Caribou May Find Calcium-Rich Tundra Hits the Spot
To the plant eaters of Alaska's North Slope, all tundra does not taste the same. Animals that survive on tundra plants may prefer tundra rich in calcium and other nutrients, a type of tundra researchers recently studied along with a more common variety on Alaska's North Slope. The difference between tundras may explain why caribou and other animals tend to stick to the coastal plain. It may also explain why some scientists are rethinking the relationship between tundra and greenhouse gases.
Skip Walker is among the scientists studying the tundra covering Alaska's North Slope. Walker, of the University of Colorado in Boulder, was in Fairbanks recently for the American Association for the Advancement of Science conference. He described two distinct types of tundra found on the North Slope-acidic tundra and calcium-rich tundra. Along with other researchers, including Terry Chapin and Chien-Lu Ping of the University of Alaska Fairbanks, Walker found the two types of tundra have distinct boundaries.
The acidic tundra, generally with a pH of 5.5 or lower, was found predominately to the south of the arctic coastal plain in the foothills of the Brooks Range. Walker said this acidic tundra is made up of cottongrass, thick carpets of moss, and tussocks that make walking less than pleasant. This type of tundra is often greener than other varieties because it contains an abundance of willow and birch shrubs.
The calcium-rich tundra of the coastal plain has a plant makeup that's quite different from the acid-rich tundra. Calcium rich-tundra has less moss and shrubs, but a larger variety of plants--twice the number of plants per square hundred meters than acidic tundra. With more plant variety comes a dramatic increase in nutrients, and the animals seem to notice.
Musk oxen feed primarily in areas with calcium-rich tundra. Barren-ground grizzlies come out of hibernation and gorge on the calcium-rich tundra plants. All three of Alaska's major caribou herds spend much of their time foraging and calving on tundra of the calcium-rich variety. The minerals they get from the tundra may help develop their bones, antlers, and milk, Walker said. Even the smaller animals--voles, lemmings and ground squirrels--seem to prefer living in the calcium-rich tundra, perhaps because many plants that make up acidic tundra have chemicals that make them bitter and harder to digest.
Although animals are attracted to calcium-rich tundra, it may be on the way out, if the Arctic warms due to global climate change, Walker said. A warmer, wetter Arctic favors the growth of acidic tundra, which may creep down from the foothills of the Brooks Range to change the character of the coastal plain. A change in tundra types also could affect the release and uptake of carbon dioxide. The scientists found that acid-rich tundra takes up more than twice the carbon dioxide and contains twice as much carbon in a cubic meter of soil than calcium-rich tundra.
That finding leads some scientists to believe that a warming Arctic may cause less of a release of carbon dioxide than was previously thought. More acidic tundra on the North Slope could act as a carbon "sink" rather than a carbon source.
