A re-assessment of high elevation treeline positions and their explanation |
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Authors: | Christian Körner |
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Institution: | Botanisches Institut, Universit?t Basel, Sch?nbeinstrasse 6, CH-4056 Basel, e-mail: koerner@ubaclu.unibas.ch,
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Abstract: | In this review I first compile data for the worldwide position of climate-driven alpine treelines. Causes for treeline formation
are then discussed with a global perspective. Available evidence suggests a combination of a general thermal boundary for
tree growth, with regionally variable “modulatory” forces, including the presence of certain taxa. Much of the explanatory
evidence found in the literature relates to these modulatory aspects at regional scales, whereas no good explanations emerged
for the more fundamental global pattern related to temperature per se, on which this review is focused. I hypothesize that the life form “tree” is limited at treeline altitudes by the potential
investment, rather than production, of assimilates (growth as such, rather than photosynthesis or the carbon balance, being
limited). In shoots coupled to a cold atmosphere, meristem activity is suggested to be limited for much of the time, especially
at night. By reducing soil heat flux during the growing season the forest canopy negatively affects root zone temperature.
The lower threshold temperature for tissue growth and development appears to be higher than 3°C and lower than 10°C, possibly
in the 5.5–7.5°C range, most commonly associated with seasonal means of air temperature at treeline positions. The physiological
and developmental mechanisms responsible have yet to be analyzed. Root zone temperature, though largely unknown, is likely
to be most critical.
Received: 3 October 1997 / Accepted: 14 April 1998 |
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Keywords: | Climate Developmental biology Forest High altitude Timberline |
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