The sugar maple (Acer saccharum Marsh.) forest is a widespread temperate forest prevailing south of 48°N in Quebec. Windthrows are the principal disturbance maintaining the old-growth status of the forest supposedly since its postglacial establishment. Nonetheless, the presence of wood charcoal buried in several sugar maple forest soils attests to the occurrence of fire during the Holocene. In this study, we aimed to elucidate the long-term fire dynamics and species composition of three sites (Témiscamingue, Saguenay, and Gaspé peninsula) currently dominated by sugar maple situated at its northern range limit. The botanical identification and 14 C dating of charcoal fragments extracted from the soil surface and the mineral soil indicate that the development of the sugar maple sites was influenced by recurrent fires at least over the last 1000 to 3500 years. Two of the studied sugar maple stands are of recent origin, with the Témiscamingue forest being established after the most recent fire in the late 18th to early 19th centuries. Our data highlight the resilience of sugar maple forests in a disturbance regime dominated by frequent fires and suggest that the northernmost sugar maple forests are young ecosystems at the Holocene timescale.Résumé : Les érablières dominées par l'érable à sucre (Acer saccharum Marsh.) sont des forêts tempérées considérées comme une formation mature dominante du Québec méridional. Ces forêts se seraient maintenues en état de renouvellement perpétuel par la chablisation du couvert forestier depuis leur établissement à l'Holocène. La présence de charbons de bois dans le sol des érablières témoigne néanmoins de l'occurrence in situ du feu dans le passé. Nous avons évalué l'importance prise par les feux et les changements floristiques survenus dans trois stations (Témiscamingue, Saguenay et Gaspésie) depuis la déglaciation. L'identification botanique et la datation au 14 C de charbons montrent que les trois stations ont été sous l'influence d'un régime de feux fréquents depuis les derniers 1000 à 3500 ans. Au moins deux des trois érablières sont apparues récemment, dont l'érablière du Témiscamingue qui s'est formée à la suite d'un feu survenu à la charnière des 18 e et 19 e siècles. Nos données mettent en évidence la résilience des forêts d'érable à sucre évoluant sous un régime de feux fréquents et montrent que les érablières du Québec situées à leur limite d'aire nordique constituent de jeunes écosystèmes à l'échelle de l'Holocène.Mots-clés : Holocène, histoire des feux, forêt à feuillage décidu, limite de répartition nordique, érable à sucre, forêt boréale.

In the St-Lawrence lowlands, sugar maple (Acer saccharum Marsh.) is considered the dominant species of old-growth deciduous forests, whereas red maple (Acer rubrum L.) tends to dominate sites recently disturbed by logging and agricultural practices. Considering that the long-term influence of fire is not documented for such stands, we reconstructed the postglacial tree composition (as deduced from charcoal species) and fire history of a sugar maple stand (Ste-Françoise area) and a red maple stand (Villeroy area) located southwest of Québec City, Canada. The sites are 10 km apart and show contrasting soil and landform features. Using botanical identification and 14C dating of soil macrocharcoal, we found that fire struck both maple stands 14–20 times since deglaciation. Most fires occurred in the early Holocene and during the last 2000 years, with the mid Holocene being a period with low fire frequency or no fires. During the last 1600 years, the Villeroy stand shifted from a Tsuga canadensis (L.) Carrière – conifer forest to a mixed forest and, most recently, to a red maple stand as fire became more frequent, possibly due to human activities of the last 400 years. This study confirms the influence of fire on the development of maple forests. Fire should be considered as an important disturbance factor in the dynamics of temperate deciduous and mixed forests.

Botany D r a f t 2 Abstract: The long-standing hypothesis that sugar maple (Acer saccharum) communities are maintained at equilibrium by present climate and small-scale disturbances is questioned as empirical evidence is accumulating about the ability of the species to withstand several stand-scale disturbances. The fire history of a sugar maple site at the northeastern range limit of the species (Gaspé Peninsula, eastern Canada) was documented to test the hypothesis that this forest type is resilient to fire disturbance. The fire history was reconstructed using radiocarbon-dated soil macrocharcoals. Two main fire periods were recorded during the Holocene. The oldest period occurred between 9055 and 8265 cal. years BP, and was characterized by the presence of conifers, including spruce. After 6900 years of fire-free activities, the second period covered the last 1335 years, and was characterized by the presence of sugar maple in the charcoal assemblage. The dominance of sugar maple after more than 1000 years of recurrent fires underlines the species resilience to frequent site disturbances. The soil of the forest stand was heavily disturbed by earthworms. However, the dense seedling and sapling bank of sugar maple suggests that earthworms do not affect negatively the regeneration and survival of the species.