Green Environment and Mental Health in the City
Green urbanism is an important component of sustainable and liveable cities in developed and developing countries. Parks and gardens in cities have aesthetic, health, and social benefits, and they improve the quality of life in an increasingly urbanized society. Densely populated megacities with inadequate provision of green spaces are associated with poorer mental health. There is growing interest and research on horticultural therapy as a strategy to promote active aging. Studies on the use of urban parks and gardens have confirmed the reduction of stress and other mental health benefits. The natural environments have restorative characteristics which could mitigate stress and aid in the recovery from fatigue. Research has shown that exposure to green spaces can be psychologically and physiologically restorative by improving mental health, reducing blood pressure and stress levels, as well as encouraging physical activity. Some cities, including Singapore, are incorporating green environments into urban design as important aspects of city planning, given their possible positive influence on mental health and even cognitive functions.
KeywordsUrban parks Horticultural therapy Mental health Restorative Exposure to green spaces
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Green urbanism is of vital importance for sustainable and liveable cities in all developed and developing countries. Trees improve air quality, reduce cooling and heating energy use, and make the urban environment aesthetically more preferable (Smardon 1988; Akbari et al. 2001; Nowak et al. 2014). Parks provide fascination and inspiration to enable people to gain a fresh perspective on life, and green spaces in a city play an important role in helping visitors to escape temporarily from buildings and the crowded streets. A park experience rejuvenates the city dwellers and provides a sense of peacefulness (Ulrich 1981; Kaplan 1983). To Frederick Law Olmsted and other park visionaries, parks were not “amenities” but “necessities,” providing recreation, inspiration, and essential respite from the city’s blare and bustle. The Central Park in New York City, Hyde Park in London, and the Singapore Botanic Gardens in Singapore are modern-day examples of parks that soften and make surrounding high-density urban environment more liveable.
Green urbanism is a valuable municipal planning approach and a key factor for city sustainability. Urban nature can provide economic benefits for both municipalities and citizens. Air purification by trees, for example, can reduce costs of atmospheric pollution on people’s health. Furthermore, the aesthetic, historical, and recreational values of many urban parks increase the attractiveness of the city and promote the tourism industry, generating employment and revenue. The debate on sustainable and liveable cities must also consider atmospheric pollution from burgeoning industries which can have dire consequences on the green environment. In Southeast Asia, the periodic haze from the burning of trees and scrublands has blanketed many cities, impacting not just the environment and health but also the economy of the region.
Impact of Green Environment on Health
In his book “Fighting for Mental Health,” Sartorius (2002) wrote eruditely on the mental health needs of an urbanized planet and commented that many governments of the world, faced with rampant urbanization, have not developed an effective strategy for the provision of health care. Although urbanization has many benefits, it is also associated with increased levels of mental disorders, such as anxiety disorders and depression (Wang 2004; Lederbogen et al. 2011). City dwellers have better access to healthcare and social services, improved sanitization, and amenities; however, they are also at greater risk for mental disorders due to a more stressful environment. A follow-up study in Sweden has shown that a high level of urbanization is associated with increased risk of psychosis and depression for both women and men (Sundquist et al. 2004).
Contact with nature promotes the physical and mental health of individuals and communities. There is now more attention on the type of nature close to where people live and work, such as gardens or parks in cities and their benefits to people. In the United Kingdom, an extensive survey used data from over 10,000 individuals to explore the relation between urban green space and mental distress as assessed by the General Health Questionnaire (Goldberg et al. 1997). Controlling for individual and regional covariates, the authors found that individuals had lower mental distress when living in urban areas with more green space. This effect was traced to the living location of the same individuals as they moved closer or further from green space (White et al. 2013), indicating that being close to nature or near small-scale green areas in cities is beneficial to urban dwellers. Other correlational studies reveal that window views that include natural elements (compared with window views that do not) are associated with improved attention, memory, and impulse inhibition as well as greater feelings of subjective well-being (Kaplan 2001).
Impact of Gardening on Health
Growing house plants is a popular recreational activity in China and Japan for centuries. The art of bonsai and Zen-Buddhist rock garden are entrenched in Chinese and Japanese traditions of gardening to maintain the equilibrium of physical and mental health. Exposure to indoor plants could have a positive effect on attention, physical health, and work productivity even in windowless environment (Wiesinger et al. 2006; Lohr et al. 1996).
