Gimme shelter: As world warms, species head for climate refugia

By David Shaw | January 8, 2019

A North American red squirrel.A North American red squirrel.

Editor’s note: This story was originally published by Undark. It appears here as part of the Climate Desk collaboration.

It’s a four-hour drive from Toni Lyn Morelli’s home near Amherst, Massachusetts to her field sites on the slopes of the White Mountains in New Hampshire. She rises long before dawn to make that drive, arriving by 8 a.m. to meet her student assistants. With her team assembled, Morelli, a research ecologist with the Department of Interior’s Northeast Climate Adaptation Science Center, spends the day, and several more to come, live trapping red squirrels (pictured above), which she tags, radio-collars, measures, and releases.

Every three weeks, someone from her team returns, telemetry antennas in hand, to track how the animals are moving about the mountains. While red squirrels shift their distribution from year to year as spruces and other conifers they feed on shed their seeds, the climatic conditions they’re sensitive to aren’t changing uniformly. Observing how the squirrels move through this environment, then, will help the researchers find areas of relative stability. These are known as climate refugia.

“Refugia provide a safe haven during periods of an unfavorable climate,” Morelli and co-authors wrote in the journal PLOS One in 2016. Indeed, such areas — whether they be on mountain slopes, in shady forests, or in deep, cool canyons — are characterized as being naturally buffered from local and regional climate changes. As global temperatures rise, these pockets could help to ensure the continued existence of valued species. In identifying refugia, Morelli and her collaborators — part of a cadre of conservation scientists working on this issue — hope their efforts will contribute to improvements in land management. “We’re looking to create a product that is as useful as possible,” Morelli says.

To be sure, those seeking to implement climate mitigation strategies face challenges, particularly when it comes to federal property overseen by the current administration. Last month, the Bureau of Land Management published a plan to strip protections for the sage grouse — a ground-dwelling bird in the American West — to open up millions of acres to drilling and mining. And in 2017, President Trump drastically reduced the size of two national monuments in Utah, shrinking Bears Ears National Monument and Grand Staircase-Escalante by 85 and 50 percent, respectively.

Still, in those areas that remain under protection, land managers play an important role in deciding how lands are allocated for conservation. Identifying and protecting refugia, Morelli admits, is not necessarily a long-term solution. But it can buy conservationists time to develop more comprehensive adaptation plans.

“On a certain timescale, everything will change,” she says. But land managers “are really on board with this and want to apply it under the existing management framework.”

The concept of climate refugia originated in the study of paleoecology, which looks at the relationships between organisms and their environment across geologic timescales. And research shows that we can credit these safe harbors with producing much of our planet’s biodiversity. The Great Smoky Mountains in the southeastern United States, for example, are home to one of the world’s most diverse temperate ecosystems because that range was a place of refuge during the glaciations and subsequent warming periods of the Pleistocene. Such areas occur from the Amazon to the Arctic and millennia after the last glaciations, they remain strongholds of biodiversity.

Today, researchers have adopted the refugia model as a way to understand how species may (or may not) persist in our current era of climate change. “We’ve been working to move the theoretical concept of paleoclimate refugia into a modern context,” Morelli says of her work. “We are looking for areas where the ecological, physical, and even socio-cultural aspects of the current climate will continue into the future.”

While large areas like the Smokies are relatively rare, refugia are not all that uncommon, particularly in mountainous landscapes. A mountain valley, for example, may receive the benefit of cold air descending from higher elevation slopes, or the cooling impact of a cold, spring-fed river. Mountain tops and high ridges can be a refuge for alpine species. Even in the face of global change, such areas can remain relatively stable.

Through a combination of field work, mapping, statistical modeling, and interdisciplinary collaboration, Morelli has been defining potential refugia in the Northeast, and working with fellow researchers on projects in western North America.

