Apr 232010

“Spring Creep” Favors Invasive Species

Spring is coming earlier, and nature is scrambling to keep up, according to scientists who say climate change is to blame.

The season starts an average of 10 days earlier in the United States than it did just 20 years ago. And that is scrambling the delicate balance of many ecosystems, as some species adapt to the change and others don’t.

“What’s happening is that the Earth is warming,” said Jake Weltzin, director of the National Phenology Network, a federal program that tracks changes in seasonal patterns. “That is causing changes in when things start in the spring. But what happens, though, is not all plants and animals respond the same.”

For reasons scientists don’t entirely understand, the climate mismatch appears to often favor invasive species over native species.

That’s what’s happening at one of the United States’ most iconic landscapes — Walden Pond in Concord, Mass., the site documented by Henry David Thoreau.

Climate change has altered the plants found in the woods near the pond, according to Charles Davis, an evolutionary biologist at Harvard University. He has studied plant life there by juxtaposing modern observations with historical records kept by Thoreau and other botanists.

“It turns out that the losers, by and large, tended to be our native plant species,” he said. “What this study documents is that climate change is not affecting species uniformly. There are certain groups that are being hit much harder than others.”

Walden Pond’s native plants — including lilies, orchids, roses and dogwoods — seem to have a harder time adjusting their flowering to match the earlier emergence of spring.

Thirty percent of the plants once found at the pond are now extinct, and another 30 percent are present in such low numbers their extinction seems likely.

“The winners, by and large, are the non-native plant species,” Davis said.

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