Long-term forest fire ecology and dynamics in southern Switzerland

1 Pollen and charcoal analysis at two lakes in southern Switzerland reveale d that fire has had a prominent role in changing the woodland composition o f this area for more than 7000 years. 2 The sediment of Lago di Origlio for the period between 5100 and 3100 Be c al. was sampled continuously with a time interval of about 10years. Peaks o f charcoal particles were significantly correlated with repeated declines i n pollen of Abies, Hedera, Tilia, Ulmus, Fraxinus excelsior t., Fagus and V itis and with increases in Alnus glutinosa t., shrubs (e.g. Corylus, Salix and Sambucus nigra t.) and several herbaceous species. The final disappeara nce of the lowland Abies alba stands at around 3150 Be cal. may be an examp le of a fire-caused local extinction of a fire-intolerant species. 3 Forest fires tended to diminish pollen diversity. The charcoal peaks were preceded by pollen types indicating human activity. Charcoal minima occurr ed during periods of cold humid climate, when fire susceptibility would be reduced. 4 An increase of forest fires at about 2100 Be cal. severely reduced the re maining fire-sensitive plants: the mixed-oak forest was replaced by a fire- tolerant alder-oak forest. The very strong increase of charcoal influx, and the marked presence of anthropogenic indicators, point to principally anth ropogenic causes. 5 We suggest that without anthropogenic disturbances Abies alba would still form lowland forests together with various deciduous broadleaved tree taxa .