Impact of logging on the structure of preindustrial forests in south-eastern Canada

Background/Question/Methods

More than 100 years of timber production in the Lower St-Lawrence region of eastern Canada have modified the structure and composition of regional forests. During the 20^th century, old uneven-aged and conifer-dominated forest communities were progressively replaced by young shade-intolerant stands. However, a precise evaluation of forest structural changes are still lacking, due to the almost complete disappearance of natural forest stands that could serve as a reference state. The objective of this study is to reconstruct the structure of a preindustrial forest landscape from a detailed survey conducted by the Price Brothers Company between 1928 and 1931. Tree stems were then tallied by diameter and species in several thousand 0.1 ha plots systematically distributed. We compared these data with recent governmental inventories conducted between 1986 and 2006. The comparison between the two periods was done for an area of 90 000 ha subdivided into three forest types, deciduous (12%), mixed (51%) and coniferous (37%), based on recent aerial photographs interpretation (2001-2008).

Results/Conclusions

Between 1930 and 2006 over the entire study area, the total basal area (all species combined) decreased by 55% while the total stem density increased by 197%. On a species basis, results show a general decrease of the basal area of balsam fir, yellow birch and white birch. Balsam fir and yellow birch decreased by 25% and 15% in deciduous stands, while white birch decreased by 18% in coniferous stands. Maple and poplar species showed the reverse trend. Maple basal area significantly increased in deciduous stands by 44%, while poplar showed a slight general increase of its basal area (< 5%). Considering stem density, yellow and white birches decreased in the three stand types, except for a slight increase of white birch in deciduous stands. Balsam fir stem density also decreased by 37%, 13% and 16% in deciduous, mixed and coniferous stands, respectively. Conversely, stem density increased by 48% for maple in deciduous stands and slightly increased for poplar (< 5%) in the three stand types. We conclude that although the forest landscape is composed of the same species throughout the twentieth century, the forest structure has been severely altered in terms of basal area and stem density.