WASHINGTON Spring comes about 10 days earlier in the United States than it did two decades ago, a consequence of climate change that favors invasive species over indigenous ones, scientists said on Tuesday.
The phenomenon known as "spring creep" has put various species of U.S. wildlife out of balance with their traditional habitats, from the rabbit-like American pika in the West to the roses and lilies in New England, the environmental experts said in a telephone news briefing.
"The losers tend to be our native plant species," said Charles Davis of Harvard University, who studied plant changes in Concord, Massachusetts, where American conservationist and philosopher Henry David Thoreau lived a century and a half ago.
"Climate change is not affecting species uniformly," Davis said. "Certain groups are hit harder than others, and those species that are not able to respond to climate change ... are being hit the hardest."
In Massachusetts, Davis said, those include some of the most charismatic species, such as lilies, orchids, roses and dogwoods.
Based on Thoreau's notes and research by botanists in the area, Davis and other scientists figure that about 30 percent of the plant species Thoreau saw are locally extinct and a further 30 percent are in scarce supply, crowded out by southern invaders that can now thrive in New England.
Invasive non-native plants can succeed in a changing climate because some of them are better able to adjust their development.
Ecological mismatches can be fatal when some species adapt to early warmth and others don't, according to Jake Weltzin of the U.S. Geological Survey.
Weltzin described a series of mysterious miscarriages by mares in the U.S. southeast that were caused by caterpillars that contained a chemical that made the pregnant horses miscarry.
Normally, the caterpillars would have been consumed by migrating birds, leaving none to fall from trees into the mares' grassy pastures. But the birds' migration was late, letting the caterpillars fall from trees and into the grass the mares were eating, Weltzin said.
In the mountainous West, the American pika could be an early warning sign of what could happen to other alpine species as the planet warms up, said wildlife biologist Erik Beever.
The pika's habitat, which stretches across 100 million acres (40.47 million hectares) between the Rocky Mountains and the Sierra Nevada, is shrinking as warmer weather begins earlier in the year.
Earlier springs in the West also make it more likely that wildfires will start because there will be more dry vegetation as fuel, the scientists said.
The regional differences and unique native wildlife around the United States could face pressure as invasive species push in, the scientists said in the call, which was arranged by the Union of Concerned Scientists.
(Reporting by Deborah Zabarenko, editing by Anthony Boadle)