Ecological potentials of trees, shrubs and hedge species for urban green spaces by multi criteria decision making

Abstract

In planning for sustainable development of urban green space at the macro and regional levels, it is imperative to examine plant species of urban green spaces and to introduce new species considering climatic conditions, environmental pollution, industrial lifestyle, and resource limitations. The present study employs multi criteria decision making techniques to assess the existing and recommended plant species (trees, shrubs, and hedge plants) in downtown and marginal parks of Rasht City, Iran. Twenty seven indicators were defined in the context of six criteria, namely regional adaptation, urban environment, aesthetics, maintenance, growth characteristics, and specific advantages. Weights were assigned to the criteria using the entropy method. They were subsequently ranked by Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), Combinative Distance-based Assessment (CODAS), Additive Ratio Assessment (ARAS), and Evaluation Based on Distance from Average Solution (EDAS) techniques. To provide a final ranking of the ornamental species, the results of these four techniques were integrated using average rank, Borda, and Copeland methods. Based on the results, Parrotia persica, Liquidambar styraciflua, Lagerstroemia indica, Pyracantha coccinea, and Ligustrum texanum were ranked highest and Aesculus hippocastanum, Koelreuteria paniculata, Crataegus microphylla, Viburnum opulus, and Berberis gagnepainii were ranked lowest. Based on the detailed results, the assessment of trees, shrubs, and hedge plants can help decision makers and planners of urban green space development.

Introduction

Urban green spaces, which are spiritual requirements of people in urban areas and industrial communities, refer to a part of open spaces whose natural, or often artificial, landscape is dominated with a cover of trees, shrubs, plants, flowers, grasses, and cover plants. They are constructed and maintained under the supervision and management of humans to improve the living, ecosystem, and welfare conditions of citizens and non-rural population centers. The plant covers of urban green spaces are so important that they are called the lungs of cities by. Plants form the basis of all ecosystems and can partially alleviate the risk of pollution in green spaces (Lohe et al., 2015). Due to their specific characteristics, plants, especially trees and shrubs, can significantly contribute to reduce pollution. Aesthetic and ecological values, resistance to pollutants, pollution tolerance, and adaptability to climatic conditions are the main criteria for the selection of ornamental plants and shrubs for urban parks (Delaman & Farahmand, 2017). Sustainability in green space means the adaptation of its vegetation with its climatic conditions. The key to success in developing a sustainable green space is the selection of appropriate ornamental plant species that are adapted to the urban area (Asgarzadeh et al., 2014). The investigation into ornamental plants in urban green spaces and the recommendation of new cultivars are of crucial significance for the development of sustainable green spaces. Ecological needs, performance, and aesthetics constitute the criteria to select ornamental plants, which is mostly done arbitrarily or with a one-dimensional perspective so that it cannot be generalized to other regions with similar resources. A vital important point to consider is the priority of selection criteria in a certain region, which can be a chilling tolerance in one region or soil status or other decisive factors in another. Most urban green space officials have a list of suitable plant species for green spaces of their respective region, which is based on local growing experiences, not science. The criteria for plant selection differ among environmentally different cities (Asgarzadeh et al., 2014). These differences are rooted in inadequate knowledge of plants in the context of ecological, performance and aesthetic principles. Plant species are mostly selected by horticulturists, agriculturists (professionals of agriculture, natural resources, and environment), or even architects (see Table 1). Obviously, they have their own visions and perspectives in this selection as described in Table 1. Horticulturists are not familiar with the principles of aesthetics and their performance, but they are mostly dominated with an economic perspective and are more inclined towards the selection of garden plants whose consequence is a private garden appearance of the green spaces. Similarly, agriculturists are unfamiliar with the principles of aesthetics and they mostly have an agronomic perspective on plant selection and mostly select crops, so they give an agronomic appearance to the green spaces by selected thwart plants, like grasses. Likewise, the experts of natural resources and environment are not familiar with the principles of aesthetics and are mostly concerned with ecology and environment, whose result is the development of tree plantations and parks that lack performance and beauty. On the other hand, architects are unfamiliar with performance, economic, and ecological principles and they are dominated with an artistic view and sometimes functional view with no attention to plant diversity. As a result, the plant appearance is beautiful only on paper and the planted species are destroyed. The lack of the dominance of a systemic and holistic perspective on the issue causes inefficiency (Hosseinzadeh Delir, 2003).