Quantification of NDVI variation within the major plant formations in Nunavik

Background/Question/Methods

Altered temperature and precipitation regimes associated with climate change generally result in improved conditions for plant growth. For Arctic and sub-Arctic ecosystems, this new climatic context favours an increase in primary productivity, a phenomenon often referred to as "greening". The development of an erect shrub cover has been identified as the main driver of Arctic greening. Although this phenomenon has been widely documented at the circumpolar scale, little information is available at the scale of plant communities. The objective of this study is to quantify the variation of NDVI within the different plant communities of Nunavik, which will allow us to identify the plant formations that contribute the most to the increase in productivity observed in this territory. The variation of NDVI extracted from Landsat images for the period 1984 to 2020 was quantified. From the Landsat scenes, annual summer NDVI mosaics with a resolution of 30 m were generated. The ecological mapping of Northern Quebec vegetation was then overlaid on the time series of NDVI maps to calculate the median NDVI per vegetation polygon for each year. Linear regression was applied to the NDVI time series of each vegetation polygon from 1992 to 2020.

Results/Conclusions

Our results show that 98.71 % of the study area experienced a statistically significant increase in NDVI (greening) during 1992-2020. The bioclimatic domain of the forest tundra had the largest relative contribution to NDVI increase (42.36%), was followed by the spruce-lichen domain (25.74%), then erect shrub tundra domain (23.68%) and finally prostate shrub tundra domain (8.22%). Forest tundra and erect shrub tundra domains contribute more to the increase in NDVI than the areas they occupy. At the cover type scale, these are scrublands with shrub cover less than 30%, lichen woodlands and coniferous forests (other than lichen woodland) that contribute the most to NDVI increases with contributions 24.56%, 22.34% and 18.35%, respectively. Only shrublands with different shrub covers contribute more to the increase in NDVI than the areas they occupy. Surface deposits, variations in mean annual temperature and variations in winter precipitation are involved in NDVI variations in Nunavik. This study has thus allowed us to quantify and qualify changes in Nunavik's vegetation communities, using fine spatial resolution satellite imagery data. This study also provided a better understanding of the determinants involved in the greening trend occurring in the Arctic and sub-Arctic regions of Quebec.