How climate change leaves Arctic caribou out in the cold

But shrubs such as alder, willow, dwarf birch and creeping juniper grow a lot faster than trees and they shade out sunshine that lichens, mosses and other alpine and tundra plants need to thrive during a growing season that is often measured in weeks rather than months.

"Shrubs also trap snow, which insulates soils in the winter, and shades soils in the summer," says Myers-Smith.

"Research has shown that soil in shrub-free zones can be almost a cold as the air above it. But that same soil that lies beneath shrubs in winter can be up to 30 degrees warmer than the air temperature. This insulating and cooling can alter soil temperatures, nutrient cycling and permafrost thaw."

"Shrubs also seem to do best in a landscape that is increasingly becoming more disturbed," she says. "The darkening of the surface associated with shrubs growing above snow could also accelerate snowmelt and cause regional warming."