‘Mappiness’ is a smartphone app developed by economist George MacKerron in order to better understand how people’s emotions are affected by their environment, both natural and urban. It randomly collects participants’ happiness ratings twice a day, along with other data such as activity, companionship, weather, time of day and work/leisure status, and uses satellite positioning (GPS) to determine geographical coordinates. It has been described as ‘the biggest happiness project ever’ and within six months MacKerron gathered more than 20,000 participants and analysed over a million data points. The results demonstrated that when controlled for other factors, such as activity and companionship, being in natural environments makes us happier, typically adding 3-6 points on a 100-point scale, greater than the difference experienced from being alone or with friends, and equivalent to the difference between going to a museum and doing housework. In other words, one of the biggest and perhaps most surprising variables, is not who you are with or what you are doing, but where you are. The study concluded that on average, study participants are significantly and substantially happier outdoors in all green or natural habitat types than they are in urban environments. Mappiness 2 is being launched in 2019.

MacKerron, G. & Mourato, S. (2013). Happiness is greater in natural environments. Global Environmental Change, 23 (5), 992.

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In two Canadian studies, researchers investigated the link between nature relatedness and happiness. The studies included measures of general connectedness, along with multiple nature relatedness and happiness indicators, and had large sample sizes of 746 and 204 respectively. The results indicated that our sense of connectedness to nature can enhance our capacity for happiness, even after controlling for other connections, and not only makes us happy in the moment, but causes us to feel happier in the future when no longer in nature. The researchers conclude that the studies support the notion that nature relatedness could be a path to human happiness and environmental sustainability.

Zelenski, J. M., & Nisbet, E. K. (2014). Happiness and feeling connected: The distinct role of nature relatedness. Environment and Behavior, 46(1), 3-23.

Seventy-one volunteers with sleep complaints participated in two-hour forest-walking sessions on 8 different weekend days. Sleep conditions were compared between the nights before and after walking in a forest by self-administered questionnaire and actigraphy data. The average sleep time of participants after a two-hour forest walk increased by 15%, or 45 minutes, with participants also reporting reduced anxiety, and improvements in depth and quality of sleep. 

Morita, E., Imai, M., Okawa, M., Miyaura, T., & Miyazaki, S. (2011). A before and after comparison of the effects of forest walking on the sleep of a community-based sample of people with sleep complaints. BioPsychoSocial Medicine, 5, 13. 

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A large-scale study, involving 259,319 Australians who completed the ‘45 and Up Study’, investigated whether neighbourhood green space was associated with a healthier duration of sleep, and found people living in greener neighbourhoods reported a lower risk of short sleep, i.e. less than six hours. 

Astell-Burt, T. Feng, X., & Kolt, G.S. (2013). Does access to neighbourhood green space promote a healthy duration of sleep? Novel findings from a cross-sectional study of 259 319 Australians. Public Health, 3, 8.

A series of experiments conducted by Dr Li in Japan have found that after 2-3 days walking in a local forest, natural killer (NK) cell activity, considered an indicator of immune function (NK cells attack and kill infected cells) is enhanced by approximately 50%, and a statistically significant increase of approximately 20% is maintained for one month after returning to urban life. Dr Li concludes that a forest-bathing trip once a month is enough to maintain a high level of natural killer cell activity. 

Li, Q., Morimoto, K., Nakadai, A., Inagaki, H. et al. (2007). Forest bathing enhances human natural killer activity and expression of anti-cancer proteins. International Journal of Immunopathology and Pharmacology, 20(2), 3-8.

Li Q. (2009). Effect of forest bathing trips on human immune function. Environmental Health and Preventive Medicine, 15(1), 9-17.

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Following Dr Li’s initial trip in 1990, in which he took 12 healthy middle-aged men from Tokyo on a three-day scientific forest-bathing trip, hundreds of subjects in different contexts and forests across Japan have participated in research investigating the psychological and physiological effects of forest bathing. Over a period of 15 years, Dr Li has measured participants’ heart rate, blood pressure, adrenaline, cortisol levels, brain activity and natural killer cell activity before, during, and after time spent in forests, and has found forest bathing to have a significant positive impact on health. His extensive research has shown that forest bathing reduces stress hormone production, lowers blood pressure and heart rate, suppresses the sympathetic “fight or flight” system, and enhances the parasympathetic “rest and recover” system, and increases natural killer cell activity (which promotes immune system health); participants also report feeling better, sleeping longer, and enjoying these effects for weeks following. 

Li, Q., Otsuka, T., Kobayashi, M., Wakayama, Y. et al. (2011). Acute effects of walking in forest environments on cardiovascular and metabolic parameters. European Journal of Applied Physiology, 111, 2845-53.

