One of my favorite walkways in the world spans a beautiful fig in the village of Falealupo on the island of Savai’i, Samoa, formerly Western Samoa. My colleague the ethnobotanist Paul Cox invited me to visit this island in 1994 at a critical juncture in its history. The 16 tribal chiefs were at a crossroads. The Western Samoan government required villages to build cement schools because their former palm-thatch construction could not withstand the frequent monsoons. But the cost of a school was over $50,000, and Savai’i did not have a cash economy. Samoans are incredibly supportive of their children and wanted the best possible education for them, but their livelihood was based on harvesting fish from the sea and fruits from the jungle. An Asian logging company offered to harvest the island’s timber in exchange for enough funds to build a new school. The chiefs were uneasy because their entire existence over many generations relied on the forest, and even their ancestors were part of this ecosystem, returning to earth as flying foxes in the canopy.
I flew to Samoa with two construction engineers to discuss the notion of a walkway. I was honored to be included in a ceremony with all 16 tribal chiefs, where they sang, drank their sacred kava, and discussed the options of logging versus ecotourism with regard to the fate of their island trees. After more than five hours, they unanimously agreed to take out a loan and build this newfangled idea called a treetop walk. They had never heard of ecotourism before but decided to trust the concept our team had proposed: that visitors would pay to explore the island’s eighth continent. Today, a platform circles the island’s largest fig, connecting to a bridge that spans to the local school. Within two years, the debt for the new school was repaid by ecotourism, not logging. As a thank-you, the senior chief anointed me “Mati,” which means “fig,” and presented me with a sacred kava stick, now a favorite treasure. I have always admired and loved figs, but in this case, one emergent Samoan fig literally saved the trees of an entire island.
Theophrastus, an ancient Greek philosopher who studied plants (circa 300 B.C.), is credited as the founder of botany, and the first person to describe fig species. He focused on Ficus carica, an important edible fig, and was unaware that hundreds of others existed, each with its own life story. He did learn about one particularly important banyan (Ficus benghalensis) from the stories of one of his contemporaries, the conqueror Alexander the Great, who claimed that 10,000 soldiers sheltered under one fig, with all its pillar roots forming an enormous leafy umbrella. Much later, in the early 20th century, the English botanist E.J.H. Corner specialized in Ficus, and described hundreds of them. One of Corner’s unique legacies was training four monkeys to fetch fig fruits in the canopy, so he could describe new species without climbing himself. He affectionately called them his “botanical monkeys.” Within six months, they collected the fruits of 350 species, far more than a human climber could.
A member of the diverse mulberry family (Moraceae), the Latin genus Ficus includes approximately 800 species of deciduous or evergreen trees, some of which are cauliflorous (meaning they flower and fruit along their main trunk instead of at the ends of branches), plus a few shrubs and vines. An estimated 150 figs inhabit the New World (Americas), and over 600 species in the Old World tropics (India, Asia, and Australia). Most are edible and germinate in the conventional way, starting life as a seedling and growing upward. Any fig that begins life as an epiphyte is called a banyan, technically part of the subgenus Urostigma, and includes the well-known strangler figs. In my global exploits as a field botanist, I found that stranglers occupy the most extraordinary lifestyle of any trees on the planet, bar none! The name itself conjures up the antics of James Bond or some Sherlock Holmes murder mystery, but the actual life history of this species engenders shock and awe. During his exploration, Alfred Russel Wallace called stranglers “the most extraordinary trees of the forest.”
My first exposure to the incredible strangler figs came when I climbed them in Australia, most notably the iconic emergent Ficus watkinsiana, named for George Watkins, the former president of the Pharmaceutical Society of Queensland and plant collector. He was an Englishman who came to Queensland in the 1800s and trained as a pharmacist. He pursued natural history in his spare time and participated in numerous expeditions. In 1891, F.M. Bailey named a fig species after him. It was called Watkins’ fig, nipple fig (due to the fruit structure), or green-leaved Moreton Bay fig. Its fruits are rounded, purple-black, and have distinct “nipple” structures, although the word “fruit” is deceptive because figs are anatomically not really fruits but a cluster of hundreds of flowers enclosed in a smooth skin. Like other fig species, the trees have male and female flowers on one plant, known as monoecious, from the Greek word for “one house.” F. watkinsiana leaves are tough, waxy, and entire, although a few fig species have lobes. Another famous Australian banyan is the curtain fig outside Atherton, Queensland, which occupies close to an acre of ground with all its aerial roots, though it’s not nearly as vast as Alexander the Great’s historical tree.
