"On average, common species are flowering seven days earlier than they did in Thoreau’s day, Richard B. Primack, a conservation biologist at Boston University, and Abraham J.
Miller-Rushing, then his graduate student, reported this year in the journal Ecology . . . 27 percent of the species documented by Thoreau have vanished from Concord and 36 percent are present in such small numbers that they probably will not survive for long. Those findings appear in the current issue of the Proceedings of the National Academy of Sciences.“It’s targeting certain branches in the tree of life,” Dr. Davis said. “They happen to be our most charismatic species — orchids, mints, gentians, lilies, iris.”
Of the 21 species of orchids Thoreau observed in Concord, “we could only find 7,” Dr. Primack said."
(Photograph of Walden Pond from the Walden Woods Project website.)
