Forest health is one of the more difficult concepts to define. Forest health in a general sense describes the resilience of the forest in response to damaging agents such as insects, diseases, pollution, storms, and fire.
Trees are subject to countless insects and diseases. Under most circumstances most do not cause significant mortality or damage. There are a few exceptions. Southern pine beetle and at times ips beetles can cause mortality and growth loss in pine plantations. Management to control outbreaks and maintain vigor are usually sufficient to minimize losses. Fusiforme rust is a disease that can kills pine trees or weaken the trunk. Fusiforme rust is often treated by removing infected stems during thinnings. Genetic selection to improve resistance in planted seedlings has also reduced its impact.
Movement of introduced insects and diseases are a significant concern for forest health.
Recently scientist have noticed increased mortality and reduced growth species in particular conditions. These are referred to as declines since the causes are not obvious. So far they have identified declines in loblolly and longleaf pine and oak.