Urban Trees in the Drought - Functional Ecology and Remote Sensing in Context (TreePulse)

Trees are dying prematurely in cities around the world before they reach the desired size as droughts become longer, more frequent and more severe. A healthy population of urban trees is essential for human well-being and a climate-resilient city. The recently launched URBORETUM project is looking at the causes and extent of the decline in the vitality of urban trees. The aim of the TreePulse work package is to clarify the mechanisms behind premature tree death and to recommend suitable tree species for specific urban environments.

We will identify factors contributing to the decline in vitality by conducting an in-situ experiment with urban trees, field observations and time series analyses of satellite images of four German cities (Karlsruhe, Heidelberg, Mannheim and Freiburg). Six deciduous tree species growing in the streets and parks of the cities were selected. We will install sensors (sap flow meters and dendrometers) to monitor the physiological parameters of the trees during the growing seasons 2024 and 2025. 2024 as a wet year will serve as a baseline. Continuous stem growth, sap flow, crown dieback, internal stem damage and root space will be measured. The physical and chemical properties of the soil, light and water availability and microclimatic parameters will be measured. The water potential of the soil and the microclimatic parameters (air temperature, relative humidity and photosynthetically active radiation) are measured by installing sensors. Terrestrial LiDAR scan data of single standing trees will be collected and linked with multispectral remote sensing data to create a vitality map of urban trees.

This study will combine the fundamentals of plant stress biology with applied aspects of mitigating drought-induced tree mortality in urban ecosystems. The research results should prevent tree mortality by helping horticultural and forestry professionals to take appropriate measures.