BRIT Collections
Megan O'Connell, PhD
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Ecosystem services: Living air purifiers
These Live Oaks on St. Charles Avenue in New Orleans help keep the city's air fresh and breathable. The leaves absorb airborne particles like carbon monoxide, sulfur dioxide and other greenhouse gases that are estimated to cause 3.7 million premature deaths globally per year.
Ecosystem services: Creating an atmosphere
Trees play a critical role in making our planet livable by producing oxygen through photosynthesis, but trees are not actually responsible for the most oxygen production on earth. While trees produce something like 28% of the earth's oxygen, 70% is produced by marine plants.
Ecosystem services: Keeping it cool
Urban trees also significantly help reduce Urban Heat Island effect, the recurring phenomenon of temperatures being higher in cities than rural areas due to the higher proportion of surfaces, like buildings and pavements, that absorb and retain heat from the sun.
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Ecosystem services: Your neighborhood sponge
Urban trees are important to flood mitigation. These trees along Buffalo Bayou in Houston absorb runoff from streets and buildings that would end up in the bayou. In part, Houston's flood history is due to the removal of trees from the wetland habitat where the city was built.
Ecosystem services: Tree-houses
Most importantly, urban trees provide critical habitat for animals that live in and travel through our cities. Which birds, small mammals, and beneficial insects can live in cities largely depends on the presence of structurally complex habitats, complexity often provided by trees.
Cities before trees?
In medieval Europe, publicly accessible parks and tree-lined roads were not common. Medieval European cities were walled and nearby forested areas were only accessed by nobility and royalty. As cities grew and greenspace was lost to development, they became increasingly polluted.
Growing with trees
On the other hand, the Aztec civilization prioritized greenspaces and regarded trees as sacred. Intricate forest gardens were built around their temples and trees were felled with respect, dignity, and ceremony. Today trees remain a big presence in cities like Mexico City.
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Getting back to the woods
The environmental revolution in 1960s America, brought sustainability to the forefront, setting the stage for cities to be designed with ecosystem services in mind. Today urban planners often strategically prioritize green and natural spaces to benefit urban dwellers.
Urban tree assemblages in the Southern U.S.
What species of trees can grow in cities largely depends on their resilience to disturbance, their growth habits, local plant communities, competition, and microclimate.
Austin, TX
Nashville, TN
Gainesville, FL
New Orleans, LA
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Live fast, die young
Researchers at Boston University found that trees living in cities grew faster, but died younger than their rural counterparts. More CO2/nitrogen and less competition for sunlight/water increased growth, but the hardships of living in disturbed habitats still increased mortality.
Healing with trees
Numerous studies have shown the mental and physical health benefits of tree-shaded natural spaces for urban dwellers. One study even found that hospital patients with tree-filled views outside their windows healed faster than patients without views.
Take a tree break
For city dwellers, time spent among trees might be a necessary component of a healthy lifestyle: studies have shown that "forest bathing" (spending time immersed in forests) can decrease cortisol and stress levels markedly compared to their levels in urban environments.
References:
3.7 million premature deaths due to air pollution: WHO
Reducing the urban heat island effect: Environmental Protection Agency
Trees absorb rain run-off: Environmental Protection Agency
Trees living in cities grow faster, but die younger: Science News Explores
Seeing trees may help people heal faster: Science
Forest bathing decreases cortisol levels: National Library of Medicine
Interested in Natural history?
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