The beginnings of canopy science

kw: book reviews, nonfiction, natural history, trees

In a post in May (Scientists that can write?) I reviewed a collection of essays and single chapters by a number of scientists who write well indeed. The Wild Trees: A Story of Passion and Daring by Richard Preston was one such chapter extract. The chapter was a fair sample of the book's excellence of writing and storytelling.

Steve Sillett's first ascent of a redwood was far from auspicious. He really ought to have died. He and a friend jumped from the top of a 70-footer to grab a small branch on the trunk of a 300-footer. Such "epicormic" branches are usually weakly attached. This one was strong enough to hold the two of them, though it also harbored a wasp nest. They free-climbed the rough bark cliff to a stronger branch and ascended to the tree's crown. Preston doesn't mention how they got back down, but I assume they managed to jump back to the smaller tree, garnering a few more stings along the way. The things 19-year-olds do! His life exemplifies the cynical definition of "expert": someone who has gotten away with really risky stuff more often than you have.

From such a beginning, Sillett grew to become a major figure in canopy research in the tallest forests. Ironically, after learning arborist rope techniques, and experimenting to adapt them to trees reaching nearly 400 feet, he is very finicky about safety with his colleagues, including Preston, who caught the tall tree bug after an interview with Sillett, went to an arborist school in Atlanta, and practically forced himself upon the scientist.

Though (now Dr.) Sillett is the central (human) figure of the book, the author includes brief developmental biographies of a number of prominent tall tree researchers, some that have used cranes and dirigibles, and others who also use ropework.

But the real heroes are the trees. The tallest redwoods (Sequoia sempervirens) are probably the tallest trees on earth today. The tallest currently known is 379 feet (115.5 m) tall. But some "mountain ash" (Eucalyptus regnans) in Australia are nearly as tall, and there were reports in the early 20^th Century of Douglas-fir (Pseudotsuga menziesii) trees that measured 400 feet (122 m) after felling...though exaggeration is likely. All these species grow in temperate rain forests, and are more than twice as tall as all but a very few tropical trees.

Whatever the species, the crown of a tall tree begins at about half the tree's total height. Few branches, if any, are found on the first hundred to 150 feet of a 300-foot tree. Just getting a drawline over the first substantial branch of such a tree requires a good eye with a crossbow, and several to many attempts. The crown itself is a maze of branches, vertical shoots off the branches that are often the size of "ordinary" trees, and a fractal structure that makes the crown seem a forest all in itself. Indeed, Sillett's wife got lost in a crown once, tied herself to a branch, and radioed her husband for help. He was no more than fifty feet away, but took twenty minutes to find her.

Such a crown is an ecosystem, one that is now thought to contain more than half the total subaerial species on the planet. The catalog of species that are either endemic to tree crowns or rare elsewhere grows daily, including lichens, mosses, liverworts, many kinds of insects and mites, that all compete for space with more familiar species such as huckleberry and other epiphytes. Some large crowns host entire small forests of shorter tree species.

As one who had to send my kid up a 20-foot ladder to install a rope swing a few years ago, I must admire these folks from a distance...at least 300 feet! They are learning what such ecosystems have to offer, as such forests are becoming vanishingly rare.