A study by the U.S. Forest Service shows a decline in urban tree cover with the nation’s cities losing about four million trees per year. Terry Ettinger reports.

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David Nowak, project leader of the U.S. Forest Service said, “The finding was that of the 20 cities we analyzed 17 had a significant reduction in canopy cover, two showed no change and one showed an increase. The one that happened to show an increase was Syracuse, NY.”

New York City, the only other New York urban area included in the study showed a 1.25 percent decrease in tree cover.

Nowak said, “The purpose of the study is to try to understand what is going on in cities. Is the tree count going up or down? If it’s on a downward trend and we understand it’s on a downward trend then the question now is what do cities want to do about it.”

Do they want to they want to enhance planting programs, increase maintenance programs to reduce mortality and enhance natural regeneration? It’s up to them locally because each city is in a different context, Phoenix is different from New York City in terms of environmental conditions - so the questions might be different or the actions might be different.

Tree cover offers a lot of benefits removing air pollutants, shade streets and buildings to reduce air temperatures, provide wildlife habitat, among others.

Nowak said, “There’s always a downside. The downside related to vegetation would be associated costs, such as raking leaves, pruning and maintaining the forest. They’re not free in many ways. Nature is (free) in terms of the growth but if you want to design it a certain way and we choose to override (nature), there’s a cost to it. There’s also an ecological cost, in terms of pollen, let’s say or things called volatile organic compounds that are given off by plants that contribute to pollution formation.”

So while more trees in New York City might help improve air quality, more vegetation in Phoenix could recreate the very problems some people moved there to avoid.