Complementary insights into high Arctic greening from absolute and relative NDVI trends across the Canadian Arctic Archipelago

The interpretation of increasing vegetation, also called greening, using the normalized difference vegetation index (NDVI) remains challenging in sparsely vegetated regions. Vegetation changes in higher latitude regions have mostly been assessed through circumpolar studies, which place its magnitude in the context of more productive, lower-latitude ecosystems. However, absolute greening trends (ΔNDVImax) may underrepresent ecologically meaningful variation where plant cover is low. Here, we used four decades (1984–2023) of Landsat-based NDVImax time series to assess vegetation change across the Canadian Arctic Archipelago combining the commonly used Absolute Greening Index (AGI) and the Relative Greening Index (RGI; percent change relative to initial NDVImax based on 1984 data). Both metrics indicated widespread but low-magnitude greening, with stronger increases at higher latitudes. However, RGI revealed clearer differences among bioclimatic zones and emphasized vegetation change in sparsely vegetated northern regions, while AGI suggested more homogeneous trends. Specific examples showed that RGI highlighted subtle NDVI increases along coastal and patchy vegetation areas, whereas AGI provided a more conservative depiction of change. Our results suggest that using both metrics provide complementary insights into vegetation dynamics, improving interpretation of greening patterns across the Canadian Arctic Archipelago.