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live in, walk on and ride on, such as buildings, parking lots, roads, sidewalks, green spaces, and public transportation (Andersson et al. 2014). Belowground component encompasses massive foundations of the buildings, subway lines, tunnels, gas lines, water and sewage pipes, stormwater management, electricity, and optical cables for providing various services to the citizens and ease in their livelihood (Sun and Cui 2018; Ma et al. 2020). Both the components of the urban infrastructures hold crucial significance and interact with each other in complex ways (Pandit et al. 2015). Aboveground infrastructures provide living spaces and comforts to the citizens, whereas belowground components play equally important services in the form of utilities, transportation, biomass, and structures which enable the urban areas for smooth functioning of the aboveground components (Ferrer et al. 2018; Ma et al. 2020). Moreover, natural components of the urban infrastructures such as plant roots and microbial communities also show strong competition for the space in the belowground components (Mullaney et al. 2015).
Land‐use and land‐cover changes are one of the major drivers of global change processes which should be taken into account considerably from ecological point of view (Vitousek 1994). Urban land cover has been projected to increase by 200% within the first three decades (2000–2030) of the twenty‐first century (Elmqvist et al. 2013). These projections revealed that there has been and would be a massive investment in the development of the urban infrastructures at the cost of consumption of natural ecosystems/landscapes (Green et al. 2016). Increase in impervious surfaces and the materials used for their formation (dark asphalt and roofing materials) due to massive urbanisation have the ability to absorb the solar irradiance and influence the local climate and hydrological conditions (Vasishth 2015). UHI effect (described later) is one of the major outcomes of the increase in such urban built infrastructures (Jaganmohan et al. 2016). For managing the urban ecological components (e.g. biodiversity, nutrient cycling, etc.) influenced by the land‐use change patterns, several conceptual frameworks, and models have been developed (Pickett et al. 2011). However, their proper implementation is lacking due to poor representation of the social components in these frameworks (Zipperer et al. 2011). Nowadays landscape urbanism is the emerging concept with non‐hierarchical, flexible and strategic planning where landscapes in the urban areas are designed and managed as per the demand of the society (Kattel et al. 2013). Detailed elaboration of such strategies and frameworks has been given in the later sections of the chapter.
1.2.1.1 Urban Heat Islands
Modifications of the physical environment by the built structures during the process of urbanisation impede the energy distribution and composition of gases in the near‐surface. It alters the microclimatic conditions by modifying the thermodynamics of the urban ecosystems which resulted in 2–5 °C higher ambient temperature than the surroundings (countryside/rural) areas (Phelan et al. 2015; Jaganmohan et al. 2016; Vasishth 2015; Duffy and Chown 2016). Such alterations in local and regional climatic conditions (temperature dynamics) by the urban infrastructures lead to the UHI effect (Dallimer et al. 2016; Zhou et al. 2017; Hu et al. 2019). The UHI effect is one of the most prominent human‐made climatic phenomena in the urban ecosystems and has considerable ecological significance (Gaston et al. 2010; Akbari and Kolokotsa 2016; Yu et al. 2017). The UHI effect leads to the alteration of local and regional climatic conditions, impedes with the wind flows, and turbulence, related with shifts in cloud formation and precipitation, air pollution, and higher greenhouse gas (GHGs) emission (Seto and Shepherd 2009; Gaston et al. 2010). The increase in air pollution, heat stress, water quality, food security, and disparity in ecosystems services due to the UHI effects further affect the health and comfort of the urban inhabitants, thus, have adverse social, economic, and ecological impacts (Chang et al. 2016; Wong et al. 2016; Battles and Kolbe 2019). Moreover, UHI effect is further expected to contribute in the global climate change by increasing the GHGs (particularly CO2) emission from the urban areas (Rosenzweig et al. 2010), and in response, the UHI effect's impact may further intensify in most of the cities (Chapman et al. 2017). However, the magnitude of the UHI effect depends on several local and regional factors such the latitude, weather and climatic conditions, diurnal conditions, rainfall, surrounding ecology, population and culture of the city, and the urban planning (Zhao et al. 2014; Vasishth 2015). For example, the increase in temperatures due to UHI effects during winter at higher altitudes, and during summer at lower altitudes may decrease and increase the costs of air‐conditioning, respectively (Vasishth 2015). Thus, the UHI effects may have variable responses depending on the location of the urban area and it needs to be explored further under the changing environmental conditions.
