Money doesn’t grow on trees, but there is something very good about it.
In a new study led by the US Department of Agriculture (USDA) Forest Service, researchers found that each tree planted in the area was associated with a significant reduction in non-accidental and cardiovascular deaths among nearby residents.
On top of that, the authors of the study confirm that the annual economic benefit of planting trees exceeds the cost of maintaining them, by a factor of more than 1,000.
Previous research has linked environmental exposure to a variety of human health benefits. Access to nature is an important factor in mental health, and this does not mean that green leaves should be the primary desert. Research shows that urban forests and street trees can provide similar benefits.
Many long-term studies have shown that exposure to more plants is associated with lower rates of accidental death, the authors of the new study, and others have also linked exposure to greenery with lower cardiovascular and respiratory mortality.
“However, most studies use satellite imagery to calculate the amount of vegetation, which does not distinguish between different types of vegetation and cannot be directly translated into visual data,” says Payam Dadvand, researcher at the Barcelona Institute for Global Health (ISGlobal) and senior officials. author of the new study.
For their research, Dadvand and his colleagues used a well-documented tree planting project that took place in Portland, Oregon, between 1990 and 2019. In those three decades, the non-profit group Friends of Trees planted 49,246 street trees in Portland.
Interestingly, he recorded the place and time each tree was planted. The researchers were able to look at the number of trees planted in a particular area, or US Census tract – each home for about 4,000 people – in the past five, 10, or 15 years.
Using data from the Oregon Health Authority, tThey then reconciled the rates for each census with the number of deaths from cardiac, respiratory, or non-accidental causes.
The results show less the number of people dying in areas with more planted trees, and researchers say that this negative relationship is important for heart and accidental death, especially among men and everyone over 65 years old.
The relationship also grows stronger as prices grow, the study found. Trees planted one to five years earlier were associated with a 15 percent reduction in mortality, while trees planted 11 to 15 years earlier were associated with a 30 percent reduction.
Older, larger trees were thus associated with a greater reduction in mortality. So, while planting new trees is good, these findings show that maintaining existing trees is more important for human health (as it is for wildlife health).
Even these links do not exactly the researchers explain how trees benefit human health, protection from large trees can be understood, because the growth makes the tree able to reduce things known to die such as air pollution, heat, and noise.
“We saw results in both green and green areas, indicating that street tree planting benefits both,” said Geoffrey H. Donovan, a USDA economist and first author of the study.
If the cost of an adult’s life is US $ 10.7 million, as some US organizations have determined, the researchers calculate that planting one tree in the 140 census tracts of Portland would result in approximately $ 14.2 million per year in saved lives.
Maintaining those 140 trees would cost between $3,000 and $13,000 a year, the study’s authors estimate.
“Our results provide important evidence for interventions (such as tree planting) to increase the longevity of people living in cities,” says Dadvand.
This study was published in Environment International.