Attention Restoration Theory
The attention restoration theory suggests that recovery from attentional fatigue requires a restorative environment like natural settings for attentional recovery and reflection (Kaplan and Kaplan 1989; Kaplan 1995; Herzog et al. 1997). Natural environments with pleasing aesthetic qualities including open views and lack of loud, distracting noises are often chosen as preferred restorative environments (Korpela et al. 2001; Hartig et al. 2003; Herzog 2003). Studies have shown that trees near public housing improved the life satisfaction of residents and decreased levels of fear and incivilities among residents (Kuo et al. 1998; Kuo and Sullivan 2001). In a paper on the restorative effects of the natural environment, Hartig and Staats (2003) commented that participants in the nature reserve experienced an increase in positive affect and reduction in anger, compared to those in the urban environment. These findings are supported by another study by Hartig et al. (2014) who reported that urban green space can improve attention and memory, and increase positive mood. Several other studies have also demonstrated that interacting with natural environments can have beneficial effects on attention and memory for healthy individuals and for patient populations (Berto 2005; Berman et al. 2008; Kaplan and Berman 2010).
Exposure to Nature Reduces Stress
Ulrich (1984) in an innovative study found that hospital patients who could look out at trees and nature from windows recovered more quickly from surgery than those whose views were restricted to buildings – supporting the observation that the natural environment has a positive influence on health. Using quantitative and qualitative data, Schroeder (1991) concluded that natural environments with plants induced a relaxed state in people compared with urban scenes with no vegetation. The benefits were due to the regeneration of emotional equilibrium, break from the daily routine, and the stimulation of a spiritual connection with the natural world.
Other Positive Impacts of Nature Experience
Based on the attention restoration theory of Kaplan (1995), a research on views of nature and impact on the self-discipline of inner city children in Chicago was published by Taylor et al. (2002). The project examined the relationship between near-home nature and self-discipline in 169 inner city girls and boys living in identical high-rise buildings with varying levels of nearby nature. Parent ratings of the naturalness of the view from home were used to predict the children’s performance on tests of concentration, impulse inhibition, and delay of gratification. The results showed that the more nature a girl could view from home, the better her test performance. However, nature views from home had no relationship with performance on the tests for boys.
Green space is thought to influence mental health through an increase in physical activity by providing a place for neighborhood residents to meet and facilitate social ties. Community studies in the Netherlands have shown that the prevalence rates of anxiety and depression are higher in areas with lower levels of local green space (de Vries et al. 2003; Maas et al. 2009; van den Berg et al. 2010). However, other studies have indicated that greater access to residential green space is associated with less depression, but there is less evidence of an association between green space and decreased anxiety (Annerstedt et al. 2012; Alcock et al. 2014). In Japan, an interesting study by Takaro et al. (2002) found that the amount of “walkable green space” around the home of elderly individuals was associated to their mortality rate 5 years later – they found lower mortality among those with higher green-space proximity.
More recently, there was research in Canada from the Ontario Health Study focusing on a large urban population. It combined high-resolution satellite imagery and tree data with questionnaire-based self-reports of general health perception, cardiometabolic conditions, and mental illnesses. The results from multiple regressions and multivariate correlation analyses showed that people who lived in neighborhoods with a higher density of trees on their streets reported significantly higher health perception and significantly less cardiometabolic conditions (controlling for socioeconomic and demographic factors (Kardan et al. 2015)). These compelling results should encourage city planners to support green urbanism to enhance liveability and promote public health.
Horticultural therapy has now been widely adopted as a therapeutic activity for persons with different psychological needs (Kaplan and Kaplan 1989). It has been noted to promote the social functioning and self-esteem of patients with psychiatric illness especially those with chronic schizophrenia (Son et al. 2004). In a study on clinically depressed patients, Gonzalez et al. (2011) showed that a 12-week therapeutic horticulture program significantly lowered their depression severity during the intervention, and this beneficial change remained stable even 3 months after the program. They also found that the program fostered group cohesiveness which facilitated the recovery of the patients, and there was increased social activity even after the program in 38% of the patients. In an earlier study of clinically depressed patients, Gonzalez et al. (2010) had shown that the program helped to decrease rumination and depression.
