Partner und Internationale Organisationen
(Englisch)
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WSL, Oulu, Tromsö, Bergen, Swansea, Hamburg,
Rovaniemi, Marseille, Thessaloniki, Lisboa
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Abstract
(Englisch)
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Data collection included: (1) monitoring of annual pollen deposition in four Alpine forest-limit areas (3 years in Grindelwald, 7 years in Aletsch, Simplon, and Zermatt; total 28 locations); (2) analysis of pollen deposition during the last few hundred years in three lakes in Grindelwald; (3) analysis of annual pollen deposition since 1900 in two peat sections collected in forest-limit situations (Grindelwald, Aletsch), in which the time scale is based on 210Pb dating provided by P.G. Appleby (Liverpool); (4) analysis of pollen deposition in a lake near the forest limit in Grindelwald in the time window 4460-4100 BC.
Summary of results. Monitoring results of pollen deposition indicate that pollen production of forest-limit trees is enhanced by a warm summer and late summer in the year prior to release, and that the actual forest limit is well characterized by threshold values of pollen deposition (publication in prep.). Evaluation of 23 pollen records covering the last few hundred years (made of lake and mire deposits for various projects) resulted in recognition of human activity as the dominant factor determining pollen deposition by forest-limit trees in most situations, and of natural factors (mainly climate) only in two cases of small mires (30 m in diameter) lying inside undisturbed forest (publication submitted). These two mires were selected for relating annual pollen deposition of forest-limit trees to climatic factors; one is a site with sub-oceanic conditions (Grindelwald), the other with sub-continental conditions (Aletsch; two publications in prep.). The results suggest that pollen production is mainly controlled by temperature, whereas precipitation plays a small or no role. In both sites the production of pollen by spruce (Picea) is favoured by warm and long summers, in the sub-oceanic site also by mild winters. Pollen production by Swiss stone pine (Pinus cembra) in the sub-continental site is favoured by warm summers. Pollen production by larch (Larix) in the sub-continental site is favoured by warm summers and late summers. Pollen production by mountain pine (Pinus non-cembra) in the sub-oceanic site is favoured by high temperatures, but seasonality is not pronounced. Pollen production by birch (Betula) is in both sites favoured by mild winters. In both sites, pollen production by green alder (Alnus viridis) is favoured by warm summers. The species grows in avalanche tracks, which explains that the period of influence is longer in the sub-continental site where the snow-free period is longer. In the time window 4460-4100 BC studied in a lake at Grindelwald, variability in the pollen deposition of spruce is smaller than after 1900 as recorded in the same lake, suggesting that the variability in average temperatures during summer and late summer was smaller. Finally, a link between pollen and dendro-ecological data was made, showing significant positive correlation between annual pollen deposition of spruce and stone pine since 1900 with selected ring width chronologies.
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