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Question: 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.

Excellently preserved subfossil pine and oak tree remains from the bottom layer of raised bog peat were dendroecologically investigated at Venner Moor (northwest Germany). Tree-ring analyses were combined with observations of stem and root morphology, preservation state, mineral soil relief, peat stratigraphy and pollen analysis to reconstruct in great detail environmental changes leading to the start of the raised bog formation. Hydrology was identified as the main determinant influencing tree growth and population dynamics at Venner Moor, as documented by different growth patterns and dying-off dates in relation to the mineral soil elevation. The woodland phase has been dendrochronological dated to the period from 2421—2077 BC (4371—4027 cal BP). In this period, a general change from more or less open landscape with dominating heath to wet pine forest and eventually to open raised bog occurred at the site. Comparisons with pine population dynamics at the nearby Voerdener Moor and with the independent Lower Saxony Bog Oak Chronology (LSBOC) indicate that the reconstructed ecological changes at Venner Moor are mainly triggered by climate variations, in particular wet shifts on the decadal timescale. This example shows the value of subfossil pine layers from northwest German bogs as a high resolution proxy archive of Holocene humidity fluctuations.

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