SUMMERTIME IN THE COLORADO ROCKIES is a wildflower lover’s heaven on Earth. And no place in the region attracts more enraptured petal peepers than the Victorian town of Crested Butte. Nestled nearly 9,000 feet above sea level on the western slope of the mountains, Crested Butte has been officially designated the “Wildflower Capital of Colorado” by the state’s legislature. In the coming months, its local paper will begin publishing a weekly “wildflower report,” and in mid-July, thousands will throng to the town’s annual festival for guided hikes, art exhibits and workshops on everything from flower pressing to cooking and wine-making with wildflowers. The main event, of course, will be viewing the blossoms in the surrounding countryside: field after field of larkspurs, lupines, gilias, sunflowers and daisies displaying every color of the rainbow against a backdrop of snow-capped mountain peaks.

Sadly, within a century, scientists warn that such iconic landscapes may vanish—not just from the Rockies, but on mountain slopes everywhere from the Sierra Nevada to the Swiss Alps to the Tibetan plateau. The evidence can be found eight miles up the road from Crested Butte at the Rocky Mountain Biological Laboratory (RMBL), where biologist John Harte leads a pioneering experiment on the effects of global warming on subalpine meadows. To simulate the temperature increase predicted for these habitats, Harte and his colleagues have used overhead heat lamps to warm a mountain meadow continuously for the past 18 years. They’ve discovered that higher temperatures spawn a major shift in vegetation—away from the grasses and colorful flowering plants that characterize subalpine meadows today toward drought-adapted shrubs such as sagebrush. “In the future, we may be known as the sagebrush capital rather than the wildflower capital of Colorado,” laments Harte, a professor of energy and resources at the University of California–,Berkeley.

The change would be more than aesthetic. While sagebrush provides wildlife food and shelter in its native lower-elevation range, scores of subalpine insects, birds and mammals in the Rockies depend completely on the seeds, leaves, pollen and nectar of nonwoody flowering plants. More significantly, as sagebrush crowds out wildflowers, Harte and his colleagues have found that the shift spurs a number of “positive feedbacks” that accelerate warming. Like the melting of the polar ice caps, “it’s a case where warming begets warming,” explains Harte. And because most climate models fail to factor in the impact of such ecosystem transformations, he believes it also is a worrisome sign that their projections, bad as they are, may underestimate how fast the planet is heating up.

When Harte began planning his project in the mid-1980s, there had been few, if any, attempts to study the effects of warming on a natural ecosystem. “The problem with relying on historical data to project the future,” he says, “is that it’s hard to separate correlation from causation—which is why I wanted to try something experimental under controlled conditions.” Calling his work “remarkable,” for both its scale and longevity, University of Maryland biologist David Inouye, who studies the impact of climate change on native species, says the experiment “is helping to make our models more realistic.”

The remote study site Harte selected features a patchwork of plants typically found in Rocky Mountain subalpine meadows: about 100 species of grasses and nonwoody flowering plants, or forbs. (At 9,600 feet, it also is near the highest elevation where sagebrush ordinarily grows.) Within the site, he and his assistants staked out ten 10-by-33-foot plots—five experimental and five control—that run along a natural altitudinal gradient. To monitor moisture and temperature, they sank 18 probes into the soil of each plot. Finally, above test plots only, the researchers strung up 15 infrared heat lamps, calibrated to mimic the average 3.6 degrees F of warming predicted by 2050 when Harte launched the project. (“Now we know it’s getting hotter faster,” he says.) The scientists switched the heaters on in summer 1991, and they’ve been running nonstop ever since.

Harte’s “warming meadow” started to look different within just a few years. Responding to higher air temperatures, soils in the experimental plots heated up by 1 to 2 degrees C and lost 20 percent of their moisture. Snow began melting about two weeks earlier, which lengthened the growing season in the heated plots. “But by far the biggest change,” says Harte, “was a shift from the beautiful forbs people pay lots of money to come here and see to the sagebrush that already carpets so much of the arid West.”

One flower that has suffered is Aspen fleabane (Erigeron speciosus), a pretty violet daisy with a yellow center. Common throughout Rocky Mountain meadows, the plant was flourishing in Harte’s test plots when he started his research. But as the plots got warmer and drier, the daisy began to produce a third fewer flowers than it once had, and its flower heads grew smaller. “It’s an example of a species that’s going to be a loser,” he says.

Even outside the heated plots, biologists are finding evidence that the daisy and other wildflowers are suffering. Since 1971, biologist Inouye has spent each summer monitoring more than 100 flowering plant species at RMBL. He’s found that many plants are blooming up to a month and a half earlier than they did three decades ago—so early that nighttime freezes still commonly occur, killing their buds. “These frosts can have cascading effects throughout the ecosystem,” says Inouye. A frequent frost victim, Aspen fleabane, for instance, is a critical nectar source for Mormon fritillary butterflies. In summers following heavy frost damage to the daisy, researchers have noted declines in the butterfly’s numbers.

Birds and mammals are also feeling the heat. Since he began living at RMBL in the mid-1970s, year-round resident Billy Barr, the lab’s business manager, has been taking meticulous notes on the seasonal behaviors of 20 animal species. A few years ago, he entered his data into an Excel spreadsheet and shared them with Inouye. The biologist’s analyses confirmed what Barr suspected: “It seemed obvious that animals were coming back sooner and emerging from hibernation earlier than they used to,” says Barr. It turns out that American robins, for example, are arriving more than two weeks earlier than they did in the 1970s, so soon that snow still covers the ground—along with the worms the birds need to prepare for the breeding season.

