Treelines Will be Understood Once the Functional Difference Between a Tree and a Shrub Is
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Trees are taller than shrubs, grasses, and herbs. What is the disadvantage of being tall so that trees are restricted to warmer regions than low stature life forms? This article offers a brief review of the current state of biological treeline theory, and then explores the significance of tallness from a carbon balance, freezing resistance, and microclimatological perspective. It will be argued that having of a woody stem is neither a burden to the carbon balance nor does it add to the risk of freezing damage. The physiological means of trees to thrive in cold climates are similar to small stature plants, but due to their size, and, thus, closer aerodynamic coupling to air circulation, trees experience critically low temperatures at lower elevation and latitude than smaller plants. Hence, trees reach a limit at treeline for physical reasons related to their stature.
KeywordsClimate Forest limit Growth Stress Temperature Timberline
With great pleasure I dedicate this article to Professor Terry Callaghan as part of the festschrift at the occasion of his retirement from directorship at the Abisko Research Station. Much of the treeline theory presented here developed during my sabbatical stays at the station. I thank Jens Paulsen for providing his unpublished statistics on global treeline climatology and Susanna Riedl for the artwork. This paper developed while funded by the European Research Council, advanced Grant 233399, TREELIM.
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