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

Abstract

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.

Dendrochronologically dated pine stumps document phase-wise bog expansion at a northwest German site between ca. 6700 and ca. 3400 BC

“…As mentioned before, the dying-off phases observed at TOMO_south show much synchronism with dying-off phases observed at other mire sites in northwest Germany (Eckstein et al, 2009(Eckstein et al, , 2010(Eckstein et al, , 2011, which emphasizes their climatic context. In addition to the temporal placing of the TOMO_south record (terminating 3400 BC) and its location in the northwest German lowland, where settlements were established later than on the richer soils of the adjacent hills, this synchrony makes it appear unlikely that anthropogenic clearance activity in the catchment area might have had a detectable influence on the bog's hydrology.…”

“…They were able to show that the tree dying-off is mostly due to hydrological changes, while fire and storm have been found to be of little relevance on the investigated sites. Particularly the observed synchrony of pine establishment and dying-off phases in different mires shows that the local mire development documented by the trees is strongly linked to climatic variations (Eckstein et al, 2009(Eckstein et al, , 2010(Eckstein et al, , 2011Edvardsson et al, 2012a, b).…”

“…The area was particularly characterized by large lowland raised bogs, which grow better under humid and cool conditions (Behre, 2008). The expansion of these raised bogs is evident since the 7th millennium BC, with a strong increase between 5100 and 3600 BC (Eckstein et al, 2011;Petzelberger et al, 1999). The peat in the area contains a valuable environmental record of the past millennia.…”

“…The trees dated absolutely by dendrochronology deliver the finest temporal reconstruction of bog expansion and local bog formation, particularly by their dying-off dates (Eckstein et al, 2009(Eckstein et al, , 2010Edvardsson et al, 2014Edvardsson et al, , 2016Krąpiec et al, 2016;Leuschner et al, 2002Leuschner et al, , 2007. Eckstein et al (2009Eckstein et al ( , 2010Eckstein et al ( , 2011 have shown that the tree dying-off occurs in phases, which are often synchronous in different mires. They were able to show that the tree dying-off is mostly due to hydrological changes, while fire and storm have been found to be of little relevance on the investigated sites.…”

Contemporaneousness of Trackway Construction and Environmental Change: a Dendrochronological Study in Northwest-German Mires

“…and pine (Pinus sylvestris), from the mires of the northwest-German lowland. The chronologies span from 6703 BC to 931 AD (at various stages described by, for example, Delorme 1983;Leuschner et al 2002;Eckstein et al 2011). The peat-preserved trees grew at sites strongly affected by hydrological change (e.g.…”