Any treeless landscape above timberline, where incessant winds scour the landscape, mean annual temperatures are low, harsh sub-freezing winters reign and moisture is minimally available is considered alpine tundra. Such extreme environmental conditions only allow the establishment of prostrate shrubs, matt-like herbaceous plants, mosses and lichens. In Arizona approximately five square kilometers of alpine tundra exist above 3,500 meters on Mt. Humphreys in the San Francisco Peaks . This isolated flora is an important refuge for a depauperate community of tundra plants considered to be an extension of the alpine tundra of the Rocky Mountains . However, the isolation of this island of tundra also tends to express an influence from the surrounding low land vegetative communities. C. Hart Merriam described the Artic Alpine tundra Life Zone in much the same manner while specifically including a precipitation range of 33 to 40 inches of annual moisture and a 30 to 90 day growing season.
Woody plants are rare in our alpine tundra. Small individuals of Bristlecone Pine (Pinus aristata), fir (Abies lasiocarpa), and spruce (Picea engelmannii) may be present in protected sites. Common herbs include our endemic Senecio franciscana as well as widespread taxa from the Rockies such as Potentilla sibbaldi, Geum rossii, Primula parryii, Silene acaulis, and Cerastium beringianum. Grasses are not as common as sedges such as Carex bella, Carex albonigra, and Carex ebenea.