High-elevation balsam fir forest (S3S4)
Balsam fir (Abies balsamea) dominates, and there is a corresponding absence or lower abundance of both red spruce (Picea rubens) and heartleaf birch (Betula papyrifera). The canopy height in this community is typically in the 2-10 m range, a reduction from the taller stature of trees at lower elevations (which grow to 20-25 m height). At higher elevations near treeline, these short trees ultimately diminish to krummholz stature (<2 m). They frequently transition to black spruce - balsam fir krummholz, red spruce - heath - cinquefoil rocky ridge, alpine/subalpine communities, or heath - krummholz communities above, and high-elevation spruce - fir forest below.
Wind is a primary disturbance factor in these forests. Blowdowns are common, often taking the form of patches of wind-induced mortality known as fir-waves. Fir-waves are linear patches of blowdown or standing dead trees oriented perpendicular to the prevailing wind, and arranged in a progression of adjacent lines of different-aged regeneration. These waves can be seen as gray undulations across mountainsides. A common theory suggests that the trees primarily die from the death of needles and roots due to chronic wind stress.
Certainly some (or many) examples of this natural community in the
Soils are similar to those found in high-elevation spruce - fir forests: nutrient-poor, acidic Inceptisols or Spodosols with a deep, slowly decomposing humus layer and the variable presence of a grey, leached E (elluviated) horizon. Drainage varies from well to moderately-well drained. Condensation from cloud-intercept contributes a significant amount of moisture to this forest community. Colder temperatures and deep, late-melting snowpacks at high elevations also contribute to high moisture levels, low soil temperatures, a shortened growing season, and accumulation of soil humus.
Characteristic vegetation: The canopy is dominated solely by balsam fir (Abies balsamea), with red spruce (Picea rubens) and birches (Betula spp.) also present but less abundant. Black spruce (Picea mariana) is occasional at higher elevations. The shrub layer may be sparse, but is usually characterized by some combination of showy mountain ash (Sorbus decora), mountain holly (Nemopanthus mucronatus), velvet-leaf blueberry (Vaccinium myrtilloides), creeping snowberry (Gaultheria hispidula), and twinflower (Linnaea borealis). A low diversity of herbs is also characteristic, but species present may include mountain wood fern (Dryopteris campyloptera), rosey twisted stalk (Streptopus roseus), goldthread (Coptis trifolia), naked miterwort (Mitella nuda), northern wood sorrel (Oxalis
Moss and liverwort cover can be quite high (as much as 80-100%), forming a deep, spongy carpet over thick (9-20+ cm) organic humus. Dominant bryophyte species include Bazzania trilobata, Mylia taylori, Hypnum imponens, and Dicranum scoparium. Cladonia spp. and other lichens are present on ground surfaces, tree roots, stems, lower branches and decaying logs. These moist moss carpets sometimes form a natural habitat for the rare heart-leaved twayblade (Listera cordata).
Other species may be encountered in sheltered openings of this community, including stiff clubmoss (Lycopodium annotinum), wild-currants (Ribes lacustre and R. glandulosum), sheep laurel (Kalmia angustifolia), Labrador tea (Ledum groenlandicum), rhodora (Rhododendron canadense), alpine bilberry (Vaccinium uliginosum), dwarf bilberry (V. cespitosum), lowbush blueberry (V. angustifolium), mountain cranberry (V. vitis-idaea), and large-leaved goldenrod (Solidago macrophylla).
Good examples of this community can be seen just below treeline on many of the state's higher mountain peaks, such as those of the Presidential Range.
High-elevation balsam fir forests often occur as part of a larger high-elevation spruce - fir forest systems.
High-elevation balsam fir forest on Mt. Bond (photo by Ben Kimball)
Fir wave in a high-elevation balsam fir forest (photo by Ben Kimball)
high-elevation balsam fir forest on North Twin Mtn. (photo by Ben Kimball)