Forest Habitat Types of Montana
PRODUCTIVITY/MANAGEMENT AND SOIL EXCERPTS

[Excerpted from: Pfister, Robert D., Bernard L. Kovalchik, Stephen F. Arno, and Richard C. Presby. 1977. Forest habitat types of Montana. Gen. Tech. Rep. INT-34. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest & Range Experiment Station. 174 p.]

THE PHYSICAL SETTING

Soils

In general, Montana forest soils are quite rocky, reflecting their mountainous setting. Because steep topography and rocky soils are so prevalent, sites capable of supporting a climatic climax are scarce over much of the forested landscape.

In northern Idaho, R. and J. Daubenmire (1968) observed that soil mantles on leeward slopes were better developed than those on windward slopes because of wind-deposited loess and volcanic ash from the west. This correlation applies also in Montana west of the Continental Divide although it is usually much less pronounced.

Nimlos (1963) described the prominent great soil groups found in Montana west of the Continental Divide. Brown Podzolic soils occupy the moister forest sites—“areas of more than 25 inches of mean annual precipitation on fine textured calcareous materials and on areas of more than 17 inches on coarse textured, acid materials.” He further stated that a Bir horizon 4 to 18 inches thick is the most diagnostic feature of these soils. Brown Podzolic soils are apparently also associated with moist forest types east of the Divide in Montana (Western Land Grant Univ. 1964). Such soils are evidently associated with the Tsuga, Thuja, Abies grandis, and A. lasiocarpa climax series we well as wetter habitat types in the Picea, Pinus contorta, and Pseudotsuga series.

Gray Wooded soils (Nimlos 1963; Western Land Grant Univ. 1964) are associated with the drier forest types in Montana. The average annual precipitation of these sites, which support the Pinus ponderosa and drier part of the Pseudotsuga series, is about 15 to 20 inches.

Chernozems are also likely to be found in the open forests where steppe understory vegetation has a dominant soil forming effect.

According to the maps, descriptions, and nomenclature of the new Soil Taxonomy (USDA Soil Conservation Service 1975) the major subgroups of soils in Montana forests are:
  1. Cryoborolls—on lower elevation slopes with grass-dominated undergrowth.
  2. Cryoboralfs—on midelevation slopes in central and southern Montana.
  3. Cryandepts—on midelevation slopes in areas of western Montana with volcanic ash deposits.
  4. Cryochrepts—on higher elevation and steep slopes throughout mountains of Montana.
  5. Torriorthents—shallow soils on the steep mountain slopes, badlands, and rolling plains in central and southeastern Montana.