Common (Translated Scientific) Name: Western Larch / Dwarf Bilberry Forest

Colloquial Name: No Data Available

Hierarchy Level:  Association

Type Concept: This small- to large-patch minor forested type occurs throughout the northern Rocky Mountains. Its presence is strongly associated with well-drained sites in frosty basins or benchlands where cold air accumulates. It is found at moderate elevations between 915 to 1220 m (3000-4000 feet) in the western portion of its distribution but occurs as high as 1525 m (5000 feet) on the Flathead and Kootenai national forests, and yet further to the east it may be found to 2195 m (7200 feet) in basins along the Continental Divide. These sites are postulated to experience frequent summer frost coupled with warm daily maximum temperatures; this factor combination is thought to be limiting to climax conifer species, which establish and grow slowly on these sites. Surface soils are mostly derived from alluvial and to lesser degree colluvial deposits, both gravelly and non-gravelly sandy loams to silts with acidic reaction (pH averaged 5.0 in Montana for comparable type). Sites with the above suite of characteristics are generally dominated by Pinus contorta in the overstory, but occasionally Larix occidentalis becomes abundantly established, the unique result of a plentiful local Larix cone crop and a stand-replacing disturbance (wildfire) and a non-serotinous local population of Pinus contorta. Pseudotsuga menziesii and Pinus contorta are present as a minor component of open canopies dominated by Larix occidentalis; Abies lasiocarpa and Picea engelmannii are present as depauperate specimens in the reproductive layers. Though short shrubs may be represented and even exhibit high constancy (e.g., Amelanchier alnifolia, Lonicera utahensis, Spiraea betulifolia, Shepherdia canadensis, Juniperus communis), it is the dwarf-shrub layer that dominates. Cover of the two indicators of the type, Vaccinium cespitosum and Arctostaphylos uva-ursi, varies markedly, from a few percent to nearly a continuous layer. Other dwarf-shrubs with a consistent presence and occasional abundance are Linnaea borealis, Mahonia repens, Vaccinium scoparium, and Vaccinium myrtillus. Calamagrostis rubescens consistently dominates the graminoid component, and frequently it fills the interstices between dwarf-shrubs to create a virtually unbroken layer. Carex geyeri and Carex concinnoides are also moderately constant within the type. Forbs are usually a negligible component with only Arnica cordifolia, Orthilia secunda, Hieracium albiflorum, and Maianthemum racemosum exhibiting moderate to high constancy.

Diagnostic Characteristics: No Data Available

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Differences in site parameters are probably insignificant among Larix occidentalis / Vaccinium cespitosum, Pinus contorta / Vaccinium cespitosum, and Pseudotsuga / Vaccinium cespitosum communities; these communities owe their canopy differences to happenstance; tree layer dominance accrues to whichever species has greater effective proximity (in a statistical sense) to an appropriate disturbed site and an abundant cone crop upwind of the site (at the time of and following disturbance). The cover values at which Vaccinium cespitosum and Arctostaphylos uva-ursi are recognized as indicators ranges from merely present and not confined to microsites (Pfister et al. 1977, Williams and Lillybridge 1983) to greater than 5% (Lillybridge et al. 1995, Williams et al. 1995), though in most keys Vaccinium cespitosum is generally accorded greater indicator potential than Arctostaphylos uva-ursi, being recognized as indicative at lower cover values.

Similar NVC Types: No Data Available

note: No Data Available