Every summer, hikers and photographers look forward to bursting blooms of alpine wildflowers in the high country of the Rocky Mountains. But as the climate changes, temperatures are rising, spring snowmelt is occurring earlier in the year, and shrubs are encroaching – a convergence of stressors that could cause the flowers to appear in smaller numbers or even go extinct.
It’s a problem that affects more than just the scenic beauty of the area. A wildflower decline could tip over a series of other dominos in the ecosystem, potentially affecting soil nutrient cycling, pollinators, invertebrate communities, and the food chains that depend on them. Researchers are concerned about these changes and are studying these ecosystems, looking for hints of the changes a warming climate could bring.
Climate change linked to local wildflower extinction in Colorado
University of Colorado postdoctoral researcher Anne Marie Panetta recently found a causal link between higher temperatures and the local extinction of one wildflower species, rock jasmine. Panetta says this short-lived species can potentially serve as an indicator species, showing scientists what might happen to other, longer-lived species.
“Zooming in on a species that completes its lifestyle within one or two years is really helpful when you’re looking for changes across generations or changes in population levels,” Panetta says.
In the high country of Colorado, Panetta and other researchers use special heated plots in the Rocky Mountain Biological Laboratory warming meadows, as well as nearby control plots, to study how plants respond to rising temperatures. Infrared radiators are strung up over certain areas of the meadow, raising the temperature of five research plots. The project has been operating continuously since 1991, enabling Panetta to analyze decades worth of data.
Starting in 2013, Panetta marked the rock jasmine in the plots and watched them for several years, noting when they reproduced and died, charting their life stages. Panetta’s resulting paper in Science Advances notes the species went locally extinct from one heated plot while “population sizes in the remaining heated plots are far below conservative quasi-extinction thresholds – the point below which populations are unable to rebound.”
“We have this large difference between heated and control plots in terms of the rock jasmine population size,” Panetta says. “That’s how we were really able to know that it was our experimental treatment that caused these populations to crash.”
Panetta’s research also suggests there is potential for the species to decline on a long-term basis. In a related experiment, Panetta found fewer rock jasmine seeds are going into underground seed banks. Many of the seeds are germinating, but fewer plants are surviving, causing the underground supply of seeds to dwindle over time. That could make it difficult for populations to recover later if conditions improve.
“These results show that populations that are warmed are going extinct – some of them are already at local extinction,” Panetta says.
However, other species, like sagebrush, may thrive in the changing conditions, shifting the plant communities. Sagebrush has a deep taproot and may be able to reach water sources wildflowers cannot. Panetta notes sagebrush is increasing in abundance in the heated plots. “[There is] a strong indication that a community level shift has actually happened in the heated plots in favor of sagebrush,” Panetta says.
An invasion of shrubs could alter ecosystems
The sagebrush isn’t the only species gaining ground. For years, scientists and recreationists have noticed shrubby woody plants like subalpine willows and spruce creeping up mountainsides and encroaching into new ecosystems. New evidence suggests this change could harm the alpine skypilot, a wildflower University of Missouri biological sciences professor Candace Galen studies.
Unfortunately for the alpine skypilot, it has a lot in common with subalpine willow, one of the invading species. The two plant species share a pollinator: bumble bees. They also share a flowering season, which Galen learned by examining study sites in the Colorado Rocky Mountains and herbarium flower records.
This co-existence is not a peaceful one: When bumble bees land on alpine skypilot flowers after visiting willows, they drop willow pollen that can clog the skypilots’ stigma, reducing germination and causing fewer seeds to form.
Indeed, Galen’s team discovered a relationship between the amount of willow pollen dropped on the skypilots and the number of seeds that they set.
“The more willow pollen skypilots received in nature, the lower the seed production that resulted from that pollination,” Galen says.
In other words, as willow creeps farther into skypilot territory, skypilot populations could decline.
While there may be a potential for the flowers to develop evolutionary mechanisms to adapt, such as changing their reproductive mechanisms or shifting flowering times so they bloom at different times than the willows, no one knows for sure if that is even possible.
Early snow melt leaves fragile buds susceptible to frost
Plants rely on natural cues – like the snow melting – to know when it’s time to start flowering. However, with climate change, the timing of snowmelt is shifting, says Gabriella Pardee, who is now a postdoctoral researcher at the University of Minnesota. Pardee studied the effects of frost on wildflowers at the Rocky Mountain Biological Laboratory for her dissertation at North Carolina State University.
“In this alpine system, the snow has melted out earlier by about two weeks over the last 40 years,” Pardee says. When the snow melts earlier, this leaves fragile buds and other structures exposed to the harsh frost – made worse by the lack of snow as insulation.
Previous research has shown frost-damaged flowers are typically smaller, wilted, and brown, and a frost-damaged plant may have fewer flowers than an undamaged plant.
Pardee studied three species of flowers and found direct effects of frost on two of them. One species had smaller and fewer flowers, while the other had reduced survival rates – and both produced fewer seeds.
“We found that frost had species-specific effects on reproduction both directly, through losses in flower production and seed set, as well as indirectly via changes in pollinator visitation rates,” Pardee says, noting the effects varied between individual species.
Such changes may ultimately reshape entire communities of plants as the more frost-tolerant species remain stable and the less tolerant ones decline due to direct and indirect effects of climate change.
In the future, the effects of climate change may compound on each other to make conditions even more challenging for many alpine wildflower species. Encroaching shrubs, pollinator-related changes, earlier snowmelt, reduced seed banks, exposure to harsh weather conditions, and other factors may make it difficult for some species to survive, causing ripple effects on wildlife and even entire ecosystem processes. As scientists work to learn more about these potential changes, they know a lot more is at stake than a perfect wildflower photograph.