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Phytoncides are the anti-bacterial natural oils secreted by plants, notably evergreens such as pine trees, cedars, spruces and conifers, to protect themselves from harmful bacteria, insects and funghi. Thirteen healthy men stayed in a hotel in Tokyo for three nights and hinoki stem oil (a phytoncide) was diffused into their rooms. Results showed that exposure to phytoncides significantly increased the numbers of NK cells (by 20%) and NK activity, as well as enhancing the activity of the anti-cancer proteins, suggesting the scent of trees can boost immune functioning. The findings also revealed significantly decreased levels of stress hormones, increased hours of sleep, and decreased scores of anxiety and fatigue, whilst the control group saw no changes.

Li, Q., Kobayashi, M., Wakayama, Y., Inagaki, H., Katsumata, M., et al. (2009). Effect of phytoncide from trees on human natural killer cell function. International Journal of Immunopathology and Pharmacology, 22(4), 951-9.

Rumination (repetitive thoughts focused on negative aspects of the self), is a known risk factor for mental illness. Thirty-eight healthy city dwellers went on a 90-minute walk through a natural environment: participants reported lower levels of rumination and brain scans showed reduced neural activity in an area of the brain linked to risk for mental illness (the subgenual prefrontal cortex, a region linked to sadness, withdrawal and general grumpiness) compared with those who walked through an urban environment. The results also showed that walking in nature alleviated negative feelings of anxiety and other negative emotions, and also increased positive thoughts. 

Bratman, G. N., Hamilton, J. P., Hahn, K. S., Daily, G. C., & Gross, J. J. (2015). Nature experience reduces rumination and subgenual prefrontal cortex activation. Proceedings of the National Academy of Sciences of the United States of America, 112(28), 8567-72.

Twenty individuals diagnosed with depression were assessed for mood and short-term memory span before taking a 50-minute walk in either a natural or urban setting and afterwards were reassessed on the same measures. A week later, participants undertook a walk in the setting not previously visited. Participants showed significant increases in mood and in memory span after the nature walk relative to the urban walk.

Berman, M.G., et al. (2012). Interacting with nature improves cognition and affect for individuals with depression. Journal of Affective Disorders, 5518.

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A Danish randomised controlled trial (RCT), considered by many researchers as the gold standard in studies, randomly allocated 84 participants suffering from stress-related illnesses to two treatments: a nature-based treatment and a validated cognitive behavioural therapy (CBT). Each treatment lasted 10 weeks and after a twelve-month follow-up, both treatments had led to a significant reduction in GP visits and a significant decrease in long-term sick leave, providing validation for a nature-based intervention as an efficient treatment for stress-related illnesses. 

Corazon, S., Nyed, P., Sidenius, U., Poulsen,D., Stigsdotter, U. (2018). A Long-Term Follow-Up of the Efficacy of Nature-Based Therapy for Adults Suffering from Stress-Related Illnesses on Levels of Healthcare Consumption and Sick-Leave Absence: A Randomized Controlled Trial. International Journal of Environmental Research and Public Health, 15(1), 137.

Thirty-eight students from Michigan University were randomly assigned to take a 50-minute walk either in a tree-lined park near their campus or on a busy street nearby, and the following week walk in the other location. Before and after each walk they performed a backwards digit span task, requiring them to remember and repeat aloud an increasing number of digits. With potential confounding variables of mood and weather conditions controlled for, performance on the task significantly improved after participants had walked in the natural environment, but not after walking along the street.

A follow-up experiment amongst 12 students who viewed either pictures of nature or pictures of urban scenes for a period of 10 minutes replicated the results, with participants reliably improving their backwards digit-span only when viewing nature images.  

Berman, M., Jonides, J., & Kaplan, S. (2008). The cognitive benefits of interacting with nature. Psychological Science, 19(12), 1207-12.

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A longitudinal study in the US examined the effects of natural settings in residential areas on 7-12 year olds from low-income families. The results showed that children who moved away to housing closer to nature had elevated levels of cognitive functioning compared with those who continued to live in areas with less green space. 

Wells, N. (2000). At-home with nature: effects of „greenness on children’s cognitive functioning. Environment and Behavior, 32(6), 775-95.

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A study involving 67 pre-school and school aged children examined the restorative effects of nature on children’s executive functioning. The children participated in two sessions in which they completed an activity to fatigue attention, then walked along urban streets in one session and in a park-like area in another session, and finally completed assessments of working memory, inhibitory control, and attention. Although no difference was found in working memory and inhibitory control, children responded faster on the attention task after a nature walk than an urban walk. 

