According to the UN, it is projected that the world population will reach 8.9 billion in 2050, increasing by 47% between 2000 and 2050. It is also estimated that less-developed regions will contribute to more of this increase by growing by 58% (United Nations, 2004). Moreover, it is known that 52% of the world population (more than 4 billion) today lives in urban areas, and in 2050, it is projected that the population in urban areas will be around 6.3 billion (UN, 2012). Facing such a big challenge and being as the engines of the economic growth, cities require great sensitivity for investment decisions in various sectors to sustain their viability (European Commission, 2008).

The critical significance of urban ecosystems and biodiversity has been well cited in the literature and global policy documents, especially with the growing concern of climate change impacts. Climate change challenges together with human impacts stimulate urban authorities to improve more ecosensitive and nature-based spatial management solutions in urban settings (Elmqvist et al., 2013; UN, 2015; McPhearson et al., 2018). This is very clearly emphasized with the press release of the UN Secretary General Antonio Guterres as follows:

“We need healthy ecosystems to achieve the Sustainable Development Goals and to address climate change: they can provide 37% of the mitigation needed to limit global temperature rise”, hence, wellbeing of citizens and nature will be achieved only by maintaining the function of urban ecosystems to provide sustainability and resilience of cities (Guterres, 2019).

In order to sustain the well-being and productivity of the cities, there has to be a fixed level of interruption of resources/assets due to human activities that reduce the ability of capacity of the cities to sustain humanity in the future (Arrow et al., 1995). Alberti summarizes this approach by stating that urbanization must consider the limits of natural resources and act not only for the people living within the boundaries today but also for the future generations (Alberti, 1996).

It is known that geographic borders of cities grow in line with the urban population; nevertheless, it is also noted that in the 2000–2015 period, the real growth rate of cities was larger than the population growth rate, which indicates urban sprawl that results due to the refunctioning and consumption of rural lands (UN, 2015). The most significant characteristics of urban sprawl are an increase in transportation distances, depletion of lands, and fragmentation of natural ecosystems that minimize the benefits provided by nature (Kışlalıoğlu and Berkes, 2010). As a result, due to the dependence of ecological equilibrium on the dimension and spatial use types of the cities (Orishimo, 1982), in order to sustain the environmental health and natural resources, ecological concerns must be considered in determining the spatial use types of the cities, or in other words, ecology-driven spatial planning must be in place (Chen et al., 2014).

In the era of climate change, deciding the proper spatial use type for a given area under specific socioeconomic conditions and adoption of sustainability concerns are critical for reducing the loss of biodiversity, natural habitats, land degradation, guaranteeing the sustainable use of resources, and increasing resilience of ecosystems. Thereof, the success of sustainable land use and management practices is decisive to ensure sustainability/resilience or mitigate degradation/vulnerability of land resources (FAO, 2018). Consequently, demand on natural resources increases in correlation with urban population/development, and therefore, the most critical concern in the urbanization process is to manage resource requirement (Vega-Azamar et al., 2015).

In general, a spatial planning process follows the steps of data acquisition (environmental, geological, socioeconomic, demographic, and physical), analysis of data, synthesis of the analyses in line with plan vision, and determination of spatial use types. Nevertheless, ecological datasets are mostly treated as a land cover instead of a living ecosystem, which neglects the real importance and value of ecosystems and leads to overuse and extinction of ecological resources (Menteşe et al., 2020). In this regard, maintaining the services and benefits provided by ecosystems in the optimum level is the fundamental component of ecological sustainability (Millennium Ecosystem Assessment, 2005). Therefore, understanding the spatial impacts of the development/investment processes is of great importance in spatial planning in order to manage and reduce possible losses in ecosystems due to spatial use changes (Kopperoinen et al., 2014).

Istanbul as the largest city in Europe and Turkey has been subject to significant urban expansion in the last decades, where its population has grown from 10 million in 2000 to 16 million in 2020 (Turkish Statistic Institute). Even though the expansion has mostly occurred in the east–west direction, recent investments in last 8 years have shifted the pressure to the northern parts where the ecological resources of the city are accommodated. Istanbul lays on two continents (Thrace Peninsula/Europe and Kocaeli Peninsula/Asia), which are part of the Pan-European Ecological Network (PEEN) in southeastern Europe with its coastal dunes and forest/heathland habitats taking place on the northern parts of the city (Biro et al., 2006; Tezer, 2020).

