Apart from beautifying our surroundings and purifying the air, trees may prove good for children's lungs. Trees are believed to have beneficial effects on air quality. To investigate trees' capacity to fight asthma risk in children, American researchers compared a census of New York City's half-million street trees from 1995 to statistics on asthma prevalence and hospitalisation rates for 1999. The proximity to pollution sources, socio-demographic characteristics, and population density for each area were also measured. It was found that as the density of trees in a neighbourhood rose, the prevalence of asthma fell. An increase of 343 trees per square kilometre, or roughly 1.5 trees per acre, resulted in 29% lower asthma prevalence. For example, asthma prevalence among 4 and 5-year-olds would be 9% in a neighbourhood with 2.5 trees per acre, but just 6% in a neighbourhood with four trees per acre. Rates of asthma hospitalisation were also lower in neighbourhoods with more street trees, but the relationship wasn't statistically significant. Nevertheless, this suggests that trees aren't a major contributor to asthma attacks. It can be concluded that street trees are associated with a lower prevalence of early childhood asthma. The researchers stated that trees can cut asthma risk by cleaning the air and encouraging kids to play outdoors, but on the contrary, the pollen they release could also contribute to asthma attacks.
Journal of Epidemiology and Community Health,
May 2008