The effects of horticultural therapy on mood and heart rate in cardiac patients were investigated by Wichrowski et al. (2005). They found that in a cardiopulmonary rehabilitation program, compared to a control group who attended education classes, patients on horticultural therapy had improved mood state and lower heart rate. Kam and Siu (2010), in a study in Hong Kong, investigated the effect of horticultural therapy on work performance and quality of life of persons with psychiatric illness. In the single-blind randomized controlled trial, 24 participants with psychiatric illness (schizophrenia, bipolar disorder, and major depression) were recruited to participate in a horticultural program and were randomly assigned to experimental and control groups. The participants were assessed on mood, personal well-being, and work behavior before and after the program. There was a significant difference in scores on the mood scale between the experimental and control groups but no difference in personal well-being or work behavior. Although the study was well designed, the sample was small and the follow-up of 2 weeks was short. With the limitations, the authors concluded that horticultural therapy was effective in decreasing the levels of anxiety and depression among participants in this pilot study but not in improving quality of life or work behavior.
In another Korean study, occupational therapists investigate the effects of horticultural therapy on the physical and psychological rehabilitation of patients with stroke (Kim et al. 2010). There were 20 stroke patients on occupational therapy plus horticultural therapy and a control group of 20 stroke patients who were on occupational therapy only. It was not a randomized controlled trial and the follow-up of 4 weeks was short. However, the authors found that those patients on occupational therapy plus horticultural therapy improved significantly on depression, communication, and self-care compared to the control group.
A study on horticultural therapy with dementia patients conducted by Jarrott and Gigliotti (2010) demonstrated that it was a desirable choice for dementia-care programs, because it engaged the patients who were often difficult to engage in activities that elicited high levels of adaptive behavior. The authors concluded that horticultural therapy represented an appropriate activity for older adults with dementia for it promoted positive engagement and could be introduced in care settings, facilitating a good person-environment fit.
However, in a systematic review by Hiroharu et al. (2014), the authors found that there were too few randomized controlled trials to draw any convincing conclusion on the efficacy of horticultural therapy. They concluded that many studies had poor methodology, small sample size, and the results were not robust. Most of these studies were naturalistic with biased samples, and the types of patients were too heterogeneous. There was also a paucity of data from Asia, Africa, or Latin America. Notwithstanding, the authors believed that horticultural therapy might still be helpful to improve the quality of life of some patients with dementia, depression, schizophrenia, and cancer. In all these disorders, horticultural therapy is not the main method of treatment and is introduced as an adjunctive therapy to improve social functions as shown in the study by Son et al. (2004) with chronic schizophrenia patients, and social connectedness as described by Gonzalez et al. (2011) in their prospect study of clinically depressed patients.
To address the gaps on horticultural therapy research, the National Parks Board of Singapore, in collaboration with the National University Health System, conducted a randomized controlled trial at the Training and Research Academy at Jurong Point (Ho et al. 2016). The study aimed to investigate the efficacy of horticultural therapy in improving the mental health and cognitive functioning of elderly people aged 65 years or older living in public housing in the community. There were 69 elderly divided into two groups – treatment (horticultural therapy) and control (wait list). Informed consent was obtained from the participants, and permission for the study was given by the university's ethics committee. The participants were assessed on neuropsychological tests using the Montreal Cognitive Assessment (Freitas et al. 2013) and questionnaires on life satisfaction (Diener et al. 1985) and social connectedness (Hawthorne 2006). To assess the psychological well-being of participants, the Zung Self-Rating Depression Scale (Zung 1965) and Zung Self-Rating Anxiety Scale (Zung 1971) were used. Blood samples were taken to check the levels of biomarkers like cytokines.
The program for the participants involved a weekly horticultural therapy session for the first 3 months, followed by monthly sessions for the next 3 months. The detailed program was designed by the National Parks Board to cultivate participants’ interest in gardening and park visits. During the sessions, they planted vegetables such as lady’s fingers and learnt gardening techniques like composting and transplanting. When the crops were ready for harvest, participants used the crops to prepare a soup dish together. The participants also visited the Singapore Botanic Gardens, Sungei Buloh Wetland Reserve, and Gardens by the Bay. These visits were facilitated by the respective park guides who shared their knowledge on the plants and the landscape features with the participants.
