New Urban Forestry Study Shows Pittsburgh Losing Tree Cover

A new study finds Pittsburgh's tree canopy may have shrunk a bit in recent years, but not everyone's convinced about that conclusion. The Allegheny Front's Kate Malongowski looks into the U.S. Forest Service's research.

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MALONGOWSKI: Between 2004 and 2008, Pittsburgh had one of the smallest tree canopy losses out of the 20 cities monitored by the U.S. Forest Service. The city had a 0.3 percent net loss due to grass and ìimpervious coverî, which includes buildings, roads, and sidewalks.

Most cities saw increased development and and decreased tree cover.

U.S. Forest Service project leader and co-author David Nowak says they didnít have any expectations about the study, except with New Orleans and Detroit, where tree cover loss was expected.

High-resolution, aerial photographs were taken at 1,000 different points in the city in 2004. Four years later, another round of photos were taken at the same locations for interpreters to compare. Nowak says itís much more accurate than other image comparison methods.

NOWAK: With computers and digital images, youíre allowed to lay the points in the exact same location and space, letís say, using GPS or GIS systems. And so you can actually do paired analysis.

MALONGOWSKI: Pittsburgh was one of seventeen cities that experienced a tree cover loss. Two other cities had no net loss, and Syracuse, New York was the only city that saw tree canopy growth.

Tree Pittsburgh Director of Urban Forestry Matthew Erb says he wasnít surprised by the results, but says the percent error of the study is bigger than the percentage of trees Pittsburgh potentially lost.

ERB: Itís really a short time frame that they did the comparison... And I believe that 0.3 percent has a plus or minus of 0.6 percent attached to it. So we may have gained a little bit of canopy or we couldíve lost a little bit of canopy, but it was such a minuscule amount that itís really indiscernible.

MALONGOWSKI: Tree Pittsburgh recently conducted a citywide tree canopy study of their own, which showed that about 40 percent of Pittsburgh has tree cover as of 2010, although the cityís 2.5 million trees are especially concentrated in parks and on hillsides.

For the Allegheny Front, Iím Kate Malongowski.