Urban Forest Health

Increases in impervious cover can dramatically increase the size and frequency of localized flooding. Typically, urban floods are short-lived, but extended flooding can stress trees, leading to leaf yellowing, defoliation, and crown dieback. If damage is severe, mortality can occur. In addition, flooding can lead to secondary attacks by insect pests and diseases. Some species are more tolerant of flooding than others. Flood-intolerant species include upland species such as bitternut and shagbark hickory, Kentucky coffeetree, and white oak.

Urban areas with one million or more people can be 2 to 13° F warmer than their surrounding rural areas due to the “urban heat island effect” from heat-absorbing infrastructure such as pavement and buildings as well as waste heat generated from manufacturing and automobiles. The urban heat island is often more pronounced in historically redlined areas with lower tree cover.