Moisture is lost through the leaves of evergreen plants, desiccating the tissue. Heat and moisture stress can result from roots covered with pavement. The paving limits moisture penetration of the soil and causes heat buildup. Street trees are subjected to this problem plus confined root area and road salt buildup during winter months. A soil test for soluble salts can potentially identify salt problems.
Pollution is an increasing problem in some areas.
Acid rain and air pollutants can damage plant tissue. Although these are not as common as other stresses, they should not be overlooked. The most physical damage is from lawn mowers and string trimmers. They can destroy the cambial tissue on the trunks of trees and shrubs. Mulching around trees and shrubs can help eliminate this problem.