Allocating tree crown pruning with ALS-data - A case study in the city of Helsinki

Trees are an essential part of urban environments. In urban areas trees are located for example among buildings, on roadsides and in parks. When growing outside of their typical natural forest habitat, the trees need to be actively managed to ensure their well-being and the safety of the citizens. One example of urban tree management is the need to make sure that the street areas are sufficiently lit. It means that trees growing very close to street-lamps need to be pruned occasionally. In this case study the need of pruning the urban trees in the city of Helsinki was studied by means of airborne laser-scanning (ALS) and GIS-analysis. An ALS-based tree register containing the main attributes and the spatial location of the trees was compared in the analysis to a lamppost register. The lamppost register included the types and the xy-locations of the lampposts. The aim of the analysis was to map the trees and more specifically tree crowns that had an effect on the lampposts and thus needed to be pruned. First, tree crowns were delineated from the ALS-data. A GIS-analysis was used to map the trees that had a crown segment influencing to a lamppost and then the tree was classified to be pruned. The classification was then compared to a field data collected from the same areas to validate the results. Based on the results, it seems it is possible to use ALS-data and GIS in planning of the tree management in urban areas.