Concerns Related to Concerns Related to Whitebark Communities Whitebark Communities Whitebark Pine Whitebark Pine Distribution of Whitebark Pine Distribution of Whitebark Pine in the GYE in the GYE Whitebark pine occurs in the upper subalpine zone of western North America, particularly in the northern Rocky Mountains, where it is adapted to a harsh environment, often consisting of poor soils, steep slopes, high winds and extreme cold temperatures. This long-lived species is well known for its diverse growth forms: some trees grow straight and narrow, while others form stunted and gnarled krummholz. While its inaccessibility and sometimes crooked growth form lead to low commercial value, it is a highly valuable species ecologically. Whitebark pine is often considered a “keystone” species of the subalpine zone. Because whitebark pine can grow under conditions tolerated by few other trees, it often serves as a “nurse” plant—a plant that creates a favorable environment in which other plants can grow—for species such as subalpine fir and Engelmann spruce. Its occurrence on wind-swept ridges serves as a snow Whitebark pine have declined over the past 50 years throughout much of its range due to the combined effects of disease, insects and forest succession. White pine blister rust— an exotic disease introduced in the early 1900s—has infected whitebark pine in parts of the Pacific Northwest, although it is possible that the severity of the blister rust infection in the GYE may be less severe overall due to the drier climate of the region. Mountain pine beetles, a native insect, are the most damaging insect to whitebark pine communities, with past outbreaks killing up to 17 million trees in the Beaverhead National Forest in one year (1932). Dwarf mistletoe can cause local damage and mortality, but is probably of relatively minor concern in the Greater Yellowstone Ecosystem. Fire regimes altered through fire suppression can allow successional species such as Engelmann spruce and subalpine fir to outcompete whitebark pine, but the extent of this concern in the GYE, where numerous large-scale fires have occurred in recent decades, is not well understood. In the past researchers believed that although severe, stand-replacing fires kill whitebark pine, post-burn reproduction would likely result in an increase in whitebark pine abundance. However, it is now clear that many factors acting Whitebark pine is a long-lived, slow- growing species that inhabits the subalpine region, typically above 8,500 feet in the GYE. Courtesy B.R. McClelland fence, allowing for snow accumulation. Yet, perhaps its best known role in these ecosystems is as a food source for a variety of wildlife species. Whitebark pine seeds are large and high in fat content, making them a valuable food source for more than 17 wildlife species. Whitebark pine seeds are an especially important food source for grizzly bears, which can find the seeds stockpiled in large quantities by red squirrels in middens. In the Greater Yellowstone Ecosystem (GYE), this food source is of such importance that annual cone production is one of the major predictors of annual survival and reproduction of the bears. Whitebark pine is classified as one of about five members—worldwide— of the stone pines in the subsection Cembrae. This group is characterized as having large, wingless seeds that are dispersed by birds. Whitebark pine seeds are a major food source for Clark’s nutcrackers, which form a mutualistic relationship with the tree by caching seeds by the thousands, thus serving as a primary means of seed dispersal for whitebark pine. NPS Photo Courtesy U.S. Fish & Wildlife Service Clark’s nutcracker Red squirrel midden with grizzly bear digging. Courtesy IGBST Distribution of whitebark pine in the Grizzly Bear Recovery Zone. Courtesy USGS