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Extensive 14C dating and botanical identification of charcoal fragments located in the organic surface soil layer and buried in the mineral podzolic solum were used to reconstruct the successional pathways of a balsam fir forest site. The studied forest site developed in a context of continuous fire disturbance over the last 9000 years with at least 26 fires occurring at a mean interval of 330 years. Tree vegetation of the site followed a four-step trajectory consisting of an early-Holocene spruce forest and a late-Holocene mixedwood balsam fir forest. Boreal-like spruce-birch and temperate-like white pine-birch forests dominated the site between 7900 and 5900 cal. B.P. and 5600 and 1275 cal. B.P., respectively. Because all forest types developed repeatedly after fire since early deglaciation, changes in forest composition, in particular the shift of white pine forest to balsam fir forest, and concurrent decline of birch (yellow birch and/or paper birch) and pine populations were most likely related to progressive cooler and wetter conditions from mid- to late Holocene. Fire disturbance on this part of the southern boreal biome has been a continuous, positive regenerative process over the Holocene, allowing the successional turnover of boreal and temperate trees under the influence of climatic change. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]