The stranglers that save lives when cyclones strike


They are demonised as brutal killers but, as two studies published this month show, strangler figs can be lifesavers — of both plants and people.

According to research in the Australian Journal of Management, they contributed to the low death toll of Cyclone Pam, which hit the Pacific island nation of Vanuatu in 2015. When the cyclone destroyed homes there, people survived by taking shelter among the aerial roots of giant strangler figs.

This is more than just an anecdote. People in Vanuatu have been using giant fig trees to escape from cyclones for thousands of years, say Lachlan Forsyth and Rebecca Olul of UNICEF.

“For as long as people have lived on these islands, the trees have been a traditional cyclone shelter,” they write in an article published this week. “During cyclones, entire villages would wriggle down into the tree’s extensive root system, tucking children into the cavities, and waiting out the storm. Even if the tree were uprooted, the entire root structure would come up, leaving those within safely cocooned and protected from flying debris.”

These refuges exist because strangler figs start out in life as seeds that germinate high on other trees. They then send down roots that merge and split and merge again, thickening into a mesh that envelopes the host tree and — in time — erases all trace of it.

While most strangler figs grow on a single host tree, some — known collectively as banyans — are much bigger specimens. Their branches produce aerial roots that thicken into stout pillars that resemble tree trunks and enable the banyan to continue to expand as it ages.

The mass of roots that descends from a banyan’s body and branches creates a matrix of hollows and thick woody walls. In Vanuatu, these chambers have saved people from cyclones for generations.

Strangulation might sound like a brutal fate for the host tree, but before a strangler fig overcomes its host it can also protect it, say biologists Leora Richard and Sylvia Halkin in the new issue of Symbiosis. When they studied the aftermath of Cyclone Oswald, which hit Lamington National Park in Australia in 2013, they found that large trees were less likely to be uprooted if they hosted strangler figs.

By building a scaffold around their host and by anchoring their aerial roots in both the ground and around other trees, the strangler figs appear to protect the trees on which they grow.

So the stranglers can not only protect people directly, as living shelters, but can also help ensure fewer trees fall when a cyclone strikes. Elsewhere fig trees protect people from drought and from extreme rainfall. They sustain more wildlife than any other trees and can accelerate rainforest regeneration.

Collectively, they have much to offer as we come to terms with our fast changing climate.


Handmer, J. & Iveson, H. 2017. Cyclone Pam in Vanuatu: learning from the low death toll. Australian Journal of Management 32

Richard, L.S. & Halkin, S.L. 2017. Strangler figs may support their host trees during severe storms. Symbiosis 72: 153–157.

Forsyth, L. & Olul, R. 2017. Unicef NZ: Climate change and preparing for the coming storm. (28 June 2017).

Photo credits:

Children play among the roots of a giant strangler fig in Vanuatu (UNICEF New Zealand)


Can living fig-tree bridges save lives in a changing climate?

By AditiVerma2193 (Own work) [CC BY-SA 4.0 (], via Wikimedia Commons

In 1841, a young Scotsman called Henry Yule was exploring the Khasi Hills of north-east India when he came upon something no other European had ever reported. There, in that challenging landscape of thick rainforest and perilous gorges, was a most extraordinary structure — a living bridge formed from the roots of a gnarly old fig tree.

The tree’s roots had somehow reached more than 20 metres across a river and taken hold on the far side. Over time, they had thickened and interwoven to form a walkway, onto which Yule now had to step. One of the roots, which in places was thicker than his thigh, provided a handrail. Side roots had descended from it and merged into the walkway, making the whole structure strong and secure. Yule could cross with confidence.

The bridge was no miracle. Long before, human hands had guided the tree’s roots across the river, training them into a shape that could promise safe passage. Yule had assumed the bridge to be “unique, perhaps half accidental”, but he soon saw several more. Their architects were local Khasi people, whose attitudes towards time, the environment and their unborn descendants we are sorely lacking in our fast-warming world.

