Tools for Changing the World

Until today, if you had come to me and told me you wanted me to plant a tree, I would have assumed you represented some sort of environmental organization (or possibly a secret all-dryad cabal, because I think like that some days).

That will teach me to make assumptions. It turns out that the presence of trees – well, greenery in general – not only improves our physical and mental health, but also reduces antisocial behaviour. So, the next tree you’re asked to plant may be for the World Health Organization or your local crime prevention unit.

The health benefits of natural surroundings have been shown in a number of studies. Surgical patients whose rooms looked out on a stand of trees healed more quickly than patients who could only see a brick wall. Exposure to natural surroundings moderated the effect of stressful life events on children. Even putting plants into an office reduced symptoms among the office workers.

But greenery also seems to have other effects. Frances Kuo and William Sullivan measured the amount of vegetation (mostly trees and grass) around buildings in an urban public housing development and analyzed its relationship to the number of crimes reported by residents over two years. After taking into account all the other crime-influencing factors they could think of, they discovered that twice as many crimes (both violent and nonviolent) occurred in buildings with very little surrounding greenery compared to buildings with a lot (buildings with a moderate amount had crime rates halfway between).

Kuo and Sullivan suggested two reasons why this might be happening. First, outdoor greenery makes public spaces more likely to be used, and the presence of lots of people tends to discourage crime. Second, greenery appears to reduce levels of aggression and violence, as Kuo and Sullivan showed in other research.

This second factor has been supported by some interesting results from other studies. In one, junior high school students misbehaved less often when plants had been put in their classroom. In another, volunteers behaved more generously when plants were put in the research lab they were using.

You can easily imagine how to use this phenomenon for good. If you’re soliciting donations or volunteers, put plants on your table or in your booth. If you’re trying to foster behavioural change, make sure the people involved have as much exposure to natural surroundings as you can arrange. And, of course, if you want to reduce urban crime, start planting trees.

As for me, I’m feeling a little grumpy. I think I’ll go curl up with a nice philodendron.