Invasion of the Pine Beetles
From the air above Yellowstone National Park, the view has turned a sickly gray. Warmer temperatures have triggered a beetle infestation in the whitebark pine and other trees that make up the Yellowstone ecosystem. Jesse Logan, former head of beetle research at the U.S. Forest Service's Rocky Mountain Research Station, has studied the northern Rockies for more than 15 years and shares his thoughts about the current infestation, the importance of whitebark, and what Yellowstone could look like in the future. It might not be a pretty picture. (The interview has been edited for length and clarity.)
Pine beetle infestations are a common occurrence in the Rockies. How is the current outbreak in whitebark pine different?
Whitebark pine is restricted to high elevations in the Rocky Mountains. Forests of this tree form an important part of the ecosystem above 8,500 feet. In the past, the climate has just been too cold in the winter and not hot enough in the summer for pine beetles to be able to complete their yearly life cycle at that elevation. Pine beetle outbreaks have historically occurred in lower-elevation stands of lodgepole and ponderosa pines. The climate in the northern Rockies is changing -- milder winters and hotter summers have allowed the pine beetle to increase its range.
Why are pine beetles so devastating to whitebark pine?
One hypothesis is that the whitebark pine didn't evolve with the beetle like lower elevation lodgepole or ponderosa pines, leaving it more susceptible to infestation. The pine beetle has a symbiotic relationship with the blue stain fungus. This fungus, which clogs up the tree's resin ducts, combines with the feeding activity of the pine beetle and its larvae to kill the tree. Adult pine beetles make feeding tunnels through the tissue that carries nutrients throughout the tree. Then when the larvae hatch, they disrupt the tree's whole circulatory system.
Why are whitebark pine trees important to the Yellowstone ecosystem?
Whitebark pine plays an important role in the hydrologic cycle of the West. Because most of the water in the West accumulates as snow, it's important to have gradual run-off. If run-off happens too fast, water is lost. This has negative impacts on the water supply. It's important to maintain forest cover at whitebark pine elevations, because a healthy tree cover helps prolong the release of water in the spring by capturing snowfall like a fence. The whitebark also has a large, highly nutritious seed that's an important food source for a wide array of wildlife, including grizzly bears. Grizzlies depend on this seed to put on their winter weight -- there isn't a large berry or fruit crop for them to feed on in Yellowstone that time of year. The whitebark pine also keeps grizzlies in the high country, out of trouble. Without it, they're coming into contact and conflict with humans, raiding garbage cans and gut piles left by hunters.
When did the whitebark pine die-offs start?
When we started investigating the health of whitebark pines in 1994, our major study site was on Railroad Ridge, in central Idaho. In the 1930s, there had been a significant death of whitebark pine, presumably caused by a bark beetle infestation, associated with a warm period in that area. At that time, the first Intergovernmental Panel on Climate Change reports had just come out, with early global warming predictions. Given what we knew from the previous die-off, we wanted to ask the question: If warming occurs in the amount the report says, what would this mean for the geographic distribution of the pine beetle? The first year that we saw significant mortality of whitebark pines on Railroad Ridge was 2003. It was a catastrophic thing. By 2006, most of the larger, comb-bearing whitebark pines were killed. We're seeing the same scenario repeated throughout greater Yellowstone. This year we completed an aerial inventory of the entire ecosystem -- we'll have concrete figures in a few months, but I'd hazard a guess that the pine beetle has infested 80 percent of the whitebark pines.
Can anything be done to save them?
This is a natural event on the scale of Katrina. Could you build a fan big enough to blow a hurricane back out to the ocean? The scale, the speed, is just too much. This is a global warming issue. Until we begin to address the reduction of greenhouse gasses, this is probably a catastrophe that's going to happen.
Last week, a court ruling put grizzly bears in Yellowstone back on the endangered species list. What does this mean for their predominant food source -- whitebark pine seeds?
The impacts of this are huge for the grizzly, but it's less clear what the impact will be for whitebarks. This may mean revising the areas that have been marked for grizzly protection. There's a real disconnect between the designation of grizzly recovery areas and where whitebark pines are being lost. But there are some places throughout greater Yellowstone where the whitebark pines are still relatively healthy. Designating these as recovery areas could keep the grizzlies fed and out of contact with people, which is good for the bears, because they always come out on the short end of these interactions.
What will the forests of the northern Rockies look like 30 years from now without the whitebark pine?
Neither I nor anyone else has a crystal ball. Other trees species could move in and colonize the habitat. Lodgepole pine, for instance, is great at recolonizing a disturbed habitat -- it made a huge comeback after the 1988 wildfires. But nothing -- not lodgepoles or limber pines or anything else -- is going to replace the unique ecosystem services provided by whitebark pines. Lodgepole pines have a more closed canopy, whereas whitebarks tend to fan out, creating cover for breeding elk and other animal species. Lodgepoles also lack the large, nutritious seeds of whitebark pines. These are really unique forests.