Urban Heat Islands Are Helping Kill Trees

The urban heat island can be both a boon and a curse for plants. On one hand, the toasty conditions asphalt- and concrete-clad cities create has been shown to make trees grow eight times faster. On the other hand, plant-destroying pests also love warmth, and their numbers in some urban areas are on the rise.

The spread of one unpleasant insect, the aptly named gloomy scale insect, is detailed in two new studies from Adam Dale and others at North Carolina State University. Dale's research poses questions about what will happen to plants as cities continue their fierce expansion. (Washington, D.C., to give one example, packed on around 11 square kilometers of impervious surface area every year of the past several decades.) It also raises the issue of what the warming climate is doing to the urban canopy.