When the gray wolf was eradicated from Yellowstone National Park in the 1920s, more was lost than just the noble and fascinating predator. The park’s entire ecosystem changed. Now, nearly a dozen years since the wolves returned, the recovery of that system to its natural balance is well underway, say ecologists William Ripple and Robert Beschta of Oregon State University.

The researchers began studying the interaction of wolves with other parts of the ecosystem somewhat indirectly. “Back in 1997, I became aware that the aspen trees in Yellowstone were declining,” Ripple explains. “There was disagreement and confusion as to why these trees were disappearing, so I set out with graduate students to unravel this mystery.”

“We went out to the park and we cored the trees and studied the tree rings which show the annual growth, and we were able to age the trees that are still there,” Ripple says. The tree ring analysis indicated that the aspen, which usually regenerate themselves by sending off new shoots rather than by producing seeds, had stopped producing new trees during the first half of the 20th century.

Ripple and his colleagues looked at several possible variables that could be affecting the trees, from climate fluctuations to a changing natural forest fire regime. But the only factor that fit, Ripple says, was the browsing patterns of elk, which like to feed on the seedlings of aspen trees, and which are also a favored food of gray wolves: “The wolves were killed off from Yellowstone in the 1920s, which correlated with the start of the aspen decline. That led us to develop the hypothesis that the wolves were connected in some way to the aspen trees.” That connection, Ripple concluded, was mediated through elk: “We connected the dots: wolves affect elk; elk affect aspen; and therefore wolves affect aspen.”

Aspen grove (photo: NPS/J Schmidt; 1977)

Ripple and his colleagues subsequently discovered other changes. In some areas, willows — small, scrubby trees that grow in wet areas along stream beds — were starting to grow taller, because they were escaping predation by elk. In other areas, however, the willows continued to be heavily grazed upon. The same patchy changes were also seen with cottonwood trees, which also grow along streams.

“The more I looked at it the more I could see that what is going on may be an ecology of fear,” Ripple says. “The theory goes like this: the browser — in this case the elk — need to make behavioral decisions and tradeoffs as to how much time and energy to put into eating food versus how much time to be staying in safe places.” Those decisions affect where the animals concentrate their feeding efforts, and therefore the distribution of the vegetation they eat. “What we started noticing is that the plants were doing better where the terrain might favor the wolf a little bit more than the elk,” he says. For example, the elk might browse less in areas with poorer visibility (more dangerous to the elk because they can’t see if wolves are on the scene), or regions littered with heavy debris (a risk because it becomes an impediment to escape in the event of an attack).

Indeed, Ripple says, “we found that aspen were growing the tallest along streamside areas that had some downed woody debris or some downed logs nearby.”

Elk behavior and vegetation distribution aren’t the only factors impacted by the return of the Yellowstone’s wolves. Ripple suspects that the ripples of their recovery are reverberating throughout the entire ecosystem, in birds, fish, insects, as well as in other plants and animal species. Beavers, for example, are probably affected, he says. “The park service has been monitoring beaver since the wolves returned, and found that they have increased in numbers every year in the northern part of Yellowstone. Before the wolves returned, there really wasn’t much food for the beaver. But now with this growth of these plants — especially the willow — the beavers have more food, and they are also using the willows to build their lodges and their dams, which may be contributing to beaver population increases.”

“We are at the beginning of a grand ecological experiment,” Ripple says. “We were without wolves for seventy years, and we’ve just had them back in for 11 years, so we’re only just starting to see changes. It could take many decades for the ecosystem to recover.”

It may be one of nature’s oddest couples: a tiny wasp that can barely be seen, and a giant fig tree, the sycomore, which shelters a remarkable menagerie of wildlife among its limbs. The wasp and the fig depend on each other for survival. Without the wasp, the tree could not pollinate its flowers and produce seeds. Without the fig, the wasp would have nowhere to lay its eggs.

The Queen of Trees shows this delicate dance of survival in exquisite detail, including spectacular close-ups of the wasp’s remarkable life inside a ripening fig. To capture such incredible images, filmmakers Victoria Stone and Mark Deeble spent two years camped out near a giant sycomore fig in Kenya’s outback, documenting the tree’s pivotal role as a source of food and shelter for everything from gray hornbills, Africa’s largest bird, to swarms of invading insects searching for food. In a surprising turn, some insects come to the tree’s aid — sparking a battle you won’t want to miss.

Online content for The Queen of Trees was originally posted April 2006.

To order a copy of The Queen of Trees, please visit the NATURE Shop.

Figs come in all shapes and sizes. Some are trees, while others are bushes or vines. Most are found in the tropics, although a few can grow in temperate climates.

