A Case Study Balancing Predetermined Targets and Real-World Constraints to Guide Optimum Urban Tree Canopy Cover for Perth, Western Australia

Abstract

Trees in urban settings are becoming increasingly important as mediators to emerging challenges that transect social, environmental, and economic factors. Trees provide shade; absorb and store atmospheric carbon and other pollutants; reduce local temperature fluctuations; provide essential inner-city fauna habitat; assist in reducing over-land stormwater flow; provide amenity; and provide many more social, environmental, and economic benefits. To secure these benefits, tree canopy cover targets are commonly employed by land managers; however, such targets are rarely quantified against the characteristics and limitations of individual urban centers. Through the generation and interrogation of qualitative and quantitative data, this case study of Perth, Western Australia presents a new conceptual tool that integrates eleven factors found to influence the capacity and opportunity for a city to support urban tree canopy cover. This tool is designed to capture and causally weigh urban tree canopy considerations based on individual city characteristics, collective values, and identifiable constraints. The output of the tool provides an “optimum” tree canopy cover result (as a percentage of the urban fabric) to better inform canopy cover targets and recommendations for urban tree strategic planning and management. This tool is valuable for urban land managers, city planners, urban designers, and communities in effective planning, management, valuation, and investment regarding urban trees as a sub-set of urban green infrastructure.

Comparison of Various Tree Features for Blocking Solar Radiation in the Arid Urban Environment

“…Shade sites can be achieved by placing shade structures close to buildings or fences, using trees and plants for screening, or partially walling the shade structures (Gies and Mackay, 2004;Grant and Heisler, 2006). Therefore, green infrastructure is a successful alternative to significantly contribute to urban centers (Parker and Simpson, 2020;Zhao et al, 2018). Large trees and multilayered planting assist in longwave radiation mitigation, more than single-layer planting, by blocking building radiation (Kwon and Lee, 2019).…”

“…The urban environment is influenced by using trees that improve the quality of life and create an eco-friendly and sustainable urban environment, especially in arid regions; it provides better environmental services and appropriate conditions for users in harmony with seasonal changes (Morakinyo et al, 2016). Trees can help to modify the air temperature, cooling the air, increase air humidity, reduce wind speed, produce oxygen, save energy, reduce stormwater, mitigate air pollution, abate noise, and modify air pollutants (De-Abreu-Harbich et al, 2015;Parker and Simpson, 2020). Moreover, it is worth noting that trees provide better shade than pergolas by helping to reduce all types of solar radiation (SR).…”