RWFM 4309 M. C. Wallace

TUNDRA - ALPINE GRASSLANDS

Tundra is found in extreme high elevations in the Southwest. This type is often only the small summit area above timberline. Alpine tundra is characterized by diverse herbaceous plants, lichens and mosses, and low-growing woody shrubs, all adapted to a brief and often interrupted growing season. In Colorado and New Mexico alpine tundra can be found on peaks above 3,500 m (Pase 1982). These communities are extensions of the larger and more extensive tundra of the rocky Mountain cordillera. Relatively contiguous alpine communities extend into the Southwest through the San Juan and Sangre de Cristo Mountains of southern Colorado and northern New Mexico. Disjunct patches occur in Arizona, San Francisco and White Mountains, and a small marginal alpine grassland on the 3,659 m summit of Sierra Blanca on the Mescalero Apache Reservation in central New Mexico is the southernmost alpine community in the U.S. (Pase 1982).

Climate

Every year alpine tundra communities are subjected to severe subfreezing temperatures, severe physiological drought, and intense insolation. Precipitation regimes vary but precipitation predominately occurs as winter snow. Growing season is short (60-150 days) and occasionally interrupted by nights of below freezing temperatures. Direct solar radiation and high exposure to winds can cause conditions of severe drought for plants. Snow accumulations can exceed 365.7 cm and may persist year round on some northern faces (Brown et al. 1982).

Dominant plants

At the lower extent of this type, twisted krummholz forms of sub-alpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmanni) border the adjacent sub-alpine forest or form small islands in the tundra. Few shrubs occur in this type although a number of root perennial forbs may have woody or semi-woody bases. Wetland species of willow (Salix spp.) mingle with sedges (Carex spp.) to form mat-like communities that hug the ground. Carex, an important component of almost every vascular community above timberline, usually dominates and often forms a grass-like cover; sometimes enough to qualify as an alpine grassland, with tufted hairgrass (Deschampsia caespitosa) alpine fescue (Festuca ovina), some bluegrasses (Poa spp.) and rushes (Juncus spp.) often intermingled with the sedges. Low mat and cushion forbs are common. Golden avens (Geum turbinatum) is an important forb often dominating many mixed forb-sedge-grass communities. Other characteristic forbs often include showy or endemic species such as: yarrow (Achillea spp.), fleabanes (Erigeron spp.), potentilla (Potentilla spp.), saxifrages (Saxifaga spp.), indian paintbrush (Castilleja spp.), bluebell (Campanula rotundifolia) and clovers (Trifolium spp.) (Pase 1982).

Wildlife and habitats

Few mammals live and breed in the alpine tundra. The climate is too severe. Pika (Ochotona princeps) is characteristic in talus (cliff base and rocky areas) and chipmunks (Eutamias spp.), yellow-bellied marmots (Marmota flaviventris), and shrews (Sorex spp.) can be found along the border with the sub-alpine zone. Bighorn sheep (Ovis canadensis), once native, have been re-introduced in the Carson and Sante Fe National Forests and Rocky Mountain elk (Cervus elaphus nelsoni) may use alpine tundra as forage areas in summer (Pase 1982). Bighorn require steep escape terrain and use nearby alpine habitat as foraging areas while avoiding forest or brushy cover that could conceal predators (Wishart 1978). Elk prefer alpine grasslands adjacent to forest cover (Skovlin 1982).

White-tailed ptarmigan (Lagopus leucurus) breeds and winters above timberline and depends upon willows for food and cover (Johnsgard 1973, Pase 1982). Other common nesting birds include: water pipit (Anthus spinoletta), white-crowned sparrow (Zonotrichia leucophrys) and occasionally broad-tailed hummingbird (Selasphorus platycercus). While other birds are present, most are migrants or late summer visitors in this region like the mountain bluebird (Sialia currocoides) and killdeer (Charadrius vociferus) (Pase 1982).

Dominant land uses

Historically grazing had a major impact. Overuse on willows caused severe declines in ptarmigan and diseases of domestic stock (particularly sheep) eliminated nearly all populations of bighorn sheep in our region (Pase 1982). Dominant use in this type today is for recreation. Hikers, backpackers, and horseback riders exert considerable pressure on flora and fauna of mountain habitats. Once damaged by grazing or trampling, recovery of soil and native biota is apt to be a slow and uncertain process due to extremely short growing season and severe climate (Pase 1982).

Literature Cited

Brown, D. E., C. H. Lowe, and C. P. Pase. 1979. A digitized classification system for the biotic communities of North America, with community (series) and association examples for the Southwest. Ariz.-Nev. Acad. Sci. 14(suppl.1):1-16.

Johnsgard, P. A. 1973. Grouse and Quails of North America. Univ. Nebraska Press. Lincoln, Neb. 553 pp.

Pase, C. P. 1982. Alpine tundra. Pages 27- 33 in: Biotic communities of the American Southwest - United States and Mexico. D. E. Brown ed. Desert Plants 4(1-4):1-342.

Skovlin, J. M. 1982. Habitat requirements and evaluation. Pages 369-414 in: Elk of North America, ecology and management. J. W. Thomas and D. E. Toweill eds. Stackpole Books. Harrisburg, Pa

Wishart, W. 1978. Bighorn sheep. Pages 161-172 in: Big game of North America, ecology and management. J. L. Schmidt and D. L. Gilbert eds. Stackpole Books. Harrisburg, Pa.