‘It’s like flowers on steroids’: what happened when scientists heated a Rocky Mountain wildlife meadow by 2C? | Endangered habitats

EEvery summer, people descend on Colorado’s wildflower capital to see meadows filled with corn lilies, aspen sunflowers, and subalpine larkspur. In January 1991, scientists set up a unique experiment in these Rocky Mountain prairies. It was one of the first (and one of the oldest) to determine how climate change would affect an ecosystem.

At the time, it was thought that an increase in temperature could lead to longer, lusher grasses. But instead of thriving, the grasses and wildflowers began to disappear, replaced by sage brush. The experimental meadows transformed into desert scrubland. Even the fungi present in the soil have been transformed by the heat.

The experience opened a window to the future. These grasslands will disappear in coming decades if warming reaches 2°C above pre-industrial levels, according to the paper published in the Proceedings of the National Academy of Sciences. The results are alarming, not only for Colorado, but for the world’s mountains as the “bush” takes over.

The experience

The Rocky Mountain Biological Lab is located in the ancient ghost town of Gothic, abandoned after its silver mines closed. In winter, the landscape rests peacefully under a bed of snow. In early spring, the only way for researchers to get to the experimental sites – at an altitude of 10,000 feet – is to ski through the countryside.

Electric infrared heaters heated five 30 square meter experimental plots all year round. Head-height heaters worked day and night on a patch of grassland, keeping it 2C above normal temperatures with an annual electricity bill of $6,000 (£4,450). They warmed the top six centimeters of the ground. Animals could come and graze and the natural system was preserved as much as possible.

Over 29 years, researchers found that shrubs increased by 150% in heated plots compared to those without warming. The soil surface was dried out by up to 20% and plants with surface roots were stressed. Some wildflowers disappeared in heated plots. “It’s a sign of things to come,” says lead researcher Lara Souza of the University of Oklahoma.

Scientists have also noted big changes in the invisible world of fungi and soil microbes. Shrubs and sage brush do not rely on fungi in the same way that grasses do. They found a decrease in fungi that help plants acquire nutrients and an increase in fungi that break down organic matter. “It shows that when there is a big change on the surface, there is probably a big change underground,” Souza says. “A rollback is very unlikely.”

Alpine meadows are often overlooked in terms of species richness. Europe’s alpine meadows are home to 50% of Europe’s flora on just 3% of the land. They are home to many plant species found nowhere else on the planet. “They’ve been there for thousands of years,” says Dr Patrick Möhl of Lancaster University, who studies Austria’s pristine alpine meadows and their disappearance due to climate change.

“The species are very diverse, we are going to lose a large part of them. It will only be forest, the same type of forest that we have further down,” he says.

Möhl has observed tree species – often pines – moving upward as the climate warms. “This is a profound change in the ecosystem: the form of life changes, moving from grasslands to a forested ecosystem,” he says.

Arctic “shrubification”

This is not only observed in mountain environments.

The expansion of shrub cover is one of the most significant changes in Arctic landscapes, with polar “greening” trends even visible on satellites. Rising summer temperatures are the main factor. Shrub cover has increased by 2.2% each decade in the western Canadian Arctic, according to data recorded between 1984 and 2020.

In cold locations, plants tend to stay small. Larger plants may be damaged by exposure to wind and cold, by the weight of snow, or have difficulty growing their leaves and stems during a very short growing season. As the climate becomes less cold and less stressful, species of shrubs and trees can take root there.

“Global warming is lifting some of the restrictions on plant growth that were associated with cold conditions in high-latitude and high-altitude ecosystems,” says Sarah Dalrymple, a conservation ecologist at Liverpool John Moores University who has studied the changes in Iceland. “There is a transition from grasslands, or heaths, to shrubs, and finally to trees. »

Grass and soil ecosystems, held in a delicate balance for thousands of years, will likely be irrevocably altered in the coming decades. “Overgrowth itself is not necessarily a problem, but the fact that we are losing Arctic ecosystems is a problem,” says Dalrymple.

Some people welcome shrubs and trees – they provide shelter for wildlife, livestock and people. “But globally, afforestation of cold environments is worrying because it is associated with thawing permafrost and the resulting acceleration of carbon emissions,” adds Dalrymple.

“It’s alarming to see this clearing process happening so quickly. The speed of change and its impact on things like the carbon cycle is really quite worrying. It’s not just about whether an individual tree is good or bad.”

“What’s ‘bad’ is our inability to control our own carbon emissions. Overgrowth is a symptom, not the cause, and we must treat it as such.”

The way we manage the planet and where we live is based on the fact that we assume that the planet will be there forever and will remain unchanged. But these changes are global and not localized to Colorado. “Everything is happening a lot faster than the projections would have us believe,” says Dalrymple.

Souza is still captivated by the insect-rich meadows around the research center. She has been coming since 2012 and the magic is unchanged.

“It’s like flowers on steroids,” she says. “It’s surreal for me, every time I come.” But this vision is tinged with sadness about what the future might hold. This fragile landscape – like so many others on our planet – is on the verge of enormous change.

Find more Age of Extinction coverage here and follow biodiversity journalists Phoebe Weston and Patrick Greenfield in the Guardian app for more nature coverage.