Similarly, Barr’s data reveal that yellow-bellied marmots are leaving their hibernation dens more than a month sooner than they did in the 1970s. “Typically, marmots emerge in mid- to late April to make a decision about whether to go back and hibernate a few more weeks or to stay out,” says Inouye. “The decision seems to be based on air temperature, which is rising in our area.” The problem is that marmots now emerge when several feet of snow still cover the plants they eat. Deep snow also blocks the animals’ escape burrows, so “more marmots are being caught by coyotes,” says Barr.

More ominous, at least from a global perspective, are the changes Harte is seeing in plant communities. As sagebrush outcompetes forbs in the heated plots, one of the positive feedbacks he’s found is that the landscape becomes darker and less reflective—or has lower albedo—than it once was. This means plants are absorbing more heat, speeding up warming and creating still better conditions for sagebrush. Extended over a large area, “even a small albedo difference can have a huge effect,” he says.

Harte also has discovered that soils in the heated plots are storing less carbon. Active photosynthesizers, flowering plants take in more carbon dioxide than sagebrush, transferring it to the soil when they die back at the end of the growing season. “A single daisy is like a tiny pump taking CO₂ from the atmosphere and depositing it into the soil,” says Harte. By the project’s fifth year, he and his colleagues found that the test plots had lost 20 percent of their soil carbon. Because the world’s soils contain four times more carbon than the atmosphere, the implications of that discovery are worrisome: “If we lost 20 percent of soil carbon globally,” says Harte, “it would mean nearly another doubling of atmospheric CO₂—or three times what humankind has done through emissions since the start of the Industrial Revolution.”

Recent discoveries from other habitats reinforce that concern. Like sagebrush, lodgepole pine favors warmer, drier conditions than the Engelmann spruce and fir trees that now thrive at high elevations in the Rockies. To investigate the impact of a warming-induced shift from spruce-fir to pine forests—a change predicted by ecological models—biologist Lara Kueppers, Harte’s former graduate student, measured soil carbon along a natural elevational gradient in Fossil Ridge Wilderness, a 45-minute drive south of RMBL. She found that the pine ecosystems stored significantly less carbon than spruce-fir forests. “If we get climate change that favors lodgepole pine over spruce-fir, we’re likely to see a loss of carbon from these systems, setting up a feedback loop that favors even more warming,” says Kueppers, a professor at the University of California–Merced.

At RMBL, meanwhile, real climate change is beginning to catch up with Harte’s simulation. For many years, it looked like the lab’s montane habitats were resisting many of the effects of warming so apparent at lower elevations. But since 2000, the area has been experiencing not only higher temperatures, but a tenacious drought that is causing snow to melt sooner in spring. According to Harte, conditions in his control plots now resemble those in the heated plots during the project’s first five years: Sagebrush is invading, wildflowers are struggling, and soil carbon is beginning to decline. “It’s a case of nature imitating science,” he says, “and validating the experiment.”

Senior Editor Laura Tangley visited RMBL last summer. To learn more about global warming and other research at the lab, see www.rmbl.org.

People and Plants: Extinctions Erode Benefits to Humanity

As global warming and other threats alter habitats by squeezing out native plants, humans may suffer along with other animal species. A recent analysis summarizing results of 44 experiments worldwide showed that ecosystems with fewer plant species produce up to 50 percent less biomass than those with more “natural” diversity. That means “species extinctions could compromise the benefits that nature provides to society,” says Bradley Cardinale, a biologist at the University of California–Santa Barbara and lead author of the study, published online in the Proceedings of the National Academy of Sciences. Such benefits range from controlling pests to absorbing the carbon dioxide that is largely responsible for global warming.

NWF Priority: Fighting Global Warming

Combating the threat global warming poses to subalpine meadows and other wildlife habitats is a top priority for NWF, which is backing congressional legislation to reduce greenhouse gases, publishing reports on warming’s impact on wildlife and collaborating with state affiliates on grassroots efforts. In addition, NWF’s Campus Ecology® program is helping colleges and universities confront global warming through climate-friendly practices that reduce their global footprint. Another program, Cool It!®, helps individuals see how everyday actions can make a difference—by conserving energy, organizing youth groups, protecting forests and recycling electronics, for example. For more information, go to www.nwf.org/globalwarming.

Web Exclusive Alpine Habitats and Global Warming Like the ecosystems that make up Colorado’s Rocky Mountain Biological Laboratory (RMBL), alpine habitats around the world are brimming with species, especially plants, that are found nowhere else. In Europe, for example, these habitats cover only about 3 percent of the continent’s land area, yet house some 20 percent of its native vascular plants. And because alpine regions are so remote, and often inhospitable, they’ve been relatively unaffected by the pressures of human population and development. At least until now. Alpine habitats, which are found between tree line and the upper elevational limits to life, are particularly at risk from global warming. Not only are alpine species more limited than others as to how far they can move in response to changing climate, they also are vulnerable to invasions from lower-elevation plants and animals that can easily outcompete them. Though hints of disruptions to alpine habitats are abundant, little historical data on these regions exist, and most studies have followed different methodologies. To solve this scientific problem, an international research project, the Global Observation Research Initiative in Alpine Environments (GLORIA), was established. With headquarters in Vienna, Austria, the project includes more than two dozen “target regions” on six continents where scientists are following standardized research protocols. Three target regions are in the United States—two in California and one in Montana—and the list is growing, with a set of four mountain peaks near RMBL scheduled to be added. Beyond documenting how these regions are responding to global warming, the project will have broader implications, according to GLORIA documents. Alpine habitats, because of their relatively pristine condition, are “early indicators of effects that will ripple through distant ecosystems.” For more information, go to www.gloria.ac.at.—Laura Tangley