Radial growth of oak trees was strongly correlated with summer drought (SPEI, Standardized Precipitation Evapotranspiration Index). In total, we analyzed ring-width chronologies from 18 forest stands and investigated their relationship with climate. petraea) stands at upland sites were analyzed to isolate the climate signal for each study region from a groundwater signal. robur stands where (a) water extraction had dramatically lowered groundwater levels and trees presumably lost direct access to it, or (b) trees have not been affected by water extraction. In three regions in the Upper Rhine Valley of Germany, we analyzed retrospectively tree-ring growth in Q. Moreover, we expected that younger trees that established under the condition of lowered groundwater tables would be less sensitive to droughts in contrast to older trees that might not be able to adapt to abrupt changes in groundwater levels. Since drought-related precipitation deficits are increasingly less compensated by available groundwater, we hypothesized that groundwater extraction would increase climate sensitivity of growth. Here, we conducted a dendroecological study in floodplain forests dominated by pedunculate oak ( Quercus robur), a widespread forest type in Europe. Yet, the effects of more frequent and prolonged dry and hot periods in combination with groundwater extraction on floodplain forests are not well-understood. European floodplain forests already experience lower groundwater tables caused by river regulations and water extraction. In future, groundwater dependent ecosystems are likely to face increasing stress from direct and indirect effects of climate change. Chair of Silviculture, Institute of Forest Sciences, University of Freiburg, Freiburg im Breisgau, Germany.
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