugars when they can’t make their own.And lab studies have shown that a single fungus can link seedlings of different tree species. But, the authors say, the lab studies compare with the forest in the same way that human cells grown in a dish compare with human bodies.The review authors found that the strongest evidence for a CMN among trees in the field comes from five studies published between 2006 and 2020 — some led by ecologist Kevin Beiler, when he was a PhD student in Simard’s group. Beiler, who is now at the University for Sustainable Development in Eberswalde, Germany, used DNA techniques to map the networks of genetically distinct fungi in patches of old-growth forest, and found that they linked many trees of different ages, all Douglas fir — and the larger the tree, the greater the extent of its connections.

Suzanne Simard is the scientist most closely associated with the idea of the ‘wood wide web’.Credit: PA Images/Alamy

But Karst says that this doesn’t prove that the fungus was simultaneously connecting different trees, because mycelia decay easily and the technique would have picked up strands that are defunct, as well as alive. And that arduous mapping exercise has been repeated for just two tree species — hardly grounds for generalization, she says.So, do these common networks exist? “The consensus seems to be they are probably there but we do need more people to go out and map them at a fine scale to show that,” says Jones.The second claim explored by the review is that resources travel through the CMN and benefit seedlings. It has three parts. The first — that resources do, by some means, travel through the soil between plants, commands some support, say the review authors. For example, they highlight research in a Swiss forest in which the canopies of certain trees had been bathed in labelled carbon dioxide. The experiment showed that carbon ended up in the roots of nearby trees.But the authors say that proving the second two parts of the claim — that a CMN is the major conduit, and that seedlings typically benefit — is tricky. Lab and field studies often cannot rule out that resources moved through the soil for at least part of the way. The review highlighted three lab studies that directly observed carbon moving from one tree seedling to another through a mycorrhizal link, and these “are still the best evidence for the movement of resources within a CMN formed by woody plant species”, say the authors.In the forest, the authors found 26 experiments reporting carbon transfer, but for each transfer, there was an alternative explanation for how the carbon travelled.Some studies don’t look for a CMN but simply assess whether growing a seedling next to an adult tree improves its performance. For every instance in which a seedling benefited, the review states, there was another study in which its growth was inhibited. The results are “a huge smear from positive effects to negative effects and mostly neutral”, says Hoeksema.The third claim is that mature trees communicate preferentially with offspring through CMNs, for example sending warning signals after an attack.“When I heard that out in public I thought ‘Holy cow, that’s extraordinary’,” says Karst.The team did find one lab experiment, published in 2017 and led by Brian Pickles, who did the work as a postdoc in Simard’s department, that found that if seedlings were related then more carbon was transferred between them. But it happened in only two of the four lineages of seedlings, and it happened even when fungi were prevented from making links with each other — suggesting that one fungus exuded it into the soil and the other picked it up, the researchers say. In the review, the authors write that, for the third claim, “there is no current evidence from peer-reviewed, published field studies”.
We must get a grip on forest science — before it’s too late
Karst says that one reason why ideas about mother trees and their kin have traction in the public domain is that Simard, in media interviews and her book, has implied that findings made in the greenhouse were actually made in the forest, making the evidence seem stronger than it is. Simard disagrees. “I do not, and would never, imply anything misleading when presenting research.”Karst gives the example of a passage from Simard’s book that describes a visit to a field site made by Simard and her master’s student, Amanda Asay. In October 2012, Asay was exploring a question that is important for forestry — do seedlings stand a better chance of survival if they grow near their mother tree, and, if so, is this because they receive preferential help through a common mycorrhizal network? Asay had blocked such connections in control seedlings by planting them in mesh bags with pores too small for fungi to fit through. What she found in that forest experiment, Simard says in her book, matched the theory that trees help their kin through networks. “Seedlings that were [the mother tree’s] kin survived better and were noticeably bigger than those that were strangers linked into the network, a strong hint that Douglas-fir mother trees could recognize their own.” Yet, when the review authors accessed Asay’s master’s thesis6, they found that her field work had discovered the opposite: that more non-kin seedlings survived than did kin (although the trend was not significant). As for the role of networks, the thesis states: “Our hypothesis that kin recognition is facilitated by mycorrhizal networks, however, was not supported”.When asked about the discrepancy, Simard says that Asay also did greenhouse experiments for her master’s thesis, which used pairs of older and younger tree seedlings, and showed that older seedlings recognized younger kin and sent them more resources than they did to non-kin. After that, Asay and others in the team did find evidence that “there are responses that clearly show kin selection in those trees”.Simard says that, when describing Asay’s findings in the forest in 2012, she made a writer’s choice to situate other findings as if they were discovered in the forest on that day. “I situated the story in the field, because that’s where the question came from.” That description, she says, encompasses “the whole body of work”.