Different from most tree seeds that germinate on the forest floor, which is relatively dark and inhospitable to a delicate seedling, stranglers start life at the top with plenty of sunlight. When a figbird ingests fig fruits, it defecates the seeds onto an upper branch. This unique beginning means stranglers literally start life as an epiphyte with adequate light, eventually sending down roots to absorb water and nutrients below. The limiting factor for a strangler seed tends to be moisture, so germination is most successful on rotting or decaying bits of branches. My fellow “arbornaut” (who explores tree canopies) Tim Laman of National Geographic studied the germination of one strangler fig (Ficus stupenda) in Asia. He placed its fruits in the canopy to determine ideal conditions for downward growth and found they grew best in moist, decaying branches or wet bark crevices. Tim also documented the many animals that disperse figs, including hornbills, gibbons, orangutans, and flying foxes.
Once a strangler is established in the crown, a latticework of downward-growing stems thickens with time and often surrounds the host, sometimes creating a hollow center if the host has soft wood and subsequently rots inside. In some cases, strong-wooded host species survive and live in tandem with the strangler, so both trees are intertwined as a massive duo. Although stranglers, or banyans, often constrict their host, they also sustain thousands of other creatures in the ecosystem. It seems astounding that other species have not evolved this adaptation to outcompete for light, space, and water by starting at the top. Seedlings that germinate on the forest floor must wait patiently, sometimes decades, for a treefall to create a light gap, plus have the good fortune of not being trampled, eaten, or buried during their precarious juvenile phase. Some figs eventually form buttresses, which are aboveground prop roots that stabilize their shallow-rooted shapes; they would otherwise be prone to fall during monsoons.
Mature Ficus (including banyans) produce thousands of fruits, an important food source in tropical food webs. Fertile figs, like the ones we eat, are distinct because of their unique fleshy, hollow receptacle with an inner surface laced with tiny flowers or fruitlets. All species have tiny male and female flowers that develop on the inside wall of a syconium, which eventually becomes a fruit. A tiny female wasp of the Agaonidae family enters a hole in the top of the syconium and passes through a tunnel lined with downward-facing scales that only allow one-way travel. The wasp finds two types of female flowers inside: stalked, short-styled flowers and long-styled flowers that are not stalked. While she pollinates the flowers, the wasp also lays her eggs and then dies. After a few weeks, her offspring hatch, and wingless males mate with winged females, then chew an exit tunnel that allows the females to fly to another fig and repeat the process. The females pick up pollen from recently matured male flowers as they exit. Some botanists originally thought all 800 species required a specific pollinator wasp, but more recent molecular analyses reveal that 119 fig species shared multiple pollinator wasp species. When a wasp dies inside the fig after pollination, enzymes (called ficain) break down the carcass; consequently, anyone who eats figs is also consuming wasp biomass. When scientists at the National University of Singapore experimentally exposed fig wasps to warmer temperatures, their lifespan significantly shortened. This suggests climate change could jeopardize Ficus pollination success, if wasps don’t have enough time to find their specific fruits. As always, it is difficult to extrapolate from the laboratory to the forest.
As with most complex interactions, additional players in the fig-wasp interactions are parasitic wasps, some of which also lay eggs inside figs, which prevents the beneficial pollinator wasps from entering. Even worse, some parasitic wasps inject their eggs through the fig’s surface without even boring a pathway inside, and their offspring feed on the pollinator wasp larvae. Hundreds of wasps function as pollinators, and each Ficus species is known to host up to 35 species of non-pollinating wasps, making their crowns a hotspot of biodiversity. In addition to wasps, over 1,200 recorded species of birds, insects, bats, and mammals, including humans, eat the fruits, making Ficus a true keystone species for the biodiversity of many tropical forests. In the Amazon, ornithologist John Terborgh wrote that if figs disappeared, the entire ecosystem could collapse. Biologist Dan Kissling correlated the number of fig species in sub-Saharan Africa with the abundance of fruit-eating bird species, and concluded figs were the keystone resource.
Figs have many uses for humans as well as for insects, birds, and animals. Their milky latex contains medicinal properties, and in the Amazon, villagers administer a teaspoon to cure stomach parasites in children. According to indigenous people in French Guiana, Colombia, and Brazil, the same sticky latex can cure cuts, fractures, and abscesses. In Nepal, Ficus benghalensis leaves, bark, and roots are used to treat more than 20 ailments; this useful banyan is also used in India to treat a wide variety of disorders ranging from tooth decay to hemorrhoids, diabetes, and constipation. At one time, figs were grown for rubber latex in India and parts of Africa. Probably the most famous fig is F. religiosa, or the Bo tree, native to India and Southeast Asia, thought to be the canopy under which Buddha received enlightenment. This is one of several species that in India and Asia dominates the center of many rural villages as an important spiritual gathering site.
Embarking on a new role as grandmother this decade, I have decided to use my Samoan nickname of Mati instead of Grandma; I will tell my grandchildren about all the wonderful figs I have encountered. Maybe someday I’ll whisk them off to the island of Savai’i in Samoa to see an incredibly special walkway in an emergent fig or to climb a few favorite stranglers in Australia.
Original article by Meg Lowman appears on Nautil.us. Excerpted from The Arbornaut: A Life Discovering the Eighth Continent in the Trees Above Us by Meg Lowman. Published by Farrar Straus and Giroux.
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