Fig tree bridge. Credit: Laurence Mitchell (

The Khasi Hills are in Meghalaya, an Indian state whose name means ‘land of the clouds’. The clouds cry often on this land, for nowhere else on Earth must people endure such heavy rainfall. Twelve metres of it falls in a typical year. After monsoon rains, the region’s rivers rise. The rush of water racing downstream renders steep gorges impassable, isolating villages and endangering lives. Yet people have lived in the Khasi Hills for at least 3200 years. For generations, they have overcome this extreme environment by harnessing the strong yet pliant roots of Ficus elastica, a fig species best known as the Indian rubber tree.

Fig roots are exceptional. They grow fast, long and strong. They can even rip apart bare lava and concrete. In many fig species, including Ficus elastica, the roots aren’t all underground. These figs produce aerial roots that flow down their trunks and drop from their branches. Their roots can merge and split and merge again, forming strong, mesh-like structures. Long ago, the Khasi people worked out how to get such fig roots to do their bidding.

It’s a practice still alive today. The Khasi and neighbouring Jaintia peoples have shaped fig roots into living ladders, whose rungs ease journeys up steep slopes. They have woven the roots into nets that hold banks of earth in place, preventing landslides and soil erosion. They have even forced fig roots to form a platform, from which to watch football games. But the masterworks of Khasi architecture are their bridges. Most — like one Yule sketched, below — form from the roots of two fig trees, one on either side of a river. The longest spans more than 50 metres, the oldest an estimated 500 years.


Building these bridges involves first guiding slender fig roots through hollow trunks of betel palms, which support, nourish and protect the roots as they lengthen. Once the fig roots are long and strong, the bridge builders bind them to those of the opposing tree or embed them in the ground on the far side of the river. They shape secondary roots that grow from these mainstays into a net that will form a walkway. They use stones and soil to plug any gaps then wait for the roots to thicken and hold everything in place.

It can take 15-30 years before the bridge is strong enough to use. But in Khasi time this is an eye-blink. The Khasi people are investors in the future. People living there today benefit from the ingenuity and foresight of their ancestors and today’s bridge builders bequeath security to future generations. The fig tree bridges don’t only make commerce and romance possible between otherwise isolated villages. They also save lives. As the climate changes, this ancient approach to bioengineering has never been more relevant.

Meghalaya was already the wettest place in the world when Henry Yule explored its forested hills in 1841. Back then, the atmospheric concentration of carbon dioxide was 283 parts per million. Today it is more than 400. More carbon means warmer air, and as warmer air carries more moisture, this means more rain. The state government’s climate change action plan says rainfall has increased in most districts of Meghalaya in the past century, with the highest increase in the West Khasi Hills. It warns that as temperatures continue to rise, so will rainfall and the risk of floods and landslides.

To architect Sanjeev Shankar, these threats call for renewed attention to living bridges. In a research paper he presented in 2015, he warned that they are being replaced by “inappropriate solutions”. Quick-fix bamboo bridges buckle and break – they can’t withstand the monsoon rains. People have died as a result. Modern steel bridges corrode, their cables weaken and snap. And because repairs are rare, these bridges last just 40-50 years compared to hundreds for living bridges.

Shankar says the living fig bridges cost next to nothing and become stronger, more robust and resilient with time and use – unlike expensive, short-lived steel suspension bridges. Indeed, some of the bridges Henry Yule saw in the 1840s are still saving lives today. Shankar urges a revival of fig-tree bridge-building, and even foresees bridge that are strong enough for vehicles to cross.

The only downside is the time it takes the bridges to grow. But Shankar sees potential to blend the old with the new. Having seen how Khasi people have used fig roots to mend steel bridges, he envisages planned hybrid structures — steel bridges that fig trees envelop with their roots and make stronger. Shankar wonders if other fig species could perform this role in other countries, helping people adapt to the changing climate.

The question is, will there be time? It’s a question for us all, as climate change doesn’t respect the short-term thinking that tends to rule our lives. The Khasi people’s approach is instructive. To build living bridges, they invest time and effort knowing they might not personally benefit but that their children surely will. Such foresight, patience and selflessness is rare.

This post was first published by the Thomson Reuters Foundation and is reproduced here with permission.

