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The climate of the tundra is exceedingly harsh. Annual precipitation is around 40 inches, but effective precipitation is far below that amount. Snow remains as permanent snow fields at some sites. Wind speeds can exceed 100 mph and mean annual temperature is below freezing. Diurnal temperature ranges are small because the air is mixed by the constant winds. The frost free season is approximately 1 1/2 months. Figure 13.32 The alpine tundra of Niwot Ridge in early May (Photo credit: Michael
Ritter)
Soils are quite variable in the tundra. Thin soils lie in the valleys scoured by glaciers. Mature residual soils are found on unglaciated ridges and between rocks brought to the surface by frost heave to form polygons. Soil ice is found in all soils in winter, and soil temperatures are low enough to form patches of permafrost.
Figure 13.33 Solifluction terraces with snow lying behind. (Photo credit: Michael Ritter)
Solifluction terraces are a common landscape feature of the alpine tundra. Solifluction terraces with willow growing on top and to the back are visible in the center of the Figure 13.33. Late lying snow patches keep conditions moist to permit willow growth. Reaching a few feet high, willows are covered in snow to protect the over-wintering buds. Willows are the tallest of any species in the alpine tundra.
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. Assess your basic understanding of the preceding material by "Looking Back at Desert and Tundra Biomes" or continue reading.
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Figure 13.34 A polygon, the periglacial feature outlined in black, was caused by frost heave. (Photo credit:
Michael Ritter)