A spruce tree root with ectomycorrhizal fungi.Credit: Eye of Science/Science Photo Library

Asay’s subsequent work has not yet been published, for a tragic reason: she died in an accident in 2022. Her death was devastating for the group and publication stalled, Simard says. “We’re about to publish those papers,” she says.Karst, Jones and Hoeksema’s overall conclusion is that CMNs do exist in the plant kingdom, and that resources can travel along them, benefiting at least one party, and sometimes both. In the forest, myriad mycelia extend through the soil that are capable of linking with trees, including those of different species. Whether they form a live thoroughfare, and whether resources travel through it between trees, has yet to be demonstrated in the field. Whether there are, in general, kin effects between plants was beyond the scope of their review, but the authors found nothing to support the idea that forest trees target kin through common mycorrhizal networks.Their review also looked at the literature and found that some scientists have selectively cited and quoted from studies, boosting the credibility of the idea. The main problem, the review concludes, is not the quality of the science. “The most concerning issue is the rigour with which the results of these studies have been transmitted and interpreted.”Rigour and reactionMost of the response to the review has been positive, says Jones. “We got a lot of letters saying ‘thank you for doing that, it’s such a relief’. But I was really surprised how many of our colleagues said ‘you are brave’. That shouldn’t be, that you would have to be brave.”But some researchers have taken issue with aspects of the review. Johnson disagrees with the team’s decision to exclude evidence for similar networks elsewhere in the plant kingdom, including between orchids and trees, and in grasslands and heathlands. It means, he says, they were “ignoring 90% of the work … our default position should be that we should expect mycorrhizal fungi to connect many plants”. It’s important, he says, to take a collective view of the evidence.He agrees with the conclusion, however, that Simard’s idea of the cooperating forest is incompatible with evolutionary theory. “It’s all about the plants supporting each other for these altruistic reasons. I think that’s completely rubbish.”Johnson’s view is that it “makes complete sense” that there are CMNs linking multiple forest trees and that substances might travel from one to another through them. Crucially, he says, this is not due to the trees supporting one another. A simple explanation, compatible with evolutionary theory, is that the fungi are acting to protect the trees that are their source of energy. It is beneficial for fungi to activate a tree’s defence signals, or to top up food for temporarily ailing trees. Pickles, who spent six years working with Simard before moving to the University of Reading, UK, says Simard’s ideas are not incompatible with competition, but give more weight to well-known phenomena in ecology, such as mutualism, in which organisms cooperate for mutual benefit. “It’s not altruism. It’s not some outrageous idea,” he says. “She certainly focuses more on facilitation and mutualism than is traditional in these fields, and that’s probably why there’s a lot of pushback.”Other ecologists agree that there is some “polarization” in ecology between cooperative and competitive ideas. “The idea that perhaps not everything is trying to kill everything else is helpful,” says Katie Field, who studies plant-soil processes at the University of Sheffield, UK.Regardless of the differences of opinion, Pickles says, “It’s good to have this rigorous analysis.”Frustrating debateSimard is exasperated by the debate.Her work, she says, has “changed our whole world view of how the forest works”. There are now “dozens and dozens” of people “who have found that stuff moves through networks and through the soil”.She says that the quality of her science has been unfairly challenged. To say that her 200 published papers are “not valid science, which I think is what they’re saying … that it was wrong … is not right,” she says. She is in the process of submitting responses to the critical papers to two journals, she says.She says that she is unfairly accused of claiming CMNs are the