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Krummholz/ˈkrʊmˌhoʊlts/[1] (German:krumm, "crooked, bent, twisted" andHolz, "wood") — also calledknieholz ("knee timber") — is a type of stunted, deformed vegetation encountered in thesubarctic andsubalpinetree line landscapes, shaped by continual exposure to fierce, freezing winds. Under these conditions,trees can survive only where they are sheltered by rock formations orsnow cover. As the lower portion of these trees continues to grow, the coverage becomes extremely dense near the ground.[2] InNewfoundland and Labrador, the formation is known astuckamore.[3][4][5]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 ofkrummholz trees in the Alps, for example, are different from those in the Rockies. The termsscrub orshrubland may be more appropriate for some communities withkrummholz trees.[6]
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 moistmicroclimate around the shrubs.[7]Krummholz might depend on less acidic soil to survive. This means that they are threatened byacid rain. The thin soils that cover mountaintops have low buffering capacity, that is the capacity to resist changes in acidity.[8] These trees are also endangered by the use of them as timber for fires, and other human activity.[6]
Common trees showingkrummholz formation includeEuropean spruce,mountain pine,balsam fir,red spruce,black spruce,subalpine fir,subalpine larch,Engelmann spruce,whitebark pine,limber pine,bristlecone pine, andlodgepole pine. Instances of thekrummholz form of black spruce,Picea mariana, are found in the northern Canadianboreal forests.[9]Krummholz-form black spruce and balsam fir are abundant in the alpine transition zone of theWhite Mountains of Maine and New Hampshire and of the same zone in theGreen Mountains ofVermont.[7]
Subalpine fir is the most common associate of spruce inkrummholz vegetation. Other associatedconiferous 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 ofBritish Columbia. Lodgepole pine (Pinus contorta var.contorta) is a minor associate in most of the British Columbia interior, except in dry alpine areas of the southwest Cariboo/Chilcotin district where it is abundant (Pojar 1985).[10]Ericaceous species (Vaccinium scoparium, V. membranaceum, V. caespitosum, Cassiope mertensiana, Phyllodoce empetriformis) are common in the snow accumulation zone around the base ofkrummholz colonies.[citation needed] In the coastal Pacific Northwest, douglas fir (Pseudotsuga menziesii) stands at higher elevation also have many examples ofkrummholz[11].
In theAlps inEurope, ascrubland ofPinus mugo is described as occupying the area above the tree line. This is formed by variants of thespruce,beech, and rarely thegreen alder. These European species were first labeled as a "krummholz belt" by scientists. In theRocky Mountains, several tree species appear in a similar stunted form, such as specific North American variants ofspruce,fir, andpine. These formations were sometimes called "elfin-wood" or "wind-timber". However, English-speaking scientists began to refer to these formations askrummholz as well.[6]
A variation ofkrummholz formation is aflag tree orbanner tree. Branches on thewindward side are killed or deformed by the almost constant strong winds, giving the tree a characteristic flag-like appearance. Where the lower portion of the tree is protected by snow cover or rocks, only the exposed upper portion may have this appearance. This is a rather common occurrence in red spruce trees of the highest peaks of the central and even the southernAppalachian Mountains, and is most often seen in the windswept high peaks and plateaus of theAllegheny Mountains.[citation needed] This formation most notably occurs with high frequency in theDolly Sods andRoaring Plains West Wilderness areas along theAllegheny Front in easternWest Virginia, typically occurring at elevations of 3,800 feet (1,200 m) and higher.[citation needed]Trade winds in tropical regions near the equator can also shape trees in a similar manner.[2] The southernmost reaches of theMagellanic subpolar forests of Chile contain many flag trees also.[citation needed]
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