Forest degradation is a process in which the biological wealth of a forest area is permanently diminished by some factor or by a combination of factors. "This does not involve a reduction of the forest area, but rather a quality decrease in its condition." The forest is still there, but with fewer trees, or less species of trees, plants or animals, or some of them affected by plagues.[1] This degradation makes the forest less valuable and may lead to deforestation. Forest degradation is a type of the more general issue of land degradation. Deforestation and forest degradation continue to take place at alarming rates, which contributes significantly to the ongoing loss of biodiversity.[2]
Deforestation is much worse than forest degradation, but it is clear and visible. On the contrary, forest degradation may start and go on without showing clear effects. It is difficult to measure and even the very term is controversial. In a paper[3] submitted to the XII World Forestry Congress, 2003, Jean-Paul Lanly states: "The situation is even less satisfactory regarding forest degradation due in particular to the imprecision and multiple, and often subjective, interpretations of the term". In 2009 Lund[4] identified more than 50 definitions of forest degradation.
Previously to this August 2017 editing, the Wikipedia page Forest degradation was redirected to Secondary forest, a forest which has re-grown after a timber harvest. This is a confusion: a secondary forest may be perfectly healthy, and a primary forest may be suffering degradation.
The term "permanently" also poses some difficulties: a forest affected by a mild seasonal drought may experience a loss of its biological wealth, but if it is seasonally reversed, then it is not considered degradation. On the contrary, a severe prolonged drought may seriously degrade a forest and make human intervention advisable to limit damages.
According to Lanly, there are three difficulties:
For mapping forest degradation in Bolivia, Müller et al. consider areas where only between 30% and 70% of the original forest cover remains. If less than 30% remains, the area is considered as deforested, and if more than 70% remains, the forest is considered intact.
Davidar et al.[5] also think that "Loss of dense and moderately dense forest cover is suggestive of forest degradation", but for the moment no parameter exists "that indicates at what speed forests become degraded and how long it will take for the ecosystem to degrade beyond the point of recovery."
The Dominican Center for Agricultural and Forest Development[6] lists the following causes of forest degradation:
Davidar et al.[5] add another:
Earth Eclipse,[7] a platform of environment research articles, adds the following causes:
Finally as an additional cause:
Generally, any measure to prevent deforestation will also reduce forest degradation. Specifically for degradation, Greenpeace[8] proposes:
Curbing emissions of sulfur dioxide (to combat acid rain) would also reduce forest degradation for this cause. If a coal-fired power plant uses low-quality coal (with a high sulfur contents), this may be alleviated by flue-gas desulfurization.