Abstract
Street trees in urban planning have a long history as providers of an amicable environment for urban dwellers. Nevertheless, street trees are not always without a challenge, their ecosystem disservices include, inter alia, cracking pavements and foundations due to wandering tree roots that destroy concrete or asphalt surfaces. Thus, effective mapping of street trees assists in planning a suitable urban environment to improve city life. The traditional method for urban tree mapping is costly, time-consuming and labour intensive. However, commercially operated multi-spectral sensors, such as WorldView (WV) provide a more viable way to map trees at the species level. This study investigates the use of WV-2 imagery in the classification and mapping of five common alien street trees in a complex urban environment. It also examined the feasibility of Random Forest (RF) and Support Vector Machines (SVM) classifiers in mapping street trees in a heterogeneous urban environment. The classifiers produced an overall accuracy of 84.2 % for RF and 81.2 % for SVM. This study provides a detailed understanding of urban tree species to the municipality of Johannesburg and offers environmental managers an insight of classification methods for mapping trees using satellite imagery to comprehend their spatial distribution.
Highlights
The mapping of tree species in an urban environment is vital for planning through strengthening our knowledge of their ecological functions in these environments (Liu et al, 2017)
Random Forest (RF) parameter tuning The best-input parameters for the classification of the five urban trees species and LULC classes were determined through optimization for training in the RF machine-learning algorithm
Our results indicate that the multispectral WV-2 sensor is suitable in urban tree species mapping using RF and Support Vector Machines (SVM) classifiers with overall accuracies of 84.2% and 81.2%, respectively
Summary
The mapping of tree species in an urban environment is vital for planning through strengthening our knowledge of their ecological functions in these environments (Liu et al, 2017). Urban trees offer essential social, economic and psychological amenities to human beings such as increased property values and improved physical/mental health (Tyrväinen et al, 2005). Even though urban trees offer various advantages, there is a debate about alien tree species use in cities. The major debate over the usefulness of alien vs indigenous tree species necessitates precise identification and mapping of trees, which is essential for city or metropolis managers to develop and sustain urban planning strategies (Li et al, 2015). Accurate spatial data on urban trees is required to assess the extent and distribution of tree species to estimate their ecosystem services and disservices (Nowak et al, 2008)
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