Dying trees in cities? Blame it on the pavement

Scale insects accumulate on a maple tree in Raleigh. Scale insects wreak havoc on maples in the midrange of studied cities in the Southeast. CREDIT; Adam Dale

A North Carolina State University study examining urbanization, scale-insect abundance and latitudinal warming on tree health in the Southeast captured a few surprising results.

The study showed more scale insects on red maple trees in the midrange of eight cities within a 10-degree latitudinal difference, from Newark, Delaware, to Gainesville, Florida.

Cities in that midrange, including Raleigh and Asheville, showed poorer tree health, due mostly to these high volumes of tree-destroying gloomy scale insects (Melanaspis tenebricosa), which appear as tiny bumps on tree branches and leaves.

"Impervious surfaces - basically concrete and pavement - near trees was a better predictor of scale-insect abundance than temperature, and thus a better predictor of poor tree health in the study area," said Michael Just, an NC State postdoctoral entomology researcher and corresponding author of a paper describing the research.

The finding was surprising, Just said, as the study's original hypothesis predicted higher scale-insect abundance at lower latitudes - the study's southernmost areas.

"What we've learned over the years in natural areas like forests didn't translate in this study, which means we may need to consider if other natural-system theories can be used in urban areas," Just said. "That's important if we want to have reliable predictive ecological models."

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The study appears in the journal Oikos.

Steven Frank, an NC State professor of entomology, and Lawrence Long, an NC State entomology graduate student, co-authored the paper along with Adam Dale from the University of Florida.

Source;EurekAlert