The Vicious Cycle of Stress

摘要

Urban and forest trees have to deal with stress from drought, pests, and increasingly high temperatures. Of course, trees have faced these challenges for millions of years, so forest trees are generally resilient to occasional bouts of stress. Urban trees have a tougher time. Urban trees may be subject to drought, pests, and high temperatures all at the same time and frequently, or even continuously, rather than occasionally. Understanding how high temperatures and drought create a vicious cycle of stress that increases tree pests and reduces tree health has been a primary goal of research in my lab. The more we learn about these stressors, the more we can plant and manage trees to avoid them.Urban nees often have more arthropod pests and damage than rural trees. In cities it is common to find trees covered in galls or scale insects or caterpillars, but take a walk in the woods and these instances are rare. Our hypothesis has been that impervious surfaces, which increase temperatures and reduce soil moisture, are primary causes of scale insect infestations. We have studied red maples (Acer rubrum) and willow oaks (Quercus phellos) for several years to understand the relative influences of heat and drought on pest susceptibility and tree growth. We study these trees because they are two of the most commonly planted urban trees and because they are frequendy infested with scale insects.