How Will Caribou Fare in a Warming Arctic? USGS Research on Alaska's North Slope

Summer ranges matter to caribou for calving, rebuilding reserves lost over winter and escaping biting insects. USGS.

Why caribou

The USGS Changing Arctic Ecosystems initiative gives Alaska's resource managers science and forecasts on how Arctic ecosystems will respond to a warming climate. For five years its focus has been the North Slope, which has warmed over the past 60 years — but unevenly, raising the question of how wildlife that depends on tundra will cope. Caribou (Rangifer tarandus) eat the plants of coastal wet sedge and upland low shrub tundra, and changes in temperature and rainfall there have unknown consequences for them — and for people who rely on caribou for food.

Four herds

Annual ranges of the four migratory caribou herds of northern Alaska. USGS.

The Western Arctic, Teshekpuk, Central Arctic and Porcupine herds all summer on the North Slope. They differ in size, range and population trend. Their numbers are driven mostly "bottom up" — by what the environment does to the plants they eat — so the availability, nutrition and digestibility of forage shape each year's reproduction and survival.

Plants and nutrition

USGS researchers have traced how a changing growing season and air temperature since the 1970s have affected the timing, quality and abundance of forage plants, linking temperature, satellite measures of plant greenness and forage characteristics. Alongside, the University of Alaska Fairbanks studies captive-raised caribou: how eating shrubs, forbs or sedges affects body mass and reproduction. Together these feed models that forecast what future habitat will mean for caribou nutrition.

Fire and lichen

Warming may also bring more wildfire, which reshapes vegetation. Fire can help species like moose (Alces alces) by renewing their habitat, but hurts species that need old forests — caribou among them. A USGS model found that more wildfire could reduce lichen, a key winter food for caribou.

Simulated relative flammability of vegetation, 2010–2100, under the ECHAM5 climate model, in the winter ranges of the Central Arctic (dashed) and Porcupine (solid) herds. Warming makes the lichen-rich boreal forest these herds winter in more flammable. USGS.

What's next

• GPS collars: high-resolution collars on adult females of the Central Arctic herd will record habitat use against temperature, forage, nutrient needs, reproduction and seasonal body-mass change.
• Comparison: a National Park Service GPS dataset will let researchers contrast the rapidly declining Western Arctic herd with the stable to declining Central Arctic herd.

Joe Welch of the University of Alaska Fairbanks collects habitat data on the North Slope for the Central Arctic herd study, September 2012. USGS.

The work already helps land managers project how climate-driven vegetation change will affect wildlife habitat and subsistence resources, summarizing the cumulative effects of vegetation change and human activity on caribou — for the National Park Service's inventory and monitoring and for conservation planning in the Arctic National Wildlife Refuge.

Sources

Based on Gustine D, Adams L, Whalen M, Pearce J, "Changing Arctic Ecosystems: Resilience of Caribou to Climatic Shifts in the Arctic," U.S. Geological Survey Fact Sheet 2014–3103; a work of the United States government in the public domain. Figures and captions from the fact sheet's PDF.