IMAGE CREDITS: Top (Aditi Verma, via Wikimedia Commons); middle (Laurence Mitchell); bottom (Henry Yule, from Yule, H. (1844). “Notes on the Khasia Hills, and people”. Journal of the Asiatic Society of Bengal. 14 Part 2, Jul-Dec (152): 612–631).

My new book —published in the UK as Ladders to Heaven and in North America as Gods, Wasps and Stranglers tells how fig trees have shaped our world, influenced diverse cultures and can help us restore life to degraded rainforests.


Frying eggs, flying foxes, dying wasps, crying shame

Crack an egg in a pan, turn up the heat and you can witness a kind of magic. In just seconds the viscous egg solidifies. Despite the rising heat, it’s the opposite of melting that occurs. I was a teenager when I heard a biology teacher explain this paradox: “The egg is full of proteins and the heat has denatured them”. Denatured. The word was new to me. Twenty-five years later I find it is a fitting descriptor of more than just wayward proteins.

My teacher explained that every protein has a temperature at which it will function best. Too hot or too cold and the protein’s shape can buckle or break. It will no longer be able to bond with other chemicals. It will cease to work. I think about that fried egg often when I consider what rising temperatures could mean for the planet.

We know that when people die of heat stroke, part of the problem is that some of their proteins have denatured. Could our cells become our jailors?

The proteins inside us and every other living thing vary greatly. Some tolerate heat better than others. Others begin to destabilise at just a couple of degrees warmer than normal. It is not the average protein that poses a problem, but the weaker links, those most liable to destabilise in extreme heat. We don’t know yet which of them are also critically important – to our food crops for instance.

As the world warms, what will happen to the millions of different proteins in the millions of different species, from spores to sperm whales, soil bacteria to sunflowers? These invisible structures are central to life itself. They give shape not only to hair and to horn but also to hormones and enzymes and DNA. They are the messengers and mechanics that control and correct processes in and between cells. Like the gaps in music that make the beats thrilling, these in-between places are where wonder is born.

It’s the same between species. Life is not a zoo of caged individuals living in isolation but a web of shared destiny. And while activists go on about polar bears or other creatures in danger, I am more curious about what climate change could mean for the way species interact and provide us gifts as a result. It’s been on my mind since the early years of my career when I lived in a rainforest in Borneo and studied the most fascinating of plants, the strangler figs.

Every one of the 750 or more species of fig trees depends for survival on its own species of tiny wasps to pollinate its flowers. The wasps in turn depend on the figs, the only places in which they can lay their eggs. This mutual reliance combines with the wasps’ short lifespans to ensure figs are available year-round, and because of this they sustain more species of birds and mammals than other plants. In return for the fig flesh those creatures disperse the trees’ seeds, and provide the same service to thousands of other rainforest plants. These interactions between fig trees and animals help to sustain the great rainforests of the world.

What does this have to do with climate change? Researchers have shown that just a small increase above current temperature levels will shorten a fig wasp’s life to just a couple of hours – not enough time to find a fig, pollinate its flowers and lay eggs. No pollination would mean no ripe figs for animals to eat, and this would mean fewer seeds get spread from place to place. Tree species that form a key part of the forest and its capability as an ensemble to lock away carbon are likely to suffer.

The tiny wasps are frail but some of the fig trees’ bigger partners are at risk too. They include fruit bats called flying foxes that can carry seeds 50 kilometres or more before pooping them out, making them some of the most effective seed dispersers around. Their vulnerability became clear early in 2014 when thousands of them fell dead from the sky during a blistering heat wave in Queensland, Australia. For both the bats and the fig wasps, the heat was too much. It will have interfered, at a cellular level, with proteins that cooked and then closed for business. These snapshots suggest trouble in store for the fig trees and the forests, whose fates entwine with our own.

Ecology teaches us that no species is an island. It’s a lesson our leaders seem to have skipped. It shows us we’re all in this together, the fig wasp and the fruit bat, the you and the me. That’s what makes the human fingerprints all over climate change all the more ironic. As we develop societies ever more distant from nature to protect ourselves from its wild whims, we risk unleashing upon these denatured societies powers we cannot hope to control or even predict.

