My research aims to reconstruct the evolution of the opening in the boreal forest in northeastern Quebec, especially focusing on the transition between stable alternative states along a latitudinal gradient. The objective of my thesis is to understand the impact of natural disturbances such as climate and forest fires, at different spatial and temporal scales, as drivers of the evolution of forest environments. This study aims in particular to better understand the transition between two distinct bioclimatic domains: the moss spruce forest (closed environment) and the lichen spruce forest (open environment), mainly composed of Picea mariana. My work is based on the analysis of geochemical indicators (XRF and magnetic susceptibility) and biological indicators (charcoal, pollen, and chironomids).