Optimizing Irrigation Strategies for Mitigating Drought Stress in Reforestation Areas: Lessons from a Drought Stress Experiment

The increasing frequency of drought events in recent years has become a major hurdle for reforesting forests after natural disturbances in many areas globally, including parts of Central Europe. As an example, reforestation projects after bark beetle disturbances have faced notable failures and losses due to prolonged drought conditions in Northern Bavaria (Germany). Irrigation is a potential measure increasing reforestation success and is currently funded by the regional government. However, historically irrigation was not a common technique in this area and there is a lack of both practical and scientific knowledge concerning irrigation strategies. The optimal timing for the irrigation of the saplings as well as the water amount applied are crucial aspects in this context. This study addresses this knowledge gap by conducting a drought stress experiment within a greenhouse environment, focusing on four commonly planted tree species prevalent in our study region in northern Bavaria. Various approaches were explored to reliably detect drought stress and identify the irrigation demand both concerning timing and amount of water applied: the experimental design integrates environmental data with ecophysiological measurements and employs drought stress indices derived from close-range remote sensing. The most promising methodology for detecting the irrigation demand, identified through rigorous experimentation, will be further explored on forest sites post-planting. Implementing such optimized irrigation strategies holds promise for safeguarding reforestation endeavors, particularly in regions prone to drought, and contributes to the sustainable management of forest ecosystems and water usage.