The multiple benefits of urban trees and green spaces
The correlation between canopy cover and lower ambient temperatures has long been established by research. Trees cool air by trapping the sun's rays, thus preventing them from reaching the ground and heating asphalted and paved areas.

As I drank another glass of water in an effort to keep hydrated and cool in the 30-degree heat this week I wondered yet again how the National Environment and Planning Agency and the Kingston and St Andrew Municipal Corporation can permit the removal of so many large shade trees in Kingston and its environs when many of these trees could easily be incorporated into the designs of residential and business complexes.

The correlation between canopy cover and lower ambient temperatures has long been established by research. A study looking at tree cover, income disparity, and temperature in the United States found on average that 15 per cent less tree cover resulted in about 1.5 degrees Celsius increase in temperature. The greatest difference found was 4.0 degrees hotter relating to 30 per cent less tree cover.

Trees provide many services other than shade. Indeed, trees are a marvel of engineering, functioning as air coolers, air filters, oxygen producers, carbon dioxide removers, flood mitigation works, drainage systems, habitat provider, and food source for life forms from insects to human beings. In addition, they are an important part of the hydrological cycle, contributing to rainfall. I can think of no human-engineered structure that comes near matching provision of all those functions.

Trees cool air by trapping the sun's rays, thus preventing them from reaching the ground and heating asphalted and paved areas. They also cool by evapotranspiration although the degree of cooling through this process is not certain. Their leaves trap rainfall, their roots filter and absorb water and provide drainage channels, thus reducing run-off, which can lead to flooding.

Apart from carbon dioxide, leaves absorb ozone and nitrogen dioxide and help to trap polluting particulate matter. They also filter out ultraviolet rays which have been linked to skin cancer.

But the remarkable usefulness of trees does not end there. More recent research has shown that trees and associated greenery are good for the physical and mental health of human beings.

The journal Scientific American reports on a 1984 study by Robert Ulrich which found that when other factors were accounted for, patients with a view of leafy trees, on average, healed a day faster, needed significantly less pain medication, and had fewer post-surgery complications than patients with a view of a brick wall. The ability of trees and associated green spaces to lower stress and induce relaxation is helpful to the immune system, promoting healing. Healing gardens are now being incorporated into many hospital landscapes and research is being done on the most effective types and designs of gardens for promoting healing.

In urban areas, green spaces and tree-lined streets encourage walking, outdoor activities, and generally healthier lifestyles. Research shows that just three to five minutes of looking at views of trees, flowers, or water can begin to reduce anger, anxiety, and pain and induce relaxation. One wonders what impact this could have on reducing violent interactions, especially among our children.

Greenery has also been found to have a positive influence on the cognitive development of children. Research on greenness and cognitive development in primary schoolchildren in Spain found an increase in cognitive development associated with surrounding greenness at home, on commutes, and at schools. The study provides evidence that investing in greenness, especially at schools, can result in increases in mental capital at population level.

Another study in the United Kingdom found that higher IQ scores in children were associated with greenness. Given these data, the approval of residential complexes devoid of trees and greenery leaves one astounded.

With the data now available on the benefits of trees and associated greenness, it is remarkable that authorities in Jamaica are removing or permitting removal of so many trees and filling potential and existing green spaces with buildings, asphalt, and concrete. Further, this is happening in a country which claims it is concerned about the effects of climate change, plagued with urban flooding and interpersonal violence, and experiences high levels of lifestyle-related diseases. Whereas many cities have established tree-lined pedestrian walkways, have set targets for canopy cover, and are planting trees to achieve these targets, Jamaica is reducing canopy cover of its largest city!

The plan by the Forestry Department to have three million trees planted across the island is commendable and should have the support and participation of all residents. Realising the benefits from these trees, however, will take several years. In the meantime, Jamaica should follow recommendations from researchers to develop policies to counter the loss of tree canopy associated with urban infill. Given the multiple and varied benefits of trees and green spaces, planning authorities should take every opportunity to preserve and increase canopy cover and greenery, especially in urban development.

Barbara Carby is a disaster risk reduction and animal welfare advocate.

Barbara Carby

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