only pathway for resources to travel between trees, and that she acknowledges other pathways in her papers and her book.In media appearances, it’s hard to make that clear, she says: “It’s a very short period of time, and I don’t get into all those other evolutionary reasons for these things.”Simard maintains that her critics attack her in the academic literature for imagery she has used only in public communication: “I talked about the mother tree as a way of communicating the science and then these other people say it’s a scientific hypothesis. They misuse my words.”She argues that changing our understanding of how forests work from ‘winner takes all’ to ‘collaborative, integrated network system’ is essential for fixing the rampant destruction of old-growth forest, especially in British Columbia, where her research has focused. Indigenous cultures that have a more sustainable relationship with forests have mother and father trees, she says — “but the European male society hates the mother tree … somebody needs to write a paper on that”.“I’m putting forward a paradigm shift. And the critics are saying ‘we don’t want a paradigm shift, we’re fine, just the way we are’. We’re not fine.”Simard also says that Karst held a position partially funded by members of Canada’s Oil Sands Innovation Alliance that constitutes a conflict of interest. Extraction of oil deposits is associated with forest loss and environmental damage, and Karst was studying land reclamation after extraction. Karst says that she held this position until 2021, terminating it before starting work on the review, and that the work it funded did not overlap with the focus of the review on mycorrhizal networks.Taking the research forwards will be challenging, says Johnson. Karst and her colleagues have produced an agenda for future field research — from mapping the genotypes of trees and fungi in a range of forests to using controls in experiments more stringently. But the agenda doesn’t impress Johnson. “It’s almost impossible to fulfil,” he says, partly because fieldwork is so fiendishly difficult.Some scientists say that Simard’s popular work has had a positive influence on the field, even if elements of it remain controversial. Her work propelled the mycorrhizal research community from an obscure and underfunded field to one that excites the public, says Field. That has unleashed funding, stimulated researchers’ imaginations and influenced research agendas.The backlash has further energized the community, she says. There are plans for a special edition of a journal she edits, and sessions have been added to the upcoming meeting of the International Mycorrhizal Society. All of this is helpful, says Field. “Anything that makes people think again and look again at the evidence is good.” More

After 15 years of discussion, geologists last week decided that the Anthropocene — generally understood to be the age of irreversible human impacts on the planet — will not become an official epoch in Earth’s geological timeline.The rejected proposal would have codified the end of the current Holocene epoch, which has been in place since the end of the last ice age 11,700 years ago. It suggested that the Anthropocene started in 1952, when plutonium from hydrogen-bomb tests showed up in the sediment of Crawford Lake near Toronto, Canada.The vote has drawn controversy over procedural details, and debate about its legitimacy continues. But whether or not it’s formally approved as a stratigraphic term, the idea of the Anthropocene is now firmly rooted in research. So, how are scientists using the term, and what does it mean to them and their fields?‘It’s a term that belongs to everyone’As head of the Leverhulme Centre for Anthropocene Biodiversity at the University of York, UK, Chris Thomas has perhaps more riding on the term than most. “When the news of this — what sounds like a slightly dodgy vote — happened, I sort of wondered, is it the end of us? But I think not,” he says.For Thomas, the word Anthropocene neatly summarizes the sense that humans are part of Earth’s system and integral to its processes — what he calls indivisible connectedness. “That helps move us away from the notion that somehow humanity is apart from the rest of nature and natural systems,” he says. “It’s undoable — the change is everywhere.”
