How Climate Change Is Affecting Thoreau’s Walden Pond

By Mica D’Alesandro

Photo by Brian PurchiaHenry David Thoreau–one of the founders of the modern, American environmental movement–lived at Walden Pond in Concord, Massachusetts from 1845 to 1847. During his stay, he kept a journal and recorded everything he witnessed and learned from nature. These recordings inspired the book Walden, and have also recently informed a climate-change study conducted by Boston University biologists.

The study began when Caroline Polgar, a graduate student with Boston University Professor Richard Primack, examined Thoreau’s unpublished observations of leaf-out times for common trees and shrubs, then repeated his observations over the past five springs. She found that trees and shrubs are blooming earlier than when Henry David Thoreau made his observations.

“All species–no exceptions–are leafing out earlier now than they did in Thoreau’s time,” Polgar said. “On average, woody plants in Concord leaf out 18 days earlier now.”

This is a dangerous practice for native plants in New England. Native shrubs like highbrush blueberry, and native trees like red maple, need to go through a longer winter chilling period before they can leaf out. But this is less dangerous for invasive shrubs such as the Japanese barberry, which are ready to leaf out quickly once they are exposed to warm temperatures.

The results of the study show that our weather is confusing the trees, and the invasive shrubs will be best able to take advantage of the changing conditions.

“By comparing historical observations with current experiments, we see that climate change is creating a whole new risk for the native plants in Concord,” said Primack. “Weather in New England is unpredictable, and if plants leaf out early in warm years, they risk having their leaves damaged by a surprise frost. But if plants wait to leaf out until after all chance of frost is lost, they may lose their competitive advantage.”

In a previous Eden Keeper post we discussed Thoreau’s decision to live “deliberately”–“to front only the essential facts of life.” Thoreau found God in nature. He could see through nature a glimpse of the divine.

It is worth thinking about how our modern-day separation from “the essential facts of life” may be threatening the nature Thoreau held so dear.

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Mica D’Alesandro is a freelance writer living in Baltimore, Maryland.

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