The Alpine Tundra

The alpine tundra is a windswept, treeless area that extends from treeline to the highest mountain peaks. Much of the tundra appears as barren rock or a cover of thin soils. Yet in many places deep soils and abundant plant cover exist. A mosaic of plants communities dot the landscape, evolving in response to variations in soils, wind exposure, snow accumulation, and other factors.

Figure 4.3 The alpine tundra of Niwot Ridge in early May (Photo credit: Michael Ritter)

In the Indian Peaks region of Colorado, the alpine tundra ranges from 11,200 to 12,000 feet depending on latitude and slope exposure. Plant communities vary significantly in shape and plant composition, and may vary in size from a few square inches to several acres.

The climate of the tundra is exceedingly harsh. Annual precipitation is around 40 inches, effective precipitation is far below that amount however. Snow remains as permanent snow fields at some sites. Wind speeds can exceed 100 mph and mean annual temperature is below freezing. The frost free season approx. 1 1/2 months. Diurnal temperature ranges are small because the air is mixed by the constant winds.

Figure 4. 4 Tundra Figure vegetation (Photo credit: Michael Ritter)

Vegetation consists of low growing shrubs, cushion plants, small forbs exploding with colorful flowers and lush meadows of sedges and grasses. These plants cover gentle slopes and rock crevices. Rock surfaces are dotted with a cover of lichens and mosses. Most species are slow-growing perennials. Plants have been forced to adapt to such an extreme environment. Ninety percent of total structure in some plants is in roots storing nutrients and energy during poor growing periods. Flowers are often large but other parts of the plant are small to save energy, and reducing exposure to the rigors of the wind. Some plants have waxy coatings or hairs thus losing minimal heat and water to the wind. The location of plant communities is correlated with the duration of snow cover. While snow is blown free from exposed sites, it accumulates in the lee of obstructions and in depressions. Community location is also related to soil, drainage, and movement of soil by burrowing animals, and frost action which is prevalent throughout much of the alpine tundra. Dense willow thickets often occupy moist depressions on the lee side of ridges. A deep cover of snow during the winter protects buds from the wind and freezing temperatures. These are the tallest perennials growing above the krummholz of the ecotone.

Figure 4.6 Solifluction terraces with snow lying behind. (Photo credit: Michael Ritter)

Soils are quite variable, from barely any soils in valleys scoured by glaciers to the mature residual soils of unglaciated ridges, and scattered in between rocks brought to surface from frost heave to form periglacial features like polygons. Soil ice is found in all soils in winter, and soil temperatures are low enough to form patches of permafrost. A common landscape feature of the tundra are solifluction terraces. These occur where water saturated soils move slowly down gentle slopes over permafrost. Most terraces possess a lush cover of forbs and sedges.

Figure 4.4 Polygon, outlined in black, caused by frost heave. (Photo credit: Michael Ritter)

The plant communities mentioned above are considered climax communities mainly because they change so slowly. Communities are often disturbed by small burrowing animals like the pocket gopher that churn up the soil and eat plant roots, or voles which can devastate above - ground biomass. Recovery after disturbance proceeds exceedingly slow, slower than any other mountain ecosystem.

In spite of their high altitude location, alpine tundra ecosystems on Niwot Ridge and in other portions of the Rocky Mountain west have been used by humans since prehistoric times. Native Americans used the high terraces as butchering and camping sites over 7,000 years ago. Domestic sheep have grazed the tundra since the early 1900s. Butterfly populations have been reduced where overgrazing has been a problem. Off road vehicles have wreaked havoc on the fragile tundra ecosystem. Hikers, unaware of their impact, have caused significant damage to this environment. A piece of litter can kill a plant it covers in just a few weeks. Soil erosion caused by trampling can have long lasting effects as it takes much longer for soil to develop in the alpine tundra.

Back to Stop Four Alpine Tundra

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| Table of Contents | Stop 1 Lodgepole Pine | Stop 2: Subalpine | Stop 3: Ecotone | Stop 4: Tundra |
| Stop 5: D1 | Stop 6: Isabelle Glacier | Stop 7: Pawnee Cirque | Stop 8: Green Lakes Valley | Wrap - up |

Created by Michael Ritter ( ) Last revised June 25, 1997