High Elevation Climate Refuges

AS OUR CLIMATE WARMS, many species are expected to migrate to habitats that match the temperature ranges they evolved to tolerate. In the Northern Hemisphere, this means plants and animals are going to shift northward in latitude and/or upward in elevation. Not surprisingly, conservationists have placed a premium on creating accurate forecasts and maps showing where suitable habitat will be in the future. But mapping the location of these future climate refugia can be tricky.

This is especially true for freshwater species in the rugged mountains of the western U.S. From fish to frogs, many mountain species are isolated in high elevation headwaters, a situation that often means they can migrate upward but not northward. Now a new study suggests previous forecasts of the amount of habitat loss for several important mountain species have been greatly overestimated. This has led the study’s researchers to conclude that things are not only looking “less dire” than was previously believed, but also that those same isolated headwaters could act as long term climate refugia.

The study, published in the Proceedings of the National Academy of Sciences, looked at stream temperature trends in the mountain west covering the years 1968 to 2011. From those temperature trends, the researchers calculated climate velocities representing how fast (as measured in river distance per decade) the thermally suitable habitats of several species of mountain fish and amphibians have been shifting.

Over the 44-year-period, stream temperatures warmed on average by about 0.10 degrees Celsius (0.18 degrees Fahrenheit) per decade, which translates into habitats shifting upstream at a rate of about 300 to 500 meters (0.18 to 0.31 miles) per decade, according to the researchers’ results. Translation: the warming effects of climate change show up in the data, but those effects are happening a lot slower than dozens of previous studies of cold water species have forecasted.

What’s more, the study notes that slow habitat shifts are primarily due to topographic steepness—meaning the climate velocities slow down as elevation goes up. Even if groundwater temperatures increase in the future, habitat shifts will remain relatively slow. This is obviously good news for species that can only move upward, but it’s also good because many of these same streams will remain so cold they will rarely be invaded by non-native species, which have warmer thermal niches and are already common in lower elevation, warmer streams.

Taken together, the researchers conclude, even if climate velocities accelerate in the future—and they are expected to—high mountain streams could remain safe havens for some important species, making them climate refugia rather than the “climate cul-de-sacs” past research suggested they could become.

The researchers got their results by sifting through a vast regional monitoring database of stream temperatures to find 923 sites with long-term monitoring records for 222,000 km (138,000 miles) of streams in the Northwest. Ranging from low deserts to high alpine tundra, the study area covered some 794,000 km (nearly 500 miles) including all of Oregon, Washington, and Idaho.

The study’s lead author, Daniel Isaak, is a research fish biologist at the U.S. Forest Service Rocky Mountain Research State in Boise, Idaho. Isaak and colleagues’ study builds on previous efforts in the conservation community to develop accurate species distribution models for mapping climatically-suitable habitats for native trout species in the mountain west. (See “Trout Need Cold, Wide, Connected Waters” in the April 2015 CIRCulator.)

Study: Proceedings of the National Academy of Sciences

Citation: Isaak, Daniel J., Michael K. Young, Charles H. Luce, Steven W. Hostetler, Seth J. Wenger, Erin E. Peterson, Jay M. Ver Hoef, Matthew C. Groce, Dona L. Horan, and David E. Nagel. “Slow climate velocities of mountain streams portend their role as refugia for cold-water biodiversity.” Proceedings of the National Academy of Sciences (2016): 201522429. DOI: 10.1073/pnas.1522429113

Photo: Spring Chinook salmon (Photo Credit: Michael Humling, U.S. Fish & Wildlife Service)

Nathan Gilles is the managing editor of The Climate Circulator, and oversees CIRC’s social media accounts and website. When he’s not writing for CIRC, Nathan works as a freelance science writer. Other Posts by this Author. 

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