## 5 Conclusions  
To conclude, the more rapid ageing and shortened lifetime of urban trees due to climate change should be considered as new 'normal' and any citywide tree management plan should always be prepared for earlier replacement and replanting. A farsighted large-scale replacement planting program with indigenous, 'right' tree species would thus present an excellent opportunity for enhancing the local biodiversity, ecosystem services, successional development, aesthetic values, as well as reducing the burden of managing potentially hazardous trees. A holistic planting concept with the idea of multifunctionality is a much preferable approach and should later contribute to the building blocks of a sustainable city. Therefore, the long-term planning of elements, structures, and management of urban forests on man-made slopes based on scientific principles is one of the most important services we could leave to the next generations.  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/1999-490](https://www.mdpi.com/1999-490)]([https://www.mdpi.com/1999-490](https://www.mdpi.com/1999-490)) 7/12/3/323/s1, Figure S1. Leaf area index (LAI) variability at sites with _Acacia_ forest in Tai Tong from April 2019 to August 2020. Six sample days were taken in April, July, October 2019, January, April and August 2020. The standard error bars are shown for sites with repeated measurements. Figure S2. Monthly average photosynthesis rate of _Acacia confusa_ in Tai Tong from April 2019 to August 2020. Error bar represents \(\pm 1\) SD. Figure S3. Monthly average photosynthesis rate of _Liquidambar fomosana_ in Tai Tong from April 2019 to August 2020. Error bar represents \(\pm 1\) SD. Figure S4. Monthly average photosynthesis rate of _Tema orientalis_ in Tai Tong from April 2019 to August 2020. Figure S5. Monthly ozone dry deposition uptake by _Acacia confusa_ in Tai Tong from April 2019 to August 2020. Error bar represents \(\pm 1\) SD. Figure S6. Monthly ozone dry deposition uptake by _Liquidambar fomosana_ in Tai Tong from April 2019 to August 2020. Error bar represents \(\pm 1\) SD. Figure S7. Monthly ozone dry deposition uptake by _Tema orientalis_ in Tai Tong from April 2019 to August 2020. Figure S8. Monthly average dry deposition velocity of _Acacia confusa_ in Tai Tong from April 2019 to August 2020. Error bar represents \(\pm 1\) SD. Figure S9. Monthly average dy deposition velocity of _Liquidambar fomosana_ in Tai Tong from April 2019 to August 2020. Error bar represents \(\pm 1\) SD. Figure S10. Monthly average dry deposition velocity of _Tema orientalis_ in Tai Tong from April 2019 to August 2020.  
**Author Contributions**: Conceptualization, A.M.C.T., A.S.L.L., D.Y.F.L., A.P.K.T.; formal analysis, A.M.C.T., A.S.L.L., D.Y.F.L., A.P.K.T., D.K.C.T., F.L.; investigation, A.M.C.T., A.S.L.L., D.Y.F.L., A.P.K.T.; writing--original draft preparation, C.H.Y.L., A.M.C.T., A.S.L.L., D.Y.F.L., A.P.K.T., D.K.C.T., F.L.; writing--review and editing, A.M.C.T., A.S.L.L., D.Y.F.L., A.P.K.T., S.S.M.L., C.W., S.C.S.T., K.T.K.N.; funding acquisition, A.M.C.T., K.T.K.N. All authors have read and agreed to the published version of the manuscript.  
**Funding**: This research was funded by the Highways Department of the HKSAR Government.  
**Institutional Review Board Statement**: Not applicable.  
**Informed Consent Statement**: Not applicable.  
**Data Availability Statement**: The data presented in this study are available on request from the corresponding authors.  
**Acknowledgments**: We acknowledge the field and logistical support provided by all the staff and helpers in data collection.  
**Conflicts of Interest**: A.M.C.T., A.S.L.L., D.Y.F.L., and A.P.K.T. received funding support from the Highways Department of the Government of the Hong Kong Special Administrative Region to work a consultancy project that is directly related to this work. S.S.M.L., C.W., S.C.S.T., K.T.K.N. are employees of the funding body.