Geologists reject the Anthropocene as Earth’s new epoch — after 15 years of debate
The concept of an era of human-driven change also provides convenient common ground for him to collaborate with researchers from other disciplines. “This is something that people in the arts and humanities and the social sciences have picked up as well,” he says. “It is a means of enabling communication about the extent to which we are living in a truly unprecedented and human-altered world.”Seen through that lens, the fact that the Anthropocene has been formally rejected because scientists can’t agree on when it began seems immaterial. “Many people in the humanities who are using the phrase find the concept of the articulation of a particular year, based on a deposit in a particular lake, a ridiculous way of framing the concept of a human-altered planet.”Jacquelyn Gill, a palaeoecologist at the University of Maine in Orono, agrees. “It’s a term that belongs to everyone. To people working in philosophy and literary criticism, in the arts, in the humanities, the sciences,” she says. “I think it’s far more meaningful in the way that it is currently being used, than in any attempts that stratigraphers could have made to restrict or define it in some narrow sense.”She adds: “It serves humanity best as a loose concept that we can use to define something that we all widely understand, which is that we live in an era where humans are the dominant force on ecological and geological processes.”Capturing human influencesThe idea of the Anthropocene is especially helpful to make clear that humans have been shaping the planet for thousands of years, and that not all of those changes have been bad, Gill says. “We could do a better job of thinking about human–environment relationships in ways that are not inherently negative all the time,” she says. “People are not a monolith, and neither are our attitudes or relationships to nature.”Some 80% of biodiversity is currently stewarded on Indigenous lands, Gill points out. “Which should tell you something, right? That it’s not the presence of people that’s the problem,” she says. “The solution to those problems is changing the way that many dominant cultures relate to the natural world.”The concept of the Anthropocene is owned by many fields, Gill says. “This reiterates the importance of understanding that the role of people on our planet requires many different ways of knowing and many different disciplines.”
Humans versus Earth: the quest to define the Anthropocene
In a world in which the threat of climate change dominates environmental debates, the term Anthropocene can help to broaden the discussion, says Yadvinder Malhi, a biodiversity researcher at the University of Oxford, UK.“I use it all the time. For me, it captures the time where human influence has a global planetary effect, and it’s multidimensional. It’s much more than just climate change,” he says. “It’s what we’re doing. The oceans, the resources we are extracting, habitats changing.”He adds: “I need that term when I’m trying to capture this idea of humans affecting the planet in multiple ways because of the size of our activity.”The looseness of the term is popular, but would a formal definition help in any way? Malhi thinks it would. “There’s no other term available that captures the global multidimensional impacts on the planet,” he says. “But there is a problem in not having a formal definition if people are using it in different terms, in different ways.”Although the word ‘Anthropocene’ makes some researchers think of processes that began 10,000 years ago, others consider it to mean those of the past century. “I think a formal adoption, like a definition, would actually help to clarify that.” More

Download the Nature Podcast 13 March 2024 In this episode:00:45 Making a map of the human heartThe human heart consists of multiple, specialized structures that all work together to enable the organ to beat for a lifetime. But exactly which cells are present in each part of the heart has been difficult to ascertain. Now, a team has combined molecular techniques to create an atlas of the developing human heart at an individual cell level. Their atlas provides insights into how cell communities communicate and form different structures. They hope that this knowledge will ultimately help in the treatment of congenital heart conditions, often caused by irregular development of the heart.Research article: Farah et al. Nature video: Building a heart atlas08:37 Research HighlightsResidue in ceramic vases suggests that ancient Mesoamerican peoples consumed tobacco as a liquid, and a wireless way to charge quantum batteries.Research Highlight: Buried vases hint that ancient Americans might have drunk tobaccoResearch Highlight: A better way to charge a quantum battery11:11 The evolution of menopause in toothed whalesMenopause is a rare phenomenon, only known to occur in a few mammalian species. Several of these species are toothed whales, such as killer whales, beluga whales and narwhals. But why menopause evolved multiple times in toothed whales has been a long-standing research question. To answer it, a team examined the life history of whales with and without menopause and how this affected the number of offspring and ‘grandoffpsring’. Their results suggest that menopause allows older females to help younger generations in their families and improve their chances of survival.Research Article: Ellis et al.News and Views: Whales make waves in the quest to discover why menopause evolved18:03 Briefing ChatHow the new generation of anti-obesity drugs could help people with HIV, and the study linking microplastics lodged in a key blood vessel with serious health issues.Nature News: Blockbuster obesity drug leads to better health in people with HIVNature News: Landmark study links microplastics to serious health problemsSubscribe 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, Google Podcasts, Spotify or your favourite podcast app. An RSS feed for the Nature Podcast is available too. More

