Importance of Whitebark Pines and Clark’s
Nutcrackers in Western Ecosystems
By Taza Schaming
Standing on a mountain top in the western United States and looking out into a whitebark pine forest, you will likely see twisted, gnarled trees surrounded by rocky outcroppings, fields full of snow or wildflowers and grey and black birds flying by. You might marvel at the beauty of the scene before you or wonder about what kind of bird you’re seeing. What you might not realize is how intricate the relationship is between everything you see — the whitebark pine trees, the birds — Clark’s nutcrackers — and the entire ecosystem.
Whitebark pines live in these harsh mountain environments from southern Canada in the north, through California’s Sierra Nevada in the south, and from the west coast eastward to the middle of Wyoming. These trees grow slowly for more than 1,000 years, growing up to 60 feet tall, but are often much shorter. In fact, they sometimes grow close to the ground in twisted, dense and stunted mats, creating an otherworldly vista for hikers and skiers. The trees can be recognized by their clusters of five needles, their smooth, pale grey bark and their short, squat cones, which contain seeds that provide high-energy food for Clark’s nutcrackers, grizzly bears and other animals. The seeds’ large size — picture the pine nuts you see on salads — and high calorie content — more calories per pound than chocolate and almost as much as butter — make them an important food. Because these seeds are so important to so many animals, the whitebark pine is considered a keystone species — one that has a disproportionate impact on its environment relative to its abundance in the area. Whitebark pines are also considered a foundation species, because they create a stable environment for other trees and plants. First to grow in high-elevation environments, these “nurse trees” colonize areas following major disturbances, such as a fire or an avalanche. Once they grow, they provide shelter and a gentler microenvironment in which other species, such as firs and spruces, can grow. Whitebark pines also have a strong impact on western watersheds because they reduce soil erosion and help to retain snow long into the summer, which in turn helps prevent spring floods and summer droughts.
These trees are also fascinating because of how they have co-evolved with Clark’s nutcrackers. This relationship has been in place for a very long time. In fact, nutcrackers are probably the reason why whitebark pines live in North America in the first place: the ancestors of Clark’s nutcrackers likely carried seeds of the ancestors of whitebark pines with them when they came to North America across the Bering land bridge, more than 1.8 million years ago. Then, over time, the nutcrackers planted the vast whitebark pine forests.
Clark’s nutcrackers are able to survive year-round in the western U.S. by hoarding tens of thousands of pine seeds every fall, then recovering and eating them throughout the harsh, cold winters. Nutcrackers depend on whitebark pines for food, but the birds are also essential for the survival of the trees. Pine cones of most species open when they are ripe to release seeds. Whitebark pine trees, however, have cones which do not open on their own. The only way their seeds can disperse into new areas is when animals open the cones and carry the seeds away. Only two animals open whitebark pine cones and remove seeds whole: red squirrels and Clark’s nutcrackers. While red squirrels pile cones in large heaps called middens where few seeds germinate, nutcrackers hide them in small caches, many of which are buried underground. In one year, a single Clark’s nutcracker may hide up to 98,000 seeds, many of which will not be recovered and eaten over the winter, but will instead germinate and grow into new trees. Most natural whitebark pine regeneration occurs in this way.
Unfortunately, whitebark pines are dying. Entire forest communities are rapidly disappearing due to decades of fire suppression, outbreaks of mountain pine beetles and widespread infection by a nonnative fungus causing white pine blister rust. Researchers report average numbers of trees infected by blister rust as high as 70 percent in Northern Idaho, though as low as 11.7 percent in California. Mortality rates of mature trees from beetle attacks have been reported to be as high as 96 percent. Even the healthiest whitebark pine stands, located in the Greater Yellowstone Area, have severely declined since 2000. In 2009, 46 percent of these whitebark pine stands were classified as “high mortality.” The decline is so severe that this summer the U.S. Fish and Wildlife Service classified the whitebark pine as a candidate for listing on the endangered species list.
The high mortality of whitebark pine will likely have serious cascading effects on the ecosystem. Though Clark’s nutcrackers eat many kinds of seeds across their range, whitebark pine is an important food source, especially in northern regions such as Yellowstone, Grand Teton and Glacier National Parks. Scientists are concerned that the tree’s loss will be reflected in the bird’s numbers. Though a reliable survey method for Clark’s nutcracker populations is still lacking, anecdotally, nutcracker sightings in Montana and Washington seem to have declined already. If fewer whitebark pines lead to fewer nutcrackers, then there will be fewer birds to cache pine seeds and we could wind up with even fewer whitebark pines.
This cycle of declining trees and birds could have a huge impact on the entire western landscape. Nutcrackers cache the seeds of at least ten species of pines, including limber pine and bristlecone pine, among others. If there are fewer nutcrackers, these conifers may still reproduce, but their seeds may not travel as far; nutcrackers carry seeds up to 32 kilometers to hide them, much further than wind or other animals could carry the seeds. In the face of current climate change, the long-distance dispersal of conifer seeds could be paramount in enabling tree populations to adapt, as it allows tree populations to move much more quickly to new habitable locations.
A decline of whitebark pines will have many other cascading effects: over 110 species are known to eat whitebark pine seeds and use the trees as shelter, so fewer trees would decrease biodiversity at higher elevations. Fewer whitebark pines will also alter animal behavior. For example, grizzly bears raid squirrel middens in the fall. When there are fewer whitebark pine cones, grizzlies move down into valleys in search of food, causing more human-grizzly conflicts. A decline in whitebark pines will also cause landscape changes. If seeds aren’t cached by nutcrackers in disturbed areas, the whitebark pines won’t be able to grow and act as “nurse trees,” so other tree species will have a harder time growing. Without whitebark pines to retain snow at high elevations, runoff would change, affecting not only the survival and breeding success of fish species like the cutthroat trout, but also our own drinking water.
The loss of the trees also changes our experience in the mountains. When you look out from the top of a mountain over a whitebark pine forest in much of the Greater Yellowstone Area, you will not see the iconic, healthy landscape, but thousands of dead and dying trees. So, instead of marveling at the landscape before you, you may start wondering what you can do to help.
It is amazing how one species can have such a profound effect on so many other species, as well as on the soil, the water and the future. As caretakers of the Earth, our duty is to help protect these amazing trees.
Taza Schaming is a Ph.D. candidate at Cornell University Department of Natural Resources and Cornell Lab of Ornithology.