Will northeastern alpine ecosystems be survivors or victims of ongoing climate and geologic change? Pick your answer and it could be true, unless the appropriate time-scale is defined. In geologic time scales, the answer is "victims." Mountains are constantly forming and then eroding away. Even the Earth with its associated climate has a finite life expectancy. In shorter time scales that humans can relate to—decades, centuries, or possibly millennia— the answer is less certain.

The popular press, fueled by legitimate hypotheses and extrapolations from the scientific community, has created the impression that global warming will cause the universal upslope advancement of forests because of favorable growing seasons, and these forests will overrun the northeastern mountain alpine areas. After all, the region's alpine ecosystems today have already been reduced to isolated, biogeographic islands atop our highest most exposed peaks. They are Arctic remnants from the last glacial melt period, of which there have been several. And these alpine areas can't migrate upward in elevation because they already are on the peaks. Strengthening this hypothesis is evidence from the European Alps of upward migration of the flora and the disappearance of glaciers in Glacier National Park. When extrapolated, such evidence reasonably hypothesizes northeast alpine ecosystem extinction because of recent global warming.

Think back more than 14,000 years ago. All but possibly the very tips of the northeastern mountains were mostly under a moving mass of glacial ice. But the Earth warmed rapidly around 14,000, and again 10,500 years ago, which was accompanied by rapid melting of the glaciers. Without doubt, the world's climate over long periods has not been static and very likely will continue to be very dynamic. We also know that living organisms have a history of changing the composition of our atmosphere's gases that, in return, can change the climate. One example of how organisms change conditions is that for almost the first half of the Earth's 4.6 billion years of existence—before blue-green cyanobacteria evolved sufficiently to undertake photosynthesis that releases oxygen as a waste product into the atmosphere—the atmosphere contained little to no oxygen. Today, humans may be altering the globe's climate as we release tremendous quantities of carbon dioxide that was captured by photosynthesis and sequestered in fossil fuels, methane, and other greenhouse gases that have the ability to trap the sun's heat in the lower atmosphere, instead of letting it radiate back into space. The outcome of this human change to the composition of the atmosphere's chemistry may be less beneficial than the release of oxygen into the atmosphere by bluegreen cyanobacteria.

The Appalachian Mountain Club's Research department has examined the hypothesis that the region's alpine areas could become extinct as a result of global warming. Through a recent grant to the AMC from the National Oceanic Atmospheric Administration (NOAA), the AMC worked with the Mount Washington Observatory and the University of New Hampshire to examine some of the best long-term climatic and other mountain data available. This included the more than 70-year-long, daily weather records from the AMC's Pinkham Notch on the lower slopes of Mount Washington and from the summit of Mount Washington, New Hampshire. We also can infer backward from this period by using earlier published research on pollen and fossil plant parts collected from the ponds in the Presidential Range of the White Mountains to reconstruct changes in the mountain's climate and vegetation responses since the last glacier. But as our results unfolded, the old axiom, The more we think we know, the less we really know, proved true again.

Our original hypothesis followed conventional thought and events reported from lower elevations in the region and other mountains in the world: northeastern alpine ecosystems are at high risk because of ongoing climatic change. But our results to date have been somewhat clumsy in supporting that thesis in its entirety. From the AMC's mapping of the treeline-ecotone boundary—where the trees stop and the alpine zone starts—on the Presidential Range and on Baxter Peak on Katahdin in Maine, we observed that the treeline differed by 1,880 to 2,168 feet in elevation, respectively. The expected cooling rate as one goes up in elevation, because of the drop in air pressure, is approximately 5.5 degrees Fahrenheit per 1,000 feet of elevation. Therefore, these elevational differences for the treeline-alpine ecotone represent a theoretical temperature difference in the range of 10 to 11 degrees Fahrenheit, and these are only 5,000- to 6,000-foot-high mountains. It also begs the question: why are the alpine areas in the Northeast some of the lowest in the world? After all, many of the much higher alpine areas of the European Alps are at similar latitude to New England or even closer to the North Pole than to New England.

