Troubling toll in Thoreau's backyard

Scientists say species drop amid warming

Some species have adapted to climate changes by flowering early and have thus remained relatively common, such as the harlequin blueflag, above. (Abraham Miller-Rushing)

In the 1850s, a few years after he had gone to "live deliberately" in a cabin in the woods at Walden Pond, Henry David Thoreau began to compile detailed records on hundreds of species of plants in his beloved Concord. Those same data now are being used to measure the effect of climate change, and the news is not good, researchers said yesterday.

Scientists from Boston University and Harvard reported that 27 percent of the species documented by Thoreau have disappeared, and another 36 percent are in such low numbers that their disappearance is imminent. These findings occur even though most of Concord's natural areas have been protected or undeveloped since Thoreau's time. During that same period, Concord's mean annual temperature climbed by 4 degrees, the researchers said.

Richard Primack, a BU biology professor who spent five years gathering the field data from Concord used in the study, said he hopes the connec tion to Thoreau and Walden - both icons in the environmental conservation movement - will underscore the relevance of the findings.

"Thoreau was the earliest person to keep detailed records of when plants flowered in the US, and as a field scientist this is an extremely valuable data set to work from," Primack said on a recent afternoon as he stood next to Walden Pond, just across an inlet from the site where Thoreau's cabin once was. "But he's also someone people know, and he's talking about common species people know. If you came out here looking for the flowers Thoreau saw, you wouldn't find many of them. It's a sad message."

Overall, the scientists, whose study appears in the journal of the Proceedings of the National Academy of Science, have found in Thoreau's backyard an evolutionary story of winners and losers.

Species that have responded to rising temperatures by flowering earlier - on average, seven days earlier than Thoreau recorded - have managed to survive. Those that did not are dying off, including many familiar families such as orchids, irises, sunflowers, dogwoods, lilies, roses, and buttercups.

Because so many of the winners and losers have been found to be phylogenetically linked (meaning they are close genetic relatives), the study is the first to report that whole groups of related plants are at extinction risk from global warming, the researchers said.

"Before this study, there was some idea that climate change would not be acting in a random way on groups of organisms," said Charles Davis, a plant evolutionary biologist at Harvard who did the genetic analysis, with Charles Willis, in Davis's lab. "But what we've established with an evolutionary diagram is that it's not just species that are going to be winners and losers, but whole groups of species that are close genetic relatives."

According to Davis, one explanation for why the plants that cannot alter their flowering time have been in decline is that their pollinators - insects and birds - have adapted to arrive earlier in the season.

The birds and insects arrive when some of the plants have not yet flowered, so the pollinators can't spread their seeds.

"Climate change is throwing off the synchronicity of nature," he said.

Abraham Miller-Rushing, who coordinates a network that encourages people to submit their own observations on how plants and animals are changing, said the research provides some of the first hard evidence that climate change is already hitting close to home.

"These are changes that we can see," said Miller-Rushing, who did the field work with Primack while he was a graduate student at Boston University. "People can see the changes in when they need to plant their garden, or when the birds arrive at their birdfeeders. It's a change that can resonate with people."

While there is much melancholy among the scientists involved in the study - Davis thinks that if Thoreau were alive today, he'd write a book called "Walden Lost" - Phil Cafaro, an environmental philosopher at Colorado State who has written a book about Thoreau's ethics, said he thinks that the findings are just one more reason to heed the advice Thoreau laid out a century and a half ago.

"Thoreau was one of the first people calling for us to protect and care for nature, and part of that caring is opening yourself up to being sad when it's harmed," Cafaro said.

"But he didn't want us to give in to that sadness. There's an awful lot of nature that is still there for us to appreciate and preserve. I think that's the message he'd want us to take from this."

Billy Baker can be reached at billybaker@gmail.com.