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Drobyshev ID, Niklasson M., Linderholm HW, Seftigen K, Hickler T, Eggertsson O Reconstruction of regional drought index in southern Sweden since 1750 AD.
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Abstract
We used a network of eight pedunculate oak (Quercus robur L.) sites (n trees = 70) and one Scots pine (Pinus sylvestris L.) site (n trees = 53) to develop drought-sensitive master chronologies for the two areas in southern Scandinavia: a SW-area centred on 57° N 12.7° E and a NE-area centred on 58.8° N 18.2° E. The ratio of actual to equilibrium evapotranspiration (AET/EET) was used as a measure of drought during the growing season defined as the period with average daily temperatures above 9 °C. Instrumental data were used to parameterize the relationship between tree-ring data and the drought index (DI) over 1922-2000 for the SW area and over 1922-1995 for the NE area. The DI reconstructions explained 29.7% (SW area) and 43.7% (NE area) of the variance in the observed DI index in the calibration period, and were extended back to 1770 AD for the SW area and to 1750 AD for the NE area.
Reconstructed drought dynamics suggested strong decadal- and century-scale temporal variability and limited regional synchronicity over 1770-2000. Large variations in DI were observed in both regions in the second half of the 1700s. Dry conditions were synchronously reconstructed in both sub-regions during 1781-1784, 1853-1855, and, to a lesser degree, during 1974 -1978. Over the 1945-1975 the SW area exhibited a trend towards drier growing seasons, whereas no such trend could be identified for the NE area. Analysis of correlation maps indicated that regional DI dynamics reflected two different climate regimes, associated with the Kattegat area (SW reconstruction) and south-eastern Swedish coast of the Baltic sea (NE reconstruction).
Hannon, G., Niklasson, M., Brunet, J., Eliasson, P., Lindbladh, M., 2010.
How long has the ‘hotspot’ been ‘hot’? Past stand-scale structures at Siggaboda nature reserve in southern Sweden. Biodivers Conserv (2010) 19:2167–2187
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Abstract
Islands-lake ecosystems are suitable for testing scale-dependence in forests disturbance theories thanks to contrasting differences in potential for fire spread on islands and mainland. We investigated past fire regime on mainland and on islands in a large lake in SE Sweden. We used dendrochronological methods to reconstruct fire disturbances on 18 small islands (0.04 - 24.1 ha) and in 43 sites in the surrounding 75 km2 landscape over the last 400 years. In the past, fires were frequent on both islands and mainland but not synchronized on the annual scale. Significant temporal changes occurred around the middle of 18th century. Before 1750, fires were less frequent on islands than on mainland (median fire return interval, FRI, 58 vs. 25 years, respectively). However, an inversion of this pattern was observed during 1750-1860: islands showed even shorter fire intervals than mainland locations, suggesting additional and likely human-related source of ignitions (median FRI 15 vs. 29 years, respectively). A substantial decrease in fire activity in both islands and mainland was apparent since 1860-1890. We suggest that the present fire regime (the last 100 years) on the small islands is largely natural since fire suppression is not present there. The dynamic nature of fire regime on islands still requires further studies: islands may, at times, attract ignitions, humans with fire, or both.
Fig. Location of the study area and fire history reconstruction sites.
