This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In northeastern North America, a stretch of mountains runs 500 miles (800 kilometers) from the Adirondacks in New York to the Gaspé Peninsula in eastern Quebec. Nearly 70 million people live within a day's drive of one of the alpine zones, the areas above the tree line where trees don't grow because of harsh conditions.
These habitats, including alpine zones in the Green Mountains and the White Mountains, are home to many rare species of flowering plants, making them biodiversity hotspots. However, climate change and rising temperatures are affecting the alpine zones, as are declining snow cover, atmospheric nutrient deposition and high-impact outdoor recreation. Hikers, hunters, bikers, skiers and others enjoying the mountain terrain may track in invasive species.
Prior research has examined greening in regions such as the Alps, the Rocky Mountains and the Arctic in relation to climate warming and other processes. But Jonathan Chipman, director of the Citrin Family GIS/Applied Spatial Analysis Laboratory at Dartmouth, noticed that a regional assessment of what has been happening above the tree line in northeastern North America was lacking. Given that Dartmouth is home to remote sensing and technical expertise in processing satellite imagery and time series data, and the Appalachian Mountain Club has a huge amount of alpine ecology expertise on the ground from fieldwork and citizen science projects, Chipman teamed up with co-author Jordon Tourville, a terrestrial ecologist at the Appalachian Mountain Club, to research the topic further.
"This study was a perfect collaboration between a university and a nongovernmental organization in the region, as we don't just want to be doing this research in the abstract, but we want to help land managers, other stakeholders, and the public understand what is happening in the region," says Chipman. In a new study led by Chipman using hundreds of satellite images spanning 40 years, the team provides the first regional analysis of greening trends in the northern Appalachian region. Published in Ecosphere, the results show that 69% of the alpine zones studied have experienced significant increases in vegetation.
Those zones represent 88% of the alpine area in the region. "In other regions such as in the Alps, as an area near the top of the mountain warms, the tree line advances, growing higher up the mountain, but the situation here is quite different," Chipman says. "Our results show that significant greening and shrubification, in which alpine plants are being replaced by shrubs, is occurring inside the alpine zone, not just where the tree line is advancing." This was especially evident in the Presidential Range in New Hampshire and on Katahdin in Maine, where greening was prominent within the alpine zone at higher elevations.
Increases in vegetation were observed among cliff plants that grow out of rocky outcrops; cushion-tussock, a dense dome-shaped plant; and sedge meadows, a hardy grass-like plant. However, according to the co-authors, this accelerated growth may not necessarily be positive if rare alpine plants start getting crowded out by more aggressive flora. "While these ecological changes are affected by a number of factors—the overall warming trend, the landscape such as the steepness of the slope and sun exposure, snow cover, soil chemistry, and nitrogen deposition from power plant emissions—what's notable in this region is the effect of wind," says Chipman.
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