Perhaps the most familiar to most people is the common fig (Ficus carica). Native to Asia and the Middle East but widely replanted elsewhere, it produces those sweet, chewy fruits found in most grocery stores. Archaeologists say that the common fig may have been one of the first plants domesticated by humans. It even makes an appearance in the Bible, when Adam and Eve use fig leaves to cover themselves in the Garden of Eden. Later, sculptors and painters used strategically placed fig leaves to provide privacy to some of their figures, too.

Christianity isn’t the only religion to give figs a prominent role. An Asian species, Ficus religiosa, is considered sacred by Hindus, Jains, and Buddhists. The Buddha is said to have found enlightenment by sitting under the sacred fig, which is also known as the bo or pipal tree. Islam also considers some figs to be holy.

Another notable group of figs are the “strangler figs.” These tropical, vine-like trees start as tiny seeds that have fallen on the branches or roots of an existing tree of another species. The seeds begin to grow, and the young trees encase the host in a tangle of roots and trunks, ultimately strangling it to death. All that’s left are the thriving figs.

Like all other figs, strangler figs rely on a tiny wasp to survive. Worldwide, scientists have described more than 600 different kinds of fig wasps. Usually, each is linked to a specific species of fig, although some figs appear to have more than one pollinating wasp.

These tiny insects pollinate figs by crawling into a tiny hole in the base of a special flower, which ultimately becomes a round or oblong fruit. Female wasps often lay eggs inside the fruit, and the young fight their way out after hatching. They then fly off to find another flowering fig. Timing is everything, since the wasps don’t live long and the trees often flower unpredictably throughout the year. Often, figs that have been transplanted to new areas become sterile because there are no wasps to pollinate them.

Researchers say there are probably several thousand kinds of fig wasps — and perhaps hundreds of new kinds of figs — still to be found and described. But they worry that habitat destruction, particularly in tropical areas, threatens to erase some of these species even before they are discovered.

A killer is stalking the Big Sur coast. And if it isn’t stopped, it could forever remake the scenic landscape featured in NATURE’s Living Edens: Big Sur – California’s Wild Coast.

The killer is a mysterious fungus, and its victims are California’s beloved oak trees, the leafy, stout-stalked emblems of the Big Sur coast. Since researchers first discovered the fungus in 1995, they’ve been struggling to understand and control Sudden Oak Death — so far with little success. In the meantime, tens of thousands of oak trees have succumbed to the disease. And scientists worry that other kinds of trees, including the towering coast redwood, could be next.

Thousands of Big Sur’s oak trees have succumbed to a killer fungus. The killer’s path is easily found. In Pfeiffer Big Sur State Park, for instance, rangers have had to cut down hundreds of trees, piling the parched logs into heaps to be burned. Thousands more stand dead on nearby hillsides. Campsites once shaded by oaks are now speckled with stumps and blasted by sunlight. Similar landscapes can be found across hundreds of miles of California.

In a bid to stop its killing spree, disease detectives have been racing to profile the stalker. An early break came when researchers David Rizzo of the University of California, Davis, and Matteo Garbelotto of the University of California, Berkeley identified Sudden Oak Death as a previously unknown strain of fungi from the genus Phytophthora (Phy-TOFF-thoruh), which means plant killer in Latin. They also determined that the killer — called Phytophthora ramorum — comes from a dangerous family: one relative caused the Irish potato famine, and another is known to have killed cedar trees in northern California and southern Oregon, eucalyptus trees in Australia, and oaks in Mexico, Spain, and Portugal.

The killer’s origins, however, are unclear. It might have recently hitchhiked into California aboard a potted plant or nursery-raised tree. Researchers are suspicious because it matches a fungus found on rhododendron shrubs in Europe. But it also could be a native fungus gone bad, turned killer by climate or environmental changes.

Thousands of Big Sur’s oak trees have succumbed to a killer fungus.

For the time being, Sudden Oak Death has spared California’s redwoods. Whatever its past, researchers are more worried about Sudden Oak Death’s future. So far, the disease has hit hardest at several costal species of oaks — including tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), and California black oak (Quercus kelloggii). The wounds are easy to spot: the fungus enters through the trunk and then causes the formation of bleeding cankers. “We see a whole range of symptoms in the field, from nasty cankers on the trunks of oaks to minor spots on the leaves of the buckeye,” says Rizzo. But the weakest trees don’t last long.

So far, other species have been spared. But, overall, California is home to 16 of the 17 species known to be vulnerable to the disease. And those include two of California’s most highly prized trees — coast redwood and Douglas fir.

At the present time, there is little evidence the towering redwoods and firs are being harmed. But “we cannot say what the effects of the infection will be long-term,” says Garbelotto. “It seems that some species are able to tolerate the pathogen better than others,” adds Rizzo.

More study — and more time — will be needed to solve this ecological mystery. “It may take years before we can start answering questions about the ecological impacts of the disease,” says Rizzo. In the meantime, those admiring Big Sur’s signature oaks can only wait, and hope for the best.

