Chronic water stress reduces recovery of oaks after extreme drought eventsDroughts threaten forest ecosystems globally, even in regions that are normally not considered water limited. Such 'wet’ forests are the groundwater-fed or former floodplain oak forests along the Upper Rhine Valley. These forests once dominated the riverine landscapes and some plains of Central Europe but are now rare because of expansion of settlements and conversion of land for agriculture. River regulation and groundwater appropriation impact on their hydrology and put these remnant forests at further risk, especially during droughts. To investigate the influence of groundwater removal on pedunculate oak forests and to determine whether access to groundwater might help trees to withstand and recover from extreme drought, researchers from the University of Freiburg examined the performance of oak trees growing at sites with contrasting groundwater availability including sites where groundwater extraction for industry, irrigation or domestic use has led to reduced water availability for trees over several decades. By examining annually resolved series of tree ring width and wood anatomical features, the team around Dr. Georgios Skiadaresis in the working group of Prof. Dr. Jürgen Bauhus was able to reconstruct the performance of oaks during droughts and in periods with favourable growing conditions. The type of wood cells as well as their characteristics (such as their number, arrangement and size) depended strongly on the climatic conditions at the time of wood formation. At the same time the characteristics of xylem vessels, the water transporting elements in broadleaf trees, reflected the level of plant performance under varying climatic conditions.
Skiadaresis, G., Schwarz, J., Stahl, K., Bauhus, J. (2021): Groundwater extraction reduces tree vitality, growth and xylem hydraulic capacity in Quercus robur during and after drought events. In: Scientific Reports 11, 5149.