Trees on roofs – biomass determination of trees on green roofs and underground parking garages as a basis for adapted statics

Green roofs with large trees are becoming increasingly important in the context of urban climate adaptation. However, there is still a lack of sound scientific data on the actual growth, biomass development, and CO₂ storage capacity of trees in artificial locations such as roofs and underground parking garages. Load assumptions currently in use are based on outdated or incomprehensible reference values, which often leads to significant overestimations of tree mass. This results in oversized support structures, increased material use, and unnecessary costs and CO₂ emissions. The aim of this research project is to collect reliable data on the morphology and mass distribution of large trees on buildings for the first time. To this end, around 30 trees on four completed projects in Austria will be measured using modern laser scanning technology. The surveys will be carried out twice a year – in leafy and leafless conditions – in order to record seasonal differences. The trunk, branch, and foliage biomass as well as the potential CO₂ sequestration will be analyzed. The results should reveal differences in morphology compared to trees growing on natural soil and provide a basis for future modeling of tree growth on roofs. In the long term, the results obtained should be incorporated into regulations and increase planning reliability. This should contribute to the wider use of intensive green roofs and make better use of their potential for urban cooling, rainwater retention, and CO₂ reduction.