When we look at the Presidential Range weather records since the 1930s, we start to see something else at play. For example, scientists report significant warming trends at lower elevations in New England but at Pinkham Notch, where the elevation is 2,000 feet above sea level, we observed warming of less magnitude. And on the summit of Mount Washington, our study results show no statistically significant warming trend. We also looked at when snow melts, temperatures when plants grow (growing degree days), and temperatures when ice thaws. The trend changes for the last seven decades were least on the summit. Melting snow on Mount Washington: warming trends at high elevation have been the least dramatic. These results parallel observations from earlier paleobotanical research on the mountain. Since the last glacier, there have been major warming and cooling trends, and the pollen and plant part records show that the composition of the forest's species on the lower and mid-slope responded accordingly, with a time lag, as would be predicted. But the subalpine forest and treeline-alpine ecotone boundary appears to have been somewhat stable for the past several thousand years.

Does this suggest climate change is not a factor for mountains? Not necessarily. Today, we know many of the world's mountain glaciers are retreating. Yet, glaciers on Mount Shasta in California are actually increasing. The magnitude and impacts of climate change will not be uniform across the world. Simply extrapolating results from lower elevations of the region or from other mountains in the world to the northeast may be problematic at times.

What we do know is that spruce and fir trees, though physically deformed in the form of krummholz because of exposure, have survived at or near the top of almost all northeastern mountains for a long time. So trees can grow in the alpine areas of the Northeast, and growing seasons and specifically temperature regimes may not be the simple, limiting explanation why trees have not overrun the alpine areas.

The hypothesis we are working with now—and it has been around for a while—is that northeastern alpine areas would be forested were it not for the regional planetary boundary layer and related typical elevation of clouds. The planetary boundary layer is the zone where air moving across the planet is well mixed because of surface friction. Above this layer, its movement is much less impeded. The planetary boundary layer is not static and migrates altitudinally on a 24-hour cycle. Typical regional cloud elevations are associated with the upper limits of this layer in the atmosphere, as are the locations of our region's alpine areas—they are typically located between 3,600 to 6,000 feet above mean sea level. The air above compared with that within the planetary boundary layer can be under quite different influences. The AMC's measurements of air pollutant concentrations show substantial differences between the alpine zone and the lower valley. The higher elevations are more polluted for certain pollutants such as ozone because long-distance transport.

Above the planetary boundary interface zone, conditions are quite different with respect to temperature, wind, and clouds, compared with lower elevations. During the winter on our higher summits, frequent cloud events and concurrent winds frequently result in heavy icing and the mechanical degradation of the forest. This allows alpine plants to survive because they are better adapted to this very physical environment with their very low, ground-hugging stature. Alpine areas extend to their lowest elevations on ridges where winds more effectively deposit rime ice, and the forest extends as krummholz to the forests' highest elevations in the gulfs, valleys, or depressions most protected from winds, even if in the clouds. The juxtaposition of the planetary boundary layer with the region's higher mountain summits helps explain why their climatic conditions are not coupled with those reported from surrounding lower elevations and why the northeastern alpine areas have continued to exist at such low elevations in this region for thousands of years when temperature-related growing season conditions may not have been entirely limiting for trees.

What we still do not know is when and if there is a threshold where continued global heating might change that dynamic. For now, based on the best records we have, we suspect there may still be some resistance in the system that has allowed northeastern alpine areas to survive, even though global warming may affect lower elevation ecosystems first. However, we cannot rule out the possibility that human actions could accelerate global warming to a threshold point that would knock this system out of its current equilibrium. Continued greenhouse gas emission is a risky experiment relative to the survival of northeastern alpine ecosystems, even within human-time scales. Our results also offer insight into the importance of protecting subalpine forests. The region's subalpine forest could become (and may have historically been) the survivors for the region's much larger and commercially more important lower elevation spruce-fir forests.

Dr. Kenneth Kimball is the director of research for the Appalachian Mountain Club. He and the research department staff have been studying northeastern alpine ecosystems for more than 25 years. The department was a lead in the successful recovery of the rare alpine plant Potentilla robbinsiana that was removed from the federal endangered species list in 2002. More recently, the AMC was the principal investigator of a NOAA-funded research project on the impacts of climate change on northeastern alpine areas, with collaborating institutions the Mount Washington Observatory and the University of New Hampshire. The results summarized here have been accepted for publication in the scientific journal Arctic, Antarctic and Alpine Research.

This story appeared in the Summer/Fall 2009 Issue of Appalachia.