Alpine Ecosystems in Temperate Mountains of North America

Abstract

The temperate zone mountains of North America contain alpine ecosystems whose distinctive plant and animal communities are adapted to the cold temperatures, winter snow cover, short growing seasons, and high winds found in the steep rocky terrain at high elevations. Although 3% of the land area is alpine, the alpine zone contains 4% of the world's flora and is therefore richer in biodiversity than expected. At the landscape scale (>100 m), wind and snow interact with landforms to form mesotopographic gradients along hillslopes. Snow redistributed by winds produces long-lasting snowdrifts on lee slopes, which increase water availability downslope, but also affect the timing and length of the growing season for plants. Along the gradient, cushion plant-dominated vegetation occurs on exposed ridgetops, followed by dry sedge meadows or dwarf-shrub heaths in less exposed positions below the ridge, moist meadows or heaths in early-melting midslope positions, late-melting snowbed vegetation, and wet meadows or bogs in valleys. Alpine plant adaptations to the harsh environmental conditions include short stature, cold tolerance, long lifespans, and vegetative reproduction. Animals cope with winter conditions by living in sheltered environments under snow and talus, hibernating, or migrating. The American pika, a potential sentinel species for climate change, is intolerant of warm temperatures and depends on winter snow cover. On Niwot Ridge in Colorado, minimum temperatures and precipitation are increasing, but declining precipitation has also been observed in the western US. Climate change and atmospheric deposition of nitrogen are likely to contribute to shifts in ecosystem properties and plant and animal species distributions, such as shrub encroachment into herbaceous communities.