Abstract
In order to ensure the safety and security of users of parks and roads, Osaka City has been implementing a safety project involving park and street trees from FY2018 to FY2024, and plans are to cut down about 19,000 tall trees in those 7 years. The current paper uses publicly available project data from FY2023 and information obtained through field observations to explain the details of this project. This paper then notes the issues with this project from four perspectives: tree cutting standards, the state of replanting, the effects of the project, and public awareness. Next, this paper analyzes tree management data from Osaka City for the period from FY2017 to FY2021, which includes both the normal maintenance of park trees and street trees and the safety project. Results revealed that pruning costs accounted for about 70 % of tree management costs, that the number of trees pruned and the pruning area decrease if annual pruning costs are constant, that less than 20 % of trees that were cut down were replaced with tall trees in either normal maintenance or the safety project, that the number of tall trees decreased by about 16,000 trees in 5 years since FY2017 as a consequence (this does not include the clearing of trees toppled by Typhoon Jebi in 2018), and that tall trees, if they are replaced, are replaced with smaller trees. Based on these findings, proposed improvements to the management of park trees and street trees in Osaka City include: having an arborist diagnose the health of trees and respecting his or her findings, clearly stating the cutting criteria, reducing cutting due to root growth to the extent possible, stopping the cutting of healthy Himalayan cedars and Abelia shrubs, properly pruning street trees, increasing the rate of replacement of tall trees when tall trees are cut down, improving the information given to the public and the way in which they are informed, publishing data such as the number of tall trees, adopting canopy cover as an index, and explaining the secondary aim of the safety project.
