In the northern Appalachian Mountains, warmer weather is making alpine regions greener

Source: The Conversation – Canada

If you visit Mount Jacques-Cartier in Québec’s Gaspésie National Park, you can expect to climb through a forest of spruce and fir trees along a trail lined with bunchberry flowers. As you approach the peak, the trees get shorter and disappear at the alpine zone, where the climate is harsh and plants cling to the ground.

But this island in the sky — like dozens of other alpine summits in the northern Appalachians region — is changing. Research by my colleagues and me, using 41 years of satellite imagery of mountains across the northeastern United States and Québec’s Gaspé Peninsula, shows that these mountains are slowly greening.

Why is this happening? And what does it mean for the future of the plants that live where the cold and wind are too extreme for trees to survive?

Life in the northeastern alpine zone

Scientists have been studying alpine plants in the northern Appalachians since the 1784 Belknap-Cutler expedition to Mount Washington in New Hampshire.

Later botanists such as M.L. Fernald documented the exceptional plant diversity of Québec’s Chic-Chocs Mountains.

They found plants that can live where it’s cold, cloudy, rainy or snow-covered, and almost unimaginably windy.

At Petit Mont Sainte-Anne, gusts can reach up to 250 kilometres an hour. Mount Washington famously recorded a 371 km/h wind in 1934, and dangerously high winds are commonplace.

In winter, these winds pick up ice particles and blast them against any plants outside the shelter of a rock or snowdrift. Plants on these mountains must be hardy, and some are found nowhere else on Earth.

Changes on the ground

Recently, botanists and ecologists have reported changes in the northern Appalachian Mountains. My colleague, terrestrial ecologist Jordon Tourville, found the treeline is advancing upward on Mount Katahdin and Mount Washington. Surveys of Mount Bigelow’s alpine zone showed increases in trees and small shrubs.

Those studies are important, but they cover individual mountains in varying time periods with varying methods. To see the big picture, we needed to step back.

We obtained and processed hundreds of images from Landsat satellites from 1984 to 2024 covering every alpine summit in the region. Building reliable datasets of greenness wasn’t easy. It required careful calibration across generations of satellites.

We also had to solve the problem of observation frequency bias. In the 1980s, Landsat-5 collected fewer images per season than newer satellites do. This increase in observation frequency means that we’re statistically more likely to capture images of peak-summer greenness today than back in 1984. That could create the appearance of a false upward trend in greenness.

To account for this, we built statistical models for each summit quantifying how greenness fluctuates seasonally. By comparing the satellite observations to these models, we were able to make better calculations of each year’s maximum greenness. This eliminated the problem of sparse data in the past, giving a high-quality estimate of actual greening.

What the images show

We detected significant greening at approximately 70 per cent of alpine sites in the northern Appalachian Mountains, or 88 per cent of the alpine area. Québec’s McGerrigle Mountains and the nearby Maine mountains are changing fastest.

This greening is occurring in the interior of alpine zones, not just along the treeline. It’s not just the forest slowly expanding upward, but ecological changes throughout the alpine zone.

One obvious cause is climate warming. Alpine greening has been observed elsewhere in the world; a warmer climate allows less cold-tolerant plants to out-compete hardy but slow-growing ones.

Other factors may be involved. The same carbon dioxide that warms the atmosphere can act as fertilizer for plants. So does nitrogen emitted by fossil fuel power plants. Invasive plant species carried to mountain peaks on hikers’ boots may crowd out native species if the warming climate lets them gain a foothold.

Greening means that the rare plants on these summits could be overwhelmed by faster-growing species taking advantage of environmental changes. Research in Europe shows increasing rates of local extinction of high-elevation alpine plant species as lower-elevation plants move in.

Some positive findings

A silver lining for the northern Appalachians is that in the windiest, most exposed locations, our satellite data seem to show greening is slower or non-existent. The region’s fierce winds may protect some of its alpine plant communities from these environmental changes.

On heavily visited alpine summits, summit stewards and other environmental education efforts are helping plants by reducing trampling of the tundra by hikers. That’s a form of greening that is beneficial.

Satellite imaging is a powerful tool for alpine ecologists, but it doesn’t replace fieldwork. We still need to climb mountains and study the plants directly. But by showing what’s happening at the regional scale, we can help scientists contextualize their field studies and understand how those might extrapolate more widely.

From climate warming to atmospheric nitrogen deposition, our environmental challenges cross borders. This study demonstrates a similarly broad approach to understanding how those changes are shaping the lives of the tiny plants that live on northern Appalachian peaks.

Jonathan W. Chipman receives funding from the Dartmouth College William H. Neukom Institute for Computational Science, the Schmidt Sciences Humanities and AI Virtual Institute, and the US National Institutes of Health. He is a current member of the Appalachian Mountain Club, the Green Mountain Club, and the Adirondack Mountain Club.

Original source: https://analysis1.mil-osi.com/2026/10/14/in-the-northern-appalachian-mountains-warmer-weather-is-making-alpine-regions-greener/