Fire history in the hemiboreal and southern boreal zones of southern Sweden during 11000 years : Relationships with past vegetation composition and human activities and implications for biodiversity issues
Sammanfattning: This thesis studies fire history over the last 11 000 years (Holocene) in central Småland, southern Sweden, on the basis of palaeoecological analyses of peat sequences from three small bogs (Notteryd, Stavsåkra and Storasjö). The main objective is to gain insights into the long-term relationships between fire, climate, human-impact, other environmental factors and the history of biodiversity in the study region. The following hypotheses are tested: 1) there are no between-site differences in i) Holocene fire history, ii) abundance of deciduous trees versus pine and forest openness over the Holocene, and iii) landscape history over the last three centuries, and 2) there are no within-site differences in the Holocene charcoal records.Hypothesis 1 (i-iii) is tested using all charcoal records (three sites) and pollen-based Landscape Reconstruction Algorithm (LRA) estimates of past percentage cover of plant taxa and land-use/vegetation units over the last three centuries (test of the LRA using historical maps), and the entire Holocene. Hypothesis 2 is tested using two parallel charcoal records from the same core at Notteryd. The charcoal data comprise continuous records of macroscopic charcoal (macro-C), microscopic charcoal records from pollen slides, and identification of charcoal fragments to plant taxa. Chronologies are based on series of 14C dates from terrestrial plant remains and age-depth models achieved using Bayesian statistics.Accumulation rates (AR) of the area of macro-C was found to be better to use than AR of the number of macro-C for interpretation of the results. Within-site differences in charcoal records exist and have to be considered. Besides climate, forest tree-composition (related to geomorphological settings) was shown to play a primordial role in Early and Mid-Holocene fire history, while land-use was a major factor in the Late Holocene. Three different histories of forest development and land-use changes within the same region are revealed, implying a multitude of landscape types over time and space. These long-term landscape histories were at the origin of the high biodiversity still existing in the 18th century. Major landscape transformations due to agrarian reforms since the 18th century resulted in a dramatic loss of landscape and species biodiversity over the last two centuries.
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