Krummholz

Krummholz or krumholtz (German: krumm, "crooked, bent, twisted" and Holz, "wood") — also called knieholz ("knee timber") — is a type of stunted, deformed vegetation encountered in subarctic and subalpine tree line landscapes, shaped by continual exposure to fierce, freezing winds. Under these conditions, trees can only survive where they are sheltered by rock formations or snow cover. As the lower portion of these trees continues to grow, the coverage becomes extremely dense near the ground.

Common trees showing krumholtz formation include European spruce, mountain pine, balsam fir, red spruce, black spruce, subalpine fir, subalpine larch, Engelmann spruce, limber pine, and lodgepole pine. Instances of the krumholtz form of black spruce, Picea mariana, are found in the northern Canadian boreal forests. Krumholtz-form black spruce and balsam fir are abundant in the alpine transition zone of the White Mountains of New Hampshire.

Subalpine fir is the most common associate of spruce in krummholz vegetation. Other associated coniferous species include alpine larch (Larix lyallii), whitebark pine (Pinus albicaulis), limber pine (Pinus flexilis, and western white pine (Pinus monticola) in southern British Columbia, and mountain hemlock (Tsuga mertensiana) on the eastern slopes of the Coast Range and in the Revelstoke area. Lodgepole pine (Pinus contorta var. contorta) is a minor associate in most of the British Columbia interior, except in dry alpine areas of southwest Cariboo/Chilcotin district where it is abundant (Pojar 1985).Ericaceous species (Vaccinium scoparium, V. membranaceum, V. caespitosum, Cassiope mertensiana, Phyllodoce empetriformis) are common in the snow accumulation zone around the base of krummholz colonies.

...
Wikipedia