Climate Change and the Alpine Zone

By Erin Trombley

Adirondack alpine zones are special places. If you’ve ever stood on the exposed rock on an Adirondack Mountain summit, you know what awe-inspiring and precious places they are. Alpine zones are home to some of the rarest and hardiest plants on Earth. From specialized mosses and lichens to tiny shrubs and herbaceous plants, alpine vegetation is specially adapted to thrive in cracks, thin soil, and cold temperatures, with high winds and UV exposure, and low amounts of carbon dioxide. Alpine ecosystems depend on these tough, tenacious organisms to ensure their continued existence.

The Threats

Climate change brings with it a number of threats for alpine plants. Among the threats, treeline expansion. It’s widely expected that as global temperatures rise, the advance of treelines, including expansion of pockets of krummholz, the twisted, stunted tree forms that occur between the treeline and open alpine terrain due to harsh conditions. These advances will lead to the displacement of some alpine species and cause division of habitats through added shade, reduced moisture, and nutrient depletion in the soil; essentially the creation of new microclimates in their understories.

Another threat as temperatures rise is atmospheric deposition. Smoke from western wildfires (increasing in frequency and scale with climate change), PFAs (so-called forever chemicals), as well as plastics are carried in the atmosphere and deposited on summits. Atmospheric deposition has 4-20 times more impact at higher elevations. These depositions change soil pH, which impact some alpine plants and bodies of water.

Upset phenology is yet another potential consequence of climate change. Within alpine ecosystems, plants, fungi, insects, and animals have all developed a symbiotic relationship to each other. As temperatures climb, this natural process may be disrupted. For example, the alpine plant, designed to bloom and reproduce quickly for its short growing season, may bloom at its normal time based on daylight, but the insects required to pollinate them may have emerged sooner based on air temperatures. When they do emerge, the pollen they need may not yet be available, negatively impacting populations. With a decline in insect population, birds that rely on those insects for food may also suffer, and so on.

The Evidence

Treeline advance, as detailed above, could be problematic for Adirondack alpine zones by creating increased shade and out-competing other plants for nutrients in substrate. The result is reduced diversity versus open spaces.

According to a 2018 article by Sarah Greenwood and Alistair S. Jump, of the University of Stirling School of Natural Sciences, Biological and Environmental Sciences Department, predictive models of treeline advance in Europe going back as far as 2003 & 2004 found that the projected degree of treeline advance severely reduced alpine areas: a conservative estimate of a 100 meter rise in the treeline position would reduce alpine heath populations by as much as 41%, for example. Most of the remaining alpine plants in the model would be relegated to pockets around boulders and on scree slopes. From these models we can also foresee alpine plant extinctions as well.

Unfortunately, this is not merely theoretical. This type of encroachment is already taking place in the Ural Mountains of Russia, in Sierra de Guadarrama, central Spain, and in Glacier National Park, Arizona. Greenwood and Jump also cite a global analysis of treeline advance published in 2009, which observed treeline advance in over 50% of studied sites. In the remaining sites, other types of changes were observed, including changes in growth, density, and tree form.

Silver Linings

There is some good news to report for the Adirondacks. Though much more research is needed, data so far seems to show that while the Northeast United States is warming faster than the rest of the continental US, the highest Northeastern elevations have not warmed as fast as lower elevations. According to Scott McKim, Research Support Specialist at the Whiteface Mountain Field Station, of the Atmospheric Sciences Research Center at the University at Albany, that’s because, “…they spend a significant amount of time in the free troposphere, above the boundary layer… and it’s the boundary where we’re seeing the most significant warming globally.”

When examining treeline advance, there are also natural factors at play which limit upward expansion. Steep inclines and areas with large boulders or devoid of substrate (soil) are not suitable for trees. The same hurricane-force winds and rime ice that make recreation a challenge on the windward side of Northeastern summits have actually proven protective against the advance of trees and krummholz on Adirondack summits. High wind and rime ice are distinguishing factors for Northeastern U.S. summits, versus those in other regions.

In other words, alpine zones that spend most of the time in the free troposphere appear to be protected from the worst effects of warming so far. For those summits above 2000 feet but below the highest peaks, which exist mostly within the atmospheric boundary layer, McKim says, “…that is where we can expect to see the most indicators of warming.”

But wait, there’s more good news! According to the 2021 article Thirteen Years of Rare Plant Population Changes in the Adirondack Alpine, from 2006-2019 a study was made of 10 rare vascular plant species in 16 Northeastern alpine areas. The study anticipated declines in plant populations due to climate change, atmospheric deposition, and recreational use from the outset. The study revealed that only 2 of the 10 species showed statistical decline during the period of the study. Similar studies published in 2010 and 2011 observing woody plants resulted in similar findings.

The article’s authors, Timothy G. Howard, Ph. D., Director of Science at SUNY College of Environmental Science and Forestry, Kayla White, ADK’s Stewardship Manager, and Julia Goren, current ADK Deputy Executive Director, attribute these surprising findings to warmer temperatures and longer growing seasons, nitrogen deposition, and less trampling by recreators. The latter is a huge, measurable win for the Adirondack High Peaks summit stewardship program, whose mission it is to educate recreators on summits and trails to prevent damage to these plants.

More Data Required

As climate change continues, we will undoubtedly see more erratic weather patterns with more extreme events. Total rain and snowfall, evaporation rates, cloud cover, and temperature patterns will continue to be affected. Flora and fauna will be impacted. Behaviors may be changing right now. But we can’t accurately say how. Long-term projected impacts of global warming on Adirondack alpine zones remain undetermined due to a lack of data. More study is needed to measure change as it happens to make reliable predictions and plan for the future.

Summit stewards play a critical part in this type of research.  Often seen by the public as “those nice people,” or mistaken for rangers, summit stewards are part of the larger scientific community, studying botany and changes in alpine plants populations. While they are engaging alpine zone visitors on ways to reduce impacts on alpine vegetation, they are also conducting research and undertaking recovery projects. They share findings and best practices with their peers in pursuit of information critical to protecting the wonders of alpine zones.