The nearly magical properties of fig trees

In Cherrapunji, India, locals mold the roots of the fig species Ficus elastica tree into living bridges. Credit: 2il.org Flickr (CC BY 2.0)

Living bridges made of fig tree roots in Cherrapunji, India

When the Indonesian island volcano Krakatoa erupted in 1883, the waves it sent forth crashed into Bantam, some 50 kilometers away in western Java, and flattened forest for a distance of more than 300 meters inland. All that remained standing, said French scientists who visited a year later, were tall fig trees, their bare branches reaching skyward.

Back on Krakatoa there was no trace of life. Much of the island had vaporized, and what was left was buried under a 60-meter deep blanket of ash. Yet before long, several species of fig trees grew there too. They had arrived as seeds defecated by wandering birds and bats. They soon produced figs that drew in more flying animals, which in time carried the seeds of dozens of other tree species. And so, from black lava, a forest grew anew.

The physical strength, resilience and animal magnetism of fig trees are powers we can tap as we grapple with the Earth’s fast-changing climate. As my book Ladders to Heaven (US title: Gods, Wasps and Stranglers) shows, humanity has long benefited from these trees as sources of materials and medicines, food, shade and security. As the world warms, we may need them more than ever.

That’s certainly true in the Indian state of Meghalaya, the most rain-soaked inhabited place on Earth. The Khasi and Jaintia people who live in the forested hills there train the aerial roots of Ficus elastica fig trees into living nets that prevent landslides and living bridges that save lives when monsoon rains turn streams into raging torrents.

Some of these bridges are thought to be centuries old. By contrast, steel suspension bridges last just a few decades. Bangalore-based architect Sanjeev Shankar says fusing fig roots with steel bridges could create stronger, longer-lasting hybrid structures. He also thinks people in other countries could use the living roots of their own local Ficus species to create structures that build resilience to extreme weather.

But fig trees aren’t only valuable in wet places like Meghalaya. They are also helping people adapt to the growing threat of drought. Farmers in Ethiopia, for instance, are embracing a fig species called Ficus thonningii. These trees need no irrigation, yet their leaves provide vital moist fodder for livestock. They enrich the soil with leaves that fall and decay, and they improve the growth of crops planted in their shade instead of the blazing sun.

Research by Mulubrhan Balehegn and colleagues at Mekelle University shows that planting this species instead of the usual fodder crops can boost production by 500 percent, while reducing inputs of water by 95 percent. Goats that eat the fig tree’s leaves produce more and better quality meat than those given only commercial feed.

Over the past decade, Balehegn and his colleagues have encouraged 20,000 households to plant this tree. They hope farmers will follow suit in the 33 other African countries where Ficus thonningii grows, and urge people to take similar approaches with fig trees in arid areas of India and China.

Crucially, planting fig trees doesn’t just improve livelihoods and help people adapt to the changing climate. By storing carbon, the trees can also play a part in slowing the rate of warming. All trees store carbon as they grow, but—as on Krakatoa—fig trees also encourage the growth of other tree species because their figs attract a diverse range of seed dispersers. In Costa Rica, Thailand and South Africa, researchers are harnessing this power by planting fig trees to accelerate reforestation on logged and mine-scarred land.

Elsewhere, people have traditionally used the presence of Ficus species to divine water, helping them decide where to plant crops or dig wells. Others have planted, or left standing, large fig trees as natural umbrellas against the heat, or have stored dried figs to turn to in times of drought and famine.

In fact, fig trees were among the first plants people domesticated. They have been helping people survive in hot and arid lands for thousands of years. As the world warms, the edible fig (Ficus carica), now grown in at least 70 countries, will grow in importance.

Rising temperatures also pose challenges to fig trees and the tiny wasps they depend on to pollinate their flowers. But this relationship between the plants and their pollinators has endured for 80 million years longer than humans have walked the Earth. The fig trees survived the extinction event that saw off the giant dinosaurs, and lived through periods warmer than what we experience today.