The first investment in the last 8 years has been the construction of North Marmara Motorway (NMM), which was started to be built in 2013. Construction of the highway is still continuing, and when finished with all linking roads, the total length of the highway will reach almost 400 km, including a bridge pass over Bosphorus (Url-1). After the completion of main highway parts that take place in the center section around Bosphorus, the second investment was started, namely, Istanbul Airport. Construction of the Istanbul Airport started in 2014, and the first phase of the project was concluded in 2019, covering 1,440,000 m² indoor area. Once fully completed by 2025, the airport will combine a total indoor area of 3,200,000 m² (Url-2).

These investments have shaped and continues to shape Istanbul’s landscape drastically in a very short period of time. The areas that are subject to the construction of these engineering investments are invaluable by means of their ecological values. Due to the ecosystem, biodiversity, and environmental assets in those areas that were/are under threat, there were severe discussions in public after the announcement of each project. Nevertheless, the first two of the projects have almost been completed, while one of them is ongoing, although there is solid scientific evidence that highlights the harms that can arise due to constructions.

It is certain that these investments are a threat to the ecosystem and its assets over the area they are built upon. Thereof, integrating ecosystem services into such projects in the planning period is of great importance so that the impacts on ecosystems can be regarded beforehand and hence the adverse effects can be reduced to minimum (Millennium Ecosystem Assessment, 2005; Genelleti, 2013).

Since the year 2005, with the release of the Millennium Ecosystem Assessment Report, the “ecosystem services” concept has replaced as an increasingly important paradigm on the agenda of global and national institutions for ensuring the resilience of environment and society being under the risks of ecosystem degradation, biodiversity loss, and climate change, which are the result especially of rampant urbanization and land cover change (Millennium Ecosystem Assessment, 2005; TEEB 2009; Haase et al., 2010). The term ecosystem services, which was used for the first time in the literature in 1981 by Ehrlich and Ehrlich, is based on the concept of nature’s services by Westman (1977), or ecosystem functions and the relation with biodiversity by Mooney and Ehrlich in 1997 which is linked with Marsh’s book of “Man and Nature,” and also is based on the Land Ethic concept of Aldo Leopold. Four of the definitions related to the ES are considered to be among the most widely accepted ones (Albayrak, 2012).

The Millennium Ecosystem Assessment (Millennium Ecosystem Assessment, 2005), as well as many other studies that followed, highlighted the importance of integrating the ES concept into strategic decision-making so that the impacts of development practices on ecosystems and on their benefits and functions can be taken into account at the beginning phase of planning (Genelleti, 2013). In this context, ES mapping emerges as an invaluable tool since ES maps bring the ES concept into implementation and decision-making level where maps can represent complex spatial information in a visual and tangible way (Burkhard et al., 2014). ES maps are also beneficial for raising awareness about how ecosystems can provide goods, regulate nature, give information about ecosystem interaction, and enhance environmental quality (Jacobs et al., 2015). Moreover, maps can be used as decision support tools in spatial development under the conditions that ES maps are based on accurate, precise, and concrete data (Müller et al., 2016; Tezer et al., 2020).

Within this context, this research focuses on the impacts of NMM projects on ES capacity in the northern part of Istanbul. The analysis is based on spatial use change between 2012 (when none of the investments were at place) and 2018 (when the construction was mostly completed). In estimations, Corine Land Cover (CLC) datasets are used, and the calculations aim at understanding and interpreting how such investments can affect ecosystems and showing how the ES concept can help enhance conventional environmental impact analysis approaches.

NMM will have a total distance of 400 km including the connecting roads when completed: in total, 14 viaducts, 37 bridges, 3 tunnels, 19 overpasses, 43 underpasses, and 118 culverts in the European part of the NMM; and in the Asian part, a total of 16 viaducts, 106 bridges, 5 tunnels, 54 overpasses, 53 underpasses, and 481 culverts are built. With the completion of the project, it is aimed to increase service quality and safety in transportation by separating regional traffic which grows and develops around the main transportation arteries in the East–West direction in the northern Marmara region created by urbanization and industrialization and intercity and international traffic passing through.