Schutte, A., & Torquati, J., & Beattie, H. (2015). Impact of urban nature on executive functioning in early and middle childhood. Environment and Behavior, 49(10).

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One hundred and twenty adolescents (age 16-18) were randomly assigned to an indoor environment with no view of nature or an outdoor school quadrangle with natural elements, with three different contexts in each environment: alone, with a friend, or with a mobile phone. Measures of restoration (including physiological, cognitive and affective states) were taken immediately following stressor tasks and again after 20 minutes spent in one of the six conditions. Findings showed greater improvement in concentration across all experimental conditions outside compared with the indoor environment; positive affect improved only after being with a friend in an outdoor environment. According to the researchers, these findings suggest that spending short school breaks in a natural environment can increase concentration, and when with a friend can have a significant positive impact on the psychological wellbeing of teenagers.

Greenwood, A., & Gatersleben, B. (2016). Let's go outside! Environmental restoration amongst adolescents and the impact of friends and phones. Journal of Environmental Psychology, 48, 131-139.

Fifty-six hikers participated in a study that involved four days immersed in nature and disconnected from multi-media and technology. Participants were tested during the trip, and the findings demonstrated a 50% increase in performance on a creativity, problem-solving task. The researchers hypothesised that this advantage comes from an increase in exposure to natural stimuli that are both emotionally positive and low-arousing, and a corresponding decrease in exposure to attention demanding technology, which regularly requires that we attend to sudden events, switch amongst tasks, maintain task goals, and inhibit irrelevant actions or cognitions.

Atchley, R.A., Strayer, D.L., & Atchley, P. (2012). Creativity in the wild: Improving creative reasoning through immersion in natural settings. PLOS One, 7(12).

Several studies have shown that when we connect with nature we are reminded that we are part of something greater than ourselves, and this can make us less selfish, more grateful, and more helpful and caring towards others. Moreover, this increase in prosocial behaviours is not just as a result of being in awe-inspiring nature, but occurs even after just looking at nature scenes or when in a room with beautiful pot plants.

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In a series of experiments, published in 2014, researchers at the University of California, Berkeley, studied the potential impact of nature on the willingness to be generous, trusting, and helpful towards others. Participants viewed different nature scenes, independently rated for their relative beauty, and were then observed playing two economics games, the Dictator Game and the Trust Game, that measure generosity and trust respectively. After being exposed to the more beautiful nature scenes, participants acted more generously and more trusting in the games than those who saw less beautiful scenes, and the effects appeared to be due to corresponding increases in positive emotion.

In another part of the study, the researchers asked people to fill out a survey about their emotions while sitting at a table where plants of differing beauty were placed. Afterwards, the participants were told that the experiment was over and they could leave, but that if they wanted to, they could volunteer to make paper cranes for a relief effort programme in Japan. Results showed that the presence of the more beautiful plants significantly increased the number of cranes made by participants, and that this increase was, again, mediated by positive emotion elicited by natural beauty. The researchers concluded that experiencing the beauty of nature increases positive emotion, perhaps by inspiring awe and a sense of being part of something bigger than oneself, which then leads to increased prosocial behaviours.

Suttie, J. (2016, March 2). How nature can make you kinder, happier and more creative. Greater Good Magazine. Retrieved from: Greater Good Science Centre at UC Berkeley.

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In a series of five studies involving 2,078 participants, researchers investigated the concept of awe and found it predicted greater generosity in an economic game above and beyond other prosocial emotions such as compassion; and lab-based inductions of awe led to greater prosocial responding. In one of the studies, 90 students were randomly assigned to look up at tall eucalyptus trees or a tall building for just one minute. Within this short period, the group assigned to the tall tress condition experienced measurable increase in awe, and in a carefully staged ‘accident’ in which the experimenter dropped a box of pens, demonstrated significantly more helpful behaviour than the control group who had stared at the tall building. On follow-up questionnaires, the tall trees group also reported increased ethicality and reduced feelings of entitlement. The researchers concluded that even fleeting experiences of nature-inspired awe can have a meaningful impact on various types of prosocial judgments and behaviour, and hypothesised that this may be explained by feelings of ‘a small self’. 

Piff, P., Feinberg, M., Dietze, P., Stancato, D., & Keltner, D. (2015). Awe, the small self, and prosocial behavior. Journal of Personality and Social Psychology, 108(6), 883-899. 

