Soil properties are significant modifiers of pedunculate oak (Quercus robur L.) radial increment variations and their sensitivity to drought

Abstract

Soil properties, drought, and the interaction between the two are significant, if unclear, driver of radial growth variations. We observed that, soil properties exert a stronger effect on pedunculate oak (Quercus robur L.; QURO) radial growth sensitivity to drought (interpreted via Standardized Precipitation Evapotranspiration Index; SPEI), than on radial increment and its variations. Soils that are strongly affected by soil water (typical and haplic gleysol) provide the most suitable substrates for QURO radial growth during drought events because they provide more continuous water sources. In contrast, QURO growing on chernozem (with sand) and solonetz (highly saline soils) are more drought-sensitive and have smaller radial increments. The influence of soil type is clearly evident in the pattern of QURO decline that has occurred across Europe (2014) and Serbia (2011–2012): QURO growing on gelysols (characterized by high soil water content) were not strongly affected, whereas marked mortality occurred in QURO forests growing on chernozem and solonetz. Based on the findings yielded by the Generalized Additive Mixed Model (GAMM) and the Linear Mixed Effects Model (LMM), the above-ground (precipitation and temperature) and below-ground (river water level and soil moisture) drought sources affect radial growth equally and its sensitivity to drought. Overall, GAMM better fitted with analyzed radial growth properties, than LMM. Likewise, based on the GAMM and LMM outputs, stronger associations between QURO radial growth sensitivity to drought and nine climate parameters were obtained compared with raw as well as detrended radial growth series.