Radial increment and defoliation of Pinus sylvestris (L.) on sandy soils relate to summer temperatures and ground water level

Abstract The study deals with the analysis of the impact of climate and ground water table level on radial increment and defoliation of Scots pine (Pinus sylvestris L.) growing on sandy soils. The research was performed in the area of the Borska nížina (i.e. Borská Lowland, situated in southwest of Slovakia), where a substantial die-back of pine trees has been observed in the last decade. Increment measurements and defoliation assessment were performed at 150 adult trees of Scots pine growing at three permanent monitoring plots within the international network of ICP Forests during the years 1989–2018. We examined the impact of climatic and hydrological factors on selected features of pine using the methods of correlation analysis and linear mixed models. Statistical analyses confirmed that the annual radial increment of Scots pine significantly depended on the mean air temperature from June to August, and mean ground water level in the mentioned months. These two factors also significantly correlated with crown defoliation. The factors explained 26% and 32% of increment and defoliation variability, respectively. From the long-term perspective, our analyses indicated that the decrease of ground water level by 0.5 m in summer resulted in the increase of defoliation by 10%. The obtained results indicate a further increase of Scots pine die-back on easy-to-dry sandy soils in regions with low precipitation totals, particularly considering the ongoing climate change and its inherent factors.