Holocene environmental change in subarctic aeolian dune fields: The chronology of sand dune re-activation events in relation to forest fires, palaeosol development and climatic variations in Finnish Lapland

Sand dune stratigraphy, radiocarbon-dated charcoal layers, palaeosol development and luminescence dating are used to reconstruct the Holocene environmental history of the dune fields in Finnish Lapland since deglaciation in the early Holocene (~10,900–10,200 cal. BP). After rapid formation and stabilisation of parabolic dunes and the immigration of Scots pine (Pinus sylvestris), forest fires are inferred to have played a key role in triggering episodes of aeolian erosion of the dunes (deflation) leading to 16 sand dune re-activation events. These events were widespread in the dune fields from ~8300 cal. BP and occurred with increasing frequency towards the late Holocene. Each event is interpreted as relating to local fires that occurred up to 100–400 years after the date of each charcoal layer; the radiocarbon age of the charcoal being affected by the age of the wood when burned, and the accumulation and/or recycling of charcoal from earlier fires. Well-developed buried iron podzols, which can develop within 500–1000 years, indicate prolonged phases of dune stability, four of which are dated to between 4500 and 1050 cal. BP. Indirect associations are evident between the sand dune re-activation events and climatic phases that were relatively cold and/or wet. These associations are explained by a conceptual geo-ecological model in which the effects of century- to millennial-scale climatic variability are modulated by the interactions between fire and vegetation. Thus, the subarctic dune field is viewed as a heterogeneous landscape of stable and unstable areas in space and through time. The unstable elements of this spatial mosaic become more extensive at times when the climatic environment promotes fire and deflation.