Mid-Holocene pine woodland phases and mire development - significance of dendroecological data from subfossil trees from northwest Germany

Abstract

Questionc Can investigations of subfossil bog-pine woodlands contribute to the understanding of mire development, especially the influence of climate fluctuations on the fen-bog transition? Location: Lowlands of northwest Germany. Methods: We investigated pine (Pinus sylvestris L.) tree remains (stumps and trunks) buried in peat deposits. Dendrochronology was used to date each sampled tree to calendar years and to reconstruct population dynamics of the pine woodlands. Ecological changes, especially changes in site hydrology during the pine woodland phases were inferred from peat stratigraphic analyses and investigations of stem and root morphology of the tree remains. Results: The subfossil pine woodlands occurred mostly during the transition from fen to raised bog conditions within the mire development. The population dynamics are strikingly wave-like whereas woodland phases of 100 to 250 years duration are separated by much shorter (10-50 years) phases of high germination and dying-off rates (GDO phases). Such GDO phases are often synchronous at different sites and are also linked to growth depressions of the independent regional oak master chronology (LSBOC), indicating a climate trigger. Conclusions: The development of raised bogs started about 7000 BC and had a main phase between 5100 and 3600 BC in northwest Germany. The subfossil bog-pine woodlands document the transitional phase towards the onset of raised bog formation, as characterized by initial dry conditions that were followed by increasing wetness of the sites, whereas this development is at least partly the result of climate variations.