Northern Australian elder George Milpurrurr shows the next generation how to do a cultural burn.Credit: Penny Tweedie/Alamy

Indigenous Australians have been using fire to shape the country’s northern ecosystems for at least 11,000 years, according to charcoal preserved in the sediment of a sinkhole. The study was published on 11 March in Nature Geoscience1.The practice of cultural burning, also known as ‘fire-stick farming’, is integral to Indigenous Australian culture and history, and is understood to have profoundly altered landscapes across the country.Fire-stick farming involves introducing frequent, low-intensity fires in small areas of the landscape in a patchy, ‘mosaic’ pattern, and is done early in the dry season. The practice is important culturally and environmentally; in particular, it reduces the amount of fuel available for burning and therefore decreases the intensity of wildfires that might spark late in the dry season because of lightning strikes or other triggers.Archaeological evidence indicates that humans have continuously occupied the Australian continent for at least 65,000 years2, but little is known about when the practice of fire-stick farming began.“You need a really long record that goes back before people were here so you can see what the natural world — the definitively unimpacted world, if you’d like — looks like and then you’ve got enough of a record to be able to see if anything changed,” says study co-author Michael Bird, a geologist at James Cook University in Cairns, Australia.The researchers found that record in the sediment of Girraween Lagoon, a permanent water body formed in a collapsed sinkhole near Darwin in the Northern Territory. The lagoon is an important site for the traditional owners of the land, the Larrakia Nation, and was made famous by the crocodile attack scene in the 1986 film Crocodile Dundee.Because the lagoon has remained full, its sediments offer a continuous record of deposition that has not been disturbed by drying out and cracking. Bird and his colleagues were able to extract a core from the bottom of the lagoon that provided a 150,000-year-long record of changes in the type and geochemistry of the deposited charcoal, and in the accumulation of pollen.Change in the charcoalThe team notes that, around 11,000 years ago, the changes in the charcoal deposits point to alterations in the intensity of fires in the area.Without human influence, fires are less frequent but have enough intensity to burn trees and leave behind charcoal, says Bird.“A less-intense fire doesn’t get into the crown — it’s burning what’s on the ground,” he says. The grass, as well as twigs and fallen tree leaves, are more likely to become charcoal than the trees themselves, he adds.Because tree-derived charcoal has higher concentrations of the isotope carbon-13 than does charcoal from grasses, the researchers analysed the composition and geochemistry of the burnt residue in the sample. The authors found a sustained change from low-frequency, high-intensity fires — the ‘natural’ fire regime — to more frequent but less intense ones, which they suggested was the result of Indigenous fire-stick farming.The authors ruled out climate change as the cause of the shift by using the ratio of tree pollen to grass pollen as a type of climate history to show that vegetation changes did not explain the shift in the charcoal record.However, Bird notes that European colonization has mostly brought an end to cultural burning practices, and has shifted fire intensity back towards a natural pattern. “Because we’ve had, 10,000 plus years of a particular fire regime, it’s the release from that fire regime that’s actually creating quite significant issues,” he says, suggesting that this shift has contributed to the return of more high-intensity wildfires.Joe Fontaine, a fire ecologist at Murdoch University in Perth, Australia, says that the growing understanding of how cultural burning has shaped the Australian landscape, particularly in the northern regions, is crucial for contemporary fire-management practices, which to a large extent have excluded Indigenous people and their expertise.“The barriers to doing cultural burning, in our arcane system of laws and bureaucracy,” are challenging to overcome, Fontaine says. There are also many more permanent structures in the landscape nowadays than there were before colonization, he says, so the challenge is to work out where and how cultural burning can be restored as a practice.The continuing work that “puts cultural burning practices out there and establishes it as something that really existed, is crucial to the evolution of contemporary fire management,” he says. More

For more than a decade, Christie Bahlai has been part of a long-running survey of ladybirds. Each summer, she and other scientists send students from their laboratories to a site on Gull Lake, Michigan, about 220 kilometres west of Detroit, to monitor 14 beetle species. Their goal: to track how invasive species are affecting native populations.The ladybird project has been running since 1989, and for 20 years had been directed by Douglas Landis, an entomologist at Michigan State University in East Lansing and Bahlai’s former postdoctoral adviser. But last year, Landis decided to retire. In December, he reached out to Bahlai, a computational ecologist at Kent State University in Ohio, to ask whether she wanted the many boxes of handwritten data sheets stored in his laboratory.