This post reproduces my contribution to Culture and Climate Change: Narratives, which launched on 24 June at the Free Word Centre. The whole book is available for free and anyone can reproduces its articles under a Creative Commons Licence.

It will take hundreds of Al Gores or millions of ‘little people’ to overcome the political inertia on climate change

Journalist Darren Samuelsohn has quoted me in a question he put to the former Vice-President of the United States, Al Gore in a rare two-hour interview for Politico magazine.

Politico Magazine: During the “24-hour project” [a Gore-led October 2013 effort to raise awareness about climate change], there were a lot of critics who said it didn’t get the right message out, that you weren’t the best messenger, either. There was one response in particular that summed it up that came from Mike Shanahan, from the International Institute for the Environment and Development: “Climate change needs a Gandhi or a Martin Luther King or a Mandela and Al Gore is none of those.” What do you say when critics note that Al Gore as a person polarizes half the country; you need someone different to lead the cause?

Al Gore: It’s not about me. And I’ve never tried to make it about me. And far be it from me to disagree with someone who says I’m not Gandhi or Martin Luther King Jr. or Nelson Mandela. I have to plead guilty to that charge. I wish that I had the greatness of those three men.

But I’m enough of a student of history to know that Martin Luther King Jr., to pick one example, was considered extremely polarizing and was by many hated and despised. And in the South it was not uncommon to hear people trying to appear reasonable on civil rights but nevertheless digging their heels in, who’d say, “Well, if King would just get out of the way this would just happen.” I think that whoever puts his head up above the trenches and says, “We’ve got to do this” is going to attract the ire of people who don’t want to do it. And there are plenty of them.

Samuelsohn had reached out to me because I had written a post here about Gore back in 2011. Ahead of his interview with Gore, Samuelsohn wanted to know if my views had changed. For the record, here’s the full text of my response to Samuelsohn.

History should judge Gore well, as someone who staked much upon his belief that climate change was an issue to tackle and who worked hard in public and private to convince people that this is a battle we can all fight together.

Too few people with his power and political connections have been so bold. That said, Gore lacks some credibility as a climate-change messenger as his interest in the subject has seemed to come and go. Nor should this task fall upon one man’s shoulders, even if they are as big as his. It will take hundreds of Gores or millions of ‘little people’ to overcome the political inertia on climate change.

Where Gore can have the most impact is not in other countries but at home, by working to show that action on climate change is a bipartisan issue that all Americans can get behind. It needs to be less about Gore the personality and more about Americans doing the right thing.

You can read Darren Samuelsohn’s full interview with Al Gore here. It is an enlightening read and it ends with Gore in an upbeat mood.

Al Gore: It’s clearly wrong to do what we’re doing. It’s clearly right to change. We will change. It’s just a matter of time. And again, how long? Not long.

Climate change: Teens teach where others don’t reach

A 13-year-old girl interviewed me last week about my job, through which I communicate with journalists around the world about climate change and other environmental issues. She is part of the generation that worries about such things, according to a new poll. It’s the generation from which real leadership on climate change will emerge.

The UNICEF poll – published on 17 April 2013 — found that three-quarters of British 11 to 16-year-olds were concerned about how global warming will change the world. Two-thirds of them also worried about how climate change would affect other children in other parts of the world.

The poll said these concerned children want their government to act on climate change, but they may need to do that themselves. They will need to be teachers too. This is because the British government had decided to remove climate change from the national curriculum for children under 14. It’s a move that scientists, business leaders and others have criticised as “unfathomable and unacceptable”.

It is more than this. Under the UN Framework Convention on Climate Change — which was agreed in 1992 and entered into force in 1994 — nearly 200 governments agreed to promote actions to develop and implement “educational and public awareness programmes on climate change and its effects”.

Their track record so far has been pitiful. By 2010, only Belgium (on behalf of the European Union), Colombia and the Dominican Republic had submitted reports on their activities. When I wrote about this on Under the Banyan in 2011, most of the readers from around the world who commented said their governments did little or nothing to educate their population on climate change.

