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Trees Lower Medication Sales for Heart and Mood Disorders

Research shows positive associations between urban trees and human health.

Although I've spent a significant proportion of my life studying social behavior in various wild mammals and birds, I've always been impressed with how being in forests and among diverse flora calms me down—taking time to smell the roses, if you will—and makes me deeply appreciate the environs in which I've been extremely fortunate to spend a great deal of time. As part of this personal rewilding, I've often wondered not only why this is so but also what the trees and other flora are experiencing—if they're thinking and feeling in their own ways. While some people have thought this is rather bizarre, recent research has clearly shown that asking if plants are intelligent, are able to learn, have their own sorts of feelings, or can actually affect our behavior isn't all that weird.

A few weeks ago, I read a fascinating book called Forest Walking: Discovering the Trees and Woodlands of North America by German forester and best-selling author Peter Wohlleben and Jane Billinghurst, which focuses on how we use all our senses when we walk in the woods and how we can become "forest detectives" and awaken "to the ancient past and thrilling present of the ecosystem around you."

I recommended this book to numerous people, and just yesterday, as I was writing to someone about it, I learned about a new research paper by Dengkai Chi and her colleagues called "Residential Exposure to Urban Trees and Medication Sales for Mood Disorders and Cardiovascular Disease in Brussels, Belgium: An Ecological Study." The essay is open access and available online, so here are a few snippets to whet your appetite for more.

To conduct their study, the researchers collected data on various traits of 309,757 trees in 604 census tracts in Brussels, Belgium. They also "used the average annual age-standardized rate of medication sales in Brussels for the period 2006 to 2014, calculated from reimbursement information on medication prescribed to adults (19-64 years of age)."

 An Ecological Study, open access.
Estimation of tree crown volume using LiDAR data and 3D convex hull algorithm: (A) LiDAR points for a delineated tree and (B) the reconstructed tree crown surface. 3D convex hull algorithm identifies the outmost points (in black), which are triangulated with Delaunay triangulation and meshed for surface generation. Note: 3D, three-dimensional; LiDAR, airborne light detection and ranging.
Source: Residential Exposure to Urban Trees and Medication Sales for Mood Disorders and Cardiovascular Disease in Brussels, Belgium: An Ecological Study, open access.

Using a number of different models, the researchers concluded: "Based on aggregated health data and comprehensive 3D tree data, we found that both tree density and tree crown volume are inversely associated with medication sales for cardiovascular disease and mood disorders. However, results of models that evaluate several tree trait exposures simultaneously suggest that living in areas with large tree crown volumes divided over relatively fewer stems may be more beneficial for adult cardiovascular and mental health than living in areas with a similar crown volume divided over a higher number of trees with smaller crowns." (my emphasis)

Just being outside can have strong psychological and physical effects.

The researchers sum up their findings, noting, "Psychological effects and indirect nature experiences provided by large trees, which are often old trees, may further strengthen the health impacts of these trees." This means that just being "out there" without having any intentions of doing anything else can be good for minds and hearts. They speculate, "Large tree crowns may reduce physical and mental stress more efficiently because the reduction of both heat and air pollution depend on leaf area, which is higher in large tree crowns."

All in all, this study shows that conserving large, old trees is good not only for maintaining biodiversity but also for human psychological and cardiovascular health.

The results of this study will be of interest to a wide audience, including academics such as conservation psychologists, who want to know what people feel when they're outdoors, and others who simply like to take walks in cities, towns, or in the woods because it makes them feel more relaxed and less pressured.

These and other data show that what they feel is supported by detailed scientific research if that matters to them. Personally, while it's nice to know there are scientific reasons why being outside with trees and other animals has always made me feel good, I know what I'm feeling, and that is why I spend as much time as I can among trees, flowers, grasses, and nonhuman beings. If it's really beneficial, that's icing on the cake, and in these stressful times, perhaps we all should be doing it more.


Are plants intelligent?

The Heartbeat of Trees: An Uplifting Spring Read.

Smarty Plants: Research Shows they Think, Feel, and Learn.