1.2.2 Urban Vegetation
Urbanisation provides a unique habitat for vegetation growth. Urban vegetation (tree, shrub, or ornamental plants) is comprised of both native and exotic species (Cubino et al. 2021). Two major processes are involved in the growth of urban vegetation, viz. cultivated vegetation growth which represents the plants that are introduced and managed by the urban inhabitants, and spontaneous vegetation growth which have been established and colonised without the human‐assistance (Cubino et al. 2021). Vegetation composition of the urban areas even differs at small scales depending on the several social factors (Čeplová et al. 2017). Introduction and cultivation of plants, especially ornamental or exotic plants for their aesthetic values by the urban inhabitants hold a crucial significance in current scenario. Exotic plants constitute a major portion of the urban vegetation; however, their contribution to the functioning and diversity at the socio‐ecological scales have been less explored (Cook‐Patton and Agrawal 2014; Pearse et al. 2018; Cubino et al. 2021). Most of the exotic species present in the urban areas are ornamental plants introduced intentionally by the humans (Čeplová et al. 2017; Lososová et al. 2018). Due to suitable environmental (heterogeneous) conditions or positive anthropogenic interferences (fertilisation and irrigation at regular intervals) in the urban areas, exotic plants have substantial scope to establish and colonise (Lososová et al. 2018). Human‐induced dispersal of the plant species in the urban areas contributes to the plant distribution and community composition (Møller et al. 2012; Lososová et al. 2018). Moreover, local fauna and their preferences for the fruits/flowers also contribute to the biodiversity of the area. For example, the preference of frugivorous birds affects the dispersal of fleshy‐fruited plant species in the urban areas (Møller et al. 2012). Moreover, birds help in seed dispersal of ornamental (exotic) trees from the gardens to the nearby natural ecosystems, thus, may facilitate plant invasion (Milton et al. 2007). Thus, exotic plants can be a major cause of ecosystem imbalances when the sufficient source of seeds/propagules and its dispersal agents are present in the nearby areas (Rai and Kim 2019).
Vegetation, particularly trees, plays a crucial role in maintaining the harmony in the urban ecosystems (Tigges et al. 2013). For example, trees store sufficient amount of carbon (C) and help in maintaining the overall C‐pool of the urban ecosystems (Davies et al. 2011). Urban ecosystems have sufficient potential to store C in their above‐ and belowground components (Hutyra et al. 2011; Nowak et al. 2013), even in dense urban areas (Mitchell et al. 2018). Urban areas have abundant shade trees (recreational purpose), trees grown for hazard removal, or exotic trees, all have potential to store substantial amount of C in their vertical structures. However, C‐density of the urban areas varies at spatio‐temporal scales (Mitchell et al. 2018; Upadhyay et al. 2021). Detailed view on the urban C‐stocks and their ecosystem services have been highlighted in the latter part of the chapter.
1.2.3 Urban Metabolism
The urban areas can be considered as an organism where consumption of materials, flow of energy and information, and waste generation (as end‐products) are the common processes occurring at various spatio‐temporal scales (Liu et al. 2013; Vasishth 2015; Verma et al. 2020a). These processes not only occur within a city but also affect the environment beyond the borders of the city, as like the natural organisms where different cells and tissues interact and involve in the metabolic processes and excrete the wastes outside the cell/body (Liu et al. 2013; Verma et al. 2020a). To understand the concept of material and energy supply for the functioning of the cities and the resultant waste (pollutants) generation in the urban ecosystems, the concept of urban metabolism has emerged (Restrepo and Morales‐Pinzon 2018). The concept was first proposed by Wolman (1965), who believed