Résumé
Microscopic (> 10 mm) and macroscopic (> 200 mm) charcoal particles were analysed in sediments from two mires in subalpine coniferous forests at c. 1800 m a.s.l. in southeastern Switzerland. Pollen and plant macrofossils suggest that since 6000 BC, Pinus mugo ssp. uncinata (DC) Domin (‘upright mountain pine’) has mostly been the dominant tree species at one of the study sites (Il Fuorn). In contrast, forests dominated by Picea abies (Norway spruce) have formed the vegetation since c. 4000 BC around the mire ‘Fuldera-Palü Lunga’. Mean fire-return intervals (MFI) varied from 250 to > 600 years, depending on forest type, climate and land use. In mountain-pine forests (Il Fuorn), local fires occurred approximately every 250 years, even before the region was agriculturally used (ie, before 3600 BC). About 2000 years ago, intensified human impact as documented by the pollen record resulted in increased fire activity at Fuldera. Post-fire vegetation dynamics suggest that the mountain-pine stands at Il Fuorn had a moderate fire regime with a mix of surface and crown fires. In alpine ecosystems, the impact of fire is generally overshadowed by other disturbance factors such as windthrow, landslides, fungal decay and by climate changes or human land use. Nevertheless, our results show for the first time that natural wildfires exerted a major control on the subalpine coniferous forest ecosystems of the Swiss National Park and its neighbouring areas, eg, by contributing to maintain Pinus mugo ssp. uncinata forests throughout the mid and late Holocene.