Just a walk in the park?

Many of us enjoy a walk in the park, or forest, or mountains, but only relatively recently have scientists begun to consider why this might be. The link between nature and biodiversity on mental health is of particular interest as incidences of mental health are on the rise and is estimated to affect over 450 million people worldwide, biodiversity is in decline and now more than half of the worlds population live in cities (World Health Organisation, 2003)(United Nations, 2007). A multitude of studies now address this link from a number of different disciplines including urban planning and environmental psychology.  

A cross sectional study by de Vries et al looked at associations between living in a highly diverse environment with general health. They compared the percentage of green-space, agricultural land, forestry, nature areas, gardens and degree of urbanity with health, measured via self reported symptoms, perceived general health and a 12 point general health questionnaire. This large study (n= 10,179) found that living in a green environment was positively related to the three health indicators and that these effects were more significant in lower income groups or those that spend more time at home (de Vries et al, 2003)(Hough, 2014). This sort of study has significant repercussions for urban planners as the way in which an urban area is designed has the ability to influence health and wellbeing.

Further work has addressed the more specific link between nature or biodiversity and mental health. There are two major explanatory theories, the stress reduction theory, or SRT, and the attention restoration theory, or ART.

SRT proposes the healing power of nature lies in an unconscious autonomic response to actual elements. Landscapes with views of water and or vegetation with high levels of complexity or biodiversity would have been most beneficial for human survival and at a preconscious level we may have evolved diminished states of arousal and negative thoughts at sites such as these (Bratman, 2012).  Ulrich, who developed this theory, carried out multiple tests. In one instance, 120 subjects were made to watch a stressful film for 10 minutes and then viewed scenes and sounds of six different settings from urban to very natural. During this process, stress indicators were measured including the subjects heart rate, skin conductance, muscle tension and systolic blood pressure was measured. Subjects were also asked to self rate their state. In all instances, subjects viewing natural scenes recovered from the stress at a faster rate than those presented with urban scenes (Ulrich, 1991). 

The ART proposes nature replenishes certain types of attention through unconscious cognitive process in response to natural landscapes. This draws on the distinction between two components of attention, voluntary or directed, and involuntary. Direct or voluntary attention requires the use of cognitive control in order to ignore distractions. After prolonged use this capability becomes fatigued resulting in irritability. Involuntary attention is used when individuals are presented with ‘inherently intriguing’ stimuli and the ART approach posits that viewing nature acts in this way. This allows neural mechanisms underlying direct attention to rest and replenish which can benefit performance on other tasks and impact levels of depression and stress (Bratman, 2012).  This also has been tested on multiple occasions. For example, Taylor et al compared children from the same population, whose characteristics and demographics only differed by their view from home; urban park or barren concrete. On average, the more natural the view, the better performance on a number of tasks used to measure attention such as the digit span backyard and Stroop colour word test (Taylor et al, 2002). 

There are many more studies that measure the links between nature and mental health in different ways and within different disciplines, although I will not go into any more at the present. Correspondingly, it seems obvious that impacts on mental health be included in the list of ecosystem services and act as another argument for biodiversity conservation. Furthermore, these links should be considered in future urban planning projects to improve the overall quality of life and health for urban dwellers. 

Sources:

Bratman, G. et al.  2012. The impacts of nature experience on human cognitive

function and mental health. Annals of the New York academy of sciences. Vol. 1249. pp 118-136. 

de Vries S et al. 2003. Natural environments—healthy environments? An exploratory analysis of the relationship between greenspace and health. Environ Plan A. Vol. 35. pp. 1717–1731

Hough, R L. 2014. Biodiversity and Human Health: evidence for causality? Biodiversity Conservation. Vol. 23. pp 267-288. 

Taylor, A.F. et al. 2002. Views of nature and self-discipline: evidence from inner city children. Journal of  Environmental Psychology. Vol. 22. pp49–63.

Ulrich, R.S. et al. 1991. Stress recovery during exposure to natural and urban environments. Journal of Environmental Psychology. Vol. 11. pp 201–230

United Nations Population Fund State of World Population. 2007. Unleashing the potential of urban growth. New York: UNFPA.

World Health Organisation. 2003. Investing in metal health. Geneva: WHO