To evaluate the efficacy of the program, assessment interviews were conducted before the program, at a 3-month point during the program, and after the program ended. In the preliminary results after 3 months, the elderly who received horticultural therapy did better than the control group in terms of their scores for life satisfaction, memory, and psychological well-being, but the differences were not significant. The only significant finding (p < 0.05) was for positive relation, which refers to social connectedness and trusting relationships. During the assessment of the biomarkers, it was found that in the sixth month of the program, the level of cytokine interleukin-6 (IL-6), a pro-inflammatory protein, was significantly reduced, as opposed to the control group. As cytokines have been found to be involved in various negative age-related health outcomes, having high psychological well-being may have a biologically protective function. Hence, the results showing significantly lower IL-6 and higher positive well-being scores may be potential factors in reducing the risk of depression. A major beneficial effect of the green environment could thus be brought about by immunoregulation.
In attempting to understand the neuropsychological basis of horticultural therapy, Kaplan’s attention restoration theory suggested that nature has specific restorative effects on the prefrontal cortex-mediated executive attentional system. High levels of engagement with technology and multitasking place demands on executive attention to switch between tasks, maintain task goals, and inhibit irrelevant actions. The theory suggests that interaction with the natural environment is particularly effective in replenishing depleted attentional resources in the brain. This theory may explain the improved mental status of busy city dwellers who spend some time at the parks or gardens. But is the same theory applicable for the patient with depression, anxiety, or cognitive impairment?
How horticultural therapy influences the brain neural systems is a new frontier of scientific research for neuroscientists. An intriguing question is: What mechanisms link decreased nature experience to the development of mental health problems? Bratman et al. (2015) have suggested that one such mechanism might be the impact of nature exposure on rumination , which is associated with increased risk for depression and anxiety. They have shown that in healthy participants, a brief nature experience in a 90-min walk in a natural setting could decrease both self-reported rumination and neural activity in the subgenual prefrontal cortex (sgPFC), whereas a 90-min walk in an urban setting had no such effects on self-reported rumination or neural activity. This suggestion draws support that at a neurobiological level, nature experience leads to decreases in sgPFC activity, a brain region that has been shown to be associated with a self-focused behavioral withdrawal linked to rumination in both depressed and healthy people. Some new studies support the finding that the sgPFC has increased activity during sadness, withdrawal, and negative self-reflective processes (Mayberg et al. 1999; Krishnan and Nestler 2008; Kross et al. 2009; Berman et al. 2011). Rumination is a maladaptive pattern of self-referential thought that is associated with risk for depression and anxiety and with activity in the subgenual prefrontal cortex (Nolen-Hoeksema 2000; Hamilton et al. 2015).
There are still many unanswered questions on the neurobiology of horticultural therapy. How does being in a park, garden, or forest alter neurotransmitters in the brain and allay anxiety and depression, or improve sociability? Future research on horticultural therapy could explore some of these questions in neurobiology using new tools of scientific studies in brain imaging, neurochemistry, neuroimmunology, or genetics.
The City in a Garden: A Case Study of Singapore
Situated at the Southeastern tip of the Asian land mass, the island of Singapore has become a busy international port along the major sea land from Europe to China. Before Singapore became a British colony in 1819, the island was covered with natural forest. During British rule, the island was designated a tropical crop-testing area, and vast forested areas were cleared for crop-testing. The deforestation also made way for the growth of rubber, pepper, and gambier plantations (Turnbull 1996). An experimental laboratory for botanical research was also established, in the form of the Singapore Botanic Gardens, which was founded in 1859. When the mental asylum, Woodbridge Hospital, was built in 1928, the Colonial Governor stipulated that the Medical Superintendent should be an officer “with some taste for gardening and farming, who will help to make the patients interested in such pursuits” (Kua 2004). The mental patients in Woodbridge Hospital were encouraged to be involved in gardening as an activity of occupational therapy . Like most mental asylums in the British Empire, Woodbridge Hospital was located away from the city and had extensive grounds around the wards – besides flowering plants, vegetables and fruits were grown for the hospital kitchen.