Taking a walk through the Amazon rainforest? Might want to keep an eye out for what look and sound like cannonballs, crashing down from above at more than 50 miles an hour. If you are unlucky enough to be in the way, you could end up dead — or at least severely dazed!

The balls, which can weigh up to 5 pounds, aren’t really fired from a cannon. They are actually the fruit of the Brazil nut tree, one of the most marvelous and mysterious trees in the rainforest. Each ball-shaped fruit or pod holds up to two-dozen seeds we conventionally know as Brazil nuts.

For centuries, however, Brazil nut trees presented a puzzle to biologists. For one thing, they couldn’t figure out what kind of animal was able to break open the rock-hard fruits so that the nuts could sprout into new trees. For another, it wasn’t clear why only trees in undisturbed forests bear fruit.

As NATURE’s Deep Jungle: Monsters of the Forest shows, researchers have begun to solve the Brazil nut’s mysteries. In addition to learning more about the tree’s mysterious existence, viewers get a look at one of the Brazil nut’s archrivals — the incredible strangler fig, which can choke a huge Brazil nut tree to death within a few decades.

Brazil nut trees are among the giants of South America’s Amazon. They tower up to 200 feet high, and their spreading branches and flowers provide habitat and food for numerous forest creatures. The Brazil nut is also the foundation of a global business worth $50 million a year. Collectors harvest the nuts by gathering fallen pods and chopping them open with sharp tools. A single mature tree can produce more than 250 pounds of nuts a year.

But how do the nuts get free from their rock-solid pods in the wild? No Amazon creature, it seemed, had jaws powerful enough to crack open the cannonballs.

One answer, it turns out, is the agouti — a small mammal that looks a bit like a large guinea pig. Agoutis have small, chisel-like teeth that can penetrate the Brazil nut’s seed case. They eat some of the nuts. But, just as important, they carry away and bury others for future meals. If forgotten, these seeds can stay dormant in the soil for years, waiting for the perfect conditions to germinate and grow into a new Brazil nut tree.

The agouti isn’t the only animal that Brazil nut trees need to survive. It appears that they also rely on certain bees, and even other plants, to reproduce. Orchid bees visit flowering Brazil nut trees to collect nectar; as they buzz about feeding, the bees inadvertently carry pollen from tree to tree, fertilizing the flowers and helping the trees produce nuts. For the bees to survive, however, the males must attract mates, and to do that, the male bees need fragrance from a particular orchid to attract female bees. If the forest is damaged and the orchids disappear, so will the bees — and the Brazil nuts.

Forest disturbance isn’t the only threat to Brazil nut trees. Competition also comes from a sneaky plant known as the strangler fig tree. Strangler figs start out as tiny, almost invisible seeds deposited on a branch by small mammals or birds. The seed sprouts, and a tiny root gains a foothold. It’s the beginning of the end.

Eventually, the root creeps down the trunk to the forest floor, stealing water and nutrients from the tree through its bark as it goes. More roots soon join in, wrapping tight around the Brazil nut tree, encasing its victim. Ultimately, over decades, the tree dies, leaving the fig standing like a hollow monument to this epic struggle.

In the Amazon — the world’s largest rainforest — trees fight to the death for water and sunlight. Giant spiders as big as dinner plates take shelter in underground lairs. Buzzing bees and scurrying mammals help hold together an amazing web of life that centers on the Brazil nut tree. One of the world’s largest rivers carries floodwaters that turn forests into massive lakes.

NATURE’s Deep Jungle: Monsters of the Forest takes you into the depths of the Amazon, home to millions of marvelous species. Here you will be treated to a front-row seat while….

Bee expert David Roubik takes on a hive of bees in the Peruvian jungle in an effort to understand the bizarre relationship among the bees, a fragrant orchid flower, and the towering Brazil nut tree.

Tarantula expert Martin Nicholas searches for a spider so big and fierce it can reputedly attack a chicken.

A sneaky strangler fig tree takes on a 160-foot-tall Brazil nut tree — and wins.

It’s all part of the amazing web of life that is the Amazon.

To order a copy of Deep Jungle, please visit the NATURE Shop.

Online content for Deep Jungle was originally posted in April 2005.

Producer: Ronnie Godeanu
Writer: Karen de Seve
Art Director: Sabina Daley
Graphic Art: Karen Mattson
Technical Director: Brian Patrick Lee
Scientific Consultant: Gianna Scaralia

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©1998 Thirteen/WNET New York

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Television Credits

A Co-Production of Thirteen/WNET and Survival Anglia Ltd.

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Funding for the TV series NATURE is made possible in part by Park Foundation. Major corporate support is provided by Canon U.S.A., Inc., Ford Motor Company, and TIAA-CREF. Additional support is provided by the nation’s public television stations.