*2.5. Congestion*

Direct over-use (congestion) of public greenspace is another indirect reason behind the demise of public urban space [3,35]. Congestion refers to the degree of competition within a public domain, or to "the numbers of individuals who jointly consume it and the range of tastes amongs<sup>t</sup> those individuals (or groups)" [3] (p. 34). When congestion generates excessive transaction costs, such as the costs of queuing or resolving conflicts between different users, economic theory predicts that there is a high probability for pressures to reform the property rights and subdivide public space either into private domains or into smaller public domains (e.g., club goods). When public domains become congested, they must be governed in such a way that use rights to public space are clear and enforceable [3,44]. However, transaction costs for designing, creating, and administering such a system

becomes increasingly high the more over-used a space becomes, and if costs for governance become too high in political or financial terms, then public space could become subject to land alienation where the local governmen<sup>t</sup> seek to dispose of the property [3].

#### *2.6. Activity Intensification*

Activity intensification can also act as a subtle driver behind the transformation of public space [45]. To cut costs and for energy conservation, planners can, for example, resort to multifunctional land use. Haccou et al. [46] distinguish four types of multifunctional land use: interweaving, intensifying, layering, and timing. Interweaving combines di fferent functions on the same piece of land; intensifying increases the e ffectiveness and e fficiency of a certain land use on the same piece of land; layering mixes functions in the vertical dimension if possible; and timing uses the same building or space for di fferent functions at di fferent moments in time [47]. The first two types are also applicable to green spaces. In Stockholm—one of the fastest growing regions in Europe—planners have been taken by surprise by the sudden population boom, with over 300,000 new homes in need of being built in the coming decade. To cope with increased urban densification and population growth, multi-functionality in the use of public parklands has become a quick fix for dealing with overcrowding e ffects [48]. However, such a development may run contrary to planners' aspiration of making cities more resilient to various effects of climate-change and for securing biodiversity that depend on green spaces of a certain size and with certain ecological qualities that do not always rhyme well with social aspirations.

#### **3. Baseline Shifts and Benefits of Nature**

As cities develop over space and time, the di fferent attributes of green spaces also change. Urban residents experience nature most of the time at "the cognitive level of urban space," that is, at the level where "people in the street" experience the city [49].

Human beings also constantly use memories of previous experiences to interpret current experiences [50]. When it comes to experience of urban nature, psychologists talk about baseline shifts, where each generation of humans tends to take the current condition of an ecosystem as the nondegraded state: the 'normal' experience, disregarding the fact that the ecosystem might have changed considerably over time [51]. Baseline shifts can lead to environmental generational amnesia [52], referring to the psychological process whereby each generation perceives the environment into which it is born as the norm, no matter how developed, urbanized, or polluted the environment is [51].

According to Hartig and Kahn [51], baseline shifts can help explain inaction on environmental problems in that people do not feel the urgency of the problems because the experiential baseline has shifted (Figure 1). Experiencing nature during childhood is crucial for shaping sustainable decision-making processes in adulthood [53].

The incremental changes of urban greenspace, previously dealt with herein, likely contribute to baseline shifts. To what extent is hard to determine. There might also be overlaps in the drivers previously dealt with, e.g., under-utilization of greenspace can at many times be explained by a lack of financial support. However, environmental generational amnesia may spread as more and more people are devoid of direct contact with nature in cities [54]. This in turn may make it more di fficult to reach public acceptance of policies to deal with environmental problems, like climate change. Environmental illiteracy may further lead to the erosion of public green spaces since people will not value the ecosystem services they derive from nature (Figure 2). This is especially the case in countries where destruction of ecological sensitive areas and open spaces are rapidly urbanized due to weak urban planning institutions [55].

**Figure 1.** Schematic illustration of a baseline shift of a hypothetical public park over a 150-year period. Each development stage is perceived as being the nondegraded (normal) state by each new generation of humans—a situation that can contribute to environmental generational amnesia.


**Figure 2.** Ecosystem services from urban greenspaces. These include provisioning services, regulating services, cultural services, and supporting services. Source: Millennium Ecosystem Assessment. Ecosystems and Human Well-Being. Reprinted from Colding and Barthel [56].

#### **4. Long-Term Resilience Planning**

The incremental changes and loss of urban greenspace elaborated on in this paper fit the pattern of decision making that the economist Alfred E. Kahn once referred to as 'the tyranny of small decisions', representing a situation in which a number of decisions, individually small in size and time, result in non-optimized and socially undesirable outcomes [57]. According to Kahn the 'small decision effects' are common in market economics. In an urban planning context, many small-scale, independent decisions taken over time by a planning unit could culminate in outcomes that are neither intended nor preferred [58]; hence, even well-intended planning decisions in countries with strong state control can result in undesirable social-ecological outcomes that run contrary to the common good of a city and its inhabitants.

Nilsson [15] has described how leading politicians often abstain from restricting options in order to handle future planning issues—a phenomenon that often leads to an ad hoc form of planning, termed "day-to-day planning". It is mainly designed to manage acute problems and to resolve problems as soon as possible and is related to a discourse of economic development "in the way in which it tries to satisfy the short-term requirements of industry and commerce, and tends to emphasize the economic dimension of sustainable development" [15] (p. 441).

Accessibility to green spaces in cities is ultimately determined by property-rights arrangements that regulate their omission or entry. Institutional scholars have long recognized the role of property rights for linking people to nature, but as institutional research suggests, no single type of ownership regimes (i.e., state, private, or common property rights) can be prescribed as a remedy for resource overuse or environmental degradation [59]. Instead, policy should focus on establishing a multitude of property rights regimes that are designed to fit the cultural, economic, and geographic context in which they are to function [20].