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A team of American researchers conducted four experiments involving 370 participants: three of the studies involved participants being exposed to images of nature or urban scenes of buildings and roads, and the fourth involved being in an office with or without pot plants. Participants were asked to complete a questionnaire which rated the importance of four life goals: wealth, fame, connectedness and community; in all four studies, those exposed to the natural world consistently ranked close relationships and community higher than they had before the experiments. The questionnaire also assessed how deeply engaged the participants were in the images. The deeper the connection to nature, the more they appreciated community and closeness, whereas those who focused more on artificial environments rated wealth and fame higher in importance.

The research also investigated levels of generosity: in two of the studies participants were given a $5 prize, which they could either keep or give to another anonymous participant, who would then be gifted an additional $5 bill. In turn, the anonymous participant could decide to return the prize money or keep it. The results demonstrated that those who were in contact with nature were more willing to share the money, and the more they were immersed in the natural environment, the better chance they would be generous with their winnings.

The researchers suggest that nature helps us connect with our true, authentic selves, with participants who focused on landscapes and plants stating they felt a heightened sense of personal autonomy, such as “Right now, I feel like I can be myself.” They also argue that nature can strip away the artifices of modern society that alienate us from one another, and can bring a stronger sense of community, and conversely, when links with nature are disrupted, we may lose some connection with each other.

Weinstein, N., Przybylski, A. K., & Ryan, R. M. (2009). Can nature make us more caring? Effects of immersion in nature on intrinsic aspirations and generosity. Personality and Social Psychology Bulletin, 35(10), 1315–1329.

In 2002 the emerald ash borer, a small green beetle, landed in the American Midwest (thought to have come from China) and decimated 100 million ash trees, creating an opportunity for one of the largest natural experiments to investigate the impact of urban trees on human health. Comparing statistics from 15 counties between 1990 and 2007, researchers found that counties hit by the borer suffered 15,000 additional deaths from cardiovascular disease and 6,000 more deaths from lower respiratory disease, representing a 10% increase in expected mortality. 

Donovan, G.H., Butry, D.T., Michael, Y.L., Prestemon, J.P., Liebhold, A.M., Gatziolis, D., & Mao, M.Y. (2013). The relationship between trees and human health: Evidence from the spread of the emerald ash borer. American Journal of Preventive Medicine, 44(2), 139-45.

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A recent Canadian study focusing on a large urban population (Toronto) examined associations between greenspace and health, and showed that the higher the density of trees in a neighbourhood, the lower the incidence of heart and metabolic disease and the higher individuals’ mental and physical health perception. Framing the results in economic terms, researchers suggested that 10 more trees in a city block, on average, improves health perception in ways comparable to an increase in annual personal income of $10,000 or being 7 years younger. They also found that having 11 more trees in a city block, on average, decreases cardio-metabolic conditions in ways comparable to an increase in annual personal income of $20,000 or being 1.4 years younger.

Kardan, O., Gozdyra, P., Misic, B., Moola, F., Palmer, L., Paus, T., & Berman, M. (2015). Neighborhood greenspace and health in a large urban center. Scientific Reports, 5, 11610. 

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A longitudinal UK study lasting five years looked at the mental health data of 1064 participants who had relocated to a different residential area between the second and third years. Pre-move and post-move mental health scores were compared and it was discovered that individuals who moved to greener urban areas had significantly better mental health in all three post-move years, supporting the view that living in greener urban areas is associated with sustained mental health improvements.

Alcock, I., White, M.P., Wheeler, B.W., Fleming, L.E., & Depledge, M.H. (2014). Longitudinal effects on mental health of moving to greener and less green urban areas. Environmental Science & Technology, 48 (2), 1247-1255.

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A UK study used secondary data sources to examine the association between the density of street trees (trees/km street) in London boroughs and rates of antidepressant prescribing. After adjustment for potential confounders, they found a 1.18 decrease in prescriptions per thousand population per unit increase in trees per km of street, suggesting that street trees may be a positive urban asset to decrease the risk of negative mental health outcomes.

Taylor, M.S., Wheeler, B.W., White, M.P., Economou, T., & Osborne, N.J. (2015). Urban street tree density and antidepressant prescription rates – A cross-sectional study in London, UK. Landscape and Urban Planning 136, 174-179. 

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A study involving 4529 Dutch respondents looked at a series of health measures including the number of health complaints in the last 14 days, and perceived measures of mental and general health, and analysed these with relation to the percentages of green space in a 1-km and 3-km radius around their homes. The results demonstrated that respondents with a high amount of green space in a 3-km radius were less affected, both in terms of their physical and mental health, by experiencing a stressful life event than respondents with a low amount of green space in this radius. 

Van den Berg, A. E., Maas, J., Verheij, R. A., & Groenewegen, P. (2010). Green space as a buffer between stressful life events and health. Social Science & Medicine, 70(8), 1203-1210.

