While most people generally acknowledge the benefits of trees, here’s a three-decade research report about some amazing and documented benefits that trees in an urban setting have had on residents. Comments afterwards.
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People in Portland Planted Trees.
Decades Later, a Stunning Pattern Emerged
By RUSSELL MCLENDON
25 November 2022
Money may not grow from trees, but something even better does.
In a new study led by the US Department of Agriculture (USDA) Forest Service, researchers found that each tree planted in a community was associated with significant reductions in non-accidental and cardiovascular mortality among humans living nearby.
On top of that, the study’s authors conclude the yearly economic benefits of planting trees dramatically exceed the cost of maintaining them, by a factor of more than 1,000.
Previous studies have linked exposure to nature with an array of human health benefits. Access to nature is a major factor for mental health, and that doesn’t necessarily require the greenery to be primeval wilderness. Research shows urban forests and street trees can offer comparable benefits.
Several longitudinal studies have shown that exposure to more vegetation is associated with lower non-accidental mortality, the authors of the new study note, and some have also linked exposure to greenery with reduced cardiovascular and respiratory mortality.
Payam Dadvand, a researcher with the Barcelona Institute for Global Health (ISGlobal) and senior author of the new study, says …
“However, most studies use satellite
imaging to estimate the vegetation
index, which does not distinguish
different types of vegetation and
cannot be directly translated
into tangible interventions.”
For their study, Dadvand and his colleagues capitalized on a well-documented tree-planting campaign that unfolded in Portland, Oregon, between 1990 and 2019. During those three decades, the nonprofit group Friends of Trees planted 49,246 street trees in Portland.
Crucially, they kept records of where and when each tree was planted. The researchers were thus able to look at the number of trees planted in a particular neighborhood, or US Census tract – each home to about 4,000 people – during the previous five, 10, or 15 years.
Using data from the Oregon Health Authority, they then associated each census tract’s tree data with its mortality rate, due to cardiovascular, respiratory, or non-accidental causes.
The results reveal lower mortality rates
in neighborhoods with more trees planted,
… and the researchers report this negative association is significant for both cardiovascular and general non-accidental mortality, especially among males and anyone above the age of 65.
The association also grows stronger as trees grow taller, the study found. Trees planted in the prior one to five years were linked with a 15 percent drop in mortality, while trees planted in the prior 11 to 15 years were linked with a 30 percent drop.
Older, larger trees were thus associated with greater reductions in mortality. So, while planting new trees is great, this finding suggests preserving large trees that already exist is even more important for public health (as it also is for the well-being of wildlife).
While these links don’t exactly explain how trees benefit human health, the seemingly greater protection from larger trees would make sense, the researchers point out, since size boosts a tree’s ability to moderate known mortality factors like air pollution, temperature, and noise. Geoffrey H. Donovan, an economist from the USDA and first author of the study, says …
“We observed the effect both in
green and less green neighbor-
hoods, which suggests that
street-tree planting benefits both.”
If the value of a statistical adult human life is US$10.7 million, as some US federal agencies have determined, the researchers calculate planting one tree in each of Portland’s 140 census tracts would generate about $14.2 million annually in lives saved.
Maintaining those 140 trees would cost somewhere between $3,000 and $13,000 per year, the study’s authors estimate. Dadvand says …
“Our results provide an important
evidence base for tangible interven-
tions (e.g., planting trees) to increase
the longevity of urban residents.”
The study was published in Environment International.
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I’ve had previous blog reports related to trees, such as the increased oxygen levels they provide. And the cooling summer shade they provide. Yet, very few people actually participate in some way to get more trees planted. One of the most important things each of us can do – and this is an activity on which our global climate change leaders don’t seem to focus their broad-scale programs and massive funding pledges. Adding D’s comments …
“The world cannot underestimate the importance of trees. Trees hold water. Trees stop erosion. Trees clean the air. Trees makes for healthier humans. Trees are the lungs of the Earth. Whenever and wherever please plant trees.
“If you live in an urban environment, most communities have a tree-planting organization or city manager of trees. Work with them to continue or expand the tree-planting program.”
The only notion I’d add to D’s is their aesthetic contribution. Millions flock to regions to experience their spectacular fall colors. And we all rejoice at the magnificent array of color that flowering trees provide each Spring … and at the array of color provided by tree foliage all summer long.
The cost to plant a tree varies with the species and, even more, by the age of the tree you’re buying. A very young tree might cost very few dollars. And many states have tree nurseries that will give you a small tree for no cost at all. While a very young tree may need help when you first plant it, such as watering once in a while during the dry season, once they’re established, trees need very little maintenance. In short …
They serve us far more than we need to serve them.
In addition to fighting climate change, seeing the documented health benefits makes planting more and more trees even more important. In your specific environment, what can you do, personally?
