Grizzlies on the Hot Seat, by Brian Peck

When we talk about the effects of global warming on big mammals, most of us focus on the plight of the polar bear, and rightly so. Predictions are that more than half of the species could be gone by 2050. Yet mountain species, from bighorns to pikas, and mountain goats to ptarmigan also face bleak prospects -- and of course grizzlies.

Grizzlies don't face a peril as clear-cut as the disappearing arctic pack ice, but threats to their existence are deadly serious because they come from so many diverse sources.

In Greater Yellowstone (GYE), the massive fires of 1988, an early warning of global warming, killed nearly 20 percent of the ecosystem's whitebark pines (WBP) -- a critical grizzly food. In addition, the warming cycle and its associated decade long drought have weakened the remaining trees, allowing the lethal white pine blister rust to infect more than 20 percent of the surviving pines. This same disease has already wiped out the whitebark pine as a major food source in the Northern Continental Divide Ecosystem (NCDE). Finally, without our historic severe winters to kill them off, mountain pine beetles are surviving in record numbers, completing their life cycle in one year instead of two, and advancing upward in the previously immune whitebark stands at high elevation.

This is disastrous for two reasons. First, whitebark pine nuts are one of the highest energy fall foods for bears before they den. The nuts are especially critical to females carrying fetuses. Second, because the pines occur at high elevation away from people, a good cone year keeps grizzlies from getting in trouble at lower elevations, and mortalities drop proportionally. In fact, in good cone years the GYE grizzly population goes up seven percent, and drops five percent in bad years. What will happen when the whitebark pine is functionally gone, and every year is a "bad cone year?"

Our moderate winter climate created by global warming is allowing trees to increasingly encroach on alpine meadows, and lower elevation trees are colonizing upward to crowd out the whitebark pines. The encroachment of trees on the alpine tends to increasingly concentrate this habitat type on mountain tops, spelling big problems for species such as bighorn sheep, mountain goats, pika, marmots and wolverine, who can only go so far uphill before they run out of mountain.

The upward "march" of forests is a huge problem for another key grizzly bear food -- the army cutworm moths. Every summer, billions of these moths migrate from the Great Plains states to feed on high elevation, flower-carpeted meadows in the GYE and NCDE. Research in Yellowstone has shown that an average grizzly feeding on moths in adjacent talus slopes can eat 30,000 fat-loaded moths per day, and that bears doing that for two months will maintain 47 percent of their yearly caloric needs!

Like the whitebark pine, these moths occur at the highest elevations, drawing bears away from increasingly developed low elevations where conflicts and mortalities soar. When the advancing forests crowd out most of these flower fields and their moths, we expect a drop in habitat carrying capacity. Federal bear managers suggest that grizzlies are "opportunistic omnivores," and will simply switch to alternate foods. However, nutritional analysis shows that no alternate foods, either individually or collectively, have the caloric punch of moths and whitebark pine.

In the Northern Continental Divide Ecosystem, the situation appears to be somewhat different, but still potentially serious. Unlike Yellowstone, where a grizzly's diet is heavy on meat protein (79 percent for males, 45 percent for females), the NCDE bears appear to be nearly 90 percent vegetarian.

Blister rust probably entered the NCDE in the 1930s, becoming very serious by the 60s, and wiping out most of the ecosystem's cone producing trees soon thereafter. Early research (the 1960s) by Chuck Jonkel of GBF demonstrated the importance of WBP to bears in the area. It is likely that the ecosystem's carrying capacity took a substantial hit, but with no one conducting research specifically on the topic, the extent of the impact hasn't been quantified. NCDE whitebark pines were largely gone before global warming could do them in. It is widely assumed that the surviving bears simply shifted to other plant foods -- the NCDE being generally more lush than Yellowstone.

Nonetheless, the area around Glacier National Park (GNP) has become something of a "poster child" for the impacts of global warming. More than a decade ago, internationally known USGS glaciologist Dan Fagre predicted that the glaciers of GNP would be gone -- replaced by perennial snow fields, or bare ground, by 2030. In a recent TV interview, however, he noted that the melting was running 8-10 years ahead of his earlier models, suggesting the demise of the glaciers by 2020-2022. Related models also show advancing forests, eliminating the GNP alpine zone by 2100.

The loss of glaciers is important because they provide a steady, year-round supply of water throughout the ecosystem and beyond. In fact, after about mid-August, 60 percent of the water in NCDE streams comes from glaciers, and their loss implies a tremendous shock to water quantity, quality, trout habitat, and vegetation that grizzlies rely on. And just as global warming can destroy species from the tops of mountains, it's likely to severely impact the grizzly's plant foods, which won't be able to "migrate" upward fast enough to compensate for rising temperatures and drying conditions. The exact future scenarios are difficult to predict, but in general, it doesn't look promising.

Finally, there are wildfires in the NCDE, where high temperatures, and a decade long drought have led to numerous intense fire seasons since 2000, even with 150,000-250,000 acre fires at once in NW Montana. While fires have been a vital part of Montana forests for millennia, the warming of the last 20 years has created firestorms of exceptional size and intensity.

In 2007, temperatures in NW Montana broke 90 degrees for 46 consecutive days and more than 100 degrees half a dozen times. Even residents in their 80s couldn't recall heat waves anything like this.

On the one hand, many of these fires will improve grizzly habitat in the long-term as overstocked forests are replaced by newly lush understories hosting more foods favored, not only by bears, but by deer, elk, and moose. This in turn is good news for wolves who will enjoy an expanded prey base, and perhaps for grizzlies, who can steal more wolf kills. Yet in the short-term, many of these fires are so severe that they kill nearly 100 percent of some stands -- temporarily lowering vital security cover in an ecosystem where poaching is the second leading cause of grizzly mortality.

A classic example of this mixed result is Glacier National Parks' Huckleberry Mountain and Apgar Range. Burned extensively in the late 60s, these mountains came back in dense huckleberry stands that drew bears from across the ecosystem. One aerial count in the last decade tallied more than 40 bears at one time. However, the range has seen two intense burns in the last five years, with nearly complete burns of vegetation over large areas. This should eventually recover the huckleberry stands, but it is estimated that it may take up to a decade for the hucks to reach maturity.

Nearly 15 years ago at the Pacific Northwest timber summit, one forest ecologist cautioned the participants that, "Ecosystems are not only more complex than we think, they're more complex than we CAN think." Perhaps that's a good thing to keep in mind as we see our only "life support system" fail in so many ways.