Notes

urban ecosystems, defined here as those areas where the built infrastructure covers a large proportion of the land surface, or as those in which people live at high densities (Pickett et al. 2001).
urban ecosystems, defined here as those areas where the built infrastructure covers a large proportion of the land surface, or as those in which people live at high densities (Pickett et al. 2001).

Urbanization is a complex and dynamic process playing out over multiple scales
of space and time (Grimm et al. 2008a , b ). Historically, cities have been compact
and have concentrated populations. Today, cities are increasingly expansive. Across
the world, urban areas are growing on average twice as fast as urban populations
(Seto et al. 2011 ; Angel et al. 2011 )

In terms of “Urban Green Infrastructure (UGI)”, these components are in a combination of natural and constructed materials of urban space that have an important role in metabolic processes, biodiversity, and ecosystem resiliency underlying valuable ecosystem services. The increase in the world’s population in urban areas is a driving force to threat the environmental resources and public health in cities; thus, the necessity to adopt sustainable practices for communities is crucial for improving and maintaining urban environmental health.

1.3 Ecosystem services
Improving the knowledge about the importance of urban ecosystem services (ESs), and their value especially in the current trend of world urbanization is necessary. Thus, the role of city planners and other disciplines and their collaboration to integrate new findings associated with ESs is necessary [12]. ESs, directly and indirectly, influence human life and thus the economic activities. For examples, the maintenance of soil fertility can secure food production, and/or providing clean air and water through the absorption of pollutants by plants, and our mental and physical health may depend on the accessibility to green spaces [13].

Abstract
Urban ecosystems are composed of biological components (plants, animals, microorganisms, and other forms of life) and physical components (soil, water, air, climate, and topography) which interact together. In terms of “Urban Green Infrastructure (UGI)”, these components are in a combination of natural and constructed materials of urban space that have an important role in metabolic processes, biodiversity, and ecosystem resiliency underlying valuable ecosystem services. The increase in the world’s population in urban areas is a driving force to threat the environmental resources and public health in cities; thus, the necessity to adopt sustainable practices for communities is crucial for improving and maintaining urban environmental health. This chapter emphasizes the most important issues associated with the urban ecosystem, highlighting the recent findings as a guide for future UGI management, which can support city planners, public health officials, and architectural designers to quantify cities more responsive, safer places for people.

1.1 Urban ecosystem
Urban areas are composed of natural and constructed systems where the human population is more concentrated, and there are complex interactions between socioeconomic factors and biophysical processes [1, 2]. In a city, an ecological process often occurs in habitat patches, which are connected by corridors in a matrix of streets and buildings. The major ecological processes between/among habitat patches include immigration and dispersal agents, also, ecological corridors that can act as links or barriers for dispersal ability [2].

Due to transport networks cities are often the entry points of many alien species [3]. Moreover, in contrast with non-urban areas, urban ecosystems have different physical and chemical properties, which highly influence species distribution and ecosystems functioning [4, 5]. As a whole, urban areas have been usually considered novel in relation to their non-urban counterparts, which are comprised of a variety of fragmented habitats [4]. Overall, in this novel ecosystems the restoration ecology, conservation, biodiversity, ecosystem services, and climate change have been the most discussed topics in literature [6].

1.2 Urban green infrastructure
A bibliographic analysis of urban sustainability indicates that the topic of green infrastructure started to be in the attention of scientists in 2010, when, the awareness of issues associated with climate change was raised and the assessment of urban ecosystem services was more considered. During a period of five years (2010-2015), topics related to health and well-being were more interesting, and the motor theme of conversation became the priority of the scientists studying the importance of green infrastructures. This demonstrates the significant importance of green infrastructure and its association with sustainability [7, 8].

The term “Urban Green Infrastructure (UGI)” refers to engineered and non-engineered habitat structures in connection with natural and semi-natural areas and other environmental features, which are designed to deliver a wide range of services from nature to humans. Green infrastructure comprises different kinds of components (for example, parks, green roofs, urban forests, road verges) which according to several number of parameters (e.g., spatial scale, dimension, location) are categorized [9, 10].

1.3 Ecosystem services
Improving the knowledge about the importance of urban ecosystem services (ESs), and their value especially in the current trend of world urbanization is necessary. Thus, the role of city planners and other disciplines and their collaboration to integrate new findings associated with ESs is necessary [12]. ESs, directly and indirectly, influence human life and thus the economic activities. For examples, the maintenance of soil fertility can secure food production, and/or providing clean air and water through the absorption of pollutants by plants, and our mental and physical health may depend on the accessibility to green spaces [13].

1.3.1 Categorization of ecosystem services (ES) at the urban level
We only consider the ecosystem services classified by the Mapping and Assessment of Ecosystems and their Services (or MAES), Urban ecosystem, 4th report (May 2016). This classification takes into account merely the ecosystem services which are more important and happen in urban areas. These ecosystem services (ESs) are including (i) provisioning services in which the food and water are the most valuable ones, (ii) regulating services including the regulation of air quality, flood and water flow regulation, also, noise and temperature reduction plus pollination, (iii) the cultural ecosystem services such as recreation, education and cultural heritage [14].

services////
Building on previous categorizations of ecosystem services (Daily 1997; de Groot et al. 2002), the Millennium Ecosystem Assessment (MA 2005) and The Economics of Ecosystem Services and Biodiversity (TEEB 2010) grouped ecosystem services in four major categories: provisioning, regulating, habitat, and cultural and amenity services (TEEB 2010) (Fig. 11.1). Provisioning services include all the material products obtained from ecosystems, including genetic resources, food and fiber, and fresh water. Regulating services include all the benefits obtained from the regulation by ecosystem processes, including the regulation of climate, water, and some human diseases. Cultural services are the non-material benefits people obtain from ecosystems through spiritual enrichment, cognitive development, reflection, recreation, and aesthetic experience as well as their role in supporting knowledge systems, social relations, and aesthetic values. Finally, supporting or habitat services are those that are necessary for the production of all other ecosystem services. Examples include biomass production, nutrient cycling, water cycling, provisioning of habitat for species, and maintenance of genetic pools and evolutionary processes.

Urban ecosystems are especially important in providing services with direct impact on human health and security such as air purification, noise reduction, urban cooling, and runoff mitigation. Yet, which ecosystem services in a given scale are most relevant varies greatly depending on the environmental and socio-economic characteristics of each geographic location.