Climate Changing Thoreau's Woods

Oct. 28, 2008 -- "I want to go away soon and live away by the pond," wrote Henry David Thoreau, "But my friends ask what I will do when I get there? Will it not be employment enough to watch the progress of the seasons?"

Indeed, it has proved useful employment for modern climate researchers. From 1852 to 1858, Thoreau kept meticulous records of the plants that bloomed in the Concord, Mass., woods near Walden Pond. Researchers who recently repeated those measurements have compared the findings, old and new, revealing the signature of climate change in Thoreau's woods.

Richard Primack and graduate student Abraham Miller-Rushing of Boston University surveyed the plants in woods near Concord from 2003 to 2007, recording the abundance of various species and what day they flowered each season. They combined these results with data collected by Thoreau in the 1850s and another naturalist in the late 1800s.

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The pair found that 27 percent of the species appearing in Thoreau's surveys have disappeared from the area, and another 36 percent are now so rare they may be gone soon. Over the last 100 years, the average annual temperature in Concord has risen by 4.3 degrees Fahrenheit.

Charles Davis and colleagues at Harvard University in Cambridge, Mass. then projected these findings onto a "tree of life"-- a phylogenetic tree that groups closely related species together, to see which groups of plants have won and lost over time as temperatures warmed.

"Plants in Concord aren't really responding to climate change in the same way," Davis told Discovery News. "Some are able to adjust their flowering time by upwards of three weeks, and others are not."

"The species that have very flexible flowering times with respect to temperature have tended to flourish," Primack said. "Those that have a very rigid flowering time are the ones which have tended to decline or go extinct on the landscape."

"For the first time, it shows that climate change is not impacting these plants in a uniform or random way," Davis added. "It is major branches in the tree of life that are being lost. It happens to be the most charismatic plants -- groups that we all know and love: the dogwoods, the orchids, members of the lily family, members of the rose family."