This study aimed to assess the adaptive capacity of the dominant tree species in Lithuania, namely Scots pine, Norway spruce, and silver birch, to current climate conditions based on their changes in transpiration expressed through the tree sap flow intensity. The species-specific responses were investigated at two typical edaphically different forest sites with water-limited and water-saturated soils. Contrasting events like overflow in 2017 and drought in 2019 provided an opportunity to detect the adaptative capacity of the monitored tree species to these meteorological extremes. Norway spruce trees, due to having both the most intense sap flow at the beginning of the growing season and the longest period of active transpiration, demonstrated the highest annual transpiration rate, regardless of the hydrological regime of the site. Their decreased resilience to subsequent biogenic damage caused by pests due to a significant decrease in sap flow density during intense and prolonged droughts may reduce their importance in Lithuanian forestry. Silver birch trees, which demonstrated a reduction in sap flow after a drought following the untimely drop of their leaves and the end of active vegetation, even at the end of a prolonged warm period, can be seen to not have appropriate adaptations to current climate conditions. Scots pine trees are the best adapted to mitigating the recent threats of climate change.

Boreal forests are exposed to larger and more frequent fires due to climate change, with significant consequences for their carbon and water balances. Low-severity fires (trees charred but surviving) are the most common fire regime in the Eurasian boreal forest, but we still lack understanding on how they impact tree functioning. This study focused on the dynamics of tree transpiration and stem growth of Pinus sylvestris in central Sweden after a large wildfire in 2018. We compared a stand impacted by low-severity fire (LM) with an unburnt stand (UM), over three years following the fire (2020-2022). We found that transpiration was on average lower and more variable within the stand at LM compared to UM. LM also had consistently lower stem growth compared to UM, resulting in larger accumulated growth for the unburnt site in the second to fourth year after the fire. Our results highlight the complex effects of low-severity fire on tree water cycling, with both direct (damage to tree xylem and roots) and indirect fire impacts (due to loss of understory vegetation and changes in soil properties). Trees affected by low-severity fire also exhibited reduced resilience to water shortages. Considering the expected increase in frequency of droughts and forest fires at higher northern latitudes, such indirect fire impacts may put additional pressure on the boreal forest.