Preferences of Young Adults concerning the Pocket Parks with Water Reservoirs in the Aspect of Willingness to Pay (WTP) in Warsaw City, Poland

: The paper presents the results of a survey questionnaire conducted in order to determine the social preferences of young adults regarding their willingness to ﬁnance pocket parks in Warsaw (Poland). The preferences concerned the impact of the appearance and attractiveness of pocket parks for the inhabitants of the capital, the impact on the microclimate, the materials used to build water reservoirs, and the effect of the respondent’s income on their willingness to ﬁnance them. The data were analyzed statistically (Kruskal–Wallis test, Mann–Whitney U logistic regression). The results show that young respondents prefer parks with natural water reservoirs. Willingness to pay was the highest in the case of natural parks and parks containing the most anthropogenically modiﬁed water reservoirs. It has been shown that the willingness to ﬁnance increased with the need for more greenery of this type and greater awareness of their positive impact on the improvement of the microclimate in the city. The higher the attractiveness of pocket parks for leisure and the higher the level of respondents’ incomes, the greater the willingness to ﬁnance them. The level of ﬁnancing also depended on the materials used to build water reservoirs in parks—the more elements made of hydrotechnical concrete, the higher the level of ﬁnancing. This type of relationship was not found for natural materials, which is surprising given the already well-known threat of climate change and the decrease of biodiversity.


Introduction
According to the report concerning the concept of the "cities of tomorrow", made by urban experts and representatives of European cities [1], cities are the key to achieving the sustainable development of the European Union. In the vision presented in this report, the future city should be distinguished with such features as being a place of advanced social progress (e.g., high degree of social cohesion, and social, health, and education services for all residents); a platform of democracy and cultural dialogue; and built-up areas, new roads, emission of pollution, and high temperature, etc.) is still the active process in cities [17] where the existing green areas are under pressure (struggling to keep their size) and the new green areas may not be designed on big surfaces in many districts, mostly in the central parts of cities. So, it is important to design smaller types of green areas, such as pocket parks, which will be useful for local people, improve their well-being in cities. The pocket park, also named the mini-park, vest-pocket park, or vesty park, is a small park with an area of not more than 5000 m 2 in general [18]. The concept of the pocket park was developed in the USA, mostly in very urbanized parts of cities. Pocket parks can be designed on public or private lands located in urban and suburban areas. Mostly, there are no places for the design of new urban parks in densely built-up areas where land prices are very high in the city. Despite this, people need green areas, even small ones, and so pocket parks could allow for their contact in mini-scale with greenery, water elements, and small architectural forms, creating cozy places for the better integration of city residents [19,20]. Such parks also provide the possibility for recreation close to home or work places.
The definition of pocket park does not exist in legal regulations in Poland, but these objects began to be designed in the big cities, such as Warsaw and Cracow. Pocket parks can be one of the innovative ways to create more urban green spaces. Therefore, it is important to know the opinions of the city's inhabitants, especially young adults (who are conscious users of public spaces and green areas and are soon be responsible for landscaping), about innovative forms of green areas, such as pocket parks, which can be beneficial elements that complement green and blue infrastructures in the city. When designing and establishing pocket parks, an important issue is not only to identify social preferences regarding their appearance, size, aesthetics, and quality of recreational facilities, but most importantly, their value depends on their acceptance by residents and their willingness to finance, protect, develop, or modernize them. Warsaw is the biggest city in Poland, where the problem with designing the new big-sized green areas exists because of densely built-up areas in numerous city districts.
The aim of the study is to determine the preferences and factors that can increase the willingness to pay (WTP) for pocket parks among city residents.

Hypothesis 1 (H1).
Pocket park preferences and willingness to pay (WTP) depend on the natural appearance of the water reservoirs in these pocket parks.
Hypothesis 2 (H2). Preferences for creating more pocket parks with water elements in cites are correlated with preferences for funding (WTP) received by young adults.

Hypothesis 3 (H3).
A higher family income has an impact on the preferences for financing (WTP) pocket parks.

Study Areas
According to the assumed goal of the study and the research problems formulated, the survey questionnaire included questions regarding preferences for the importance and suitability of water features. Participants were 321 young adults, students (18-37 years old) from Warsaw University of Life Sciences-SGGW in Warsaw, Poland. In the future, they could shape the green areas of cities because they study landscape architecture, urban gardening, and forestry. The family places of residence of these students were represented by cities, towns, and villages. They filled the questionnaire in May 2021, in which the questions concerned presented pocket parks with different types of water reservoirs ( Figure 1).

