Dendroecological investigations at Venner Moor (northwest Germany) document climate-driven woodland dynamics and mire development in the period 2450-2050 BC

Abstract

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 log yak 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.