CAMBRIDGE, Mass., Oct. 29 (UPI) -- Two-thirds of the plants writer Henry David Thoreau chronicled at Walden Pond in Massachusetts have disappeared due to global warming, a U.S. study contends. The Harvard University report said some of the hardest-hit plants include lilies, orchids, violets, roses and dogwoods. Plants that have thrived in the warmer temperatures include mustards, knotweeds and various non-native species.

"Some plants around Walden Pond have been quite resilient in the face of climate change, while others have fared far worse. Closely related species that are not able to adjust their flowering times in the face of rising temperatures are decreasing in abundance," Charles C. Davis, assistant professor of organismic and evolutionary biology in Harvard's Faculty of Arts and Sciences, said Monday in a news release.

The report said about 27 percent of all species Thoreau recorded in the 1850s around Walden Pond in Concord, Mass., are now locally extinct and another 36 percent are so sparse extinction may be imminent.