Figure 1.
Pocket parks with the different types of water reservoirs: (A)-a natural water reservoir with accompanying aquatic and rush vegetation; (B)-a semi-natural water reservoir, with accompanying water and rush vegetation of a linear or surface character, with the participation of small hydrotechnical structures made of environmentally friendly materials (stone, wood, and gabions); (C)-a medium-anthropogenically transformed water reservoir of a linear or surface character, with a significant share of water and rush vegetation, and the introduction of regulatory elements made of environmentally friendly materials and elements that play a communication role (bridges, walls, and balustrades) or an aesthetic role , e.g., fountains, cascades, and sculptures; (D)-a water reservoir strongly anthropogenically transformed, of a linear or surface character, with a negligible share of water and rush vegetation or only with introduced decorative vegetation, with the introduction of hydraulic concrete regulatory elements and elements serving only a communication role (bridges, walls, and balustrades) or an aesthetic role, e.g., fountains, cascades, and sculptures (photos: Beata Fornal-Pieniak, Marta Kiraga, 2021).

Methods and Statistical Analysis
The research has been conducted with the use of the original questionnaire. According to the assumed goal of the study and the research problems formulated, the survey questionnaire included questions regarding preferences for the importance and suitability of water features. Due to the hypotheses and statistical analyses used, only these questions selected from the questionnaire were used.
To verify Hypothesis 1, in order to assess whether the pocket-park-type variables affected the level of park preferences (2 variables), a non-parametric Kruskal-Wallis test was used. Due to the limitations of the analysis arising from the nature of the variables, in (C)-a medium-anthropogenically transformed water reservoir of a linear or surface character, with a significant share of water and rush vegetation, and the introduction of regulatory elements made of environmentally friendly materials and elements that play a communication role (bridges, walls, and balustrades) or an aesthetic role , e.g., fountains, cascades, and sculptures; (D)-a water reservoir strongly anthropogenically transformed, of a linear or surface character, with a negligible share of water and rush vegetation or only with introduced decorative vegetation, with the introduction of hydraulic concrete regulatory elements and elements serving only a communication role (bridges, walls, and balustrades) or an aesthetic role, e.g., fountains, cascades, and sculptures (photos: Beata Fornal-Pieniak, Marta Kiraga, 2021).

