CONCORD, Mass.  Henry David Thoreau endorsed civil disobedience, opposed slavery and lived for two years in a hut in the woods here, an experience he described in “Walden.” Now he turns out to have another line in his résumé: climate researcher.

He did not realize it, of course. Thoreau died in 1862, when the industrial revolution was just beginning to pump climate-changing greenhouse gases into the atmosphere. In 1851, when he started recording when and where plants flowered in Concord, he was making notes for a book on the seasons.

Now, though, researchers at Boston University and Harvard are using those notes to discern patterns of plant abundance and decline in Concord  and by extension, New England  and to link those patterns to changing climate.

Their conclusions are clear. 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. Working with Charles C. Davis, an evolutionary biologist at Harvard and two of his graduate students, they determined that 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.