Region-wide shrubification of Betula glandulosa inferred from combined ground and satellite observations in Nunavik

Arctic greening is widespread and especially pronounced in Nunavik, northeastern Canada. Local studies identify glandular birch (Betula glandulosa) encroachment as a contributor, but its regional association with greening remains poorly quantified. We combined 1,117 vegetation plots across Nunavik with satellite embeddings to map glandular birch presence at 30 m resolution and examine its spatial overlap with Landsat-based greening over 1984–2024. The random forest classifier performance was intermediate overall (Kappa = 0.38 [0.34–0.40]; F-score = 0.50 [0.46–0.52]) with high specificity (0.85 [0.84–0.86]) and moderate sensitivity (0.57 [0.51–0.65]). Greening trends were derived from cross-sensor calibrated annual maximum Normalized Difference Vegetation Index (NDVI) corrected for variation in observation frequency. Greening magnitude was positively associated with birch presence probability (R² = 0.34); we attribute 31.7% of regional greening to glandular birch encroachment, rising to 65.1% for high magnitude greening (> 0.005 NDVI yr⁻¹). We interpret this overlap as consistent with potential birch encroachment under the strong working hypothesis that birch expansion or canopy densification contributed to greening where birch is present at the end of the Landsat time series. Partial-dependence analyses indicated that biogeographic position (latitude, elevation) has greater predictive performance than local terrain, yet encroachment declined strongly with wetness, and weakly but consistently with slopes and colder facing aspects. Together, these results show that glandular birch is a widespread, locally contingent, driver of Nunavik’s greening and provide species-explicit maps to disentangle shrubification from other processes (e.g., treeline dynamics). We argue that this attribution is a necessary step toward estimating the climatic and ecological consequences of Arctic shrubification, moving beyond greening signal amplitude to the mechanisms that control albedo, snow–canopy interactions, species interactions and permafrost energy fluxes.