Methods and Statistical Analysis
The research has been conducted with the use of the original questionnaire. According to the assumed goal of the study and the research problems formulated, the survey questionnaire included questions regarding preferences for the importance and suitability of water features. Due to the hypotheses and statistical analyses used, only these questions selected from the questionnaire were used.
To verify Hypothesis 1, in order to assess whether the pocket-park-type variables affected the level of park preferences (2 variables), a non-parametric Kruskal-Wallis test was used. Due to the limitations of the analysis arising from the nature of the variables, in order to examine the level of differences between pairs of variables, a non-parametric Mann-Whitney U test was used for a deeper statistical analysis.
Variables analyzed for H1: Impact of the appearance/condition of water reservoirs on the attractiveness of a pocket park for different types of pocket parks types (A-D): A-a natural water reservoir with accompanying aquatic and rush vegetation; B-a semi-natural water reservoir; C-a medium-anthropogenically transformed water reservoir; D-a water reservoir strongly anthropogenically transformed (types are shown in photos and detailed descriptions in Study Areas section).
F1-more pocket parks in cities are recommended (five-point scale: 5 meaning that the respondent strongly agrees with a statement, 4-agrees, 3-neither agrees nor disagrees, 2-does not agree, and 1-strongly disagrees with a statement).
F2-the current appearance of the water reservoirs/facilities should be preserved with the addition of recreational infrastructure elements for different types of pocket parks (types A-D) (five-point scale: 5 meaning that the respondent strongly agrees with a statement, 4-agrees, 3-neither agrees nor disagrees, 2-does not agree, and 1-strongly disagrees with a statement).
Logistic regression analysis was performed to verify the second and third hypotheses. The analysis was summarized by using logistic regression-an econometric tool allowing the impact of factors (variables) on the willingness to pay (WTP) for pocket parks.
This type of regression allows the determination of the effect of multiple independent variables (regressants) on a dichotomous dependent variable (regressor). A dichotomous qualitative variable (Question I from the survey) was used as the dependent variable of the logistic regression model to make a prediction of "pocket park funding readiness". The values of the dependent variable (regressor) are "Yes" or "No". The predicted value is "Yes". In the regression aimed at predicting the financing of pocket parks, more independent variables (explanatory variables) were used whose influence on the decision to finance parks they wanted to evaluate. Only those that qualified for the model (whose effect on the dependent variable was statistically significant at the α = 0.05 significance level) are presented in Table 5. The obtained values of the regression coefficients make it possible to determine the OR odds ratios while maintaining the other variables at a constant level.
In the logistic regression model, the dependent variable Y signified the WTP for specific independent variables. Here are the seven variables: • F1-More pocket parks in cities are recommended (five-point scale: 5 meaning that the respondent strongly agrees with a statement, 4-agrees, 3-neither agrees nor disagrees, 2-does not agree, and 1-strongly disagrees with a statement); • F2-There should be more funding for pocket parks (five-point scale: 5 meaning that the respondent strongly agrees with a statement, 4-agrees, 3-neither agrees nor disagrees, 2-does not agree, and 1-strongly disagrees with a statement); • F3-Pocket parks' influence on improving the urban microclimate, e.g., by purifying the air (dichotomous nominal variable); • F4-Pocket parks are/could be attractive places for recreation for residents and tourists; • F5-Introduction of hydrotechnical elements made of environmentally friendly elements, such as stone, wood, and gabion elements, have a positive effect on the aesthetics of water reservoirs (five-point scale: 5 meaning that the respondent strongly agrees with a statement, 4-agrees, 3-neither agrees nor disagrees, 2-does not agree, and 1-strongly disagrees with a statement); • F6-The introduction of hydrotechnical concrete elements has a beneficial effect on the aesthetics of water reservoirs (five-point scale: 5 meaning that the respondent strongly agrees with a statement, 4-agrees, 3-neither agrees nor disagrees, 2-does not agree, and 1-strongly disagrees with a statement); • F7-Income per capita in EUR of the respondent's income-quantitative variablecategorized by per capita income in order to divide the respondents into 3 groups according to the affluence of their household, treated as a rank variable after categorization. Additionally, the respondent's gender-dichotomous nominal variable.
Analyses of each set of independent variables and models generated upon their basis were carried out to verify the following: the statistical significance of model parameters, the accuracy level of case classification, and the assessment of the model's adjustment to the data.
To assess the statistical significance of the test statistics in the Kruskal-Wallis test, the Mann-Whitney U test, and the structural parameters for the logistic regression models, the assumed significance level was α = 0.5.

Results
Participants of the research were aged between 18 and 37 (average-21.95 years). Women constituted 42.95% of the entire group, and men 57.05%. A total of 90.88% of respondents declared having secondary education, whereas the remaining 9.12% reported having higher education. The largest groups (41.56%) were the students from cities with over 100,000 residents and those with an income between EUR 521 and 800 per person (50.34%). The following groups were residents of rural areas (19.38%), and towns of up to 50,000 residents (17.60%) and over 50,000 residents (21.56%). Income under EUR 521 was reported by 27.18% of the respondents, whereas another 22.48% declared income over EUR 801 (Table 1). To verify H1, namely whether the impact of the appearance/condition of the water reservoirs on the attractiveness of a pocket park level was dependent on the water reservoir's natural character, the Kruskal-Wallis test was executed. At the significance level of α = 0.05, it was demonstrated that the pocket park's natural character level made a significant difference in the perception of the pocket park (Type A-the most-natural water reservoirs, Type D-the least-natural water reservoirs).
In the case of the impact of the appearance/condition of water features on the attractiveness of a pocket park, the respondents rated the Type A pocket park the highest (232.43 rank average), and Type D the lowest (117.89 rank average). The Kruskal-Wallis test employed confirmed that there were statistically significant differences between the pocket park type and this variable ( Table 2). In order to precisely verify the statistically significant relationship between a foresttype preference level and its development level, pairs of forests were compared using the Mann-Whitney U test.
In the case of the impact of the appearance/condition of water reservoirs on the attractiveness of a pocket park, all the correlations were statistically significant, with the exception of the comparison between the B and C pocket park types. In the case of the opinions on preserving the current appearance of water reservoirs/facilities with the addition of recreational infrastructure elements there is only correlation between D-type pocket parks and A-and B-type pocket parks (Table 3). Table 3. Statistical dependence between the type of pocket park (water reservoirs natural character) and preference levels (Mann-Whitney U test for pairs of pocket park types).