How to digitize your lab notebooks
Bahlai already had digital scans of the documents. Still, she wanted the originals. “What if there’s a note on the data that didn’t come through on the scans, or some other crucial context?” Bahlai explains. “And so, I received my inheritance over Christmas vacation.”Generally, “the easiest and most productive” way to compile data is to type them directly into a spreadsheet, says Miguel Acevedo, an ecologist at the University of Florida in Gainesville. But using a computer, tablet or even a smartphone in the field isn’t always practical. The Puerto Rican rainforest, where Acevedo studies malaria infection in lizards, is prone to unexpected downpours, so his team logs its data in pencil-drawn tables in waterproof notebooks. Bahlai and her colleagues record species counts by hand while working in dusty cornfields, their fingers often covered in sticky insect-trap goo.To be useful, handwritten data must be digitized into a form that can be analysed. But because this is one step removed from data collection, the process is rife with potential for error. Whether carrying over data manually or using software tools such as optical character recognition (OCR), researchers need to think about how to keep damage to a minimum. Here are five tips to do just that.Make a digitization integrity planOne of the first things Acevedo tells his students is that correcting mistakes in data becomes an order of magnitude more difficult with every step towards publication. He calls this the 1/10/100 rule: incorrectly writing down a lizard’s length in millimetres instead of centimetres is easily fixed — a metaphorical $1 mistake. But the cost jumps to $10 if the data point slips through the digitization process, and to $100 after it’s been analysed. Standardized protocols and workflows help to prevent such errors and minimize the cost, he says.In Bahlai’s lab, a “meticulous and reliable” student volunteer transfers the data from the original paper sheets to Google Docs. They annotate anything that they’re unsure of — a smudged number, for example — and tag Bahlai, who will take a closer look. After a second student double-checks the data, Bahlai transfers them into a spreadsheet, for more in-depth quality checks.Acevedo’s set-up is different: students work in pairs, with one reading out the data and the other typing them in. He also insists on including in each notebook a metadata page that contains acronym definitions, units of measurement and other elements. “If somebody is looking at notebooks 20 years from now,” he says, “they’ll know exactly what they’re looking at.”Here’s another must-do, says Joel Correia, a human–environment geographer at Colorado State University in Fort Collins: invest the time and resources upfront to train the people doing the fieldwork. Correia studies the social and ecological effects of long-term land-stewardship practices in three Indigenous nations in the Ecuadorian Amazon. His team teaches members of those communities social-science research methods, such as designing and conducting interviews and surveys in their local language. In such multilingual, multicultural contexts, he says, having shared clarity around the concepts underlying the research is crucial, especially when taking written field notes that will be translated and digitized.Back up your paper, ASAPOnce you’re back from the field, do some rough digitization as soon as you can, Correia advises. Scanning your notebooks to PDFs, or even photocopying them, will safeguard you from the pain of seeing stacks of interviews destroyed by rain, fire or other unforeseen events. “I have not had that experience, but I have certainly heard of other people who have,” he says.Use several pairs of eyesOne common way of reducing errors is by having a number of people input the same data, and then correcting inconsistencies between the versions. How many pairs of eyeballs do you need? Make it an experiment, suggests Acevedo: test your error rate with different numbers of double-checkers, and find the point of diminishing return.