By contrast we are new here. Our future is made insecure by the slow pace at which we are removing carbon from the atmosphere, and our limited capacity to adapt to the resulting climatic change. The good news is that fig trees can help us to do both.

This post was first published (here) by Scientific American.

Photo credit: 2il.org Flickr (CC BY 2.0)

Read more about fig trees in my book Ladders to Heaven (published in North America as Gods, Wasps and Stranglers). For a summary and reviews from Annie Proulx, Deborah Blum, Michael Pollan, Sy Montgomery, Simran Sethi, David George Haskell and others, visit this page.

Three-books-mind-blow

Scientists reveal yet another reason fig trees are titans of biodiversity

insectivores

Biologist David Mackay got a surprise when he began studying the birds visiting fig trees in his native Australia: While he expected to see plenty of species coming to eat the figs, he didn’t expect the insect eaters to outnumber them two-to-one.

Mackay already knew that figs feed more bird species than any other fruit. His research, published in June, would show that fig trees are disproportionately important for insect-eaters too. It adds to growing evidence that fig trees are titans of biodiversity with important roles to play in conservation.

What makes fig trees so crucial is their ancient relationship with tiny wasps. The trees depend on the wasps to pollinate their flowers, while the wasps can only breed and lay eggs inside their partner’s figs. Thanks to this partnership, figs are available year-round and have been called ‘keystone’ resources for fruit eaters. Mackay’s study is the first to show that fig-wasps emerging from figs before they ripen are also valuable year-round resources for a diverse variety of insect-eating birds.

Altogether, Mackay recorded 55 bird species visiting Ficus rubiginosa fig trees to feed on insects. They included ten species — such as the superb fairy-wren and the shining bronze-cuckoo —whose recent declines in numbers have concerned conservationists. Mackay and his colleagues say fig trees are “very likely” to be similarly important to insect-eating birds throughout tropical, subtropical, and temperate regions globally.

To support this view, Mackay points out that in just his study and two others in localised areas of India and Costa Rica, researchers have already identified more than a hundred insect-eating birds visiting fig trees. “The presence of avian insectivores in figs in these three continents strongly suggests their occurrence in figs is ubiquitous,” he says.

“I can hazard a wild guess that there are at least several hundred species of insectivorous birds that forage in fig trees worldwide,” Mackay told me. “This has important implications for the conservation of insectivores, many of which have suffered and continue to suffer declines in response to habitat loss and fragmentation.”

As Mackay points out, the number of fig-wasps emerging from figs on a single Ficus rubiginosa tree in just a few weeks could approach ten million. He adds that insect-eating bats would also relish fig-wasps, many of which fly at night. His study adds to a growing body of evidence that fig trees are centrepieces of vast food webs that include tens of thousands of species.

“I suspect fig trees could play an important role in conservation of declining insectivores as well as contributing to the conservation of other species in the wider communities they inhabit, including frugivores and the other plants that depend on them for seed dispersal,” Mackay said.

Increasingly, researchers and conservationists are turning to fig trees to boost rainforest regeneration by attracting seed-dispersers. Mackay said that using fig trees could also slow or even reverse declines of insect-eating birds: “If we don’t do these restoration projects with figs then we stand a chance of losing these birds altogether.”

This post was first published by Mongabay.com on 6 July 2018 and is reproduced here under a Creative Commons licence.

Read more about the ecological and cultural importance of fig trees in my book, published in the UK as Ladders to Heaven and in North America as Gods, Wasps and Stranglers.

Reference

Mackay, K.D., Gross, C.L. & Rossetto, M. 2018. Small populations of fig trees offer a keystone food resource and conservation benefits for declining insectivorous birds. Global Ecology and Conservation. Published online on 20 June 2018. https://doi.org/10.1016/j.gecco.2018.e00403

Photo credits

Left to right —  Superb fairy wren (Malurus cyaneus): Patrick_K59 / Wikimedia Commons; Eastern yellow robin (Eopsaltria australis): Graham Winterflood / Wikimedia Commons; Eastern spinebill (Acanthorhynchus tenuirostris): DavidFrancis34 / Wikimedia Commons