Groundwater extraction reduces tree vitality, growth and xylem hydraulic capacity in Quercus robur during and after drought events

Abstract

Climate change is expected to pose major direct and indirect threats to groundwater-dependent forest ecosystems. Forests that concurrently experience increased rates of water extraction may face unprecedented exposure to droughts. Here, we examined differences in stem growth and xylem hydraulic architecture of 216 oak trees from sites with contrasting groundwater availability, including sites where groundwater extraction has led to reduced water availability for trees over several decades. We expected reduced growth and xylem hydraulic capacity for trees at groundwater extraction sites both under normal and unfavourable growing conditions. Compared to sites without extraction, trees at sites with groundwater extraction showed reduced growth and hydraulic conductivity both during periods of moderate and extremely low soil water availability. Trees of low vigour, which were more frequent at sites with groundwater extraction, were not able to recover growth and hydraulic capacity following drought, pointing to prolonged drought effects. Long-term water deficit resulting in reduced CO2 assimilation and hydraulic capacity after drought are very likely responsible for observed reductions in tree vitality at extraction sites. Our results demonstrate that groundwater access maintains tree function and resilience to drought and is therefore important for tree health in the context of climate change.

Coupled Hydro-Climatic Signals in the Radial Growth of Oaks Benefitting from Groundwater Availability

“…With the inclusion and merging of additional sample trees and shifting the timescale of analysis, our results only partly confirmed the previously identified missing climatic signal in the radial growth of oaks in the Szenta Forest [16][17]. The correlation analysis revealed the remarkably weaker influence of the summer weather conditions, e.g., of early summer precipitation, on growth, compared with a number of sites in the greater region and in Central Europe, including floodplain forests and sites with various hydrological regimes [3,8,16,[54][55]. A common climatic signal of March precipitation previously re- Such changes in the correlation of the TRWI chronology with climatic variables coincided with clear shifts in the climatic conditions, assessed comparably in 30-year moving averages (Figure 6a).…”

“…Water 2022, 14, 3328 2 of 16 shifts in the precipitation and evaporation regimes, can adversely affect the hydrological conditions and groundwater availability in these areas [1][2][3]. These environmental changes can impose significant stress and challenges on the affected forest ecosystems, indicating the importance of dedicated forest ecosystem restoration efforts.…”

“…Some of their analysis found significant relationships between measured water-level fluctuations and radial tree growth [7,8,11]. Studies from the Rhine Valley in Germany compared sites with different ecohydrological conditions, without using an exact hydrological time series [2,3]. Yet, all of these studies are of the same mind that groundwater availability plays a crucial role in the vitality and productivity of trees and forests dependent on them.…”

Management alters drought‐induced mortality patterns in European beech (Fagus sylvaticaL.) forests

“…However, higher growth variability, as in this case, should not be mistaken as a stress signal but seen as an indication that trees with more growing space, in contrast to those growing under high competition, actually have the capacity to respond to favourable climate conditions with increases in radial increment (e.g. Skiadaresis et al 2021). There are, however, few studies on the effect of thinning and partial harvesting on drought-related tree mortality (e.g.…”

“…Skiadaresis et al . 2021). There are, however, few studies on the effect of thinning and partial harvesting on drought‐related tree mortality ( e.g .…”