In the early 1980s, a sharp increase in dieback of sugar maple (Acer saccharum Marsh.) was reported across large areas of the northeastern American continent. Despite numerous studies, there are conflicting interpretations as to the causes of dieback that can be linked to uncertainties as to when the occurrence of the visual symptoms appeared. Three different approaches were used to determine the onset period of the visual symptoms of dieback in Appalachian sugar maple stands: (1) dendrochronological analysis; (2) retrieval of information in official documents that reported dieback symptoms; and (3) development of a questionnaire sent to private forest land owners. Dieback severity was evaluated annually in 104 Appalachian sugar maple stands in southwestern Quebec. Results indicated that the pattern of dieback progression did not vary significantly among the five different types of sugar maple stand that were examined. The three investigative approaches led to the conclusion that the onset of the visual symptoms occurred between 1974 and 1978.Key words: Acer saccharum Marsh., dieback, sugar maple, symptoms, progression Au début des années 1980, une augmentation subite du dépérissement de l'érable à sucre (Acer saccharum Marsh.) a été reportée dans de nombreuses régions du nord est de l'Amérique du nord. En dépit de nombreuses études, il y a des interprétations conflictuelles sur les causes du dépérissement qui peuvent être associées aux incertitudes de l'apparition des symptômes visuels. Trois approches différentes ont été utilisées pour déterminer la période d'apparition des symptômes visuels du dépérissement des érablières des Appalaches: (1) l'analyse dendrochronologique, (2) la recherche de documents officiels traitant des symptômes de dépérissement, et (3) l'envoi d'un questionnaire à des propriétaires d'érablières. Le dépérissement a été évalué sur une base annuelle dans 104 érablières appalachiennes du sud-ouest du Québec. Les résultats du suivi annuel ont indiqué que le taux de progression du dépérissement n'a pas différé significativement entre les cinq différents types d'érablières étudiées. Les trois approches ont permis de conclure que les symptômes visuels de dépérissement sont apparus entre 1974 et 1978.

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Claytoniacaroliniana (Michx.) is a perennial early-flowering species regularly occurring in northeastern American maple forests and frequently possessing accessory (B) chromosomes. A cytological study of Claytonia populations growing in eight maple stands diversely affected by dieback has shown important variations in their B chromosome levels. The severity of dieback was negatively correlated with the presence of the B chromosomes, the observed data being adequately adjusted (R = 0.957 and 0.947) to the values estimated from the explicative variables. Different hypotheses are considered to explain the phenomenon: coincidence with a preexisting situation related to marginal habitats; ecological changes in dieback-damaged zones; or the present influence of stresses affecting both B chromosomes of Claytonia and maple trees by divergent or anologous processes.