Between the timber line and tree line of a high alpine or taiga zone there lies a zone where some trees can survive, but no trees can thrive.

German for "bent wood", Krummholz refers to the distorted forms of the trees that live in these zones.

Extreme cold can cause dwarfism, but high winds cause most forms of krummholz. These winds generally have a prevailing direction, especially in alpine zones, and the tree's trunk and limbs are pushed downwind.

Frequently, vegetation can grow only in the lee of the tree trunk, resulting in a distinctive "flag form" appearance.

Sometimes, a tree will sprout in the shelter of a rock, and will only be twisted downwind as it attempts to grow above the rock.

Another common occurrence is the protection of the bottom limbs of a tree due to their being buried under snow during the winter.

As the observer gets closer and closer to the tree line, conditons get worse and worse, trees become more and more twisted and stunted.

      ->             //****       ->             ->                  .==*===* 
                     ||*=****            __                        *//=****** 
          ->         ||==***         __.- __   _.-------._      ***//****   * 
                     ||***        .=<.----._  /           \    ****||**** 
     ->           ***||****      //--=<_  _   \       /    |  *****||***** 
               ******||*==****   || `----<_    |  \  /     | ******||****** 
             _*******||********  ||           /    |       |*******||******* 
-.____.------'        `-------.__||___________\        \  /________||******** 

"Krummholz" can also refer to abnormal forms of trees in other conditions, such as a tree planted near an ocean shoreline, which is twisted inland because of the salt spray that kills anything trying to sprout on the ocean side.

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