Dendrochronologia 30 (2012) 93–103 Contents lists available at SciVerse ScienceDirect Dendrochronologia journal homepage: www.elsevier.de/dendro South Swedish bog pines as indicators of Mid-Holocene climate variability Johannes Edvardsson a,∗ , Hanns Hubert Leuschner b , Hans Linderson a , Hans W. Linderholm c , Dan Hammarlund a a Quaternary Sciences, Department of Earth and Ecosystem Sciences, Lund University Sölvegatan 12, SE-223 62 Lund, Sweden b University of Goettingen, Albrecht-von-Haller-Institute, Department of Palynology and ClimateDynamics, Untere Karspüle 2, 37073 Goettingen, Germany c Department of Earth Sciences, University of Gothenburg, Box 460, 405 30 Gothenburg, Sweden article info Article history: Received 10 August 2010 Accepted 14 February 2011 Keywords: Dendroclimatology Scots pine Raised bog Holocene Thermal Maximum abstract Dendroclimatic investigations of subfossil Scots pine (Pinus sylvestris) from two raised bogs in southern Sweden yielded a continuous floating 1492-year long tree-ring record. By cross-dating with bog-pine chronologies from Lower Saxony, Germany, the South Swedish record was assigned an absolute age of 5219–3728 BC. The cross-match between ring-width chronologies from these two regions, sepa- rated by 500–700 km, is remarkably strong and the correlation positive, which indicates that large-scale climate dynamics had a significant impact on the growth of bog pines during the Holocene Ther- mal Maximum (HTM) when bog-pine distribution reached a maximum in both regions. However, local population dynamics were also influenced by peatland ontogeny and competition, as shown by differences in replication and mean tree age between the Swedish and German records. Com- parisons with chronologies developed from modern bog pines in southern Sweden indicate that more coherent climate was controlling pine growth on natural peatlands during warm periods in the past. This study demonstrates the usefulness of Swedish subfossil bog-pine material as a cli- mate proxy, with particular potential for decadal- to centennial-scale reconstructions of humidity fluctuations. © 2011 Istituto Italiano di Dendrocronologia. Published by Elsevier GmbH. All rights reserved. Introduction Scots pine (Pinus sylvestris L.) is a tree species commonly found on peat bogs in southern Sweden (Rydin et al., 1999), and it usu- ally invades open and exposed sites rapidly after disturbances like drainage, deforestation, fire or insect invasion (Zackrisson, 1977; Freléchoux et al., 2000; Eckstein et al., 2010). Growth dynamics of trees growing on bogs usually differ from those on solid ground by being highly dependent on the depth and variability of the water table beneath the root system (Boggie, 1972; Freléchoux et al., 2000; Vitas and Erlickytë, 2007; Eckstein et al., 2009). High groundwater tables generate unfavourable growth conditions as a result of several physical, chemical, and biological processes, of which perhaps the most important is reduced availability of nutrients in the saturated zone (Boggie, 1972; Mannerkoski, 1991; Vitas and Erlickytë, 2007). Groundwater lowerings in peat deposits commonly lead to enhanced tree growth because of the increased availability of nutrients in the unsaturated zone (Penttilä, 1991), but also invasion of trees due to improved germination on drier ∗ Corresponding author. Tel.: +46 46 222 39 59; fax: +46 46 222 48 30. E-mail address: johannes.edvardsson@geol.lu.se (J. Edvardsson). peat surfaces (Freléchoux et al., 2000). Consequently, increased effective precipitation on peat bogs where the groundwater table is close to the surface results in an even shallower unsaturated zone (Schouwenaars, 1988; Hunt et al., 1999), which in most cases leads to stress and growth reductions in trees growing on the peat surface (Boggie, 1972; Leuschner et al., 2002; Linderholm et al., 2002; Eckstein et al., 2009). Given the strong link between groundwater fluctuations and the growth and establishment of trees on bogs, it can be assumed that ring-width records provide information on inter-annual to decadal-scale hydrological changes associated with regional climate change and variability in the past (Leuschner et al., 2002; Sass-Klaassen and Hanraets, 2006; Eckstein et al., 2009). Studies of establishment and degeneration phases in bog-tree populations may also provide information on changes in bog-surface wetness, hydrology and climate on the centennial time scale (Gunnarson, 2002). Previous studies have demonstrated that bog pines are of lim- ited use as high-resolution climate proxies, mainly because of weak correlation between ring-width patterns and observed mete- orological parameters. Moreover, correlations between tree-ring records between neighbouring sites, or even within a single site, may be low. For example, negative correlations were observed between trees growing on the same peat bog in Lithuania (Pukiene, 1125-7865/$ – see front matter © 2011 Istituto Italiano di Dendrocronologia. Published by Elsevier GmbH. All rights reserved. doi:10.1016/j.dendro.2011.02.003