Alpine Zones Greening Across Northeastern North America

A new satellite analysis shows 69% of alpine zones in northeastern North America have experienced significant vegetation increases from 1984 to 2024. This greening trend affects 88% of the total alpine area in the region, signaling a major ecological transformation driven by climate change and other factors.

Researchers identified 35 major alpine zones across a 500-mile mountain range stretching from New York's Adirondacks to Quebec's Gaspé Peninsula. Using hundreds of Landsat satellite images over four decades, they monitored 50 square miles of alpine terrain south of the St. Lawrence River. The study area included zones in the Green Mountains and White Mountains, with nearly 70 million people living within a day's drive of these vulnerable ecosystems.

Vegetation shifts include shrubification and expansion

Significant greening and shrubification are occurring inside the alpine zone itself, not merely at the advancing tree line. Alpine plants are being replaced by shrubs. This growth is accelerating on sheltered mountain slopes while being suppressed on wind-exposed sides. Increases in vegetation were observed across diverse habitats, including cliff plants, cushion-tussock communities, and sedge meadows. Greening was especially evident in the Presidential Range in New Hampshire and on Katahdin in Maine.

Climate, wind, and legacy pollution drive changes

Multiple interacting factors are altering these high-elevation landscapes. The overall warming trend, declining snow cover, slope steepness, sun exposure, soil chemistry, and nitrogen deposition from historical power plant emissions all play a role. Wind is a particularly notable influence in this region, causing alpine zones to start at lower elevations than elsewhere at similar latitudes. The wind suppresses growth on exposed slopes but enables accelerated growth in sheltered areas. In the late 20th century, nitrogen from Midwestern power plant emissions acted as a fertilizer, favoring some plant species over others.

Findings aim to inform conservation in vulnerable ecosystems

The alpine zones are biodiversity hotspots home to many rare flowering plant species. The acceleration of growth may not be positive if these rare alpine plants get crowded out by more aggressive flora. Human activity adds pressure, as hikers, hunters, bikers, and skiers may inadvertently track in invasive species. The co-authors warn that these changes necessitate updated stewardship. They hope the analysis will directly inform future land and ecological management practices for these vulnerable ecosystems.