Laurie-Anne Chabot
Master student
Department of geography
Laval University

Supervised by:

Martin Lavoie (Regular member)

Research project description

Contemporary and long term dynamics of cedar stands on peat in the St. Lawrence Lowlands physiographic region

Introduction: Since the early 20th century, the peatlands of the St. Lawrence Lowlands (SLL) have been characterized by an accelerated process of afforestation. Although these ecosystems can present a relatively dense forest cover naturally, current rapid afforestation is often a result of disturbances of anthropic origin. These disturbances foster the establishment of terrestrial generalist species and the formation of mixed forest stands. We do not yet know if this phenomenon also affects cedar stands on peat, since these wetlands have been little studied in Québec. However, eastern white cedar seems to present regeneration problems, due in part to white-tailed deer grazing. Could the combination of this regeneration deficit and anthropic disturbances facilitate the establishment of generalist plant species such as red maple and transform cedar stands on peat over the decades to come? Objectives: The general objective of my master’s project is to describe and understand the contemporary (19th-20th centuries) and long term (several millenia) dynamic of several cedar stands on peat in the SLL. Specifically, the project aims to: 1) map the distribution of peatlands in which eastern white cedar is a dominant or co-dominant species and where there is a simultaneous presence of red maple, characterize the environment of current stands on some of these sites by dendrochronology and other observations in the field (contemporary dynamic), describe the evolution of ligneous species in one of the cedar stands studied since its origin by paleoecology (long term dynamic). This will also enable me to determine if these environments are characterized by a process of densification of their forest cover and the establishment of new species, such as red maple. Study sites: The study sites are situated in the SLL physiographic region in southern Québec. These are forested peatlands dominated or co-dominated by eastern white cedar, along with red maple. About five cedar stands on peat will be selected. One is currently being studied, whereas the others will be selected during the summer of 2022. The site presently being characterized is located on the north shore of the St. Lawrence River, on land belonging to Université Laval’s Montmorency Forest. It is a wooded minerotrophic peatland. In addition to eastern white cedar, the other main tree species are red maple, black ash, yellow birch and balsam fir. Red maple is abundant among the regeneration, while only a few seedlings of eastern white cedar are present. Dendrochronological analyses show that some eastern white cedar originated in the mid-19th century. Material and methods: First, I will map the distribution of the cedar stands on peat based on inventory data from the Ministère des Forêts, de la Faune et des Parcs (MFFP). This will make it possible to identify peat environments characterized by the concomitant presence of eastern white cedar and red maple. For the contemporary component of the project, a sample plot (400 m2) will be staked out on each site where data will be collected: tree diameter at breast height will be measured, sample cores will be collected for dendrochronological analyses, regeneration will be counted, and dead trunks on the ground will be identified. For the long term component, peat will be excavated on a site in order to extract, identify and date pieces of buried wood at different depths. Finally, aerial photographs will be examined in order to identify disturbances that took place on or on the periphery of the study sites over the course of time. Expected results: My hypothesis is that cedar stands on peat have been characterized by a forested structure of arborescent coniferous species for a very long period of time. However, they are increasingly characterized by the establishment of generalist species like red maple, due to anthropic disturbances. I also expect that eastern white cedar will present an important regeneration deficit, linked to deer presence. These factors could cause red maple to become increasingly abundant over the coming decades. My study will be conducted in close partnership with the MFFP. The results will make it possible to refine our knowledge about the potential vegetation of these wetlands. Based on indicator species, the concept of potential vegetation consists of attributing an ecological classification to each population, to identify the species grouping that should dominate the vegetation in the final stage of ecological succession.

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