Changes in soils along a vegetational (altitudinal) gradient of the northern Rocky Mountains

Abstract

As one moves from the warm dry plains of eastern Montana to the cool moist peaks of the northern Rocky Mountains he might pass through a series of native vegetation types: Bouteloua gracilis, Agropyron spicatum, Featuca idahoensis, and Festuca scabrella grasslands; Pinua ponderosa, Pseudotsuga menziesii, and Abies lasiocarpa forests; and alpine tundra (Kuchler 1964, Muggler and Handl 1974, Pfister et al. 1977).

It is commonly observed that when one moves up a vegetational gradient he moves up a soils gradient (e.g. Eyre 1963, Whittaker et al. 1968, Hanawalt and Whittaker 1976 and 1977). In the northern Rocky Mountains, Thorp (1931, N Wyoming) observed that organic matter increased, that pH decreased, that the depth to free lime increased and that the thickness of A- and B-horizons increased as he moved up a vegetational gradient similar to that described above. The same trends, as well as a tendency for nutrients to become most available at the grassland-forest boundary, were observed along a similar vegetation gradient in British Columbia (Spilsbury and Tisdale 1944). Such trends correlate well with broad groups in the 1938 Soil Taxonomy (Agricultural Experiment Station 1964 and Nimlos 1963) as well as in the 1977 Soil Taxonomy (Weaver 1978).

The objects of this paper are I) to describe the change in soils observed along this gradient in more detail, 2) to consider their genesis briefly, and 3) to consider their importance to plants.