More recently, some countries have begun to act. Last year, the government of El Salvador made it mandatory for all educational institutions to incorporate climate risks into their teaching materials. In March this year, the Dominican Republic launched a national teacher training programme on climate change. In the United States, new science teaching standards will include extensive lessons on human-made climate change. Suddenly it looks like British children are being left behind.

Kenya’s new national climate change action plan – unveiled in March 2013 — called for climate change and its impacts to be on the primary school curriculum. It says students at secondary schools also need “to be equipped with skills to support a future climate resilient economy” and that “at university level, climate change should be infused into the various professions.” It says:

 “Civil engineers, for example, need to learn how to design and develop structures that can withstand climate shocks. Doctors need to be aware of the effects of climate change on human health, while architects should have the skills and training to design houses that are climate-proofed and energy efficient. Teachers ought to be equipped with knowledge about climate change in order for them to be suited to teach a curriculum that integrates climate change across all subjects taught at schools in Kenya. Whereas it is already the case that climate change as a subject is now being taught at Kenyan universities, there will be a need for institutions of higher learning to develop policies to ensure that all students educated there are familiar with climate change, its impact and strategies for adaptation and mitigation.”

These are all initiatives to applaud. But given that governments took nearly 20 years to act upon pledges to educate their people on climate change, it seems clear that the people will also need to teach themselves.

While parents have a role to play in climate change education, they find it hard to be truthful about climate change without scaring their children. The Yale Forum on Climate Change and the Media published a long essay on this topic. But where governments fail and parents feel unsure, young people can talk with confidence to their peers.

They include Esther Agbarakwe, the 19-year old Nigerian who each Wednesday uses Twitter to coordinate a live conversation between climate experts and anyone worldwide who is interested (see #climatewednesday). Or 18-year old Merna Ghaly from Egypt, a leading member of the Arab Youth Climate Movement. This month Newsweek Magazine, in the United States, named her one of the top ‘125 Women of Impact’, alongside heads of state and business leaders. Or Esha Marwaha, the 15-year old student and member of the UK Youth Climate Coalition who organised a campaign that called on the UK Department for Education to reinstate climate change into the school curriculum.

These three young women are just some of the members of new band of passionate communicators who are not waiting for teachers or parents or politicians to lead the way. They are growing in number and are increasingly connected. They cooperate internationally in ways that nations will need to if they are to tackle climate change. They are the future and they are here today. More power to them.

This post is based on the 27 April editorial I wrote for The Thumb Print magazine (India).

A changing climate demands change in narratives

Last year I wrote — here and here — about my study of how media portrayals of pastoralists in China, India and Kenya can contribute to policy narratives that limit people’s resilience to climatic variability. IIED has now published my research and a short briefing paper that presents the main findings and recommendations.

Here is a summary of the research paper, which you can download here [PDF].

Resilient food systems depend on appropriate policies that enable people to take advantage of their own adaptive capacity. Pastoralists use their mobility to take advantage of resources – pasture and water – that are patchily distributed in space and time. Pastoralism can make major contributions to food security, livelihoods and economic prosperity. However, these benefits often go unacknowledged – by policy makers, donors and the public at large. This is in part because of development and media narratives that paint pastoralism as something bad that needs to change. This paper explores how the media portrays pastoralism. To do so, we analysed the content of newspaper articles about pastoralists in Kenya, China and India, and also invited journalists in these countries to complete an online survey and telephone interview. We identified significant gaps – and inter-country differences – in the media’s portrayal of pastoralists.

And here is a summary of the briefing paper, which you can download here [PDF].

Mobile pastoralism contributes substantially to food security, livelihoods and economic prosperity, and can increase resilience to climate change; but policymakers, donors and the public at large tend not to appreciate its benefits. Policy narratives portray pastoralism as an outdated practice, and the media stories that help shape policy processes and public opinion often contribute to these false portrayals. An IIED study analysed the content of stories from media outlets in Kenya, China and India, and surveyed journalists in each country. It identified significant knowledge gaps and inter-country differences in how journalists perceive and portray pastoralists and pastoralism. The analysis also found that media outlets in these countries under-report climate change, the economic value of pastoralism and the links between pastoralist mobility and resilience. Journalists, researchers and pastoralist communities need to work together to improve media coverage of pastoralism, and by doing so highlight pastoralism’s potential contribution to sustainable development in a changing climate.