Located on the European side of Istanbul, by the Black Sea shore, the new airport is situated at the junction of Çatalca–Göktürk–Arnavutköy, between the Tayakadın and Akpınar villages. Covering an area of 76.5 million square meters, Istanbul airport serves as a global transportation hub between Asia, Africa, and Europe.

Canal Istanbul is a controversial project that has been subject to many discussions in recent years. The main aim of the canal construction has been announced as minimizing the negative effects of ship transportation on the Bosphorus Strait in the environmental impact assessment (EIA) report of Canal Istanbul (2019). In the EIA report, it is stated that the number of ships passing from the Bosphorus Strait in one year can reach up to 86,000 by 2070, which must be reduced in order to sustain the ecological, social, and cultural assets of the Çinar Mühendislik Müşavirlik A.Ş. (2017).

The proposed canal route crosses Istanbul from the Black Sea to Marmara Sea, dividing the city into three pieces and creating an island part in the middle (Figure 1). The total length of the canal is estimated to reach around 45 km with a width of at least 275 and depth of 20.75 m. Construction of the strait is estimated to conclude in 7 years and provide service for at least 100 years (Çinar Mühendislik Müşavirlik A.Ş. (2017)).

Within the project, in addition to the strait, specific sections are planned to be built such as emergency docks, command centers, logistical centers, a marina, bridges, and shore facilities. The proposed route is generally surrounded by agricultural zones, partially forests and residential and water bodies. Along these water bodies, Sazlıdere Dam, which has the capacity to provide water for Istanbul inhabitants for 24–25 days, is the most important one that has to be canceled if the canal is built (ibid). Approximate locations of the projects are given in Figure 1.

In this context, the developed methodology benefits from the ES mapping approach and aims to evaluate the impacts of NMM, Istanbul Airport, and Canal Istanbul on ecosystem services within their impact zones. The analysis is based on before–after comparison regarding the construction times of the investments. For ES mapping, the matrix model developed by Burkhard et al. (2009) is adopted. The matrix model basically depends on assigning scores for the ES potential of each spatial use type. A figure adopted by Burkhard et al. (2009) and Jacobs et al. (2015) is given in Figure 2.

In the matrix as shown in Figure 2, “SU_n” corresponds to a “spatial use type” and ES_n corresponds to an ES type such as water regulation, air regulation, and CO₂ uptake that this spatial use type provides. As a result of the matrix, total ES potential is calculated by adding up each ES type for each spatial use type. Then the summation is multiplied with the areal quantity of that spatial use type since ES capacity increases in line with the areal quantity of the relevant spatial use type. For each spatial use type, the total ES potential is calculated as in Eq. 1. In the equation, ΣESp_SUT1 corresponds to the ES potential of spatial use type 1, ES1 corresponds to ES capacity score of ES type 1, and Area_SUT1 corresponds to areal quantity of spatial use type 1. ∑ E S p SUT 1 = ( E S 1 + E S 2 + E S 3 + E S 4 + ⋯ + E S n ) × A r e a SUT 1 . (1)

After the total ES capacity for the spatial use types are calculated, their summation results are calculated as the total ES potential for the whole area (Eq. 2). In Eq. 2, ΣESc corresponds to the total ES capacity value for the study area. ∑ ESc = ∑ E S p SUT 1 + ∑ E S p SUT 2 + ∑ E S p SUT 2 + … + ∑ E S p SUTn . (2)

In the implementation of the methodology, Corine Land Cover (CLC) dataset (https://land.copernicus.eu/pan-european/corine-land-cover), which is commonly used for ES mapping, is used as the base data (Burkhard et al., 2009; Jacobs et al., 2015; Müller et al., 2016). Another advantage of using the CLC dataset is the acknowledged standards of the dataset that reduce the risk of data accuracy and precision. In the NMM and Istanbul Airport impact analyses, 2012 and 2018 CLC datasets are used for before–after comparison, and for Canal Istanbul’s future impact analysis; 2018 CLC dataset is compared with the proposed spatial plan of the Canal Istanbul project since the implementation of the canal has not started yet. ES scorings are gathered from a previous study carried out by the Istanbul Metropolitan Municipality where, for each spatial use type, an ES capacity score was produced to evaluate overall ES capacity in Istanbul (Istanbul Metropolitan Municipality, 2017). The ES scoring table is given as appendix (Supplementary Appendix A1).

