Global Warming Kills Whitebark Pines, Threatening Mountain Ecosystems
Millions of dying whitebark pine trees could be disastrous for the delicate ecosystem that supports grizzlies, birds and Western water supplies.
Across the American West, whitebark pine, a linchpin of high-altitude ecosystems, is rapidly falling victim to the aggressive mountain pine beetle. Warming temperatures allow the native beetle to thrive in previously inhospitable high-elevation forests, where the insect bores into and kills whitebark pine trees. Swaths of dead whitebarks now stretch across the landscape, their telltale red needles bearing witness to the unprecedented impacts of climate change in this iconic ecosystem.
Whitebark Pine: A Keystone Species
Whitebark pine is the foundation species for alpine ecosystems of western North America, its range stretching from California and Nevada in the south, through the Northern Rocky Mountains and the Cascades, to British Columbia and Alberta in the north. Whitebark pine grows at high elevations, and provides food and shelter for animals where few other trees can even survive.
Dead and dying whitebark pines near Goodwin Lake, WY (Photo by Whitney Leonard). Click to view more.
Consider the Yellowstone grizzly bear, one of the most iconic species affected by the whitebark decline. In the fall, just before hibernation, grizzlies raid caches of whitebark pine cones stored by other animals. It’s an efficient way to get large, nutritious, whitebark pine seeds at a critical time of year. When these caches of high-quality food are not easily available, female grizzlies risk entering hibernation with fewer nutritional reserves, and give birth to fewer cubs.
In addition, if whitebark pine crops fail, grizzlies are driven to forage in lower-elevation areas where they risk encountering, and being killed by, humans. These well-documented threats to whitebark pine were a key factor in the September 2009 decision by a federal judge to put Yellowstone grizzlies back on the endangered species list.
Whitebark pine seeds are also an important food source for Clark’s nutcrackers, whose forgotten seed caches help plant new whitebark stands. Red squirrels and a host of other small mammals and birds also rely on whitebark pine seeds in high mountain environments where food can be scarce.
Moreover, whitebark pine forests stabilize and shade the snowpack, reducing avalanches and extending precious snowmelt flows into the summer months. This slow melting process not only keeps rivers cool for trout and other aquatic wildlife but also helps maintain sufficient water resources for the people living in the arid American West.
Threats to the Future of Whitebark Pine: Blister Rust, Global Warming and Mountain Pine Beetles
Although whitebark pine survives the harshest weather conditions in the western mountains – frigid temperatures, high winds and lightning strikes – it is no match for the relatively recent impacts humans have caused. White pine blister rust, a lethal disease accidentally brought to the continent on imported seedlings, has wiped out roughly 50 percent of the whitebark pine in the Rocky Mountains since its arrival in the early 20th century. In some areas such as Glacier National Park, it has killed 85 to 95 percent of the whitebark pine. Infected trees can take a long time to die, but the disease can also cause their cone production to drop significantly, affecting grizzlies and other wildlife.
Climate-Driven Mountain Pine Beetle Infestation in Whitebark
Exacerbating the effects of blister rust is a new threat: the mountain pine beetle, a recent arrival to the high-elevation ecosystems where the whitebark pine lives. This small insect bores into mature pine trees, killing them by eating critical tissue under the bark. When the beetles hatch in the summer, huge swarms attack a forest all at once. Cool year-round temperatures and freezing winters once kept this beetle confined to low-elevation forests, where native lodgepole pines evolved natural defenses against beetles. Global warming, however, has allowed the mountain pine beetle to expand its range into high-elevation forests, where the whitebark pine is virtually defenseless against this newcomer and its explosive attacks.
Beetles attack the mature whitebark pines and blister rust kills the smaller trees, creating a perfect storm; together, beetles and blister rust could wipe out whitebark pine as a functional component of high-elevation ecosystems. Entire hillsides have turned red with the dried needles of dead whitebark pines. As the needles drop, the hills turn gray. The term “evergreen” no longer applies to these once majestic forests.
In December of 2008, NRDC submitted a petition to the U.S. Fish and Wildlife Service, asking the agency to list the tree as endangered under the Endangered Species Act. In response to litigation by NRDC, USFWS finally released a positive 90-day finding on whitebark in July 2010, indicating that listing the species may be warranted. The agency is now conducting a year-long status review, to determine whether or not they will list whitebark, and – if it is listed – whether it should receive “threatened” or “endangered” status.
Endangered Species Act protections could help federal agencies focus their whitebark efforts and could bring increased resources for research, conservation, and restoration efforts.
last revised 12/7/2010
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