Trees at Walden Pond putting out leaves earlier with climate change

Trees at Walden Pond are leafing almost 18 days earlier than when Henry David Thoreau made observations at the Massachusetts lake in the 1850s, a study found. That could be a serious problem for native species, Boston University biologists conducting climate-change studies say, as some invasive shrubs are better suited to the warming conditions in Concord than native species. "By comparing historical observations with current experiments, we see that climate change is creating a whole new risk for the native plants in Concord," biology Professor Richard Primack said. "Weather in New England is unpredictable, and if plants leaf out early in warm years, they risk having their leaves damaged by a surprise frost," he said. "But if plants wait to leaf out until after all chance of frost is lost, they may lose their competitive advantage." The spring growing season is of increasing interest to biologists studying the effects of a warming climate, and in coming decades non-native invasive shrubs are positioned to win the gamble on warming temperature, Primack said. The researchers compared Thoreau's unpublished observations of leaf-out times for common trees and shrubs in Concord in the 1850s to observations over the past five springs. "All species -- no exceptions -- are leafing out earlier now than they did in Thoreau's time," study co-author Caroline Polgar, a graduate student, said.