Urban trees under climate stress: Functions and reactions
Urban trees provide shade, cool the air, bind CO₂ and offer many other ecosystem services that improve the urban climate and benefit people. But how well can they still fulfill these important functions under changing environmental conditions? To answer this, we use a specialized individual tree model. This allows us to precisely calculate how effectively selected urban trees contribute to cooling, carbon sequestration and other ecosystem services. In our analysis, we take into account both the specific characteristics of the tree species and the environmental conditions at its respective location. We also aim to understand how stress impacts tree performance. To do this, we combine:
✅ Short-term observations: Monitoring growth and drought stress by measuring tree dimension, diameter fluctuations, and as soil moisture.
✅ Long-term analyses: molecular markers reveal the extent to which environmental stress limits the functional performance of trees.
This sub-project is a collaboration between researchers from the Plant Ecophysiology Group at the Institute of Meteorology and Climate Research – Atmospheric Environmental Research (IMK-IFU) and the Institute for Technology Assessment and Systems Analysis (ITAS).
Results
In Subproject 03 (Plant Ecology Research Group at KIT’s IMKIFU), changes in the diameters of urban trees have been recorded (so far) over the course of one growing season (10 plane trees, 10 maple trees, 10 linden trees, and 10 oak trees each, distributed across open and impervious sites) (Figure 1). To convert these measurements into moisture content and thereby determine the degree of drought stress, an ecosystem model (LandscapeDNDC) was also enhanced with new functions (using measurements from other sites; a corresponding journal article is currently under review).
Preliminary analyses show that the growth of urban trees depends on the degree of soil sealing at the site (Figure 2). The correlation with separately recorded stress markers (TP02), as well as comparisons with preliminary simulations, strongly suggest that this is due to the reduced water availability at these sites. Furthermore, it has been shown that each of the tree species studied depends to varying degrees on water reserves in the trunk (maple the most and sycamore the least) (Figure 3).
These results suggest that modeling can be used to individually assess drought stress in urban trees on a tree-species- and site-specific basis. After calibrating the new model with additional growth and soil moisture data, it can be used to estimate drought stress and, if necessary, irrigation requirements (to mitigate the consequences of severe stress) based on this information.
Pictures
