Trees in cities provide manifold services, such as structuring urban environments or regulating local climate. Though, they are also exposed to intense stress, such as heat or salt stress, and tree hydraulics (i.e. water transport from roots to crown) are known to be crucial for tree vitality. Green, photosynthetic tissues in stems were suggested to support transport functions and help avoid and repair critical bubble formation, so-called embolism, blocking tree water transport. This project deals with the relevance of green stem tissues to tree hydraulics of urban trees. Based on numerous methods, such as sap flow and stem diameter measurements or acoustic emission analyses, the functional importance of these tissues during drought
and frost will be tested on potted trees of several species. Manipulation experiments (covering of green tissues, salt stress) will enable additional insights. On adult sycamore trees in Ghent and Innsbruck novel real-time tree monitors will be installed to compare their hydraulic performance under natural drought and winter stress in a temperate versus alpine climate. Furthermore, a Citizen Science approach will enable citizens to participate in monitoring of tree growth in the two cities. The project is a cooperation of Ghent University (PI Steppe) and the University of Innsbruck (PI Mayr). Based on the unique expertise of both PIs, pioneering results with high impact potential for both basic and applied research are expected.