Differences between earlier results and this study were mostly in degree, not direction. Overall, fewer respondents knew IGS in their neighborhood or used it for recreational purposes in Sapporo in this study than in the postal survey conducted in 2012 [ 23 ]. These differences could be the result of a slight bias in responses of the original postal survey towards residents interested in the topic. In contrast, differences were less pronounced in regard to evaluation as well as perceived benefits and problems. Following the recommendations outlined in the earlier study, it is thus important to take a closer look at residents’ preferences for management goals and approaches.

The results of this survey suggest IGS is a part of everyday life and a common feature of the urban landscape, not only in Sapporo, where IGS in Japan was first studied, but also across shrinking Japanese cities. Furthermore, the findings provide strong evidence supporting the following conclusions from prior IGS research in Japan [ 23 25 ]. Many respondents perceive IGS to be biodiverse and to possess a range of potential benefits, from ecosystem services such as air filtration and cooling to wildlife habitat and opportunities for nature contact. Despite the near-absent discussion of recreational IGS use in the Japanese literature, every fifth respondent across all cities reported already engaging in such use—a majority of them without encountering problems. Proximity was again the most common reason why respondents used IGS, a topic that merits renewed attention as Japan’s population ages and its mobility declines. On the other hand, as in prior research [ 23 ], many respondents felt IGS affected their daily lives in both positive and negative ways, with littering, weeds and pest animals, and the aesthetic appearance of IGS identified as major potential problems. These findings underline how important it is both to realize the potential of IGS and develop adequate approaches to manage it, especially in shrinking Japanese cities.

In their opinions about strategic directions for shrinking cities in general, respondents not only favored using space that becomes available for recreational green space and urban agriculture, they also supported giving up land use for human purposes to return it to nature. In contrast, respondents rejected using space opened up through population decline to increase housing size, even though Japanese houses and apartments are on average much smaller than housing in Western cities. These opinions align well with calls by researchers to focus on contact with nature and green infrastructure as a source of improved human wellbeing [ 4 56 ]. In a larger context, the results may reflect a shift in focus from material wealth to non-material wellbeing in the Japanese public that has occurred since the early 1970s ( Figure 11 , [ 57 ]). Overall, respondents’ opinions signal support for Japanese urban green planning to expand its ambitions beyond the unambitious current policies, which often target only preserving existing green space rather than creating new ones. As budget constraints are partly to blame, the question then is to what degree participatory management approaches are supported by residents.

Respondents preferred active IGS management to a hands-off approach. Furthermore, they strongly favored management as green space over conversion to parking space or other urban land use. One such management goal is the creation of new parks using IGS where size and characteristics are suitable. These results are in line with earlier research that found Japanese respondents are overall hesitant to embrace the concept of urban wilderness, a concept that has figured prominently in work on IGS from Europe, North America and Australia [ 27 50 ]. Yet this does not imply that residents do not perceive the value of IGS as a different kind of urban green space. However, it suggests cultural factors could be influencing residents’ perception and evaluation of IGS, something that has been suggested before in more general discussions of nature perception and culture [ 26 51 ]. This, again, may be a matter of degree rather than direction, as some respondents critical of IGS in Australia also mentioned impressions of neglect and abandonment as reasons for their negative perception of IGS. What follows is a dilemma: on one hand, vacancy often has negative cultural associations [ 52 ], while on the other hand a freedom of purpose can be a freedom from purpose, opening up space and possibilities that would otherwise not exist. Such notions have been explored in detail in prior work on IGS [ 53 55 ]. This issue then brings into focus more general opinions on using space in shrinking cities.

4.3. Preferred Management Approaches

Despite numerous benefits participatory IGS management could provide (e.g., realizing recreational potential, reducing financial burden to public funding etc.), the results of this survey suggest that residents will only accept such arrangements if they think it will improve IGS appearance—a primary concern reflected throughout perceived IGS benefits and problems as well as preferred IGS management goals. However, respondents did expect IGS appearance would improve through participatory management. Having residents manage IGS then stops being simply a strategy proposed by scholars to solve surrounding issues, and emerges as a new management approach supported by both professionals and stakeholders. This expected positive outcome also provides the basis on which the details of participatory IGS management can be discussed.

