Climate Change Leaves Wildflowers in the Cold

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The wildflowers in the fields of Crested Butte, Colo., do not give up their secrets easily, but David Inouye believes they have something important to say about the changing climate and our future in it. He has been visiting the montane meadows of the wildflower capital, 9,000 feet above the Colorado plain, every summer for the past 35 years to spend the season conducting a unique natural experiment.

A University of Maryland professor of conservation biology, Inouye says he first arrived in the region as a graduate student in the summer of 1971 to study insects but soon found himself captivated by the mysteries of the region’s abundant wildflowers.

“I started out studying bumblebees but soon discovered I also needed to understand something about the plants those bees pollinate,” he said.

His methodology is simple. Over the years, he demarcated 30 undisturbed wildflower plots, each two meters square, scattered throughout the highlands around the Rocky Mountain Biological Laboratory. He visits each of them every other day during the summer to take a census. “It takes about one and a half to three hours each day, depending on how many of the plants are in bloom.”

During his rounds, he takes a comprehensive survey of the flowering plants in each plot, noting their condition and the phenological phase in their growth cycle.

His initial timing was fortuitous. Conducting one of the United States’ longest-running phenological experiments, Inouye now says, “I seem to have come in at a time of transition.”

Until that time, climate change had not been noted as having significant impacts at higher elevations. But, he says, during the mid-1990s, things began to change.

Since then, he says, “Spring seems to be arriving earlier,” reflecting a trend widely observed in ecosystems at lower elevations. But, up on the butte, he also made a unique finding: With the warming trend, wild sunflowers began disappearing from his plots.

Inouye struggled to tease out the cause, finally and paradoxically attributing it to frost damage caused by a warming climate.

Nonlinear Timing
Susan Mazer, a professor of biology at the University of California, Santa Barbara, says the impact of climate warming has not been strictly linear in its effects on seasonal events and that this is particularly so for high elevations, such as Crested Butte.

For such regions, the evolutionary biologist says, the date of snowmelt has retreated to earlier in the spring, while the date of the first frost in the fall has been delayed, resulting in a longer growing season.

The timing of seasonal events between those markers, however, has proven less elastic.

One such event, on Crested Butte, Inouye says, is the last hard frost of the spring. Warming has not substantially altered its date. Occurring around or between June 10 and 15, this cold snap now portends a mid-season die-off of immature, frost-sensitive plants. The sunflowers he has been observing for more than three decades, Inouye says, have been among these.

He explains it this way. Snowmelt signals the start of the growing season in the alpine environment of the butte. Over the years of Inouye’s study, the prodigious winter season snow accumulations, up to several feet deep in the region, have declined significantly. Lighter snow means an earlier thaw.

The early exposure of the ground to sunlight warms the soil, giving vegetation a head start on the growing season, but as a consequence, the sunflowers reach their budding phase weeks earlier than previously observed. Inouye says some of the plants that reach this delicate stage before the season’s last deadly freeze, in early June, do not weather it well. And among those, the frost-sensitive sunflowers fail to reproduce.

Inouye, however, says frost is apparently not the only villain. He has found that plant species not sensitive to frost damage have been disappearing from the meadows as well. Though he has yet to discover the direct cause in these instances, he says both types of losses seem to correspond to the earlier snowmelt.

Inouye says all of this points to declining diversity in the high-elevation habitats of the western United States, which has implications beyond affecting the natural ecology.

No Taste for Sagebrush
According to Inouye, if the trend toward shorter winters and earlier springs continues, the summer spectacle of colorful wildflower meadows of Crested Butte and similar ecosystems could eventually be reduced to mirror the uniform populations of sagebrush, blanketing the arid terrain at lower elevations.

Beyond the obvious impacts on sightseeing tourism, for which the area has become famous, he says this could raise prices at the grocery. According to Inouye, cattle ranchers have customarily relied on patches of mountain wildflowers in the national forest system in the western U.S. as low-cost forage for their herds. A takeover by sagebrush, less than ideal fodder for cattle, would force ranchers to seek alternative, and perhaps more costly, food sources for their stock.

Mazer says Inouye’s findings show how little we know of how wild lands might respond to environmental change. If similar effects occurred in other fragile ecosystems, particularly in areas bordering farmland, she says, there could be important implications for native pollinators, essential to efficient agricultural production but dependent on wildflowers.

According to Mazer, however, much research has yet to be done, and this highlights an urgent need for increased funding for basic research in biology. She believes adapting to shifting times may require adopting new priorities. “(The National Institutes of Health’s) budget has doubled in the past 15 years, but the same has not been true of (the) National Science Foundation, and that is the only source of federal funding available to support basic research in biology.”

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