Tree climbers -- the people up among the leaves or ice-covered limbs wielding chain saws -- have three traits in common: They enjoy working outdoors, are game for a physical challenge and don't mind working at heights, said Ron Rubin, regional operating officer of the Care of Trees.

Workers in the trade include college graduates with forestry or horticulture degrees. At the Care of Trees, employees first learn how to operate knots and run equipment on the ground. As apprentices, they learn how to set lines and move around in trees. Level 1 climbers focus on pruning, Level 2 climbers remove trees, and Level 3 climbers are proficient enough to remove trees in tight spaces. Many climbers are accredited as arborists by the International Society of Arboriculture.

It is a physically demanding job, Rubin said. "You're working against gravity . . . using your upper-body strength to move around. I consider tree climbers to be industrial athletes," he said. Many also are rock climbers. Rubin's climbers train, stretch and warm up to avoid injury.

"The work itself is dangerous," Rubin said. "We want to do it at the safest and highest level of workmanship possible."

David Booth, who works out of the Dulles office of the Care of Trees, labors on a dead oak tree.