| Document informations | ||
| Author(s): | Sonja Wipf | |
| Original article: | Wifp, S. (2007): Warmer Winters: How are plants reacting? http://www.forestknowledge.net, 30.03.2007. | |
| Online version: | Status: 30.03.2007 | |
| Editorial office: | WSL, CH | |
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Warmer winters: How are plants reacting?
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| Fig. 1 - Due to warmer winters the snow cover is melting earlier. |
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| Fig. 2 - Using an "artificially forced snow melt" the scientist investigates how plants react to the early snow melt. |
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Fig. 3 - Vegetation surveys provide insight into how changes in climate affect tundra species Photos: S. Wipf (SLF) |
Our climate is getting warmer - especially in winter. The winter temperatures in the past decades have in many places risen twice as much as those in summer. The snow in the mountains is therefore melting earlier. Can the plants use this prolonged summer for growth? Is the vegetation changing because of this? A Ph. D. student investigates what effect a change in the properties of snow cover has on plants.
Since 1980 snow ablation at the tree line in Davos has been taking place, on average, 3 weeks earlier. In certain areas this means that the length of time without snow cover has increased by a quarter. How plants are reacting to this phenomenon is still virtually unknown.
For her dissertation a researcher simulated the climate change by manipulating the snow cover. During the winter she removed snow which meant that the insulation effect of the snow cover was reduced, the ground cooled down and froze. In spring she speeded up the snow melt and measured the changes in the life cycle, the growth rate and the reproduction of the plants.
The scientist carried out surveys of the vegetation and measured phenology, growth and reproduction. The experiments and the vegetation surveys are taking place on the one hand in alpine tundra at the tree line in Davos and on the other in the sub artic tundra in Alaska. The species composition in both areas is similar, but the winter temperatures and snow cover vary considerably.
First results
- In the past few years a temperature increase has taken place, which causes the snow to melt earlier. In spite of these warmer air temperatures the earlier melt is accompanied by lower ground temperatures and an increase in frost.
- An earlier snow melt has led, in certain species, to a higher mortality rate, a slower life cycle and reduced growth. This is most probably due to lower spring temperatures and frosts.
- The leaves of dwarf shrubs which were free from snow early on were smaller, contained less chlorophyll and were less prone to insect damage. In an experiment with decomposing litter these leaves decomposed more slowly.
- The decomposition of litter was slowed down by a thinner snow cover and an earlier snow melt. This was probably due to the lower ground temperatures, which reduced the activity of the decomposing micro-organisms.
- In places where a winter with less snow and correspondingly lower ground temperatures was simulated the nitrate levels in the soil were found to be higher in spring.
The warmer climate is leading to an earlier start of the vegetation period. This can paradoxically lead to cooler spring temperatures and an increase in frost for alpine plants, because the isolating snow cover is lacking. This was probably the reason why most plant species in the experiment could not profit from the longer summer, with some growing not at all well.
Translation: Dawn Meister, Stallikon
Contact
Sonja Wipf
Swiss Federal Research Institute (WSL)
Alpine Ecosystems
Flüelastrasse 11
CH - 7260 Davos DorfTel: +41 81 417 02 15
Fax: +41 81 417 01 10
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