The tree line is the edge of a habitat at which trees are capable of growing and beyond which they are not. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions. The tree line is sometimes distinguished from a lower timberline, which is the line below which trees form a forest with a closed canopy.
Tree line above St. Moritz, Switzerland. May 2009
In this view of an alpine tree line, the distant line looks particularly sharp. The foreground shows the transition from trees to no trees. These trees are stunted in growth and one-sided because of cold and constant wind.
Alpine tree line of mountain pine and European spruce below the subalpine zone of Bistrishko Branishte, with the surmounting Golyam Rezen Peak, Vitosha Mountain, Sofia, Bulgaria
An alpine tree line in the Tararua Range
Krummholz — also called knieholz — 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. In Newfoundland and Labrador, the formation is known as tuckamore. Krummholz trees are also found on beaches such as the Oregon coast, where trees can become much taller than their subalpine cousins.
Krummholz Pinus albicaulis in Wenatchee National Forest
Wind-sculpted krummholz trees, Ona Beach, Oregon
Picea engelmannii flag tree in Colorado, at the tree line
Banner tree, Torres del Paine National Park, Chile