Principal issues of participatory IGS management are the questions of whom it should concern, and who should be responsible for it. It is not surprising that most respondents identified IGS management as a topic of concern for those living in the neighborhood, not just the land owner, as many knew of IGS in their neighborhood and felt it affected their daily lives. Yet at the same time, most saw the main responsibility for managing IGS lying with the city administration—even though overall respondents thought residents in the neighborhood would know better than the administration how such management should happen. This shows IGS management is situated in a triangle of concerned parties—owners (whether present/known or absent), neighbors and the city administration.

The opinion that taking care of land is an issue of concern to neighbors is not unique to IGS. Regulations across different countries affect everything from how houses may be built to how private green space should look. However, with IGS a number of complicating factors are introduced. First, depending on the type of IGS, the degree to which appearance and management is considered an issue likely varies, both among land owners and neighbors—a gap between walls or fences likely draws less attention than an overgrown vacant lot or fence. The issue becomes even more problematic if the owner is absent (e.g., living in a different area, corporate or public owner) or unknown, a problem that has lead the Japanese Ministry of Land, Infrastructure and Transport to produce over 300 pages of guidelines for dealing with unclear land ownership [ 58 ]. Not only does this mean the owner may be less invested in managing the space, neighbors may also have a harder time communicating their concerns about the space. This trend is to some degree exacerbated by land ownership fragmentation, which can lead to the generation of informal green spaces even in growing cities such as Tokyo [ 59 ]. Furthermore, eminent domain (or resumption/expropriation) is an exceedingly complicated issue in Japan [ 60 61 ]. On the other hand, social pressure can be perceived by owners as meddling in someone else’s affairs. In the context of rapid aging, property maintenance can also be a task older people may no longer be physically able to carry out, creating a potential source of neighborhood friction. Even if relevant regulations exist, it may be difficult for the city administration to enforce them, and providing assistance in managing privately owned IGS would require using already strained public funding. A participatory IGS management framework would thus need to mediate between neighbors and space owners without the city administration abdicating from the responsibility respondents perceive it to have.

Three core issues are likely to play an important role in the outcome of participatory IGS management. First, the variety of IGS characteristics (type, size, ownership etc.), the inherent subjectivity of IGS evaluation, and the social nature of the relationships involved would favor a flexible approach to management. However, survey results show a plurality of respondents favored strict rules over case-by-case and informal management. This further supports a role of the city administration in providing a framework for IGS management, even though such a framework would need enough inherent flexibility to process diverse cases. Second, a principal goal of IGS management should be to realize its potential for recreation [ 29 ] and conservation [ 62 63 ]—a goal this survey shows is supported by respondents. However, a plurality of respondents rejected allowing residents to use IGS without permission. This means participatory IGS management would require a mechanism to establish consent to IGS use, whether through communal opt-in or opt-out approaches or incentive/disincentive-based arrangements. For temporary uses, agents involved in the event planning can facilitate this process [ 64 ], while in other cases non-governmental organizations fill this role (e.g., 596 Acres in New York). Third, because the issue of liability has been identified as an important barrier to IGS use, participatory IGS management should attempt to at least ameliorate this problem. Liability has a long history alongside a record of court decisions seeking to solve this problem [ 65 ]. However, current arrangements often require land owners to make IGS inaccessible to avoid liability, thus reducing its use value for recreation (for conservation, the outcome likely depends on the particular species and types of barriers to movement involved). In this case, respondents in general saw IGS users liable for damages, suggesting that this issue could be ameliorated, possibly by offering reduced owner liability in exchange for consenting to IGS use by residents. Once the three core issues above have been addressed, what remains to be discussed are necessary support and timeframes of IGS use.