With a surge of immigrants from China, India, and Indonesia in the last century, Singapore’s population grew. The greening of modern Singapore started in 1963 when then Prime Minister, Mr. Lee Kuan Yew launched the first Tree Planting Campaign by planting a tree and asked for 10,000 trees to be planted a year. In the early 1960s because of the rapid industrialization and urbanization of the country, there was an effort to green up areas wherever possible, to make up for trees destroyed due to economic development (Wong et al. 2014). The Garden City Campaign was later introduced by Mr. Lee Kuan Yew in 1967 to transform Singapore into a city with lush greenery and a clean environment in order to make life more pleasant for the people. In 1968, the Parks and Trees Division (which later expanded to become the Parks and Recreation Department) was set up within the former Roads Branch in the Public Works Department. This was followed by the formation of the School of Ornamental Horticulture at the Singapore Botanic Gardens in 1972. Green urbanism cannot possibly succeed without political will. There was political resolve when the Government set up a “Garden City Action Committee” tasked with overseeing policies and coordinating activities of various government agencies for building a city with abundant greenery, parks, birdlife, and lush street planting.
The land area of Singapore covers approximately 718.3 km2. Given the small land size and a high population of 5.61 million (Department of Statistics, Singapore, June 2016), it faces multifaceted challenges in reconciling liveability, environmental sustainability, and economic competitiveness. To overcome the issue of land constraints, Singapore needs to consider industries that it needs for economic growth and competitiveness but do not require huge land areas. Working collaboratively across government departments and actively engaging both the private sector and people are also key in coming up with effective solutions (Khoo 2014).
Hence, the urban planning authority takes on a consultative approach in its master planning. To ensure a pleasant city for living in, visiting, and business, about 9% of land in Singapore has been allocated for parks and nature reserves. There are 24 designated nature areas including the four nature reserves at Bukit Timah Nature Reserve, Central Catchment Nature Reserve, Sungei Buloh Wetland Reserve, and Labrador Nature Reserve. To provide shade from the tropical heat, strong and fast-growing species like the Rain Tree and the Angsana were planted and are ubiquitous today. It is envisioned that 85% of residents will live within 400 m of a park by 2030. There will also be the proposed Round Island Route, stretching 150 km, which will provide an uninterrupted leisure route around the island, linking major cultural and historical sites, and cycling networks. These green spaces provide ample opportunities for city dwellers to exercise and interact besides enjoying the flowering plants, trees, and lakes.
Building technologies for a green city and capabilities to fulfill sustainable development are important. Urban agriculture includes orchards for harvesting fruits to crops growing at different scales, from large plots to small rooftop gardens and lawn spaces around residential estates. Urban agriculture is now a growing interest – it provides fresh food at a low cost at the local supermarkets and encourages the integration of composting facilities to recycle household organic waste. Many private enterprises have seized these opportunities with governmental support to establish start-ups which can potentially be expanded to other Asian cities looking for new ideas in green urbanism. A biophilic city endorses natural processes in the landscaping of buildings – the increased greenery increases energy efficiency in buildings.
The Singapore experience has shown that for green urbanism to flourish, there should be adequate water management and conservation to develop resilience against adverse climate conditions. There is a national endeavor to focus on the ecosystem services provided by the green infrastructure to ensure the sustainability of the city. Many private and public organizations work together to enhance sustainability and liveability in the dense urban environment. Singapore has now about 72 ha of rooftop greenery – the size of over 100 football fields. Contributing to this landscape are buildings, including hotels and hospitals, which have been retrofitted with greenery on their roofs and walls, and new developments that incorporate greenery in the building designs. In the area of nature conservation, legislation is in place. For instance, written approval must be obtained for the removal of trees in a designated tree conservation area, vacant land, or a heritage road green buffer. Tree planting verges are a required provision for various categories of roads.
Going beyond the provision of adequate green spaces, the National Parks Board has a keen interest to optimize recreational parkland to promote public health. Since 2015, it has started to carry out research on the health benefits of nature such as horticultural therapy and its impact on the mental health of the elderly. The outcomes of the research study on horticultural therapy mentioned earlier provide empirical evidence for the effectiveness of horticultural therapy in improving the psychosocial and cognitive well-being of the elderly and reducing healthcare costs. With its clinical implications, this initiative could potentially persuade policymakers and healthcare providers of the need to support cost-effective horticultural therapy as a strategy to engage older adults in a more active and healthier lifestyle.
