Trends in the Leaf Growing Seasons of Urban Trees in Graz, Austria: A Remote-sensing Approach for Long Term Monitoring of Green Infrastructure

Abstract Submission: The changing climate creates challenges for green spaces everywhere. A special case is presented by the urban tree, which has several harsh environmental conditions to deal with, i.e. compacted soil, polluted rainwater, etc. Climate adaptation strategies for cities involve the urban tree due to its high potential for heat island mitigation and reducing surface runoff. Managing water resources efficiently is receiving more attention with measures including alternative resources for irrigation or incorporating more drought-resistant species, while the effects of changing macro- and micro-climatic conditions on urban trees are only now becoming subject of scientific scrutiny.
An important indicator for a tree’s living conditions and water demand at a certain location is the start and end of the leaf growth. As temperatures rise, plants will have shorter dormancy periods, resulting in earlier flowering and longer growing seasons, increasing both water demand and vulnerability to damage.
In this study, we compare the growing cycles of urban trees across varying locations in the city of Graz over a period of 20 years. Tree specific information is taken from the city’s tree register. Growing cycles are evaluated using a remote sensing approach. NDVI-timeseries are calculated for the locations of the trees using openly available satellite imagery to identify changes in dormancy and evaluate a possible trend. The influence of parameters such as location, micro-climate, species and date of planting are investigated using statistical analysis. The generated knowledge will help in the prediction of water demand and choice of tree species depending on planting location.

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