Monitoring the water supply can make an important contribution to the planning and maintenance of urban trees. The water availability of urban trees is limited by the high degree of sealed and compacted surfaces. However, soil moisture and water supply play a decisive role in tree vitality and are therefore relevant for the ecosystem services the trees can provide.

To gain further insights into the water supply of urban trees, we measure the stable isotope signature of water isotopes in both the tree and the soil. In conjunction with other ecohydrological measurements such as sap flow, stem water content and soil water content, we can assess how much and from what depth the tree gets its water. On the other hand, we apply minimally invasive geophysical methods such as geoelectrics and ground-penetrating radar to monitor soil moisture over larger areas. In addition, with our geophysical methods, we can characterize the local infrastructure in the subsurface around urban trees and we can detect potential obstacles that may hinder water flow or roots.

To cover a wide range of urban trees, various test areas with different tree species and varying degrees of sealed surfaces were selected for a one-year monitoring within Brunswick. The aim is to correlate the water balance with tree vitality in order to contribute to the planning and maintenance of urban trees.