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What an Active Volcano Reveals About Missing Trees

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What an Active Volcano Reveals About Missing Trees
A view of the Piton de la Fournaise crater. Malavika Vyawahare

By Malavika Vyawahare

Giant tortoises and flying foxes once roamed La Réunion, a volcanic island off the eastern coast of Africa. Then humans arrived and decided to stay. Within 150 years of their appearance, large fruit-eating animals like the giant tortoises (Cylindraspis indica) and flying foxes (Pteropus niger), a type of bat, were wiped off the face of La Réunion.


This speck of land in the western Indian Ocean, an overseas department of France, was one of the last corners of the planet to be colonized by humans. It is also home to the Piton de la Fournaise, one of the most active volcanoes in the world. It was recently in the throes of another eruption, having erupted almost 240 times since 1650.

The scars from these eruptions are now helping scientists uncover the lasting effects of permanent human settlement on life on the island, including the loss of large-fruited trees like Sideroxylon borbonicum, known locally as bois de fer de Bourbon, and Labourdonnaisia calophylloides, or bois de natte à petites feuilles.

The fates of flora and fauna are linked. Animals and birds are important to plants; they help to disperse seeds, transporting them near and far. Which seeds and how far they get scattered depend on the kind of creatures that get their paws or beaks on the seeds. The largest fruit eater inhabiting the island today is the Réunion bulbul (Hypsipetes borbonicus), a bird a thousand times smaller than the now extinct giant tortoise. The bulbul can't feed on fruits that the tortoise could eat.

Not many would consider living in the shadow of an active volcano good fortune. For Sébastien Albert and his colleagues at the University of La Réunion, however, the frequency of eruptions at Piton de la Fournaise has proven providential. They recently published a paper in the Journal of Ecology describing the loss of large-fruited trees by creating a timeline over several centuries. Because the time of each eruption is known, it is possible to see how the plant community changed before and after human colonization.

Albert described the island as a "paradise" before humans established themselves there around the mid-17th century. The forests were dotted with towering trees that bore large, fleshy fruits enclosing chunky seeds. Seeds come in all sizes; the biggest in the world is the genitalia-shaped seed of the coco de mer (Lodoicea maldivica) found on Seychelles, an archipelago north of La Réunion. It can grow 30 centimeters (1 foot) across and weigh more than 15 kilograms (33 pounds). At the other end of the spectrum, some orchids produce seeds that are a fraction of a millimeter across, finer than a grain of sand.

The Réunion bulbul can only consume seeds smaller than 13 mm, or about half an inch. A larger species of bird native to La Réunion, the Mascarene parrot (Mascarinus mascarin), went extinct before the turn of the 19th century. So did the Réunion fruit pigeon (Nesoenas duboisi).

Throughout the Mascarenes — the Indian Ocean islands of Mauritius, Rodrigues (which is today part of Mauritius), and La Réunion — this is a familiar tale. The extinction of the dodo (Raphus cucullatus) in Mauritius is emblematic of creatures lost to human exploitation.

Overhunting, habitat loss and invasive predators contributed to the animals' disappearance. Giant tortoises were hunted by European sailors for their meat even before human habitation began. Their eggs fell prey to invasive species like pigs, cats and rats. Henri du Quesne, a French naval officer, wrote of the tortoises: "Their Flesh is very delicate; the Fat better than Butter or the best Oil, for all sorts of Sawces." Another account from 1671 noted that it was not possible to go six steps without coming upon one of these friendly giants. By 1800, they were all but gone.

The difficult part is linking their disappearance to impacts on tree diversity. "There is evidence for declines in large-seeded species that rely on large vertebrates for the dispersal of their seeds. Examples include Africa, Peru, and Brazil," said Elizabeth Wandrag, a plant ecologist at the University of New England, Australia, who was not involved in the study.

"It is not always possible to explicitly link the loss of large frugivores, and wholesale losses of species — many tree species that rely on large frugivores for dispersal are still present in forests that have lost those dispersers but have instead become more aggregated and/or show lower survival," Wandrag told Mongabay in an email.

Which is where the lava flows come in. Lava flow from a volcanic eruption is a major disturbance for any ecosystem; it tears through forests, burning everything in its path. It presents a kind of clean slate (literally) to see how plants recolonize. For existing forests, entangling the effects and even pinpointing the collapse of a species may not be as simple.

By studying how plant communities recovered after each eruption, the researchers realized that large-seeded species were not fully recovering because the fauna around them had changed since the previous eruption. "We analyzed 151 vegetation surveys on lava flows dated between 1401 AD and 1956 AD," the authors write in the paper. Tracking the changing vegetation over five centuries "has helped to pinpoint the important role that these lost animals played for these forests." The scientists say this is because when the animals that were best suited to disperse their seeds disappeared, the trees also started to fade away from the landscape.

"It was nice that the findings of this study mirrored some of those we have seen in our research on Guam without frugivores, some tree species simply aren't colonizing newly disturbed locations," Wandrag said. "In this case, the much longer history of defaunation, long-term chronosequence of plant communities, and botanical records allowed the authors to link that pattern to the resulting adult tree community."

Reposted with permission from Mongabay.

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In early October, Britain's Prince William teamed up with conservationist David Attenborough to launch the Earthshot Prize, a new award for environmentalist innovation. The Earthshot brands itself the "most prestigious global environment prize in history."

