Montane landslide barren and thicket (S3S4)
Landslides, sometimes called "debris avalanches," are sizable slope failures that produce mosaics of outcrop, cliff, talus, and successional forest communities. Landslide scars are visible as linear tracks on mountain slopes where rock, soil, and vegetation slumped and slid down during intense rain events. They can be very narrow or quite broad. Landslides obliterate the existing forest, creating opportunities for pioneer and early successional species. The White Mountains currently have more than 500 landslide scars in various stages of recovery. The upper parts of landslide tracks consist of cliff, outcrop, and talus material, and the process of forest recovery may take centuries here.
Montane landslide barren and thicket communities are found on the lower portions of landslide tracks. These areas are characterized by substrates of exposed basal till and deposits of mixed rubble debris, this stony material sometimes appearing plastered to the exposed bedrock. This is an ephemeral community type. Vegetation succeeds through barren and thicket stages and eventually becomes forest. Lower tracks succeed to forest more rapidly than the open rock areas above, but talus barrens in landslide tracks still require decades to establish lichens, and centuries to accumulate enough soil to support sparse woodlands.
Pioneer species include sedges, grasses, rushes, hay-scented fern (Dennstaedtia punctilobula), whorled aster (Oclemena acuminata), other weedy forbs, willows, alder, and mosses. Common pioneer woody species include heartleaf birch (Betula cordifolia), paper birch (Betula papyrifera), pin cherry (Prunus pensylvanica), balsam fir (Abies balsamea), and mountain maple (Acer spicatum). Understory species include numerous grasses, composites, and raspberries and blackberries (Rubus spp.), among others. Mosses and lichens are also common. At higher elevations, alpine/subalpine species may occur, such as mountain sandwort (Minuartia groenlandica), alpine bilberry (Vaccinium uliginosum), highland rush (Juncus trifidus), three-toothed cinquefoil (Sibbaldiopsis tridentata), and boreal bent-grass (Agrostis mertensii).
Forest re-development is slow on steep, eroded till areas. Birch, spruce, and fir saplings are typically stunted at no more than a foot high for at least 20 years. The most rapid successions occur in deposit areas where pioneer hardwoods completely crowd out light-dependent pioneer herbs within 30 years. Shade-tolerant forest herbs may take up to 70 years to recover after a landslide.
Good Examples occur in Franconia and Crawford Notches, and on North and South Tripyramid, Mt. Osceola, Mt. Flume, and Mt. Guyot/West Bond.
Montane landslide barren and thickets may occur as part of montane acidic talus systems and alpine ravine/snowbank systems, and also within high-elevation spruce - fir forest systems.
montane landslide barren and thicket community occurs in a stream valley below
an open landslide scar on the north side of North Twin Mtn. (photo by Ben Kimball)
steep landslide strips on West Bond Mtn. (photo by Ben Kimball)
the base of a large landslide scar below Mt. Guyot in the White Mountains
supports a montane landslide barren and thicket community
(photo by Dan Sperduto)
montane landslide barren and thicket community occurs below an open
landslide scar on the east slope of Franconia Ridge (photo by Ben Kimball)