Forest physiography; physiography of the United States and principles of soils in relation to forestry . ke the cold timber line, This line is at sea level in Alaska and northern Canada, where it defines the polar limitof the subarctic forest and may be called the continental timber line. North of it is a zoneof tundra and barren grounds corresponding to the zone of alpine flowers above the coldtimber line on the mountain slopes and summits of temperate latitudes. 232 FOREST PHYSIOGRAPHY the dry timber line may be independent of latitude and altitude, itsposition depending almost entirely upon
Forest physiography; physiography of the United States and principles of soils in relation to forestry . ke the cold timber line, This line is at sea level in Alaska and northern Canada, where it defines the polar limitof the subarctic forest and may be called the continental timber line. North of it is a zoneof tundra and barren grounds corresponding to the zone of alpine flowers above the coldtimber line on the mountain slopes and summits of temperate latitudes. 232 FOREST PHYSIOGRAPHY the dry timber line may be independent of latitude and altitude, itsposition depending almost entirely upon the amount of rainfall. Belowthe dry timber line of the Great Basin are, in some cases, treeless,grassy to arid plains and valleys, while in other cases the dry tree linemerges into the zone of juniper. In central Idaho the cold timberline is at 10,000 feet, the dry at 7000 feet. Its position in thePrairie Plains province in eastern Kansas and Nebraska is dependentupon the gradual increase of rainfall eastwardly from the Rockies andHigh Plains. The dry timber line disappears in humid regions, as in. Fig. 63. • ?Typical view oi desert vegetation, southern Great Basin, near Goldfield, Niev.(Ransome, U. S. Geol. Surv.) the Adirondacks and the White Mountains. The meeting of the dry andthe cold timber lines on those ranges in the Great Basin that are bothcold above and excessively dry below, as the White Mountains ofwestern Nevada, Plate IV, results in the complete absence of forestgrowth.^ While the upper timber line is determined usually by temperature, otherfactors may have a determining local influence and in nearly all caseshave an important influence. Among these factors are the slopes of thesurface, the degree of exposure to the sun, the depth of the snow, the I. C. Russell, Timber Lines, (Abstract) Bull. Geol. Soc. Am., vol. 14, igo3, pp. 556-557. GREAT BASIN 233 severity of the winter storms, etc., though the dominant cause is thelow temperature.^ The most abundant and
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