Skywalking for Science

When Stephen Sillett climbed his first giant redwood tree, back in 1987, he didn't know that a new world awaited him up there.

- Jeanne Miller

At that time the tops of the ancient trees in old-growth redwood forests were unexplored. Scientists assumed they were biological deserts, containing only tree branches. But when Sillett reached the crown of the 300-foot (91-meter) tree, he found a forest above a forest. At its top was a sunny glade alive with mosses, lichens, and even small trees. Growing from a rotting stump in the middle of the crown were huckleberry bushes, laden with berries. It was a thriving ecosystem in the air.

Sillett started climbing trees when he was a student at Reed College, in Portland, Oregon, in the 1980s. Those experiences led him to become a botanist, a scientist who studies plants. Today, he teaches botany and forestry at Humboldt State University in Northern California and spends much of his time at the top of tall trees. Coast redwood trees (Sequoia sempervirens) are his specialty.

An Aerial World