A silver station wagon loaded with climbing gear, computers, electrical wiring and a few scientists from Harvard University stops near a stand of pine and oak trees in the Harvard Forest, about 70 miles west of campus. Physiological ecologist Andrew Richardson, leader of this expedition, slips from the driver’s seat and grabs gear to ascend a metal tower among the trees. Its peak affords Richardson a clear view of his living laboratory: the forest canopy. Above the treetops, he checks a cl...