Will climate change kill off the Northern Rockies' ancient whitebark pine forests?

Whitebark forests (both live and beetle-killed are shown here) grow on SW Montana's Snowcrest Range at an elevation of 10,000 ft. 

Anne Carlson

Climate change often sets off a cascade of events within an ecosystem that affects both plants and animals alike. When one species disappears, an entire food chain can collapse or change forever.

This could be the case in the Northern Rockies, where a team of Wilderness Society ecologists is investigating the current and future impacts that climate change has on select species that help to support whole forest ecosystems.

Nearly two in three Americans believe climate change is already upon us, according to a Yale study. Believer or non, what is certain is that ecosystems are reacting to the effects of rising temperatures, and we need to prepare for what that means for environments around the globe. This is why our scientists are using mapped data (we'll explain exactly what this means in a bit) to predict the ways that various climate change scenarios will impact keystone species such as the whitebark pine.

An ecological support system

A tree species of timberlines found only at high elevations, whitebark pine is a valuable high-energy food source for many forest animals. Scientists consider whitebark pine to be a keystone species because it supports and contributes to the the survival of vast mountain ecosystems in Idaho, Wyoming and Montana. 

One way the whitebark pine does this is by creating a stable environment for other trees and plants to flourish. First to grow in high-elevation environments, these “nurse trees” colonize areas following major disturbances, such as wildfires or avalanches. Once they grow, they provide shelter and a gentler microenvironment in which other species, such as firs and spruces, can grow. 

Whitebark pine also support forest ecosystems by offering vital nutrients for animals such as Yellowstone grizzly bears who depend on whitebark pine nuts as one of their favorite food sources. Pine nuts allow grizzlies to consume a significant source of fat and calories before they hunker down for hibernation and after they emerge from deep slumber. These nuts are more than just calories, as biologists believe that the grizzly bear's behavior and reproductive and mortality rates are greatly impacted by the availability of this resource. Grizzlies raid squirrel food-stashes in the fall, but when there are fewer whitebark pine cones, grizzlies move down into valleys in search of food, causing more human-grizzly conflicts. Additionally, because the trees are located at high elevations, they draw the bears up and out of harm’s way. Research has shown that because of these qualities, grizzly bears in the Yellowstone area have higher reproductive rates in years of good whitebark pine crops. In years when the whitebark pine seeds are less available, bears have higher mortality rates. 

Another forest critter whose survival depends on the success of whitebark pine is the Clark’s nutcracker. A close relative of blue jays and crows, the Clark's nutcracker collects whitebark pine nuts and stores them in the soil with the intention of eating the food later. If the Clark’s nutcrackers do not return for their feast, as is wont to happen, the nuts will then germinate and grow into new trees. These two species display a truly symbiotic relationship, and 

Whitebark pine cones contain nuts that many species rely on for fat and calories before hibernation. Photo: Matt Lavin, Flickr

A forest in decline

In recent years, whitebark pine has experienced high levels of mortality due to the introduction of a non-native blister rust fungus, fire exclusion (the man-made suppression of naturally occurring wildfires) and a warming climate. Fire suppression policies of the past allowed trees intolerant of fire (such as subalpine fir) to overtake whitebark pine forests, creating a tinderbox of sorts. This left older whitebark pine at greater risk of being consumed by future fires, which are now larger and burn more severely than ever before, thanks to climate change.

Whitebark pine stand. Photo: Matt Lavin, Flickr

Mapping the future of climate change in the Northern Rockies

Working with Hopa Mountain Native Science Fellow, Dominique Davíd-Chavez, Wilderness Society ecologists are using something called "mapped habitat viability data" to predict future distribution of whitebark pine under several climate change scenarios. This means that by manipulating existing maps and their associated biological data, our scientists can analyze projected climate scenarios to see how they might affect the conditions of Northern Rockies forests and the wildlife that live in them.

What they've found is that climate change is predicted to reduce the total area of whitebark pine habitat by 86 percent across the west, which would degrade thousands of acres of habitat for many forest species.

The Wilderness Society is interested in how the distribution of whitebark pine habitat may change with respect to wilderness areas and other protected lands. Currently, about 38 percent of the whitebark pine population grows in wilderness areas across the west. As climate change reduces the total area of viable habitat, the distribution of whitebark pine in wilderness may increase to 62 percent by 2060.

This analysis allows us to understand the potential impacts that climate change will have on this keystone species, and will inform us of appropriate areas to advocate for active forest restoration and conservation strategies. Ultimately, this analysis will help us better conserve biodiversity and untrammeled wilderness character across landscapes that support this important tree species.

Map of current, 2010 (left) and projected future in 2060 (right) distribution of whitebark pine in the northwestern U.S. 

Preserving whitebark pine in the face of climate change across the entire western U.S., including the Northern Rockies, will require diverse conservation approaches including restoration and wilderness protection. With its bevy of scientists and a commitment to public land protection, The Wilderness Society is uniquely prepared to confront these issues, and will work to solve this specific problem brought on by a warming climate.