Krummholz

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Krummholz (German: krumm, "crooked, bent, twisted" and Holz, "wood") — also called knieholz ("knee timber") — is a type of stunted, deformed vegetation encountered in the 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.^[1] In Newfoundland and Labrador, the formation is known as tuckamore.^[2][3][4] Krummholz trees are also found on beaches such as the Oregon coast, where trees can become much taller than their subalpine cousins.

The labeling of diverse sets of tree species in different ecological contexts may be problematic. The ecological requirements of krummholz trees in the Alps, for example, are different from those in the Rockies. The terms scrub or shrubland may be more appropriate for some communities with krummholz trees.^[5]

Krummholz trees can cover nearly all of the area in which they inhabit, with only patches of moss and flowers in between. Frequent fog and cloudy conditions, along with cool weather, create a rather moist microclimate around the shrubs.^[6] Krummholz might depend on less acidic soil to survive. This means that they are threatened by acid rain. The thin soils that cover mountaintops have low buffering capacity, that is the capacity to resist changes in acidity.^[7] These trees are also endangered by the use of them as timber for fires, and other human activity.^[5]