Historic range of variability in the fire regime of a Fennoscandian boreal forest : the Trillemarka-Rollagsfjell Nature Reserve

Fire is the principal natural disturbance process in the boreal forest. Thus, knowledge about the historical fire regime is essential for understanding present day forest ecosystems, which in turn is important for implementing ecosystem management. In this thesis, I document spatial and temporal aspects of forest fire history (i) to better understand the historic range of variability (ii) to improve sampling procedures and evaluate methodological issues regarding how fire scar records should be interpreted and applied in retrospective studies, and (iii) to see to what extent human activity, climate and vegetation change has influenced the fire history. The fire regime, characterised by the numbers, frequency, rotation, severity, seasonality, as well as spatial extent of fires occurring in a given area, were compared with historical climate proxies, vegetation maps, and historical written sources. The research has been carried out in the southern part of Trillemarka-Rollagsfjell Nature Reserve in south-central Norway, where 650 samples with 1391 fire scars were collected and successfully cross-dated from stumps, snags and living trees of Scots pine (Pinus sylvestris L.). The work is primarily based on dendrochronological methods applied to fire scars (Paper I, II and III). In addition, the fire-scar datings were combined with datings of charcoal layers in peat columns to reveal fire history over the Holocene (Paper IV)