Study finds complexity to climate changes underway at 9,500 feet in Colorado

Work of 15 scientists at Rocky Mountain Biological Laboratory synthesized to help understand changed interactions among wildflowers, birds, and insects

by Allen Best

Changing climates have started disrupting schedules of almost everything everywhere. As temperatures rise, spring snow in the Rocky Mountains melts earlier. How has this changed the dance between birds and bees, flowers and the trees?

Plenty, according to a new study of research conducted in Colorado during the last half-century, and in far more complex ways than you might think.

Published by the Proceedings of the Royal Society B, a scientific journal of papers in life sciences, the study examined the voluminous evidence accumulated by 15 scientists since 1975 at the Rocky Mountain Biological Laboratory near Crested Butte. The scientists have studied plants, insects, and birds in the outdoor laboratory amid the forest and meadows at an elevation of about 9,500 feet.

RMBL, pronounced “rumble,” also has a continuous record of temperature and other weather data beginning in 1975. Average summer temperatures at the lab, which is headquartered at the old mining hamlet of Gothic, have increased 0.4 degrees C each decade. Those in autumn rose 0.2 degrees per decade.

Something similar is happening with snowmelt. The date of bare ground has arrived an average of 2.4 days earlier per decade. With this earlier snowmelt, first spring activity advanced significantly across all the species examined except migratory birds. This makes sense because bird migration is determined by cues along their travel from winter grounds farther to the south and not solely by conditions in their breeding grounds in the Gunnison River Basin.

The study found that this shifting climate has not had uniform effects on the plants, insects, and birds that have been studied since Gerald Ford was president. Some interactions, such as those between particular wildflowers and pollinators, may no longer occur. Hummingbirds may no longer arrive while glaciers lilies are in bloom, for example. And, taking cues from the shifting climate, new species may be entering into the mix in different ways.

Rebecca M. Prather, one of four lead authors of the study, compares what has been observed at RMBL to the dining schedule of two people who had habitually gotten together for lunch at a restaurant for a long time. Suppose one of the patrons had a disruption, causing the person to cancel their noon get-togethers. The second person might take up with others, and the one with the disruption might instead arrive in evening.

In the natural world, the warming climate is changing the timing of interactions — or causing missed dates.

Prather explains that a specific flower can rely on a specific pollinator. And if the flower starts flowering before the insect arrives—well, the flower may not be able to reproduce, because it needs that insect to help it accomplish that task.

The study also emphasized the importance of examining which cues are driving a species’ entire distribution of seasonal activity. For example, first date of flowering by a wildflower may not be a good predictor of its peak flowering.

The study yielded some surprises, said Prather, a post-doctoral researcher at Florida State University’s Department of Biological Science who first studied the effects of changing climate on prairie ecosystems in Oklahoma.

Before the data collection began in 2021, she says, researchers assumed the earlier snowmelt in spring and the accompanying warmer temperatures mattered almost entirely in determining how the birds, insects, and plants interact. They do matter, but the study instead found that other things were also at play. For example, precipitation and temperatures from up to 18 months before can alter interactions among actors in the natural world.

“While we didn’t test the mechanisms for why climate in both short and longer time frames matters, we do know that cues can accumulate over time and interact with an organism’s physiological demands,” Prather explains.

“Extended lag times may be more common at high altitudes or latitudes because there is a shorter growing season, or time for organisms to obtain and store energy. An example that we use in the paper is that alpine bistort pre-forms its leaves and inflorescences four years prior to blooming.”

The study was not focused on quantity, such as the number of bees or flowering lilies, but only the timing of their interactions – and, on the flip side, non-interactions.

Midsummer Rocky Mountain Biological Laboratory, David Inouye photo

Scarlet gilia, blue flax, and other wildflowers make for a happy midsummer setting at the Rocky Mountain Biological Laboratory near Crested Butte. Top, a broad-tailed hummingbird visits flowers of the dwarf larkspur. Photos courtesy of David Inouye

David Inouye, another of the study’s authors, began spending his summers at Gothic in 1971 studying bumblebees, flies, and hummingbirds, as well as their interactions with the plants that can, in extremely warm years, such as was the case in 2022, flower in the high mountain meadows into October.

Now living in semi-retirement in Paonia after a teaching career at the University of Maryland, Inouye similarly stresses the greater complexity of interactions that the study found. “Individual species do not all respond in the same way,” he says.

For example, migrating hummingbirds might arrive after the flowers, blooming earlier than before, have disappeared. Bumblebees wintering underground might also have jostled timings relative to their vegetative hosts.

“This points to a more complicated picture than we assumed at first,” he says. “It makes it more complicated, but also more interesting. It also points to the need for detailed long-term studies, to tease apart these interactions.”

Why might somebody in Boulder or Durango care about this?

“A lot of people, no matter where they live, have an appreciation for nature and a curiosity about how nature works and curiosity about how things are changing due to climate change,” he says.

“Anybody who spends time outdoors and has done that for a decade or more has a personal understanding that nature is changing. And I think they will also have an appreciation for learning some of the details about how it is changing that we have gained from decades-long studies like ours and with a variety of species.”

Ian Billick, executive director of RMBL, said the study demonstrates how the laboratory is uniquely positioned to provide a systems-level understanding of how ecosystems around the world will respond to a changing climate.

In terms of climate, the lab’s 45 years of data is but a glimpse. Other records go back much further, especially when considering ice cores and coral reefs.

“But from an organismal perspective, this is the gold standard,” he explains. “There are very few organismal studies that go back 50 years.”

Billick also emphasizes the importance of the study at two levels. If not the first such study, it nonetheless provides a “powerful example of how we can start to integrate across individual studies to develop and better predict how species will respond to climate change.”

Second, he says, this study will help climate scientists broaden their understanding of what lies ahead. Today’s climate change models focus on atmospheric conditions. They must also include earth-system models. In other words, they must incorporate what is happening on the ground—and underground, too—and the interaction with the atmosphere.

“Organisms are a huge driver of carbon cycles, and there are strong feedback loops between organisms and carbon/climate,” Billick explains. “We’ve made a lot of progress on climate models abstracting away the organismal component, but bringing biology back into those models will be very important to reducing uncertainty.”

This paper, while not focused on climate models predicting the future, “is a step in harnessing that complexity in the service of more predictive earth-system models,” he says.