Decline of the maple-dominated forest in southern Quebec: impact of natural stresses and forest management

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Abstract
Forest decline was rather ubiquitous throughout the industrialized world in the 1980s. Maple decline was particularly severe in southern Quebec and large research programmes were put together to determine cause–effect relationships, as well as understand the mechanisms involved in forest decline. The present review of the causes of the decline of the maple-dominated forest in southern Quebec is heuristic in nature and not exhaustive in that we do not address the role of atmospheric pollution, a likely predisposing factor that has received wide scientific coverage over the last 15 years. Rather, we discuss the potential role of natural stresses and forest management practices on forest decline. The process of natural selection and forest succession and the trend toward monocultures of sugar maple in sugar bushes are emphasized as important predisposing factors of forest decline. Climatic stresses and insect defoliations appear to have been major triggering factors, whereas insects and pathogens were likely contributing (killing) factors. Changes in forest management practices that would favour tree species diversity and decrease the likelihood of physical injury, tree disease, and insect epidemics are suggested to increase tree vigour and, therefore, decrease the susceptibility of the maple forest to decline. The evolution in time and space of the last forest decline in southern Quebec, as well as its repercussions on forest monitoring and the regional economy are also reviewed.Key words: biodiversity, climatic extremes, forest decline, forest management, insect epidemics, maple.