Holocene solifluction, climate variation and fire in a subarctic landscape at Pippokangas, Finnish Lapland, based on radiocarbon-dated buried charcoal

A large number of radiocarbon dates from charcoal layers buried beneath stacked solifluction lobes at Pippokangas, in the northern boreal zone of Finnish Lapland, are used to reconstruct a Holocene history of solifluction. Although the site is surrounded by Scots pine forest, the solifluction lobes occur on the lower slopes of a kettle hole, the microclimate of which prevents the growth of trees. Samples from the upslope end of charcoal layers have enabled the recognition of four synchronous phases of solifluction lobe initiation: 7400-6700, 4200-3400, 2600-2100 and 1500500 cal. yr BP. Rates of lobe advance are shown to be lobe-dependent and age-dependent: initially, average rates were commonly 0.14-0.19 cm yr(-1), later falling to 0.02-0.07 cm yr(-1) or less as the lobes approached the bottom of the slope. The absence of charcoal prior to 8000 cal. yr BP, together with single IRSL and TL dates, indicate a relatively stable early Holocene landscape. The onset of solifluction around 7400 cal. yr BP. appears to have followed the immigration of pine around the site, which increased the frequency of forest fires. Phases of solifluction activity seem to have been triggered by millennial-scale variations in effective Moisture (the climatic hypothesis), rather than episodic burning of the surface vegetation cover (the geoecological hypothesis), although climate may also have affected fire frequency and severity. Copyright (c) 2005 John Wiley & Sons, Ltd.