The Yellowstone Ecosystem
The Yellowstone ecosystem is home to the iconic and historical Yellowstone National Park, the first U.S. national park created in 1872. Its high-elevation mountains of alpine and sub-alpine forests, are a UNESCO World Heritage site, spanning the rugged region where Idaho, Wyoming and Montana meet. Whitebark pine is the ecosystem’s foundation tree, living in the highest and harshest parts of the region, where few other trees survive. Moreover, whitebark forests stabilize and shade the snowpack, reducing avalanches and extending precious snowmelt flows into the summer months. The slow melt keeps rivers cool for trout and other wildlife and helps maintain water resources for people in the arid American West. But warming temperatures are threatening these majestic pines by allowing the mountain pine beetle to move into higher elevations, where it is decimating the defenseless whitebark forests on an unprecedented scale.
A Home for Threatened and Endangered Species
The whitebark pine is an imperiled foundation species of the Yellowstone ecosystem that provides critical food and essential habitat to many species at higher elevations. Elk use these forests as shelter. Small mammals and birds, such as the red squirrel, chipmunk and Clark’s nutcracker, rely on whitebark pine seeds as a primary food. Perhaps most importantly, pine seeds play a key role in the survival of Yellowstone’s threatened grizzly bears. The pine seeds are a high-calorie, high-fat food source that the grizzly eats to build fat stores essential for surviving winter hibernation. Whitebark pine is the engine that drives the health of the Yellowstone grizzly bear population: because of its remoteness, whitebark pine helps keep grizzly bears up high and out of harm’s way during their fall feeding frenzy. Moreover, when whitebark pine seeds are abundant, more cubs are produced, whereas when whitebark pine food crops are poor, bear reproduction suffers.
Climate Change Threats
As global warming progresses, increased temperatures at higher elevations allow the mountain pine beetle—once confined by cooler temperatures to lower elevations—to move up the mountains. Whitebark pines have no significant defenses, causing yearly die-offs. As the beetles attack the adult tree, an invasive pathogen called blister rust is attacking the smaller trees, creating a perfect storm where whitebark pines are being wiped out. A recent study by the NRDC and the U.S. Forest Service revealed that 82 percent of the whitebark pine forests in the Yellowstone ecosystem showed either high or medium mortality; only 18 percent of the ecosystem’s whitebark pine forests are healthy. Based on this study and current changes, experts predict that whitebark pine will be functionally extinct in the ecosystem—failing to provide food, shelter and hydrological functions—in five to seven years.
If the grizzlies do not have pine seeds, they migrate to lower elevations searching for other food, where conflicts with humans occur. Over the past few years, bears have wandered farther from high-altitude havens where they would normally be feasting on whitebark pine seeds, resulting in more conflicts with hunters, campers, and residents and often the bears’ lethal removal.
Needed Conservation Measures
Nonprofits, federal and state agencies are exploring future forest management options. The Greater Yellowstone Coordinating Committee’s whitebark pine subcommittee has mapped the priority whitebark pine conservation and restoration areas for the Yellowstone ecosystem. Continued monitoring and efforts to search for beetle-resistant whitebark pine trees will be critical. The U.S. Forest Service and other agencies are already collecting blister-rust-resistant seeds and raising seedlings for replanting. While still small in scale compared with the extent of beetle-impacted whitebark, restoration projects have the potential to expand and target critical habitat areas throughout the tree’s range. At the same time, adaptation programs and strong protections for grizzly bears can be part of a program to respond to the effects of declining whitebark in Greater Yellowstone.