urrently, much public concern and research effort focuses on forest dieback in industrial countries. Factors associated with air pollution, such as acid rain, nitrous oxide, changes in the ozone level, and heavy metal deposition are often considered responsible for tree mortality on both sides of the Atlantic. While it is absolutely clear that air pollution from nearby smelters can cause stand-level tree mortality by toxification (Smith 1981), the acid-rain relationship with forest dieback (Ulrich 1981, 1982) is as yet highly conjectural (Cramer 1984, Johnson 1983, Kandler 1983, Nihlgard 1985, Rehfuess 1983, Schiitt and Cowling 1985). This article is not intended to diminish concern about air pollution's relationship to forest dieback. The objective instead is to point out that stand-level dieback in forests is by no means a new phenomenon and further that, in many cases, it is due to natural causes. While it is sometimes possible to distinguish between manmade and natural causes of standlevel dieback, it is usually difficult to determine the exact causes. Dieback is the death of groups of neighboring trees rather than isolated trees dying in an otherwise green forest matrix. Dieback stands are forest segments having significant loss of canopy. In these stands the majority of trees are either dead or display reduced vigor. The term dieback is