Climbing Into an Unexplored Frontier

In his pioneering work atop the world's tallest trees, a determined scientist has uncovered an endangered ecosystem no one knew existed

08-01-2008 // David Lukas

BEFORE STEVE SILLETT came along with his boundless energy and technical tree-climbing skills, no one had figured out how to get up into the crown of a redwood, the world's tallest tree species. For decades, scientists considered redwood crowns to be little more than a bunch of needles and branches, and biologists who wanted to study forest canopies focused on tropical rain forests.

But Sillett had a secret. In 1987, while a college student, he accomplished the unimaginably dangerous feat of climbing more than 300 feet to the top of a redwood without ropes or safety gear, and got his first glimpse of something no one else knew existed: a canopy full of elaborate fern gardens and succulent huckleberry bushes. When he returned to the forest a decade later as an ecology-botany professor at California's Humboldt State University, he was eager to venture again into the treetops and uncover the secrets of this mysterious, unexplored frontier.

Unlike giant sequoias, which are shorter but broader and grow in the Sierra Nevada, redwoods are found only along a strip of foggy forest on the northern California coast. The first branches on a redwood trunk may be 250 feet off the ground and the true height of the tree usually is hidden by the dense crown. But over the past decade, experts have located 151 of the trees that are taller than 350 feet, with the record currently held by a living specimen known as Hyperion that is just over 379 feet tall.

These trees are among the last remnants of a vast forest that carpeted western North America 60 million years ago. When the mild tropical climate began a cooling and drying trend 24 million years ago, redwoods retreated to the wet California coast, showing a capacity to survive climate change that is only one of their many remarkable attributes. They are among the fastest growing trees in the world; a seedling can top 100 feet in a mere 50 years. And not only do genetic individuals seem to persist indefinitely by resprouting after fires and damage, they also have no fungal or insect enemies. Other than from humans, their greatest threats come from windstorms and landslides.

Even the wood itself seems to last forever and is nearly impermeable to decay, making redwood an extremely popular building material. As a result, by the 1980s, all redwood forests outside of protected parks had been logged at least once, in most cases twice. But when the Maxxam Corporation acquired Headwaters Forest in northern California--the last remaining tract of unprotected redwood old growth--and began cutting down the trees in the mid-1980s, such logging finally catapulted to national attention. Protests and tree-sitters kept the issue front-page news until a deal was reached with the state in 1999 to protect what was left of the Headwaters Forest.

Today, an estimated two million acres of redwood forest survives, including about 80,000 acres of old growth that have been protected in a patchwork of remnant stands surrounded by an ocean of commercial timberland. Surprisingly, the total acreage covered by redwood forest has changed little over time. But as Sillett notes, "The character of the forest changed dramatically when it was cut and today we only have two extremely different classes of trees: Those that are very old and those that are very young, with almost no trees in between."

Initially, in the mid-1990s, Sillett was not particularly concerned with these issues when he shot his first arrow and fishing line over a high redwood branch and started hauling up climbing ropes. He was more interested in learning the details of the dazzling treetop world he had discovered years before, and he picked as his starting point the newly discovered Atlas Grove in the state's Prairie Creek Redwoods State Park. "I climb hundreds of days a year now," says Sillett, returning again and again to map out the unbelievably complex canopy structure of these giants. One tree alone, he found, has 209 separate trunks, created in a process called "reiteration" and fused together in multiple places by cross branches.

In a 2007 report based on this research, Sillett describes how redwoods age and develop a high degree of individuality based on the reiteration of multiple trunks and fusion of old branches. This mix of breaks, crotches and broad limbs accruing over hundreds or thousands of years creates sites high off the ground where a profusion of ferns begin to grow, eventually creating extensive beds of soil as deep as six feet. One fern he measured weighed 660 pounds when dry and held 422 gallons of water when wet. In fact, there was so much water in these soils and fern mats that the climate of the canopy was far more humid and stable than researchers expected.

Sillett and his colleagues also were surprised by the astounding number of species that lived in the canopy, including 85 species of mites and many other varieties of invertebrates, as well as the only canopy-dwelling salamander ever discovered outside of the Tropics. Overall, wildlife in these ancient trees is nine times more abundant than in a control group of commercially mature redwoods because there are so many niches and prey available in their giant crowns.

In uncovering the secrets of this wondrous treetop world, Sillett also has discovered how little of these canopy habitats remain. The rich beds of soil and invertebrates are not even found on so-called "mature" redwoods; they reside solely on the biggest and oldest trees that survive in small pockets within a handful of national and state parks. They represent a "web of life" that beats only in the heart of absolutely pristine ancient redwood forest, and their future may be in jeopardy. Even a park boundary doesn't protect these canopy habitats when the forest is reduced to a narrow ribbon, as is the case in many stands, and the edges of the forest begin to dry up.

Sillett laments that we are "standing on a knife edge right now because a lot of redwood forests have been protected but no one knows how to restore them." By studying these remnant stands, the scientist hopes to generate momentum for experimenting with techniques that could actively re-create structural complexity in younger stands of the trees. "We've got to get to work," he says, "before it's too late."

Californian David Lukas is a naturalist who lives near Yosemite National Park.

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