The biology of alpine treelines in a carbon source-sink context

Background/Question/Methods

When temperatures or water supply get critically low, trees are replaced by other, low stature plant types. Such life form boundaries offer test fields for the theory of plant growth control. The global low temperature tree limit is a most pronounced biogeographic boundary that varies in elevation from sea level in the subarctic to more than four kilometers in the tropics at a surprisingly uniform isoline of seasonal mean temperature. In this presentation we will explore the causes of the low temperature tree limit from biological principles related to thermal constraints of uptake and structural investment of carbon. 

Results/Conclusions

It will be shown that the treeline is only a special case of a general principle that applies to any higher plant growth at low temperature, including winter crops. The basic reason why trees are affected at a common isotherm, while low stature plants thrive at much higher elevation, is related to the aerodynamic consequences of tree stature, but not to a specific physiolological weakness of trees. Processes related to cell differentiation in meristems (structural growth) are far more sensitive to low temperature than photosynthesis, and thus, are setting those ultimate limits when it gets cold. The treeline is an example where sink control dominates over source control, similar to effects of moderate drought. There is no evidence of C limitation at the low temperature limit of plant growth. Reference: Körner C (2012) Alpine Treelines. Springer, Berlin. Hoch G, Körner C (2012) Global patterns of mobile carbon reserves in trees at high elevation treelines. Global Ecol Biogeogr DOI: 10.1111/j.1466-8238.2011.00731.x