Allegheny County tree canopy declining

The tree canopy in Allegheny County is in decline, a trend that hurts the region’s natural stormwater flooding and landslide management capabilities, according to Matt Erb, director of urban forestry at Tree Pittsburgh.

Mr. Erb said the environmental nonprofit’s tree canopy survey report, released Tuesday, found that the county experienced a canopy loss of 10,148 acres from 2010 through 2015. And not one of the county’s 130 municipalities showed an increase in canopy cover.

“We are seeing drastic changes in the number of trees in Allegheny County,” Mr. Erb said. “It’s very alarming. There were some causes we could predict, such as pests, but the man-made losses were over whelming in comparison.”

He said canopy cover in the county declined from 265,257 acres, or 56 percent, in 2010 to 255,109 acres, or 54 percent, in 2015.

“It’s a significant change,” Mr. Erb said. “As the trend continues, we are losing parts of our natural system of stormwater management, which could lead to more flooding and landslides, because trees help hold back stormwater and help stabilize our hillsides.”

Although forest pests like the emerald ash borer and oak wilt had an impact on canopy loss, the survey found a bigger role was played by housing, road, utility and rail expansion, and gas drilling and pipeline development, especially in the Forward and Elizabeth areas in the southern part of the county.

Only 3 to 5 percent of the lost canopy acreage was attributable