But the information she and other scientists are after does not come easily. “In many places, we just do not have the fine scale data needed to map these attributes,” Morelli says. “We just don’t know enough about what is there now, let alone what will be there in the future. For ecology and behavior, we need supportive research.” Trying to understand the survival threshold for every species in a study area is all but impossible. As a shortcut, then, researchers look for a representative species — a creature well studied and understood, or one confined to a specific habitat. They might also look for a species that, like the red squirrel in the Northeast, can tell us something about the forests in which they live — an indicator for the ecosystem as a whole.

In addition to her work in the eastern United States, Morelli has also studied potential refugia high in the mountains of California’s Sierra Nevada. The Belding’s ground squirrel makes its home in these meadows. A true hibernator, the species is awake for as little as three months a year, during which time it must forage, put on sufficient fat, breed, and construct underground burrows. The squirrels rely on snowpack for efficient hibernation. Too little snow, or mid-winter melts, and they find themselves exposed to dangerous shifts in the temperatures outside. However, if snowpack remains stable, Belding’s ground squirrels survive, and co-existing species are likely to persist as well. Morelli describes Belding’s squirrels as having a narrow “pinch point”— if their environment falls much outside of a certain range, they can no longer survive.

Rather than looking at single species or even a single habitat within the Sierra Nevada, Julia Michalak, a research scientist at the University of Washington’s Urban Ecology Research Laboratory, takes a broader approach employing geographic information systems, a tool for building digital maps of the environment. Placing a grid overlay upon a map of the Sierras and indexing each cell according to the existing climate, Michalak can flag areas that warm or cool less than one degree Celsius and have little or no change in precipitation as potential refugia.

Finding refugia is about defining thresholds, Michalak says. “We looked at historic range boundaries of a whole bunch of different species, (trees, amphibians, birds, and mammals) and calculated a metric of precipitation and temperature variables.” Using these two important climate metrics, Michalak says, researchers can apply different climate scenarios to determine how the landscape will change, or not. Just how those thresholds are set, however, “can really affect how many refugia or analogous climates are found,” Michalak notes.

Of course, defining potential refugia based on arbitrary assignments of what is an acceptable change in temperature or precipitation is problematic. After all, what seems a minor change from the perspective of a computer model may push a species across ecological thresholds where it can no longer survive. But factoring in the historic data, Michalak says, can help make those thresholds less arbitrary and more biologically-informed. Still, one of the biggest challenges, she admits, is working with “a limited understanding of how any individual species will respond.” Species like the Belding’s ground squirrel.

If models indicate that snowpack will be consistent and sufficient for the squirrel’s survival then, those areas are almost certain to be effective refugia. The combination of Morelli’s and Michalak’s differing strategies may be one of the most effective methods to find natural areas resistant to climate change. In such areas, alpine meadows, the squirrels, wildflowers, and innumerable other dependent species may persist, even if surrounded by shifting ecosystems.

While it may be hard to square why society should value such species, or care if their habitats disappear, conservationists say, their fates may be indicative of our own. Belding’s ground squirrels’ survival depends on snowpack, and that same snowpack provides water to parched communities in the West. If researchers like Michalak and Morelli can determine where Belding’s ground squirrels are likely to survive, then that information could also be used to predict which rivers and streams will continue to flow through the summer, providing much-needed water to the farms, ranches, and towns in the valleys below. Back in the Northeast, red squirrels serve as an indicator of the health of the boreal forest ecosystem, reflecting how the economies that depend on it (namely timber and tourism) will fare.

Even with refugia identified, however, simply setting land aside is not enough. While many potential refugia fall in mountainous areas that bear some level of protection as public lands, Carlos Carroll, a conservation biologist at the Klamath Center for Conservation Research in California, notes that “in order to move to and between refugia, [some] species will be forced into unprotected lowland areas.” Assuring the existence of intact corridors, then, may be as important as conserving the refugia themselves.

“That,” Carroll says, “is a much greater conservation challenge.”

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