The treeline of Polylepis tarapacana on the volcano is as high as 5,200 m above sea level, one of the highest altitudes trees can be found growing anywhere in the world.
It is restricted to a narrow swath of treeline vegetation (scrub, stunted trees and Polylepis woodland) situated between montane forest and Páramo grasslands that is often just hundreds of meters wide.
The moss may also colonise stony soil, boulders and snowy grikes above the treeline.
The mountains are rich in flora with about 25% of the country's plant species being found above the treeline in alpine plant habitats and grassland with mountain beech forest at lower elevations (of the eastern side but not in Westland).
In the Presidential Range of New Hampshire's White Mountains, for example, cairns are found at ten-foot (three-meter) intervals along trails above treeline, so that hikers forced to crawl by heavy winds and occasional infamously lethal weather can find their way to safety.