Green spaces are of a strategic importance for the quality of life of an increasingly urbanized society. The natural environment not only enhances the aesthetic landscape of the city but also fosters social connectedness within neighborhoods by providing settings for groups to meet formally and informally for recreational or leisure pursuits. Besides improving the environment in air purification and noise filtering, natural areas are of crucial importance for the liveability of modern cities and the well-being of city dwellers. With the fast pace in city life, urban parks offer city dwellers a respite from the daily grind.
Densely populated megacities with the inadequate provision of green spaces are associated with poorer mental health. Studies on the use of urban parks and forests have confirmed the belief about stress-reduction benefits and mental health (Hartig et al. 1991). The natural environments have restorative effects which could mitigate stress and aid in the recovery from fatigue. Several other research studies have shown that exposure to green spaces can be psychologically and physiologically restorative by promoting mental health, reducing blood pressure and stress levels, as well as promoting physical activity (Humpel et al. 2002; Pretty et al. 2005; Richardson et al. 2013). Some cities, including Singapore, are incorporating benefits of green environment into urban design as important aspects of city planning that may influence mental health and even cognitive functioning (Jackson 2003; van Dillen et al. 2012; Ward Thompson et al. 2012). The multiple benefits of greenery extend to users of different profiles. The spin-offs for “economical” health arising from natural environment include the capacity for parks and gardens to improve the productivity of workers and recovery rates of patients in hospital. Larsen et al. (1998) have suggested that contact with nature could improve overall health, as well as reduce the number of sick days and employee absences. With better understanding, the mental health benefits of nature can be incorporated into a wide array of initiatives and investments in sustainable cities and conservation.
However, as mentioned by Hiroharu et al. (2014), there should be better research in horticultural therapy in randomized controlled trials to provide cogent evidence on its health benefits. What is it in plants, forest, or gardening that is therapeutic? Should there be more neurobiological studies to understand the underlying mechanisms in horticultural therapy? At the moment horticultural therapy is still an adjunctive therapy for depression, anxiety, and early dementia. Understanding the neuroscience is important to provide a better insight into green urbanism and mental health. As a method to promote mental health, horticultural therapy is an important strategy for preventive psychiatry.
Governmental support is sine qua non in green urbanism. It is not just the responsibility of city planners and politicians but also the community including mental health professionals who can have an advocacy role. Involvement in the green movement will allow the community to articulate commonly shared values on the environment. Being volunteers in the planning of a therapeutic garden for elderly at the HortPark in Singapore has provided a platform for the psychiatrists involved to address issues concerning aging and mental health – it is also an opportunity for the destigmatization campaign to speak up for mental illness. In several Asian mental hospitals today, horticultural therapy has been introduced for patients with chronic schizophrenia. In Indonesia, Thailand, and Malaysia, a few hospitals have fruits and vegetable plantations – small enterprises which have given patients much satisfaction and better quality of life. In a recent psychiatry meeting in Singapore, some Asian leaders of psychiatry shared their experiences and favorite leisure activity, which fortuitously was gardening , a hobby decreed by His Majesty’s Government in 1928 (Kua 2011).
The natural environment constitutes a health promotion platform with potential for the prevention of mental health disorders (Pryor et al. 2006). Public health needs to focus on both the social and environmental aspects of human health. A socioecological approach to health enhances human health, social health, and environmental health. Such a strategy with a socioecological approach to public health and the natural environment will increase sustainability for all. Collaboration among the key stakeholders including government departments, nongovernmental bodies, volunteer organizations, and the general public is crucial.
City planners will face difficult decisions about building and conserving green cities, promoting economically growing cities, and advocating social justice – these are issues of the environment, politics, and economics (Campbell 1996). There is always tense economic debate about urban redevelopment and the preservation of the city’s park and green spaces. There are challenges in green urbanism that will impact the United Nations Sustainability Development Goals. It is undeniable that long-term city sustainability is dependent on having policies which can address and advocate improvement in carbon reduction, resource efficiency in energy, water conservation, and green urbanism.
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