Department of biology, chemistry and geography
Guillaume de Lafontaine (Regular member)
IntroductionPlant species distribution is controlled by global climate cycles. Finer fluctuations control species distribution within their climate envelope. Knowledge of interspecies and species-climate interactions is possible through retrospective study of historic forest composition. Such studies require proxies to view the past, often fossils found in sediments or inorganic soil. Some proxies, such as lacustrine pollen and charcoal, are carried from afar by wind. This spatial distribution reduces the minimum resolution for specie’s location. To correct this problem, the use of other proxies, such as ancient lake sediment DNA fragments, whose nature only allows them to be deposited directly into the lake’s catchment, is required. In situ proxies, such as large charcoal from terrestrial inorganic soil, allow maximum spatial resolution but require more sampling effort. No single proxy offers a complete history and a combination of several is required to reconstruct the forest’s actual past. ObjectivesThe main goal of this thesis is to study the past dynamics of the northern limit of maple stands and the larger mixed boreal forest. First, the analysis of charcoal extracted from inorganic soil will be used to follow the colonization and evolution of marginal northern sugar maple (Acer saccharum) stands. Second, sedimentary ancient DNA (sedaDNA) from three northern lakes will be used to reconstruct the historic forest composition of Quebec’s mixed boreal forest. Finally, proxy results from terrestrial charcoal, lacustrine pollen and sedimentary ancient DNA will be combined to form a first-of-a-kind multi-proxy analysis of the historical composition of Quebec’s mixed boreal forest. Study sitesTo complete the first part of the thesis, six study sites were distributed along the breadth of the western yellow-birch-fir region of Quebec. Each sampling site was comprised of three plots: one in a hilltop sugar maple stand, the second in a coniferous stand at the base of the hill and the third in a coniferous stand on an adjacent hilltop. For the second part, three lakes were selected whose pollen profiles were already established and who were in proximity to terrestrial charcoal sites. They are lake Bélanger in the Haute-Mauricie region and lakes Francis and Labelle in the Abitibi region. Material and methodsSoil from 20 points at all six sites across the western yellow-birch-fir region of Quebec is sampled, all charcoal particles are removed and analyzed and all identified maple remains are dated using radiocarbon analysis. The sedaDNA analysis requires the development of specific markers that distinguishes maples (Acer saccharum; A. rubrum) from other plant species. Additionally, a universal marker is to be used to determine general forest composition. All amplicons created from the sedaDNA analysis will be sequenced and compared (BLAST) with an existing genetic library. Expected resultsPreliminary results indicate that northern maple stands went through two phases during the Holocene period. From its beginning to around 4k years before present (cal. BP), sugar maples were present, but their stands were few and far between. During that time, the climate changed from the relatively cold Post-Glacial to the warm Thermal Optimum. Around 5k cal. BP, the Thermal Optimum ended and the colder and wetter Neoglacial began. Coinciding with this climate shift, sugar maple abundances greatly increased. We predict that these results will be reflected in the sedaDNA.
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