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This week:

The Green Space Cure 

The Psychological Value of Biodiversity

Frank S. Muscara & Susan C. Saegert
City University of New York Graduate Center

As we chip away at and move away from the natural world, contact with it becomes more valuable: urban design now recognizes that access to green space is an important part of quality of life. A new study by Fuller, Irvine, Devine-Wright, Warren and Gaston ("Psychological Benefits of Greenspace Increase with Biodiversity," from Biology Letters - see abstract), suggests that not all green space is equal in this regard. Fuller and colleagues found that the more biologically diverse the green space, the higher its psychological value.

The University of Sheffield researchers conducted their study in Sheffield, England, a historically industrial city of about 500,000. The research sites included fifteen green spaces located within a wedge-shaped transect stretching from the dense city center to the sparsely populated western suburbs. The researchers identified and counted all herbaceous plant and woody species in the green spaces, as well as distinct habitat types, including mown and unmown grassland, woodland, scrub, water, and amenity planting. In addition, researchers surveyed butterfly and bird richness.

The researchers interviewed 312 users of these various green spaces between July and October 2005, using closed-ended questions designed to measure psychological well-being. To gauge well-being, the researchers looked to concepts derived from environmental psychology, particularly theories on restorative environments, place identity and place attachment, with a focus on green space "as a source of cognitive restoration, positive emotional bonds, and sense of identity." Participants were also tested on their ability to perceive the species richness of the green spaces.

Restorative space

The researchers measured several indices of mental health. A key measure was an effect the researchers called reflection, which referred to the participants' reported ability to clear their heads, gain perspective on life and think more easily about personal matters. The study revealed a positive correlation between reflection and green space biodiversity and size, but not between reflection and bird and butterfly diversity. Overall, the richer, more complex green spaces clearly provided more restorative benefit than did simpler areas with just trees and grass.

One possible explanation comes from Stephen Kaplan's theory of restorative environments, which suggests that attention is the mediator between green space and psychological benefit. Kaplan hypothesizes that natural environments allow our directed attention to rest as nature engages an involuntary and effortless form of attention that he calls fascination; this in turn improves mood, directed attention, and cognition afterwards. If higher biodiversity is indeed more restorative, then it follows that there biodiversity and attention may be correlated. Perhaps, for example, richer environments provide a more interesting field of perception that more readily engages involuntary attention.

Sense of Place

The Fuller study also examined whether a space's biodiversity or size affected users' sense of special attachment to the particular green space they visited, as expressed by such statements as "I like this park" and "I feel happy when I am in this park" and by such factors as a feeling of belonging, their memories of the space and whether they missed it when they were away from it. Although the study showed that participants perceived green spaces more positively as size and biodiversity increased, this sense of personal emotional attachment to a particular place did not vary with richness and size. Attachment increased, however, with bird diversity and number of habitats.

The correlation with bird biodiversity raises questions about the role of perception in forming attachments to place. We notice a variety of plants primarily by sight, but we can both see and hear the variations in a bird population. So visual sensation might not play much role in a sense of attachment to a place. Or it may be that the engagement of multiple sensory streams enhances attachment. In any case, these differences in how perception affects attachment to place make it clear that a variety of mechanisms affect our sense of connection to natural environments. Exploring them further should help refine the evolving (and still contested) concepts about place identity and place attachment.

Tabulating nature's gifts

Along with examining how biodiversity adds psychological value to green spaces, the researchers tested their subjects' abilities to quantitatively perceive biodiversity. Respondents rated the number of species they thought were in the park on a four-point scale. For plants, the choices were fewer than 10, 10-100, 100-300 and more than 300.

Results showed that participants were indeed aware of biodiversity for plant species -- though less so for bird diversity. (Plant diversity may be easier to detect than bird diversity, since it's much easier to distinguish plants from one another than birds, and they tend to be more visible.) This sensitivity suggests that urbanites are more closely connected to nature than one might suspect.

This study clearly strengthens the argument that oases of biodiversity -- the more diverse the better -- can provide valuable mental-health benefits to urban residents. What is good for the urbanite, of course, is good for the environment, for fostering stronger relationships with nature will in turn increase city dwellers' regard for and treatment of the environment.

Frank Muscara is a Ph.D. student in the environmental psychology program at the City University of New York Graduate Center. His current research focuses on the urban experience of restorative environments. Susan Saegert, who has written extensively on urban stress and restoration, is a professor of environmental psychology and director of the Center for Human Environments at the CUNY Graduate Center. For the fall of 2007, she is visiting professor of human and organizational development at Peabody College, Vanderbilt University.

Suggested further reading:

For basic material, see Rachel Kaplan's site at the University of Michigan, her book on design with people in mind, and this nice article giving an overview of the Kaplans' research, with an emphasis on Rachel's work on the effects of what you see out the window. You can also find considerations of monasteries, museums and, finally, pipe-smoking as restorative environments. And from the department of editorial indulgence, here's some restorative space at Oberlin College, the alma mater I happen to share with the Kaplans. -- Mind Matters editor David Dobbs