No Quick Fix for Replacing Mature Trees

As the East Coast tallies the cost of lost trees and looks to replant after Sandy, there’s no quick fix for losing the benefits that mature trees provide a city. Not all street trees are created equal, and mature trees are infinitely more valuable than young ones. It takes years for newly planted trees to produce the kinds of economic and environmental benefits of older trees. What’s lost when older trees go down?

Last year’s Tropical Storm Irene took down about 3,400 trees in New York City and another 10,000 went down from the winds of Superstorm Sandy, but many of them, especially in Central Park, were old and as large as six feet in diameter.

“The bigger the tree, the more carbon it captures, the more particulate matter it filters, the more storm water it captures,” says Bram Gunther with New York City’s Parks and Recreation Department, “so it’s a huge number in terms of environmental benefits and what it does for a community.”

Twenty-four hours after the storm, the department sent people walking, riding and bicycling all 33,000 blocks of New York City with handheld computers, reviewing damage and putting in work orders.

A study from the U.S. Department of Agriculture shows that the city’s more than 5 million trees remove 42,000 tons of carbon and about 2,000 tons of air pollution per year. They are valued a $5.2 billion.

While the city is already ahead of schedule in its commitment to plant 1 million trees by 2017, because newly planted trees are small, it will be years before the city can replace its fading urban forest. Read the full NPR article, Thousands Of Trees Gone, Ripped Out By Sandy.

A recent American City’s article laid out the research on the benefits of mature tree canopies in an urban environment vs. younger trees. This includes reducing air pollution, creating shade and mitigating the impact of urban heat islands, and managing storm water runoff and flooding.

Also, helping reduce crime. The article cites a study of tree cover in Baltimore that conservatively concluded that even a 10% increase in tree canopy was associated with a nearly 12% decrease in crime. This magnitude was 40% greater on public land.

A USDA Forest Service study examining how trees affect local and regional air quality by altering the atmosphere of urban environments found that large, healthy trees greater than 77 centimeters (30 inches) in diameter remove 70 times more air pollution annually than small, healthy trees less than eight centimeters (three inches) in diameter.

As with other benefits of trees, size matters. According to research conducted in Chicago, taller trees offer increased shading during the summer, when the sun is high, and increased solar access below the canopy in winter, when the sun in low. In sum, energy savings increase with tree age and size.

Planting a million trees is great. But planting even 500,000 in conditions that allow them to survive, thrive and mature is exponentially greater. Read the full American City’s  article, “Urban Trees: Let’s Grow Old Together,” with links to research and charts.
ACTrees, Treebune News, Nov. 26, 2012

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