Différenciation biotique de la flore des tourbières ombrotrophes du sud du Québec : une étude historique de 1982 à 2017
This thesis aims at determining whether ombrotrophic peatlands from the St. Lawrence lowlands, which are isolated in a highly disturbed environmental matrix, have suffered a loss of floristic diversity in the last three decades. In order to achieve this objective, a historic floristic study was conducted, by comparing old and recent inventories. More precisely, 76 plots inside 16 bogs were surveyed in 1982, and resurveyed in 2017 using the same methodology. For this study, only the vascular flora was analyzed. More specifically, I compared species richness as well as species abundance and frequency, while considering their shade tolerance and preferential habitat (wetland, facultative or upland). Finally, beta diversity changes were analyzed, and a beta diversity decomposition was performed in order to identify the principal component of the changes. My results show a significant increase in alpha diversity and beta diversity in the last 35 years, indicating a taxonomic differentiation and a floristic community change. The increase in alpha diversity was associated with a change in abundance and frequency of shade tolerant species and facultative wetland species. Moreover, species replacement was the main factor linked to the beta diversity increase. At last, I observed an increase in shrub and tree species cover over the past 35 years. Although the exact causes of the observed changes were not studied, our results suggest a regional drying of the peatlands likely linked to agricultural drainage in the area, and potentially enhanced by climatic changes. Our results let me suppose that these changes will continue with time, which could lead to future loss of biodiversity in these ecosystems due to the replacement of bog species by facultative species.
bog Beta diversity Biotic differentiation Vascular flora Species richness Diversity