Trees Bring Benefits Even Before Birth

WASHINGTON — It is a well-known fact that spending time among the trees boosts mental and physical health. Trees filter out carbon dioxide and release oxygen and help reduce our stress levels. Trees may even provide benefits before birth.

The Association Between Tree Planting and Birth Outcomes

Researchers at Drexel University wanted to investigate the relationship between newly planted trees and the birth weight of newborns. Their study was published in the May 2025 issue of the Science of the Total Environment Journal.

Dataset

Friends of Trees, an environmental nonprofit, planted over 50,000 trees between 1990 and 2020. Friends of Trees operates in two ways: they provide trees to any resident who requests them, often these requests come from people in higher-income neighborhoods. They also intentionally plant trees in disadvantaged, lower-income neighborhoods that are less green. 

For this study, researchers do not know exactly how many trees were planted according to which protocol. However, Friends of Trees focused on large-scale planting in disadvantaged neighborhoods — 73% of the new trees were planted in neighborhoods that were either low-income, low-canopy (meaning short, sparse trees), or had an above-average population of people of color.

Participants and Trees

For this study, researchers narrowed down the years from 2015 to 2020. They used birth data in Oregon to collect 36,654 single live births that survived at least one year after birth born between Jan. 1, 2015, and Dec. 31, 2020, in Portland, Oregon. Most mothers were white and completed a college education.

Then, they noted how many new trees were planted within 100 meters of the addresses for 10 years before the births. They also noted the tree and canopy levels before the new ones were planted.

Researchers controlled for variables that often influence birth weight, including the mother’s race, BMI, education, and previous pregnancies.

Results

The researchers found a correlation between the number of trees planted in an area, higher birth weights, and lower risk of being underweight or born prematurely. Unlike previous studies that compared greenspace and birthweight, this one controlled for previous trees to isolate the impact of new trees.

Here are the key findings. Each tree planted within 100 meters of a mother’s home within 10 years before birth led to:

• A 2.3 gram increase in birth weight.
• A 4.3% lower risk of small-for-gestational-age birth.
• A 4.9% lower risk of a preterm birth.

The benefits level off at 10 trees — living within 100 meters of 10 trees led to a 50-gram increase in birth weight.

Researchers state that newly-planted and established trees can improve birth outcomes, making a case to protect existing trees and plant new ones as a public health measure.

One Exception

Despite the positive correlations, researchers also noticed that birth weights in Portland decreased over the five years. However, this may have been due to wildfire smoke from 2020 and increasing air temperatures. 

Potential Mechanisms

How does living near more trees boost an infant’s health? The first potential mechanism the researchers identify is stress. Higher stress levels can increase the chance of a premature birth.

Researchers hypothesize that living near older trees, rather than the newly planted trees, may play a greater role in stress reduction. Older trees can cause a “soft fascination” when observing and being with them. Living in overly built and developed areas can be “psychologically draining.”

Existing trees with larger canopies are also better at filtering air pollution and reducing road noise, which can reduce stress and improve physical health, potentially improving the infant’s future health.

Researchers also cite earlier studies on trees and birth outcomes, which add that living around trees increases physical activity and opportunities for social connection, two more mechanisms that can improve the health of both mother and infant.

Save the Trees

Preserving existing trees and planting new ones improves air quality, provides shelter and nutrients for other plants and animals, and yields physical and mental health benefits for humans. 

Future generations benefit, too. The new study suggests that mothers who live within 100 meters of trees may give birth to infants with high birth weights and less of a risk of preterm birth. However, researchers note that a more specific, controlled study should be done on the topic for future implications.

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