The Tripartite Greening of Northern Quebec, Canada: 1986-2010

In the words of McManus et al. (2012), "global vegetation models predict rapid poleward migration of tundra and boreal forest vegetation in response to climate warming," noting that "local plot and air-photo studies have documented recent changes in high-latitude vegetation composition and structure, consistent with warming trends." Therefore, "to bridge these two scales of inference," as they put it, they used fine-scale Landsat observations to quantify vegetation changes within and among plant cover types over the past quarter-century," focusing on "a latitudinal transect across the forest-tundra biome boundary in northern Quebec, a region that has experienced rapid warming in both winter and summer seasons during the satellite era," carefully selecting "time series of peak-summer Landsat data to evaluate changes in vegetation composition and structure rather than changes in phenology," i.e., temporal changes in the initiation and termination of the growing season.

Results indicate that "30% of the observable (cloud-free) land area experienced a significant (P < 0.05) positive trend in the Normalized Difference Vegetation Index (NDVI)," with low shrub and graminoid (grass-like) tundra contributing "preferentially to the greening trend." Across the entire transect, for example, they report that "the area-averaged LAI increase was ~0.2 during 1986-2010," while "a higher area-averaged LAI change (~0.3) within the shrub-tundra portion of the transect represents a 20-60% relative increase in LAI during the last two decades." This "observed association between shrub cover types and increased NDVI," in the words of the eight scientists involved in the study, "is generally consistent with the concept that woody plants can take advantage of warmer conditions and grow more vigorously."