1. Introduction
Urban landscapes are social–ecological systems
[1] and occur across much of the world
[2]. Nearly two thirds of the world’s population is expected to live in cities by 2050
[3], including 89% of the population within the USA, requiring sustainable growth to ensure environmental integrity, ecological function,
[4] and human wellbeing
[5]. Urban landscapes have high spatial heterogeneity
[6] as well as demographic and social diversity, impacting resource access and function
[7]. The ecosystem services (ES) framework assesses ecosystem benefits by translating ecological structures, functions, and processes into value based operations and objects
[8]. Ecosystem services include supporting services (e.g., soil formation and nutrient cycling), provisioning services (e.g., food, fresh water, fuel, fiber, and other goods), regulating services (e.g., climate, water, and disease regulation as well as pollination), and cultural services (e.g., educational, aesthetic, and cultural heritage values as well as recreation and tourism)
[9].
Many models and theoretical constructs within ecosystem services exist, most are predominately ecological frameworks or anthropocentric frameworks
[10]. Most ecosystem services frameworks evaluate single function landscapes
[11], not multifunctionality nor the wider range of ecosystem services available
[12][13]. In urban landscapes, ecosystem services originate from multiple and diverse biophysical, social, economic, political, and cultural landscape features that fluctuate with spatial scale
[14]. The interrelationships between these diverse landscapes regulate ecosystem functions
[4][15], which provide benefits, or ecosystem services, to populations
[16]. The need for an integrated, comprehensive assessment of ecosystem services is increasingly acknowledged
[17][18].
Established land suitability analyses commonly applied in spatial planning (e.g., hierarchical, ordinal) do not fully represent the diversity of ES related functions and benefits
[19] and have limited capacity to quantify the multifaceted relationship between social and ecological systems
[20]. Multifunctionality, however, acknowledges the supply of a diverse set of ecosystem services which lead to numerous environmental, social, and economic benefits. Multifunctional landscapes integrate ecosystem services and human wellbeing, they support livelihoods, protect species, and provide recreational needs
[21][22]. Multifunctional landscapes are characterized by diverse land use and complex landscape structure, thereby including the many, often competing, interests and values of different landowners and stakeholder groups. Multifunctional landscape analyses are better able to interpret the complexity of their socioecological systems and their values. Overall, a multifunctional landscape approach to ecosystem services assessment increases sustainable development strategies
[23].
Literature supports a comprehensive planning approach which includes multifunctional ecosystem service assessment
[24][25]. However, the application of an ecosystem services approach to landscape analysis, sustainable planning, and decision making is still lacking in the spatial planning process
[26][27][28]. During the past decade, many spatial landscape frameworks and environmental planning tools have been developed which incorporate the concept of ecosystem services
[29]. Few, however, have comprehensively captured the diversity of ecosystem services, particularly within urban and urbanizing landscapes
[30][31]. In China, urban greenspace system planning has been placed within urban planning and serves to control urban sprawl and improve urban ecosystem services but lacks the inclusion of nonbuilt greenspaces such as forests and wetlands
[32]. Elsewhere, in Berlin, Germany, concrete decisions and management actions did not result from the ES assessment used. Here, only informal planning strategies could be agreed upon due to unclear and disagreed upon ecosystem service outcomes among a diverse stakeholder group
[33]. Other barriers to ES planning integration and operationalization strategies remain and include a lack of understanding for exactly how ES informs decision making
[34] and at which point the ES concept should be applied
[28]. Overall, there is a continued need to examine and define possible methods and tools for ecosystem service assessment in planning and policy documents e.g.,
[26][35][36]. Literature’s different methods used for ES classification and mapping limit the comparability of outcomes and call for a more consistent but flexible approach
[37][38][39].
This recognition has led to the concept of “Green Infrastructure” (GI)
[40] to help manage functional ecosystems through strategic land use planning. GI encompasses an interconnected network of natural, seminatural, and artificial ecosystems and greenspaces within, around, and between environments, at varying spatial scales
[41][42]. These GI areas can be managed to deliver a wide range of ecological, social and economic benefits or ecosystem services
[5]. Overall, GI is able to improve the environmental quality, livability, and sustainability of people and communities through multifunctionality
[43]. The GI concept is a valuable tool for “translating” the complex topic of ES into more comprehensible terms and is better suited to convey ES language to diverse stakeholders and disciplines
[29]. Furthermore, GI can be spatially mapped and applied towards sustainable planning policy.
2. Green Infrastructure as a Framework for Multifunctional Ecosystem Service Analysis
One of the main strengths of GI is its landscape multifunctionality, i.e., promoting spatial areas that can serve more than one purpose, such as climate change mitigation, biodiversity conservation, food production, the creation of recreational greenspaces, and provide employment opportunities
[44]. GI addresses multiple demands and contributes to finding solutions for a range of environmental, social, and economic pressures
[45]. Multifunctionality, here, is described as the capacity of green infrastructure to provide multiple ES
[46] and is regarded as a core principle of the GI approach
[47][48][49]. Multifunctionality is closely related to physical connectivity. Connectivity is important to GI and the delivery of ecosystem services through the concept of flows
[50][51]. This connectivity supports and enhances GI; it increases ecological resilience to stressors from urbanization and climate change
[52] and strengthens regional economic stability
[53]. As an interconnected landscape framework which can assess ecosystem services, the GI framework emphasizes the quality and quantity of these diverse landscapes, as well as their multiple functions and the importance of interconnections between them
[42][54].
Notably, if systematically planned, developed, and maintained, GI has the potential to contribute to ecosystem services and sustainability
[55]. GI is able to identify the positive synergies among ecosystem services found within diverse landscapes
[56]. However, literature demonstrates that consistently quantifying multifunctionality, even within the GI framework, is difficult
[57], as is operationalizing multifunctional ES within spatial planning
[58]. The concept of GI has been interpreted divergently and no consensus regarding GI’s components nor a method to identify and map GI has been reached
[59]. For example, biodiversity as a key ecosystem service is often assessed through strictly ecological benefits and planning considerations (e.g., connectivity, species diversity), which does not capture societal values such as socioemotional wellbeing and human disease resilience
[60]. These and other synergistic benefits within GI remain difficult to document and quantify.