PORTLAND, Ore. — Could making neighborhoods greener be the secret to longer, healthier lives for residents? One long-term project that saw nearly 50,000 trees planted over three decades in Portland shows a significant correlation between overall health and longevity among the surrounding population.
Between 1990 and 2019, an Oregon-based campaign called Friends of Trees added 49,246 trees to Portland’s streets and kept record of where and when they did so. Although there is existing evidence for an association between nature and reduced risk of death, prior research hasn’t been so reliable. “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,” says Payam Dadvand, ISGlobal researcher and senior author of the study, in a media release.
The team looked at the number of trees planted in a specific area with ~4,000 people living in it over the last 5-15 years. Using data from the Oregon Health Authority, they compared the data with mortality due to cardiovascular, respiratory or non-accidental causes of death in that area.
Findings show that neighborhoods with more planted trees also had lower mortality rates, with statistically significant findings for cardiovascular and non-accidental causes of death, especially for men and those 65 or older. The relationship was stronger with trees planted 11-15 years beforehand, demonstrating double the effect in reducing death rates compared to those planted within 1-5 years.
This means that planting trees is important, but preserving and taking care of existing trees may be especially crucial.
Though this study shows a relationship between planting trees and reduced death rates, it doesn’t delve into the direct ways that trees improve health outcomes overall. The finding that suggests that older trees have a great impact on mortality reduction is particularly of interest, and makes sense with what we know so far. Mature trees have a greater capacity to absorb air pollution and regulate temperatures, which both play a role in human health.
The team additionally considered confounding factors that could skew results such as income, education and racial implications with neighborhood design and location, but they still found similar results. “We observed the effect both in green and less green neighborhoods, which suggests that street tree planting benefits both,” says Geoffrey H. Donovan, from the USDA Forest Service and first author of the study.
Researchers conclude that the benefits of tree planting outweigh the negatives, ultimately generating close to $14.2 million per year in lives saved, while only costing $3,000-$13,000 to plant and keep up with one urban tree in each area. That’s an investment any city official should consider.
The findings are published in the journal Environment International.