For her research, climatologist Linden Ashcroft often has to digitize historical sources, such as this page of climate data from 1837.Image courtesy of the National Archives of Australia. NAA: PP430/1, VOLUME 4.

But don’t overlook the human element, says Linden Ashcroft, a climatologist at the University of Melbourne, Australia. Ashcroft has run community-science efforts to digitize hand-written records in farmers’ diaries and other historical sources, some going back 200 years. She says that the World Meteorological Organization recommends that such data be double- or triple-keyed — that is, input independently by two or three people. But she knows of projects involving as many as eight individuals. “Is that really a good use of people’s time?”A good rule of thumb, Ashcroft suggests, is to calibrate your error rate to your project goals. “If you’re doing a deep dive into the weather and climate of a particular place, you want to lovingly correct the data,” she says. But if your data will be just a few of a million entries in an international database that researchers use to predict weather patterns, a slightly higher error rate probably won’t affect the outcome.Home in on outliersIf you are working with numbers, you can program your software to flag outliers, improperly formatted values and seemingly illogical data. For instance, Acevedo recalls discovering that lizards measured in one year were an order of magnitude smaller than usual. “I was there, so I knew that the lizards were not particularly small.” After he examined the notebooks from that period, he saw in the metadata that the numbers were recorded in millimetres rather than centimetres, and corrected the data.But that approach doesn’t always work, Ashcroft cautions. Outliers in her data can reflect unusually heavy rain or aberrations in atmospheric conditions, such as temperature or air pressure — real variation that is simply unexpected. “You don’t want the statistical test to kick those [values] out, because extremes are how we’re going to be affected climate change,” she says.Try OCR (and other software)OCR software can be used to convert scanned images into machine-encoded text. Many such tools are available — and most of them can successfully capture data sets in which handwritten text and numbers are written clearly and do not bleed out of their designated columns.But off-the-shelf software often falls short when applied to historical handwriting, in which s’s might look like f’s, for example, says Stuart Middleton, a computer scientist at the University of Southampton, UK. It also performs poorly in the face of image noise, such as creases or shadows in a scanned image or text that spills over from one column of a table into another. In the documents he works with, he says, “there are all sorts of horrors going on.”
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In such cases, researchers with a bit of computer-science savvy can try using different OCR models. Those models — available on the open-source machine-learning platform Hugging Face, for instance — are generally pre-trained on a wide array of images, but feeding them training images that are similar to your data could improve their performance, says Middleton. Scientists with advanced skills in coding and artificial intelligence can also modify the networks to better fit their projects. Middleton’s team is developing more-advanced, multistep OCR solutions for working with historical weather data, including new ways of training, as well as image post-processing.Options exist for digitizing other data types, too. Eliza Grames, an integrative biologist at Binghamton University in New York, uses historical data — largely graphs and charts from studies in the late nineteenth and early twentieth centuries — to map long-term insect-population trends. A program called metaDigitise (and a similar, browser-based program, WebPlotDigitizer) allows her to redraw the plots and calculate the underlying data. She also uses Inkscape, an open-source alternative to Adobe Illustrator, to digitize old species range data into a format that is readable by geographic-information-system mapping software.OCR still requires extensive expert oversight to clean up irregularities and check for errors, Ashcroft warns. She prefers to harness the efforts of volunteers around the world. “To me, the historical weather observations are a really valuable opportunity to engage people with climate science in a fun and easy way,” she says. “People get to be a part of the story.”And OCR is not always worth the trouble. For smaller projects, scanning every page and checking for errors after processing it through software might not yet be more efficient than having students do the job by hand, Acevedo says. But at the rate software is advancing, he says, that could soon change. “Maybe if we have this talk in 2025.” More