Climate-smart thinning for improving tree resilience to drought? A tree’s perspective

Climate change is increasing the frequency and severity of droughts, threatening forest health and productivity. Thinning is widely proposed as a climate-smart management strategy to reduce competition for water and improve tree drought resilience. This thesis investigated how forest density affects soil water availability, tree water status, and growth in European beech, Douglas-fir, and Scots pine forests in the Netherlands. Combining field measurements, tree-ring analyses, and physiological modelling, the results showed that reducing forest density increased soil water availability but did not consistently improve tree water status. Instead, trees appeared to use the additional water to support greater transpiration and growth. Growth generally increased with decreasing density in beech and Scots pine, whereas Douglas-fir showed limited growth responses. No intermediate forest density was found that simultaneously minimized water stress and maximized growth. These findings highlight that thinning involves ecological trade-offs and that climate-smart forestry requires species-specific management strategies rather than a universal thinning approach.