Some 27 percent of the flowers around Henry David Thoreau's stomping grounds have vanished since the mid 19th century, and another 36 percent are on the brink of disappearing.
John Nordell / The Christian Science Monitor / FILE
We know this because we have meticulous records of Walden's plant species and birds, taken by none other than Henry David Thoreau. On nearly every spring morning from 1851 to 1858, the transcendentalist writer explored the woods around the pond, noting the first seasonal blooms of 465 species of flowers.
Since then, other naturalists have revisited the area to maintain and expand on Thoreau's record. Their collective efforts have formed a detailed, long-term study on how the timing of biological events for a given area has changed over the past century and a half.
The changes are striking. Writing in the journal of the Proceedings of the National Academy of Science about their own five-year survey of Walden, Boston University scientists have observed that species are now flowering an average of seven days earlier than in Thoreau's time. Some are flowering three weeks earlier. But many aren't adjusting at all.