Sierra Nevada Subalpine Zone - Vegetation - Composition

Composition

Shrubs and herbs are usually sparse, but can be common in stands where snow melts earlier in the growing season. Diversity of herbs in the subalpine zone is usually less than lower-elevation zones such as upper and lower montane. Broad classifications of herb and shrub communities can be found in Sawyer and Keeler-Wolf. For a fine-scale classification of subalpine meadow communities, see Benedict.

The composition of tree species within Sierran subalpine is variable with comparatively high diversity for subalpine. Subalpine stands in the Rocky Mountains, for example, are usually dominated by a single tree species. Stands in the Sierra may be mixed, with up to five species present, or pure, monospecific stands, depending on the range of the species and microsite conditions.

Whitebark pine (Pinus albicauls) is possibly the most widespread component of subalpine woodland in the central and northern regions of the Sierra. This species is found at higher elevations than all other species in this region, forming dense monospecific stands of krummholz near the tree line and near ridgetops. At lower elevations, whitebark pine can co-occur with lodgepole pine, Sierra juniper (Juniperus occidentalis ssp. australis) and mountain hemlock (Tsuga mertensiana).

Lodgepole pine (Pinus contorta ssp. murrayana), which occurs in vast stands in the upper montane zone, is found mostly in mixed stands in subalpine woodland, particularly with whitebark pine. Lodgepole is not usually found near tree line, although it does occasionally form krummholz.

Western white pine (Pinus monticola) can be found in pure stands, especially on exposed slopes, where snowpack is shorter-lived. More commonly however, western white pine grows in mixed stands with lodgepole, mountain hemlock, Jeffrey pine (Pinus jeffreyi) and/or red fir (Abies magnifica)

Mountain hemlock may be the most common tree species in the subalpine zone, especially in the central and northern Sierra. This species forms dense, pure stands on protected slopes with moist soil, but can also co-occur with Sierra juniper and whitebark pine. Mountain hemlock often exhibits two growth forms on the same individual, with one stem upright and several branches at the base extending out along the ground. It forms a hedge-like growth form near tree line.

Sierra juniper is sparse in subalpine, occurring strictly on exposed, rocky slopes, usually among granite boulders. Limber pine (Pinus flexilis) occurs in pure stands on nutrient-poor, often steep slopes along the east side of the Sierra, and forms mat-like krummholz growth forms at tree line. Foxtail pine (Pinus balfouriana) grows on shallow soils on exposed slopes in mixed stands at lower elevations and pure stands close to tree line. This species does not form krummholz and can be found as single-stemmed trees even at very high elevations. Foxtail pine is restricted to the southern part of the Sierra, forming pure stands where whitebark pine would dominate further north.

In addition to the species described above, Jeffrey pine and red fir, which are more commonly found in the upper montane zone, can be found at low abundances in the subalpine zone, particularly on exposed slopes where snow does not linger as long.