What To Look For - Dead trees do not necessarily indicate an unhealthy forest, but they may indicate a problem. While some individual species may be lost, the diversity of a mixed-species forest gives it resilience. The private owner of a small acreage may, however, be concerned over the death of any tree, and will be particularly concerned about the potential to lose additional trees. Consequently, monitoring should focus on the health of living trees and on the current tree species mix. Bark beetles, defoliators and other insects as well as root and stem decays and infectious cankers are generally symptoms of trees that are stressed by drought, competition, age, or physical damage.
Death often results from a complex of insects, disease and stress rather than a single factor.
The condition of the crown is the best early indicator an of unhealthy tree that can incur and spread additional damage and tree mortality from various agents. Normal color also can vary for the same species growing in different environments, so it is important to confirm what normal is for your forest stand by looking at nearby, similar environments with the same species. Abnormal reddening or browning of the crown in patches is often is often from insects or needle disease but widespread color changes usually indicate a problem with the cambium of the tree - the living, growing layer just under the bark. Cambium problems can be due to heat or drought alone or are often caused by bark beetles feeding and their associated fungi, or by fungi alone with systemic decay or girdling cankers. Late afternoon sunlight makes abnormal color more visible, and wearing polarized sunglasses, especially with a red tint, greatly enhances your ability to see a abnormal crown color many months before it is visible to the unaided eye.