How space and property rights are arranged to ensure access to urban nature will be of direct importance for building general urban resilience to human wellbeing in the long-term [14]. The gradual shift towards privatization of public property in cities, and even of common property systems [60,61] is a worrisome sign since it may negatively a ffect resilience planning, which needs to be long-term oriented. Property-rights could be viewed as slow variables in urban transformation. In resilience science, slow variables—like evolution, coral regrowth, or nutrient transportation through soils—play a substantial role for a system's resilience to change [62]. C.S. Holling's work [63] demonstrated that an ecosystem can absorb an entire chain of disturbances without being adversely a ffected until it suddenly changes to a completely di fferent state where past functions and services no longer can be provided. A gradual loss of the system's slow variables often causes such abrupt change. Critical, slow social variables are characterized by normally being stable or changing slowly over long periods of time, providing continuity of functions. However, even property rights that have existed for millennia may change abruptly, causing changes in land use, social disruption, and even declines in human well-being [60,64].

Lindholm [10] describes how sightlines in cities commonly become blocked by new private developments, with less daylight reaching the ground and with more land areas constantly in shadow, resulting in poorer conditions for plants and biodiversity, and also how people at the eye level of cities experience their local socio-physical environment. New sightlines are often aggravated due to visible landmarks of private interest. Hence, indirect e ffects of private property may negatively impinge on ecosystem services that are nurtured in the public domain. While private building consortia often launch their development projects as "sustainable", they often constitute examples of "green washing" [10]. An often-time neglected aspect of green roofs and green walls that commonly replace natural areas on the ground, is that they only are accessible to a limited set of urban residents.

The slow variables, such as the amount and quality of public green spaces, determine how a fast variable, like daily visits to green spaces, is possible when external drivers are in operation, such as excessive heat waves or pandemics. The gradual transfer of public to private property rights and services will in the long run weaken the power of local planning units and local authorities. If left unchecked, the increasing privatization of public space could ultimately become a huge democratic problem.

#### **5. Concluding Remarks**

The ratio of public/private land is diminishing, a ffecting cities in a multitude of ways. The drivers of incremental change of urban greenspace presented herein are ultimately a result of urban densification schemes (spatial and/or population), which seemingly propel a monoculturalization of property-rights regimes towards economic e fficiency and private and semi-private solutions. As elaborated on herein, congestion in the use of public space is but one outcome of urban densification, leading to such phenomena as the separation of attributes, activity intensification, and even to alienation of public space to private interests. Underutilization of greenspace coupled to inadequate funding for greenspace managemen<sup>t</sup> make these spaces more vulnerable to urban encroachment, especially when cities grow inwardly, posing an overall negative e ffect on the maintenance and generation of ecosystem services.

To counter shifting baselines that may result from the incremental demise of urban green spaces, Hartig and Kahn [51] propose that cities should provide more opportunities for people to experience more stable, healthy, and even wilder forms of nature. Property rights, however, ultimately determine such opportunities, as no single space should be expected to meet the demands of all users at all times, nor will any single type of property-rights arrangements fulfill the multitude of functions that a vibrant city depends on. Designing urban commons as an alternative to land privatization is no guarantee, however, for halting the demise of urban greenspaces, as the effects of privatization and commodification of commons is also high in some countries, such as in Europe [65]. However, maintaining a well-balanced diversity and mixture of property-rights regimes could be a wise policy for planners to adhere to in order to increase preparedness to meet an increasingly disturbance-prone future.

Although common property resource systems have been known to collapse due to overuse, there are promising signs that these systems are experiencing a revival in urban settings and boosting collective environmental action [44,66]. There are important linkages among urban common property systems, social–ecological learning, and managemen<sup>t</sup> of biodiversity and ecosystem services. Urban gardening projects provide not only cultural and provisioning ecosystem services but also regulating ecosystem services to city neighborhoods [44]. There are also examples of whole public parks being managed as common property systems [67]. By granting managemen<sup>t</sup> rights of greenspace to residential collectives and social networks, local governments can still maintain control and ownership of public space. Long-term leaseholds and the establishment of 'user rights contracts' that transfer managemen<sup>t</sup> rights of public space to civil society groups can be a viable interim solution for local governments in order to survive periods of fiscal shortcuts. Studies have shown that urban common property systems can serve a multitude of social-ecological purposes [11] and turn spaces into meaningful places that urban residents themselves can manage to improve and protect urban nature. The transferring of proprietor rights down to local levels can also lower transaction costs for greenspace managemen<sup>t</sup> and governance [44]. To safeguard ecosystem services policy makers and planners should take advantage of these benefits and more meticulously address the incremental demise of public greenspace.

**Author Contributions:** Conceptualization, J.C. Writing—Original Draft Preparation, J.C., S.B., Å.G.; Leading of the writing process, J.C.; Corresponding author, J.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** Johan Colding's and Stephan Barthel's work have partly been funded by University of Gävle. Barthel's work has also been funded by FORMAS/The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning. The project is called Spatial and Experiential Analyses for Urban Social Sustainability (ZEUS) (reference number: 2016-01193). Barthel's work is also funded by the Stockholm Resilience Centre. Johan Colding's and Åsa Gren's work has also been partly funded through a research gran<sup>t</sup> (reference number: 2017-00937) received from the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS), and through means provided by the Stockholm County Council and the Stockholm University (SU-SLL Grant 2017: no. 20160884), and from core funding provided by the Beijer Institute of Ecological Economics, Stockholm, Sweden.

**Acknowledgments:** The authors wish to thank Jonas Adner for the nice Figure illustration.

**Conflicts of Interest:** The authors declare no conflict of interest.