If we cook these tiny wasps, we put the heat on hundreds of other species


From the wings of tiny creatures hang the fates of hundreds of bird and mammal species, and perhaps even entire rainforests. They are fig wasps and they play a disproportionate role in the grand drama of life on Earth. They shape our own story too because of this. But new research warns that these insects could be “extremely vulnerable” to global warming.

This matters because each of the 750+ species of fig tree (Ficus species) relies utterly on particular species of fig wasp to pollinate its flowers. Without the fig wasps there would be no fig seeds to create the next generation of trees, and there would be no ripe figs for animals to eat.

In the case of any other group of trees this would not be such a big deal, but figs are special. Their pollinator wasps only live for about a day and each wasp species can only lay its eggs inside the flowers of its specific fig partner. So, to keep their pollinator species alive, each fig species needs to produce flowers and figs year-round. This means a year-round supply of food for birds and mammals, and helps to explain why figs feed more creatures than any other trees do (see A job for conservation’s keystone cops).

In the late 1990s, I set out to find out just how many animal species eat figs. The answer is an astounding 1,200-plus species, including ten per cent of all birds and six per cent of all mammals – see Who eats figs? Everybody). That’s the variety of life that stands to suffer in some way if fig-wasps disappear. Now, in a new study in the journal Biology Letters, Nanthinee Jevanandam of the National University of Singapore and colleagues provide a chilling insight into what a warmer world could mean for these wasps.

In a laboratory, they exposed the pollinators of four Ficus species to temperatures between 25°C and 38°C and to a various levels of humidity. The lifespan of all four species fell steadily as the temperature rose. By 36°C, the lifespan of three of the species had fallen to just two hours. In the wild this would give the wasps hardly any time to find a fig of the right species in which to pollinate and lay its eggs. It would hurt both wasp and fig species. This is the Achilles heel of a partnership that has existed for 80 million years. It is here that we might expect to see the relationship break down, with consequences for other species.

This has happened before. In the 1990s, fig-wasps in northern Borneo went locally extinct after a severe drought, and in Florida they disappeared when a hurricane wiped them out. In both cases, fig-wasp populations eventually bounced back — thanks to the fact they can disperse for tens of kilometres in the day or two they live. But a sustained temperature increase — like that which climate scientists predict will be a reality worldwide by the end of the century — is a different matter. As we turn up the global temperature we change the chemistry of life.

I asked Nanthinee whether she thought fig-wasps could adapt to a rise in temperature, either in their physiology or their behaviour — by flying at a cooler time of day for instance. “Fig wasps can produce up to 12 generations in a year in the aseasonal tropics, and so acclimation or genetic adaption is a possibility,” she said. “But more research has to be carried out to ascertain this. As to the possibility flying at different times, it is difficult to predict.”

The wasp species she and her colleagues studied came from distinct branches of the fig-wasp family tree, so they think their results will be relevant to hundreds of other fig-wasp species, the trees they pollinate and the animals that eat their figs. But these little wasps might have surprises in store for us yet. After all, they survived the mass extinction that saw off the dinosaurs, 65 million years ago. They might outlive us too.

Their story is a reminder that we are just new here, and that between our kisses, our fights and our smiles, we tend to stumble about breaking things before we know how they work.

Photo credit:
Valisia malayana fig-wasps at a fig of their host tree Ficus grossularioides (Nanthinee Jevanandam)

Related posts:
The humbling history of the tiny wasps that upset a Jurassic Park narrative.

Jevanandam, N., Goh, A.G.R. & Corlett, R. 2013. Climate warming and the potential extinction of fig wasps, the obligate pollinators of figs. Biology Letters 9: X-X.  Published online March 20, 2013 doi: 10.1098/rsbl.2013.0041