Impact of the Appearance/Condition of Water Reservoirs on the Attractiveness of a Pocket Park
The The presented results allow for the partial verification of H1, i.e., in the case of attractiveness of a park there was a relationship in that young respondents prefer parks with natural water reservoirs.
The respondents' declarations regarding their opinion about the current appearance of the water reservoirs/facilities, namely that they should be preserved with the addition of recreational infrastructure elements, also showed statistically significant differences depending on the pocket park type. However, although the Type D pocket park (175.84 means of ranks) was the most preferred among the respondents, the least preferred pocket park turned out to be Type A (150.37 means of ranks).
In addition, it was investigated whether the level of preference for a particular type of pocket park depended on the propensity of consumers to finance this type of park. Regarding the influence of the appearance/condition of the water reservoirs on the attractiveness of the pocket park, statistically significant difference between the opinions of consumers who were willing or unwilling to pay were shown for pocket parks A and D, i.e., the most natural and the most anthropogenically modified water reservoirs. However, when it comes to the importance of maintenance, the current appearance of the water reservoirs/facilities with the addition of recreational infrastructure elements showed a statistically significant difference between opinions about the C-type pocket park (Table 4). The presented results allow for the partial verification of H1, i.e., in the case of the attractiveness of a park there was a relationship that young respondents prefer parks with natural water reservoirs A logistic regression test was performed to examine factors related to the possibility of influencing consumer preferences, which, if changed, could reflect an increase in the propensity to finance pocket parks. The model had a good fit parameter (the C statistic is 0.93). Variables were selected using the backward elimination method and only variables with a p value < 0.05 were included.
Positively, an increase in the chance of pocket park funding can be affected by an increase in opinion on recommending more pocket parks in cities; each single level increase in this opinion results in a 124% increase in the chance of funding pocket parks (OR: 2.239; 95% CI: 1.25-4.00). Additionally, when consumers have a positive opinion about the need to fund such parks, each single level increase in opinion results in a 98.2% increase in the opportunity to fund pocket parks (OR: 1.982; 95% CI: 1.21-3.25).
Consumers who are unaware of the positive impact of pocket parks on improving urban microclimates, e.g., cleaning the air, are 66.4% less likely to fund them compared to those with the opposite opinion on this matter (OR: 1.982; 95% CI: 1.21-3.25). Those with no opinion on the question "Pocket parks are/could be attractive places for recreation for residents and tourists" are 93% less likely to fund pocket parks compared to those with a positive opinion on the topic.
In the case of water elements in pocket parks, an increase in the opinion of respondents on improving the aesthetics of the water reservoirs by introducing water elements with environmentally friendly elements resulted in a 54.57% decrease in the chance of funding the parks (OR: 0.453; 95% CI: 0.27-0.76). At the same time, in the case of an increase in the opinion on increasing the aesthetics of a water body by implementing hydrotechnical concrete elements resulted in a three-fold increase in the chance of pocket park funding (OR: 2.979; 95% CI: 1.97-4.52).
If income per capita (converted to EUR and divided into three categories) increases, the chance of funding pocket parks rises as income grows. If this income is in the range of EUR 521-800, the chance increases by eight times for people with an income below EUR 520 per person (OR: 7.995; 95% CI: 2.74-23.36), and for those with an income above EUR 800 per person the chance increases by more than 17 times for those with the lowest income (OR: 17.599; 95% CI: 5.13-60.40) ( Table 5).

