Results/Conclusions The most frequently mentioned taxa were (% 1852-1903; % 1894-1949): spruce (Picea spp.) (20.8%; 19.6%), balsam fir (Abies balsamea) (19.7%; 22.6%), white cedar (Thuja occidentalis) (19.1%; 15.3%), white birch (Betula papyrifera) (12%; 13.9%), yellow birch (Betula alleghaniensis) (10.3%; 12.8%) and sugar maple (Acer saccharum) (6.0%; 6.6%). In comparison, univariate statistical tests indicate that current forest composition has considerably less cedar and spruce and more trembling aspen (Populus tremuloïdes), sugar maple, and fir. For both land survey periods, analyses showed that fir, cedar and sugar maple were dominant taxa, whereas spruce, yellow birch and white birch were more often seen as second, third, or fourth dominant taxa within stands. Through co-occurrence analyses we identified three major recurrent species assemblages for the period 1852-1903: (1) cedar-spruce-fir (2) fir-spruce-white birch-yellow birch (3) sugar maple-yellow birch. The sugar maple group was dominant on hill tops, whereas stands with cedar ranked first were more abundant in the low lands. Forest composition changes since preindustrial time provide guidelines for sustainable forest management in the Lower St-Lawrence region.