Quantification des Changements Récents à 'Écotone forêt-Toundra à Partir de 'Analyse Numérique de Photographies Aériennes

Arctic ecosystems at the forest-tundra ecotone are particularly sensitive to climate-driven vegetation changes. Many recent studies have observed shifts in vegetation cover, particularly an increase in shrub growth. Here, vegetation changes were assessed at the local scale near Umiujaq, northern Quebec (Canada, 56.55°N, 76.55°W) using colour aerial photographs (1994 and 2010). By applying semi-automated image classification methods and change-detection analysis, we were able to detect and map the dominant vegetation cover changes. Comparison of classification results shows a 12% increase in shrub cover, loss of nearly 8% of lichen cover, stability of the spruce zones, and disappearance of nearly a quarter of thermokarst ponds. The 2 resulting maps were superimposed to spatialize the change. Change-detection analysis revealed that a shift toward shrub-dominated landscape was the most important change in the 1994 vegetation classes. This shift affected 18% of the studied area in the valley. The resulting “from-to” land-cover change map illustrates the general ongoing shrubification in the region.