Changes in temperature regime, and a higher frequency of extreme weather conditions due to global warming are considered great risks for forest stands worldwide because of their negative impact on tree growth and vitality. We examined tree growth and water balance of two provenances of Norway spruce growing in Arboretum Borová hora (350 m a.s.l., Zvolen, central Slovakia) that originated from climatologically cooler conditions. The research was performed during three meteorologically different years from 2017 to 2019. We evaluated the impact of climatic and soil factors on intra-species variability in radial stem growth and tree water status that were characterised by seasonal radial increment, stem water deficit and maximum daily shrinkage derived from the records of stem circumference changes obtained from band dendrometers installed on five mature trees of each provenance. The impact of environmental factors on the characteristics was evaluated using the univariate factor analysis and four machine learning models (random forest, support vector machine, gradient boosting machine and neural network). The responses to climatic conditions differed between the provenances. Seasonal radial increments of the provenance from cooler conditions were greater than those of the provenance originating from cooler and wetter conditions due to the long-term shortage of water the latter provenance had to cope with in the current environment, while the provenance from the cooler region was more sensitive to short-term changes in environmental conditions.

We monitored seasonal dynamics of stem water status of four coniferous species (Abies alba, Larix decidua, Picea abies and Pinus sylvestris) planted at the Borová hora Arboretum (300 m a.s.l., Zvolen valley, Central Slovakia) beyond their ecological and production optima, in the region with warmer and drier climate compared to the sites of their origin. Species-specific stem water deficit and maximum daily shrinkage were extracted from diurnal band dendrometer records of stem circumference recorded by digital band dendrometers DRL26 installed on five trees per species, and correlations with environmental variables were analysed. The seasonal stem circumference increment of all tree species was higher in 2017 than in the drier and hotter year of 2018. The greatest seasonal stem circumference increment in the observed periods of 2017 and 2018 was observed for A. alba and P. sylvestris, respectively. The highest and lowest values of daily and seasonal stem water deficit were observed for L. decidua and A. alba, respectively. The analysis of trees' short-term response to extreme climate events seems to be the promising and suitable method for detecting tree species tolerance towards drought.

In the paper, the intra-annual growth patterns and tree water balance of four different tree species (Pinus sylvestris, Picea abies, Larix decidua and Abies alba) were examined. Seasonal radial increment, tree water deficit (ΔW) and maximum daily shrinkage (MDS) were derived from the records obtained using high-resolution digital band dendrometers. The study area was located in Arboretum Borová hora (350 m a. s. l., Zvolen valley, Central Slovakia) characterised by a warmer climate (Picea abies) and warmer and drier climate (Abies alba, Larix decidua, Pinus sylvestris) compared to the sites of tree origins. Monitored species exhibited remarkably distinct growth and water balance patterns over the 2015 growing season characterised with the highly above normal temperature and uneven precipitation distribution. A. alba exhibited smooth continuous growth least affected by varying environmental conditions. Of all analysed species, only A. alba showed significant positive correlations of radial growth and ΔW with temperature and global radiation, despite environmental water limitations. The lowest cumulative growth, lower negative values of ΔW and greater MDS of L. decidua indicate a higher water limitation of this species. The results showed more pronounced sensitivity of P. sylvestris to increased temperature and drought. All monitored variables of environmental conditions, except precipitation, significantly influenced MDS values of all studied tree species. Based on 30 variables describing radial stem growth patterns and water status we identified large inter-species variability and discrete species-specific groups, while the indicators of growth and water status of L. decidua and P. sylvestris were similar and the most different patterns were observed between A. alba and L. decidua. The behaviour of P. abies was closer to A. alba than to the other two species.

The frequency and intensity of droughts and heatwaves in Europe with notable impact on forest growth are expected to increase due to climate change. Coniferous stands planted outside the natural habitats of species belong to the most threatened forests. In this study, we assess stem circumference response of coniferous species (Larix decidua and Abies alba) to environmental conditions during the years 2015–2019. The study was performed in Arboretum in Zvolen (ca. 300 m a.s.l., Central Slovakia) characterised by a warmer and drier climate when compared to their natural habitats (located above 900 m a.s.l.), where they originated from. Seasonal radial variation, tree water deficit (ΔW), and maximum daily shrinkage (MDS) were derived from the records obtained from band dendrometers installed on five mature trees per species. Monitored species exhibited remarkably different growth patterns under highly above normal temperatures and uneven precipitation distribution. The magnitudes of reversible circumference changes (ΔW, MDS) were species-specific and strongly correlated with environmental factors. The wavelet analysis identified species-specific vulnerability to drought indicated by pronounced diurnal stem variation periodicity in rainless periods. L. decidua exhibited more strained stem water status and higher sensitivity to environmental conditions than A. alba. Tree water deficit and maximum daily shrinkage were found appropriate characteristics to compare water status of different tree species.