400 Shojanoori and Shafri: Review on the Use of Remote Sensing for Urban Forest Monitoring Arboriculture & Urban Forestry 2016. 42(6): 400–417 Review on the Use of Remote Sensing for Urban Forest Monitoring Razieh Shojanoori and Helmi Z. M. Shafri Abstract. Urban forests are vital in urban areas because they clean the air, absorb water, and protect the environment from intense heat. Destruction of the urban forest by increased urbanization is a considerable threat to the ecosystem. Hence, urban planners must obtain and manage information about urban forests, but the complexity of urban areas has made these tasks difficult. With developments in remote-sensing technologies, the monitoring and detection of urban forests can be achieved without performing any field measurements. In this study, different remote-sensing imageries and various methods are evaluated to obtain urban forest information. This review dem- onstrates that very high resolution (VHR) satellite imagery, such as from WorldView-2, is the most efficient data that can be used to obtain urban forest information. The use of the combination of LiDAR data with VHR imagery increases the accuracy of information, particularly about tree crown delineation. Traditional pixel-based classification methods are not effectively applicable to obtain urban tree information because of significant spectral variability in urban areas. An object-based classification technique, which uses spatial, textural, and color information, can be a potential method to detect urban forest and tree species discrimination. The new VHR imag- ing method, which uses the object-based technique, is recommended to overcome limitations of collecting urban forest information. Key Words. LiDAR; Object-Based Classification; Pixel-Based Classification; Satellite Imagery; Tree Crown Delineation; Tree Species Detection. Urban area is commonly defined as having spaces with artificial surfaces and a dense popula- tion, with vegetation that covers an urban area is considered an urban forest. Urban forests may include any type of vegetation in a metro- politan area; types of vegetation include trees, shrubs, and woody plants on the roadside, or plants on a larger scale, such as a forest park. Urban forests not only result in social and eco- nomic advantages, such as recreational spaces and tourism, but they also provide several benefits to the ecosystem. The most important effect of urban forests in the ecosystem is with regard to the urban atmosphere, and can be divided into four main issues: 1) influence on microclimate and decrease in temperature because shadows are created on surfaces, wind speeds vary, and water is trans- pired; 2) air pollution removal; 3) release of volatile carbon-based compounds; and 4) energy waste minimization by providing shade to buildings to reduce consumption of heating and cooling energy. ©2016 International Society of Arboriculture Urban forests also affect urban hydrology. Urban trees can help solve issues related to water quality by reducing the overflow volume of storm water and minimizing the destruction of flooding because water is absorbed by the roots and soil erosion is avoided. Aside from problems related to the urban atmosphere and hydrology, sound pollution is another issue in urban areas. The leaves and stems of urban trees and shrubs can reduce noise by scattering the sound; thus, plant- ing trees and shrubs in an urban area leads to a decrease in sound pollution (Nowak and Dwyer 2007). In conclusion, the most important advan- tages of the urban forest include the following: protection of biodiversity, avoidance of soil ero- sion, carbon storage, nutrient cycling, improve- ment of air and water quality, slowing wind and reducing water volume caused by storms, moderating local climate, providing shade to homes, and decreasing heat islands (Conine et al. 2004; Gobster and Westphal 2004; Xiao and
November 2016
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