It is seen in Supplementary Appendix A1 that forests are accounted as the most valuable ecosystems among others by means of providing ES supply. In all three categories of ES (regulating, cultural, and provisioning), forests are considered way more important than others. It must be noted that forests in Istanbul are an integral part of the urban form and their services are highly benefited by the inhabitants of Istanbul. Istanbul forests are known to provide vital benefits such as mediation of air quality that provides clean air to southern urban zones, pest control that provides natural protection for the agricultural zones around the forests, timber production, and recreational activities (Güneralp et al., 2013; Avcı, 2014). Thereof, loss of forests has much more meaning than spatial changes in Istanbul.

The methodology applied in this research is adopted to provide a more holistic outlook to ecological impacts influenced by the three major infrastructure investments. Although there are EIA reports for each project, the methodology applied here can add supplementary benefit to the understanding of such investments’ overall impacts, which is critical to enhance the implementation process and reduce the risks against ecosystem.

In order to implement the methodology, first the dataset that covers whole Europe was clipped to Istanbul boundaries using ArcGIS software (Figure 3). After the clipping operation, zones where NMM and Istanbul Airport are constructed are cropped from the dataset as the analysis dataset. The attributes and values of the dataset are then transferred to tabular format and calculations were carried out.

Although cities are the driver of many unsustainable development trajectories, they are the settlements where the solutions to these problems are accommodated sooner or later. In the Istanbul case here, we aimed to emphasize the significance of “still surviving” pristine ecosystems, rich biodiversity abundance, and their role for ecosystem services potential. Existing and future scenarios are also taken into account to compare the results on ES provision. In this regard, we wanted to highlight how the ES concept can be utilized in the spatial planning, development, and/or decision-making process by using a specific technique called the “matrix model” in the ES literature. The outputs of the study indicate that the methodology can be efficiently used to evaluate and interpret how an investment or a plan can impact ES capacity on a given area. The proposed methodology is also valuable by means of enabling the end-user to grasp a holistic view about the end-results of a plan or project.

Compared with conventional environmental impact assessment methods, especially as implemented in Turkey, adaptation of the ES concept has significant advantages. The first is that in the current environmental impact assessment process, it is hard to find an analytical result regarding the impact of a case, meaning that, although evaluations are mostly data driven, results are quite qualitative. This may result in a misunderstanding of the comments or synthesis that emerges through the impact assessment reports. Therefore, in controversial studies such as NMM, there may occur speculative discussions on the impact assessment reports. Establishing an analytical approach in environmental impact analysis studies can easily suppress the misguided discussions. Second, current environmental impact assessments rely on situational changes instead of functional or processual changes. For example, the impact analyses mostly focus on the amount of change; nevertheless, from an ecological aspect, the interaction between different components of the environment must also be incorporated, and in addition to their static value/quantity, their functions and potential benefits to humanity and other living organisms must also be taken into account. Therefore, putting the ES concept in the center of the environmental impact assessment process can reduce the qualitative uncertainties and provide integrity to the estimations. It is seen that the EIA process may vary based on the type of the project, concept, and implementation area. Since EIA reports are generated based on strict regulations, their context may reach reasonable volumes, which makes it hard to grasp an overall understanding about the actual impacts. The matrix model, on the other hand, provides a systematic, analytical, and efficient approach not only by means of its applicability but also by means of its detailed insight on the ecological impacts.

Regarding Istanbul’s urbanization speed and patterns in the past, it can be predicted that the aforementioned major infrastructures will not only cause habitat loss but also bring new urban forms to the area which will put extra loads on the carrying capacity of the limited natural resources. Combined with the effect of climate change, cascading effects of these investments will possibly worsen sustainability and resilience of Istanbul’s ecosystems in the near future.

Nevertheless, there may still be room for development and optimism if the current level of ecological functions is preserved and sustained. Even though Istanbul’s urban development has not been in favor of the ecological assets, Istanbul is still invaluable by means of its ecosystems, biodiversity, and environment. Therefore, methodologies and approaches as in this study must be enlightening the road of development for Istanbul and allow decision makers make the right call for a more sustainable and resilient city.