The Ghost Forests of Whitebark Pine
Posted October 17, 2012 in Saving Wildlife and WIld Places
Avalanche Peak, Yellowstone National Park
A couple of weeks ago I had the awesome experience of hiking the Avalanche Peak Trail in Yellowstone. It is definitely in my top ten favorite hikes. Having spent a lot of time in Utah hiking in places like Arches, San Rafael Swell, Goblin Valley, Great Basin, and the Wasatch and Uintah mountains, that’s saying a lot. At the summit of this immense peak, I saw the most expansive and breath-taking views of this particular ecosystem type ever.
The wildlife we encountered included squirrels, chipmunks, and birds such as Clark’s nutcrackers which are critical for the dispersal and germination of whitebark pine seeds. We saw tracks from a bighorn sheep on the slope just below the ridge and a young mule deer buck resting in a shady patch under a tree. The animals that were starkly missing from this wildlife landscape were grizzlies. As little as ten years ago, this would have been prime grizzly habitat and hikers would have done well to keep a keen eye out for any bear signs, make noise so as not to surprise a bear, and assure their can of bear spray was on hand and easily accessible. We still followed these precautions, but we knew it was unlikely that we would see a bear that day and this is why: most of the key food source for grizzlies in this area is dead. And I mean, almost completely gone.
In the midst of the surrounding beauty was the evidence of death everywhere you looked. We walked through hundreds of dead trees, and could see thousands from the summit. The most curious of these areas were ones where multiple types of evergreens were growing – fir trees, spruces, lodgepole pine, and mixed in were hundreds of dead whitebark pine trees. How did they die? Why did the other types of trees survive? The answer is one of the best examples of a species range changing in direct response to climate change currently known: the invasion of the pine bark beetle.
This is not a new species of beetle; it has been around for thousands of years and has coevolved with lodgepole pine at lower elevations. During this coevolution, successive generations of lodgepole pine trees developed physiological and chemical defense mechanisms to prevent fatal beetle infestation. Whitebark pine trees grow at higher elevations and have not changed significantly in an evolutionarily sense, because until recently there was no such threat to their survival. What’s new is that the warmer temperatures have allowed the beetles to survive the winters affording the beetles the opportunity to invade trees in higher elevation areas as a result. Combined with the fact that whitebark pine trees have fewer defense mechanisms against pine beetle attacks than other trees, we are left with a forest of firs, spruces, lodgepole, and a bunch of dead whitebark pine trees.
So how does this affect the presence of grizzly bears? It has been well-documented by scientists and biological researchers that whitebark pine seeds are one of the four main food sources for grizzly bears in Yellowstone National Park. Long-time entomologist studying whitebark pine, Jesse Logan formerly of the United States Forest Service, Colorado State University, and Virginia Polytech Institute and State University explained the factors that led to such a widespread killing spree. Jesse’s vast knowledge and experience, his humble and confident personality, and his entertaining anecdotes created an intriguing and inspiring learning adventure. Along with Adam Markham, president of Clean Air – Cool Planet, we spent the day learning about the tell-tale J-shaped entry tracks of the beetle, how it takes 70 to 100 years for whitebark pine trees to begin producing cones (and therefore seeds for animals to eat), the visual difference between a beetle-killed tree with the ghostly terminal branches remaining and a fire-killed tree without the fluffy gray appearance, and how the pine beetle has sped up its reproductive cycle in response to warmer winters. The most alarming fact is how quickly the beetle epidemic has taken out whitebark pine trees and therefore dramatically reduced the availability of a key grizzly bear food source.
As we approach the petition by the government to again de-list the grizzly bear as a threatened species protected under the Endangered Species Act as early as 2014, we know that the current status and predicted future of whitebark pine trees is an important factor. Unfortunately, not everyone is listening to that information. Some are carelessly assuming that the grizzly bear as a flexible omnivore will adapt to this widespread loss of a key food source. It is estimated that at least 70% of all whitebark pines in Yellowstone have been lost in the last decade or so to beetle infestation. With no end in sight to global warming trends, it is possible that we will functionally lose this species in the Yellowstone ecosystem entirely, perhaps even within the next century. There is clear indication that the availability of whitebark pine seeds affects the reproductive success of grizzly bears. The consequences of losing whitebark pine trees to this isolated grizzly bear population will not fully be understood for at least another decade as their reproductive rate is the slowest of all land mammals in North America. Here’s hoping the bears don’t get de-listed until we have good evidence that they will have enough food to keep their population size where it needs to be for long-term population survival.
(Photos: Christine Wilcox)