... because they last far longer than any human experiment may last and nature performs these tests with all natural factors in action, not what can be simulated experimentally.

1 - Creux du Van. Note the "Bonsai" trees in the foreground and the normal forest in the back.

One of these marvellous pieces of experimentation by nature is a steep rock amphitheatre, called Creux du Van, in the Swiss Jura mountains. A pocket of ice was trapped under block fields and scree at 1250 m elevation when the glaciers retreated c. 13000 years ago. Screened from the southern sun for most of the year and steeply sloped to the north, this ground has preserved ice (permafrost) until today, causing soil to be as cool as at treeline, while air temperatures are typically mid-montane, normally permitting luxurious tree growth.

Within a distance of only 30 m we find tall montane forest and thawed ground and "Bonsai" trees on permafrost.

2 - Foreground: Normally growing Picea abies. "Bonsai" trees on permafrost in the light zone behind.

3 - Temperature measurements confirm: No difference in air temperature, but a significant difference in soil temperature in otherwise similar (calcareous) substrate. Soils under the Bonsai forest show a seasonal mean temperature of 6.5 °C, the global mean for treelines. Nature's experiment in the Creux du Van seems to support the critical role of low root zone temperatures for tree growth.

29 August 2011
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