Forests are environmentally and economically important in North America, and forest health is monitored to enable policy decisions to be made on factors affecting forest health. Forests are subject to several stresses, natural and human, and these stresses have various effects. Data for monitoring systems are used to separate the causes of observed damage to forests.
North American forests are divided into seven biomes and forest health is described for each. Mortality in North American forests is generally within the normal range for forests and is mostly caused by natural thinning. A variety of known insects, diseases, and abiotic factors killed trees and damaged tree crowns. Some forests are stressed by land use practices. Incidence of pollution-like symptoms occurred in several biomes and on many species. Where these symptoms were observed, trees are being studied to determine the cause and extent of damage.