How planting trees can help address inequality and improve health

Trees can save lives.

Many thousands of deaths could have been prevented by growing more trees and greenery in urban areas of the US over the past 20 years, according to a new study from Boston University.

The researchers used NASA images to examine differences in tree cover around various US cities. The satellite photos show how the amount of green vegetation has changed between 2000, 2010 and 2019.

Researchers calculated that the greenery around 35 US cities had grown by an average of 2.86% between 2000 and 2010, and then by another 11.11% between 2010 and 2019.

The team then looked at mortality data for people aged 65 and over. They estimated that increasing vegetation by an extra 0.1 units of their measure would have led to a 34,000-38,000 reduction in the number of deaths from all causes in 2000, 2010, and 2019.

The shade that trees provide cools the air and the ground in urban areas, NASA notes.

Cities can be hotter than rural areas because buildings, streets and other manmade infrastructure absorbs heat and then releases it back into the urban surroundings.

Trees can help combat this phenomenon, which is known as the “urban heat island effect”.

By reducing how much heat city dwellers have to live with, trees and greenery can help prevent heat-related deaths, the Boston researchers noted in their study, which is published in the journal Frontiers in Public Health.

When people live near parks or green spaces, it can also mean they have more exercise and leisure time, which in turn can reduce the risk of chronic diseases like obesity, the researchers add.

A separate study cited by NASA found that lower-income neighbourhoods in urban areas in the US have an average of 15.2% less tree cover.

Of the 5,723 communities studied, 92% had 15.2% less tree cover in low-income areas. They were also 1.5°C hotter during the summer than higher-income neighbourhoods.

The study, completed by environmental organization Nature Conservancy and published in the journal PLOS ONE, found that there are 62 million fewer trees in low-income US neighbourhoods compared with high-income areas.

Investing $17.6 billion in tree planting and natural regeneration is needed to rebalance this inequality, Nature Conservancy says. This would benefit 42 million people in low-income neighbourhoods, it adds.

Trees can also protect people living in cities from pollution-related diseases, such as air and water pollution, says technology initiative the Centre for the Fourth Industrial Revolution (C4IR) India.

In a blog for the World Economic Forum on the benefits of urban trees, a C4IR specialist cites a study by the US Forest Service suggesting that covering 30% of all urban land with trees could prevent up to 400 premature deaths from air pollution every year.

Trees can protect people by capturing pollutants from the air and improving air quality, explains the Woodland Trust, a conservation charity in the United Kingdom.

Urban trees can also improve mental health. A study in Germany found that living within 100 metres of a tree can reduce the need for antidepressant drugs. And doctors in Scotland were authorized to prescribe nature to their patients in a pioneering initiative.

With urban greening initiatives being introduced in cities and urban areas around the world – including Paris, Madrid, Seoul and Singapore – NASA’s satellite images should become even more tree-filled over the next decade.