Study could help cities improve tree planting

More than half the world's people and 80 percent of the U.S. population live in urban areas. Trees benefit these residents by filtering the air, reducing temperatures and beautifying landscapes. According to a new study led by Adam Dale, a UF/IFAS assistant professor of entomology, these benefits are reduced when trees are planted in unsuitable urban landscapes. However, guidelines can be developed to lead urban tree- planting decisions in a more sustainable direction.

Dale spearheaded the study while at North Carolina State University in Raleigh, North Carolina. Previous research by Dale and his colleagues found that impervious surfaces raise temperatures, which increase pest abundance and tree stress, ultimately reducing tree health. He and his team examined the so-called "gloomy scale insect," which feeds on tree sap and appears as small bumps on the bark of trees.

In the new study, Dale and his team developed guidelines that landscape professionals can use to make more informed urban tree-planting decisions. Although the new study was done in North Carolina and limited to red maple trees, Dale said the findings may be applicable to trees throughout the Southeast.

Through their research, scientists developed thresholds of impervious surface around planting sites. In other words, they defined points at which the amount of pavement around a tree reduces its condition. Using these established levels of impervious surface, landscape architects and other landscape professionals can plant trees in a way that reduces pest damage and economic loss.

"This study demonstrates the effects of the most common features of urban landscapes -- roads, parking lots, and buildings -- on insect pests and trees, and proposes guidelines for mitigating them," Dale said.

The study also proposes a method that can be used at a planting site. It's called the "Pace to Plant" technique. By simply walking 100 steps around a site, landscape professionals can estimate the amount of surrounding impervious surface and use the developed thresholds to guide their tree-planting decisions.

"The hope is that more informed planting will minimize pest infestations and maximize the vigor and performance of street trees," researchers said in the study, published in this month's issue of the journal Arboriculture and Urban Forestry. "The decision-making tools presented here will help planners and urban forest managers get the right tree in the right place to reduce future maintenance costs and increase tree survival and services."