Alpine Wildlife and Snowpack Dynamics in the North Cascades

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Mountain ecosystems are expected to change with continued reductions in annual snowpack that have been observed worldwide over the past half-century. Recent snow droughts in North America have been attributed to unusually warm temperatures that cause winter precipitation to fall as rain, rather than snow. Many species of alpine wildlife depend on snowpack for insulation from extreme cold and for cover from predators. Beneath the snow, air temperature is stable near 0°C, even when ambient temperatures fall far below freezing. Snowpack also influences the availability of forage for wildlife through the timing of melt-off and provision of water for plants during the growing season. Without snowpack, plants are more vulnerable to frost damage, which can lead to changes in habitat quality for wildlife.

Hoary marmots can be seen near large boulders in alpine meadows from Washington to Alaska.

Hoary marmots can be seen near large boulders in alpine meadows from Washington to Alaska. 
(Credit: Roger Christophersen, National Park Service. Public domain.)

Understanding why alpine ecosystems change with snowpack can help managers conserve wildlife.

Scientists have been studying American pikas (Ochotona princeps) and hoary marmots (Marmota caligata) in North Cascades National Park and beyond to understand how alpine ecosystems might change in a future with less snow. Many alpine mammals, like pikas and marmots, depend on snowpack and are important to ecosystem function as herbivores and prey for other wildlife. Pikas and marmots can be useful indicators of change in alpine ecosystems because they are climate-sensitive and differ in their life-history strategies for winter survival. Marmots hibernate, whereas pikas are active throughout winter and hoard food to survive. Populations of pikas and marmots fluctuate with snowpack. Possible mechanisms for such relationships include fatal exposure to extreme cold in the absence of snowpack. Alternatively or in addition, altered growing seasons of principal forage species for pikas and marmots may extend periods without green vegetation and lead to starvation.

 

The responses of pikas and marmots to weather and snowpack dynamics have been species-specific.

The responses of pikas and marmots to weather and snowpack dynamics have been species-specific.   (Public domain.)

In 2015, warm temperatures led to a record-low snowpack in the Pacific Northwest, which provided an opportunity for scientists to evaluate how pikas and marmots cope without snowpack in North Cascades National Park. Whereas pika abundance declined markedly at elevations below 1400 m, it increased slightly at higher elevations that retained snow during the low-snow winter. Pikas showed a lagged response to the snowpack anomaly suggestive of reproductive failure at low elevations, rather than direct mortality from exposure to extreme cold, in the absence of snowpack. Relative abundances of marmots declined by 69% between 2007 and 2016; the most-severe losses occurred at warm, dry sites. Pikas and marmots appeared to be affected more strongly by physiological stress rather than changes in forage availability associated with weather and snowpack dynamics.

Will these populations recover? Can alpine wildlife adapt to a future with less snow? What are the best strategies for conserving alpine wildlife over the next century? Scientists will continue to seek answers to these questions, so that future generations can enjoy the diversity of alpine ecosystems.