Jeanne Léger
Master student
Department of biology, chemistry and geography

Supervised by:

Guillaume de Lafontaine (Regular member)

Co-supervised by:

Martin Lavoie (Regular member)

Research project description

Postglacial vegetation and fire history of barren high peaks along a latitudinal gradient from commercial boreal forest to forest tundra (Groulx Mountains - Caniapiscau) in Québec

Introduction: A process of gradual opening of the forests is underway in Québec’s boreal region, from the spruce-moss forest to the forest tundra. The more open landscapes towards the north reflect ecological interactions between fires-climate-topography-vegetation that have been underway for several millenia. This opening is the result of fires that have become more frequent during cold periods, which impedes the regeneration of black spruce. However, this process seems to have intensified in recent centuries, and more recently in commercial forest. This raises questions in regard to sustainable forest management in a context of contemporary climate change that are likely to alter the ecological processes governing the resilience of boreal and subarctic landscapes. While subarctic deforestation has been studied to the tree line, we still know little about these dynamics further south, where the potential for opening-up of forests is high.Objectives: The main objective of my master’s project is to describe and explain the process of forest fragmentation that led to the establishment of lichen tundra on several high mountain sites distributed along a latitudinal gradient in the boreal region, from the Groulx Mountains to the Caniapiscau reservoir. More specifically, for each site, I aim to i) reconstruct the millenial fire history of the summits and the adjacent forests on their slopes, ii) identify the ligneous species that were once present locally, and iii) date the period of forest opening. Achieving these objectives will enable evaluation of the period during which the forest on each of these sites was resilient against the fire regime, before shifting toward a deforested environment. Study sites: The study region for my project corresponds to a latitudinal transect of about 400 km, extending from the Groulx Mountains region (spruce-moss bioclimatic domain) to the area around the Caniapiscau reservoir (transition between the spruce-lichen and forest tundra bioclimatic domains). This region is primarily situated above the northern limit of commercial forests. The summit on four sites will be studied: the Groulx Mountains, Fermont and Caniapiscau (South and North). The recurring physiographic pattern over the entire study region consists of 1) summits characterized by lichen tundra (treeless), 2) slopes composed of open black spruce forests, and 3) valleys populated by black spruce-lichen or spruce-moss forests, depending on the latitude. On the high summits in commercial forest (Groulx Mountains), alpine lichen tundra is bordered by subalpine spruce-white spruce forest. Material and methods: The plurimillenial fire history will be reconstructed using macroscopic charcoal particles (Ø > 2 mm) preserved in the mineral soil. These charcoal pieces were deposited locally during a fire, and buried in situ in the soil. They resist decomposition, remain preserved for several millennia and testify to the presence of ligneous species and fire regimes of the past. For each of the four study sites, three topographic positions (summit, hillside, valley) will be studied. At each location, I will quantify the presence and abundance of charcoal particles by collecting 20 samples measuring 750 cm3 from a 1000 m2 plot. The vegetation (grass, mosses, lichens) as well as the presence and abundance of ligneous species will be noted for each of the plots. In the laboratory, the charcoals will be subjected to taxonomic identification base on wood anatomy using and incident light microscope. Several pieces will be radiocarbon dated (14C). Expected results: I will test the hypothesis that the lichen tundra on high summits is the result of a process of deforestation by fire that occurred during the late Holocene. For each of the sites, my results will make it possible to determine if the fire history regimes were similar over the entire altitudinal gradient, or whether the summits were disturbed at a greater frequency than slopes and valleys. The presence of white spruce, a species intolerant to fire that persists on the high summits of the Groulx Mountains and Fermont, could show a more modest role of fires and opening of climatic origin at high altitude on the summits, whereas black spruce, which dominates the slopes of Fermont and Caniapiscau further north, testifies to the impact of fires in these environments. Finally, my project will provide data on the interactions between climate-fire-vegetation in the context of the creation of protected zones by the provincial government of Québec.

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