Discussion
Pocket parks, which belong to green and blue infrastructures, are designed to provide ecosystem services and biodiversity protection [21]. In Warsaw, pocket parks are usually created on the initiative of residents and are financed from civic budgets in municipalities [22]. Currently, there are not a large number of pocket parks in Warsaw, but according to the surveys, there is a need to design more of this type of green area.
The quality of life in the city is undoubtedly improved by more green areas, which provide many physical, psychological, and social benefits for residents [23][24][25], regardless of their area and kind/type. Research conducted among Warsaw's young residents indicates that respondents are willing to pay more for the maintenance of pocket parks, if more such facilities are established. Additionally, also important is the fact that these areas are open to the public, often with an infrastructure conducive to recreation, which is not without significance. Even though these objects are mostly small green spaces, their significance to the population is very high [26][27][28][29][30] especially in the era of the COVID-19 pandemic [19]. The willingness to pay by young adults for urban forestry itself is variable and depends on many factors, including, for example, the structure of the forest and small architecture, etc., [23,[31][32][33][34][35]. Determining the accuracy and reliability of the hypothetical WTP amounts reported is also significant. The discrepancies between hypothetical declarations and actual payments confirm that this is difficult to verify [36,37]. The text surveys the opinion of over 300 full-time and extramural students of the university with traditions related to the protection and shaping of the environment, which was even emphasized in the name of the university-Warsaw University of Life Sciences-SGGW.
Almost 80% of the respondents of young adults declared their willingness to pay for the maintenance and eventual financing of pocket parks in Warsaw. This is a similar level of indicator compared to the other studies on forests located in urban areas. This is in comparison to 76% in UK urban recreational parks [38], and in the territory of Finnish Joensuu, urban forests varied from 62% to 84% [39] (depending on question options). Higher WTP was found in Tarnów city's urban forests in Poland-97% [40]. The city's green spaces are attractive for residents' recreation [41]. This is confirmed by studies in the urban forests of Tarnów, which showed and proved that young respondents were very willing to rest in forest areas in cities. The urban forests with park features and numerous elements of small recreational architectures were of particular interest to young adults [35]. The study showed that as awareness of the attractiveness of green spaces increases, the willingness to fund them grows. The most important factor in choosing urban parks for recreation is often their aesthetics [25]. The presence of natural and cultural values and the availability of facilities for recreation, their technical condition, and the level and quality of tourist services, also affect the level of funding. This confirms that WTP defines social attitudes, not the economic opportunities of the respondents themselves [42,43]. Other determinants of the dependency of the WTP contributions to the pocket parks are the appearance of the parks and the selection of materials used in the planning of the recreational infrastructure. The conducted surveys indicate that as the amount and quality of hydraulic concrete components used in water reservoirs increase, respondents are willing to contribute higher amounts of WTP. So, according to the opinion of young adult respondents, the elements made of this material have a positive impact on the esthetics of water reservoirs in pocket parks and the other types of greenery [35]. Such a relation was not indicated for the use of natural elements, such as stone or wood, which is surprising given the already well-known threat of climate change, the decrease of biodiversity, and an advanced environmental education at all learning levels (perhaps this education is not efficient enough). Perhaps this is because in the long term, in the mind of young respondents, the concrete still looks more attractive in comparison to natural materials, e.g., wood, which with the passing of time is rotting, mucking, and decaying. It is fair to assume that in the future, there will be no need for additional costs to upgrade concrete elements. They are more permanent and resistant to damage and water and wind erosion. The choice of concrete elements as the most desirable building material of hydrotechnical structures is surprising. Perhaps the respondents were guided by the colloquial definition of the water structure, as one that requires solid, sealed foundations, and any filtration is a negative phenomenon. On the other hand, the results of the study may lead to a wider discussion on the effectiveness of environmental education in terms of the ecological sensitivity of young people. A higher level of the young respondents' preferences for water reservoirs with elements made of hydrotechnical concrete is in some discordance with the lower direct availability to water for people and wild animals in such artificial water reservoirs (the respondents do not feel the need for wild animals to have the availability to water?). This is an important message for the municipal authorities, as it indicates the need for interdisciplinary expert teams to manage green areas and the necessity for the better ecological education of inhabitants. The level of financing in green urban areas is undoubtedly influenced by the wealth of the individual respondents, householders, as well as the whole society [44,45]. In general, it has been noted that the richer the society, the higher the WTP [38,[46][47][48][49][50][51]. The research carried out in Warsaw pocket parks is in line with this trend. However, there is no shortage of scientific reports that do not support this relationship [33][34][35]38,43,52]. This possibly comes from the fact that most often no entrance fees are charged to these types of facilities, and any costs of maintaining them are usually borne by local/municipal or state budgets.

Conclusions
These research results will be practical and very valuable in supporting future management and planning processes for the access to public green areas and their use in large urban agglomerations. Moreover, public consultations regarding the preferences of users about green areas are very important, which was confirmed by the example of the survey conducted on pocket parks in this article. The results of these consultations will make it easier for protectants who design the pocket parks in line with the expectations and preferences of young adults. This is a very positive aspect for further new green areas. People know that they have an impact on design new green spaces in the city. Moreover, they want to support the founding of this type of green area, so it means that they are responsible for them. It is important to increase the ecological education of young adults focused on the significant functions of natural elements in the urban landscape. Actual knowledge about this issue is not satisfactory, which was presented in our results. Furthermore, the same young adults, after completing their studies, should complete once again this questionnaire. We will have achieved answers if they (young adults) have better knowledge of the role of natural elements in green areas. If the results are similar (insufficient knowledge about natural elements in urban areas), the education program in universities should probably be modified. The conclusion is that good specialists are required to develop the concept of the green city, which is strictly connected with the quality of education.