The world-famous wildlife broadcaster and his royal sidekick appear to have played an active role in the prize's inception, and media coverage has focused largely on them as the faces of the campaign.

But the pair are only the frontmen of a much larger movement which has been in development for several years. In addition to a panel of experts who will decide on the winners, the prize's formation took advice from the World Wildlife Fund, Greenpeace and the Jack Ma Foundation.

With more and more global attention on the climate crisis, celebrity endorsement of environmental causes has become more common. But why do environmental causes recruit famous faces for their campaigns? And what difference can it make?

'Count Me In'

"We need celebrities to reach those people who we cannot reach ourselves," says Sarah Marchildon from the United Nations Climate Change secretariat (UNFCCC) in Bonn, Germany.

Marchildon is a proponent of the use of celebrities to raise awareness of environmental causes. In addition to promoting a selection of climate ambassadors who represent the UN on sustainability issues, Marchildon's team has produced videos with well-known narrators from the entertainment world: among them, Morgan Freeman and Mark Ruffalo.

"We choose celebrities who have a lifestyle where they are already talking about these issues," Marchildon explains.

"Sometimes they reach out to us themselves, as David Attenborough did recently. And then they can promote the videos on their own social channels which reach more people than we do — for example, if they have 20 million followers and we have 750,000."

Environmental groups focused on their own domestic markets are also taking this approach. One Germany-based organization that uses celebrities in campaigns is the German Zero NGO. Set up in 2019, it advocates for a climate-neutral Germany by 2035.

German Zero produced a video in March 2020 introducing the campaign with "66 celebrities" that supported the campaign, among them Deutschland 83 actor Jonas Nay and former professional footballer Andre Schürrle. They solicit support as well as financial contributions from viewers.

"Count me in," they say, pointing toward the camera. "You too?"

"We are incredibly grateful for the VIPs in our videos," says German Zero spokeswoman Eva-Maria McCormack.

Assessing Success Is Complex

But quantifying the effectiveness of celebrity endorsement of campaigns is not a straightforward process.

"In order to measure effectiveness, first of all you need to define what is meant by success," says Alegria Olmedo, a researcher at the Zoology Department at the University of Oxford.

Olmedo is the author of a study looking at a range of campaigns concerning pangolin consumption, fronted by local and Western celebrities, in Vietnam and China. But she says her biggest stumbling block was knowing how to measure a campaign's success.

"You need a clear theory of change," explains Olmedo. "Have the celebrities actually helped in achieving the campaign's goals? And how do you quantify these goals? Maybe it is increased donations or higher engagement with a cause."

A popular campaign in China in recent years saw famous chefs Zhao Danian and Shu Yi pledge to abstain from cooking endangered wildlife. While the pledge achieved widespread recognition, both Olmedo and Marchildon say it's difficult to know whether it made any difference to people's actions.

"In life we see a thousand messages every day, and it is very hard to pinpoint whether one campaign has actually made a difference in people's behavior," she explains.

Awareness Is Not Enough

Many campaigns that feature celebrities focus on raising awareness rather than on concrete action — which, for researcher Olmedo, raises a further problem in identifying effectiveness.

"Reach should never be a success outcome," she says. "Many campaigns say they reached a certain number of people on social media. But there has been a lot of research that shows that simply giving people information does not mean they are actually going to remember it or act upon it."

But anecdotal evidence from campaigns may suggest reach can make an active difference.

"Our VIP video is by far the most watched on our social media channels," McCormack from German Zero says. "People respond to it very directly. A lot of volunteers of all ages heard about us through that video."

However, some marketing studies have shown that celebrity endorsement of a cause or product can distract from the issue itself, as people only remember the person, not the content of what they were saying.

Choosing the Right Celebrity

Celebrity choice is also very important. Campaigns that use famous faces are often aiming to appeal to members of the public who do not necessarily follow green issues.

For certain campaigns with clear target audiences, choosing a climate scientist or well-known environmentalist rather than a celebrity could be more appealing — Attenborough is a classic example. For others, images and videos involving cute animals may be more likely to get a message heard than attaching a famous face.

"We choose celebrities who have a lifestyle where they are already talking about these issues," says Marchildon from the UN. "You need figures with credibility."

McCormack cites the example of Katharine Hayhoe, an environmental scientist who is also an evangelical Christian. In the southern United States, Hayhoe has become a celebrity in her own right, appealing to an audience that might not normally be interested in the messages of climate scientists.

But as soon as you get a celebrity involved, campaigns also put themselves at risk of the whims of that celebrity. Prince William and younger members of the royal family have come under fire in recent years for alleged hypocrisy for their backing of environmental campaigns while simultaneously using private jets to fly around the world.

But Does It Really Work?

While environmental campaigns hope that endorsement from well-known figures can boost a campaign, there is little research to back this up.

"The biggest finding [from my study] was that we were unable to produce any evidence that shows that celebrity endorsement of environmental causes makes any difference," says Olmedo.

This will come as a blow to many campaigns that have invested time and effort into relationships with celebrity ambassadors. But for many, the personal message that many celebrities offer in videos like that produced by German Zero and campaigns like the Earthshot Prize are what counts.

The research may not prove this conclusively — but if the public believes a person they respect deeply personally cares about an important issue, they are perhaps more likely to care too.

"I personally believe in the power this can have," says Marchildon. "And if having a celebrity involved can get a single 16-year-old future leader thinking about environmentalist issues — that is enough."

Reposted with permission from DW.

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