White-bark pine ravaged throughout Yellowstone

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The clear, high peaks of the greater Yellowstone region once were studded with huge stands of majestic white-bark pine forests, some of the trees 1,000 years old.

A decade or so ago, big pockets of rust started appearing as the green pine needles succumbed to infestation and disease. Since then, it’s become worse: Unable to fend off invading armies of mountain pine beetles, large swaths of the forest have simply died. An alarming part of the high-elevation landscape across the mountains of Wyoming, eastern Idaho and southern Montana is gradually turning eerie and gray.

‘You get a picture of how breathtaking it is from the air,’ said Louisa Willcox, a senior researcher with the Natural Resources Defense Council, which has completed a first-ever aerial survey of the greater Yellowstone ecosystem to document the extent of the threat to the region’s white-bark pine forests. ‘All the gray you see in the eastern part of Yellowstone Park and the Absaroka Mountans are gray ghosts [of dead trees]. Basically, white-bark pine [there] is functionally gone, functionally lost.’

The big culprit, most researchers believe, is climate change. Hard winters once killed off the beetles that bore into the trees; beetles have been surviving the milder winters and have extended their range farther north than at any time in modern history, as far as northern British Columbia.

Scientists had known there was a problem, but until the vast aerial survey undertaken this year by the NRDC and Ecoflight, patrolling, photographing and documenting 21 mountain ranges across the three states -- the entire 20 million-acre Yellowstone ecosystem -- no one was sure how wide-ranging it was.

What the survey showed was much worse than expected: 85% of the forests showed signs of mortality, likely due to infestations of white-bark pine beetles and blister rust, more than half of them showing ‘high mortality,’ while barely 5% showed no signs of beetle infestation, according to the report.

‘White bark is basically a sitting duck to the mountain pine beetle,’ Willcox said in a telephone briefing with reporters.

The infestation has huge consequences for the region. The die-off of high-elevation forests leaves the surrounding countryside more vulnerable to avalanches and early, heavy spring runoff, detrimental for fish in the streams below. Just as worrying, Yellowstone’s beleaguered population of grizzly bears, re-listed last year under the federal Endangered Species Act, depends heavily on the caches of white-bark pine nuts stashed across the mountainsides by red squirrels. In years when white-bark pine forests bear few seeds, studies have shown that grizzlies, not as fattened for the long winter denning season, bear fewer cubs.

The infestations also threaten a potentially fatal death cycle for the forests: With declining numbers of Clark’s nutcracker birds, which break open the pine cones to feed on the seeds, the forests stand to lose their capacity for natural regeneration, scientists say.

The first major outbreaks of beetle infestations became apparent in 2004, Willcox said, and have continued since then at levels far more serious than any recorded in studies that have looked at the entire 1,000-year life cycle of the oldest trees, including the outbreaks that accompanied several warm winters during the 1930s.

‘There is nothing comparable. This is clearly a climate-related phenomenon, unlike anything that has happened before,’ she said.

Only four areas surveyed showed relatively healthy stands of white-bark pines: the Tetons, the highest, glacier-studded ridges above Yellowstone, the core of the Wind River mountains and the Beartooth Plateau.

The NRDC has petitioned to have the white-bark pine protected under the Endangered Species Act. In an initial study, the U.S. Fish and Wildlife Service has concluded there may be reason to consider it. ‘Based on our review, we find that the petition presents substantial scientific or commercial information indicating that listing P. albicaulis [white-bark pine] may be warranted,’ the agency said in a notice this week. The announcement launches a 12-month review of the petition.

-- Kim Murphy