EIn the very summer, people descend on the wildflower capital of Colorado to see grasslands filled with corn lilies, poplar sunflowers, and subalpine larkspur. In January 1991, scientists began a unique experiment in a Rocky Mountain meadow. This is one of the first (and longest-running) studies to determine how climate change affects ecosystems.
At the time, it was thought that rising temperatures could cause grass to grow longer and greener. But instead of flourishing, the grasses and wildflowers began to disappear, replaced by brushes of sage. Experimental pastures were transformed into desert-like scrubland. Fungi in the soil were also changed by the heat.
Scientists installed equipment to heat the ground and measure the effects on vegetation. Photo: William J. Farrell
This experiment provided a window into the future. The resulting paper, published in the Proceedings of the National Academy of Sciences, says these pastures will disappear in the coming decades if global warming exceeds pre-industrial levels by two degrees Celsius. The findings are alarming not just for Colorado, but for mountains around the world that are undergoing “shrubification.”
experiment
Rocky Mountain Biological Laboratory in Gothic, Colorado. Photo: RMBL
The Rocky Mountain Biological Laboratory is located in Gothic, a former ghost town that was abandoned after the closure of a silver mine. During the winter, the landscape lies quietly under a bed of snow. In early spring, the only way for researchers to reach the 10,000-foot-altitude laboratory is by skiing across the country.
Electric infrared radiators heated five experimental plots of 30 square meters all year round. Head-height heaters were installed throughout the meadow day and night, keeping the temperature two degrees above normal, and the annual electricity bill was $6,000 (£4,450). They warmed the top 6 inches of soil. Animals could come and graze, and natural systems were preserved as much as possible.
The researchers found that over 29 years, the number of shrubs increased by 150% in the warming plots compared to the non-warming plots. The soil surface dried by up to 20%, stressing shallow-rooted plants. Some wildflowers have become extinct in hot patches. “This is a sign of things to come,” said lead researcher Lara Souza of the University of Oklahoma.
Scientists also noticed major changes in the invisible world of soil fungi and microorganisms. Unlike grasses, shrubs and sagebrush do not rely on fungi. They found that the number of fungi that help plants acquire nutrients decreased, and the number of fungi that degraded organic matter increased. “This highlights that if there are big changes above ground, there are likely to be big changes below the surface,” Souza said. “The chances of going back are very low.”
On a meadow in the Rocky Mountains, researchers used a device to heat a patch of pasture to 2 degrees Celsius to study the effects on the pasture. Photo: William J. Farrell
Alpine grasslands are often overlooked in terms of species richness. Europe’s alpine meadows contain 50% of Europe’s plants on just 3% of its land. It is home to many plant species found nowhere else on Earth. “They’ve been here for thousands of years,” says Dr Patrick Mohr of Lancaster University, who studies Austria’s pristine alpine grasslands and their disappearance due to climate change.
“It’s a very diverse species and we’re going to lose a lot of it. It’s going to be just a forest, the same kind of forest that we have in the understory,” he says.
Mohr observed that tree species (often pines) migrate uphill as the climate warms. “This is a significant change in the ecosystem. There is a change in life forms from grassland to woody ecosystems,” he says.
“Shrubification” of the Arctic
This is not only observed in mountain environments.
Expansion of shrub cover is one of the most important ways in which the Arctic landscape is changing, and the polar “greening” trend can also be seen by satellite. Rising summer temperatures are the main factor. Data recorded between 1984 and 2020 show that shrub cover expanded by 2.2% every decade in the western Canadian Arctic.
Double quotes It’s alarming to see shrubbing happening so quickly. The knock-on effects are…really very worrying Sarah Dalrymple, Conservation Ecologist
In cold locations, plants tend to remain small. Large plants can be damaged by wind, cold, and the weight of snow, or have difficulty developing leaf and stem tissue during a very short growing season. As the weather gets colder and less stressed, shrub and tree species may move in.
“Global warming is lifting some of the restrictions on plant growth that were associated with colder conditions in high latitude and highland ecosystems,” said Sarah Dalrymple, a conservation ecologist at Liverpool John Moores University who is studying changes in Iceland. “You move from grassland, or heather, to shrubs and eventually trees.”
Grass and soil ecosystems, which have maintained a delicate balance for thousands of years, may be irreversibly altered in the coming decades. “Shrubification itself isn’t necessarily a problem, but the fact that we’re losing Arctic ecosystems is,” Dalrymple said.
Increased scrubbing recorded between 1987 (left) and 2019 (right) at the same site in Qikiktaruk, Herschel Island, Canada.Increased shrublanding recorded at the same location between 1987 (left) and 2019 in Qikiktaruk, Herschel Island, Canada.
Some people welcome shrubs and trees. They provide shelter for wildlife, livestock, and people. “However, at a global level, tree planting in cold environments is of concern as it is associated with permafrost thaw and subsequent acceleration of carbon dioxide emissions,” Dalrymple added.
“It’s alarming to see this process of shrubbery happening so quickly. The speed of change and the knock-on effects on things like the carbon cycle are really very worrying. The question isn’t just whether individual trees are good or bad.”
“What’s ‘bad’ is that we can’t control our own carbon emissions. Bushification is a symptom, not a cause. We need to treat it as such.”
How we manage the Earth and where we live is based on the assumption that the Earth will be there forever and will never change. But these changes are global and not limited to Colorado. “Everything is happening much faster than expected,” Dalrymple said.
Souza remains fascinated by the insect-rich grasslands surrounding the research center. She’s been here since 2012, but the magic hasn’t changed.
“It’s like a flower on steroids,” she says. “Every time I come here, it feels unreal to me.” But this vision is tinged with sadness about what will happen in the future. This fragile landscape, like many on Earth, is on the brink of great change.
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