A large Japanese study, involving 3,144 older adults over the age of 70 years living in urban areas, discovered that the probability of living longer over a five-year period increased with the amount of accessible green space close-by and their perceived ability to walk to parks and in tree-lined streets.

Takano, T., Nakamura, K. & Watanabe, M. (2002). Urban residential environments and senior citizens’ longevity in megacity areas: The importance of walkable green spaces. Journal of Epidemiology and Community Health, 56 (12), 913–918. 

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A much larger Canadian study involving 575,000 adults and conducted over a thirty- year period, has confirmed an association between living near a green space and a long-term reduction in mortality. 

Villeneuve, P.J., Jerrett, M., Su, J.G., Burnett, R.T., Chen, H., Wheeler, A.J., & Goldberg, M.S. (2012). A cohort study relating urban green space with mortality in Ontario, Canada. Environmental Research, 115, 51-8. 

In his pioneering ‘hospital window’ study, Roger Ulrich compared the recovery records of 23 matched pairs of surgical patients, with half of the patients in a room with a window looking out over trees and the other half in an identical room, but with a window looking onto a brick wall. He found that those patients with a window view of trees spent less time in hospital post-operation, elicited fewer negative comments about their progress from nurses and took fewer moderate and strong analgesics, compared with patients who had a view of a brick wall.

Ulrich, R.S. (1984). View through a window may influence recovery from surgery. Science, 224, 420-21.

In a series of four studies researchers investigated the impact on perceived attention restoration and stress recovery of a variety of bird songs and calls, and found that bird sounds were the type of natural sound most commonly associated with perceived stress recovery and attention restoration.

Ratcliffe, E., Gatersleben, B. & Sowden, P.T. (2013). Bird sounds and their contributions to perceived attention restoration and stress recovery. Journal of Environmental Psychology, 36, 221–228.

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Participants listened to sounds recorded from natural and artificial environments, while their brain activity was measured in an MRI scanner, and their autonomic nervous system activity was monitored via minute changes in heart rate. The team found that activity in the default mode network of the brain (a collection of areas which are active when we are resting) was different depending on the sounds playing in the background: when listening to natural sounds, the brain connectivity reflected an outward-directed focus of attention; when listening to artificial sounds, the brain connectivity reflected an inward-directed focus of attention, similar to states observed in anxiety, post-traumatic stress disorder and depression. There was also an increase in rest-digest nervous system activity, associated with relaxation of the body, when listening to natural compared with artificial sounds, and better performance in an external attentional monitoring task.

Gould van Praag, C., Garfinkel, S., Sparasci, O., Mees, A., Philippides, A., Ware, M., Ottaviani, C., & Critchley, H. (2017). Mind-wandering and alterations to default mode network connectivity when listening to naturalistic versus artificial sounds. Scientific Reports, 7.

Phytoncides, the natural oils secreted by plants to protect them from bacteria, insects and funghi, have been found to have a significant positive impact on natural killer cell function. Dr Li took 12 healthy men to stay in a hotel in Tokyo for three nights, and diffused hinoki stem oil (a phytoncide smell) into their rooms whilst they slept. They worked as usual during the day and limited their physical activity to the distance walked on an average working day. Results showed that exposure to phytoncides significantly increased the number of NK cells and NK activity, as well as enhancing the activity of the anti-cancer proteins; significantly decreased the levels of stress hormones, increased hours of sleep, and decreased scores for tension/anxiety, anger/hostility and fatigue/confusion. 

Li, Q., Kobayashi, M., Wakayama, Y., Inagaki, H., Katsumata, M., Hirata, Y., & Miyazaki, Y. (2009). Effect of phytoncide from trees on human natural killer cell function. International Journal of Immunopathology and Pharmacology, 951–959.

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Two nurses who experienced very high levels of stress and fatigue at work set up a study to investigate the impact of diffusing essential oils through their department. Before the study 41% of staff reported feeling work-related stress very often, and this dropped to just 3% after the oils were diffused. Before the use of oils, 13% of staff reported feeling well equipped to handle stressful situations and this rose to 58% afterwards, and perceived energy levels increased from 33% to 77%. At the end of the study 84% of staff ‘strongly agreed’ that diffusing essential oils contributed to a more positive work environment. There are now 68 hospitals and other institutions throughout the US, listed as employing essential oils to enhance wellbeing and decrease stress amongst staff and patients.

Reynolds, J., & Card, E. (2016). The effect of Essential oils on perceived stress of nursing staff in the holding room. Journal of Perianasthesia Nursing, 33(6).