KROOF3B: To the point of failure-water transport along SPAC

Forests fulfill a variety of important functions. They provide habitats for animals and plants, are important reservoirs of carbon and water, serve as recreational areas for people, provide protection against a wide range of natural hazards and, last but not least, are also of great economic importance. However, these highly valuable ecosystems are coming under increasing pressure. Climate change, in particular, poses major challenges for forests. In recent years, there has been a significant increase in long and intense droughts, which have also caused extensive damage in Central Europe. Scientists and practitioners around the world are working to make our forests fit for the future. Knowledge of the resilience and adaptability of potential tree species and a better understanding of the mechanisms involved in drought induced mortality are key. The `Kranzberg Roof Project (KRoof)` provides a rare opportunity to study the effects of long- term drought stress on mature trees in detail, and to combine the findings of different research groups. In 2010, 12 plots were established in the Kranzberg forest near Freising (Germany), each containing several 70 to 90-year-old spruce and beech trees. Automatic roofs were installed on six of the plots to keep rainfall off the ground during the growing seasons from 2014-2019. In the summer of 2019, these roofs were removed and all the trees were re- watered. Before, during and after rewatering, numerous studies were conducted to analyse drought tolerance and adaptability to summer drought stress, and to identify long-term (i.e. legacy) effects. In a third phase, trees that have previously been exposed to drought stress, but now given five years to recover, will be re-exposed to severe, potentially lethal drought stress. A variety of techniques will be used to continuously monitor relevant hydraulic parameters from the roots to the leaves. Comparison with neighbouring trees exposed to the same drought stress for the first time and with control trees without artificially induced drought stress should provide important new insights into the mechanisms of drought-induced mortality along the tree, show where potential weak points lie, and whether previous events improve or even weaken resistance. In contrast to the previous two funding phases, the third phase will also include young plants in order to identify age-related differences and to obtain information on the future natural regeneration capacity of the forests. The project is a collaboration between the University of Innsbruck (Institute of Botany) and the Technical University of Munich (Plant Ecophysiology).