Over recent decades, cold-climate ecosystems have exhibited a pronounced increase in vegetation greenness, and shrub encroachment is a major ecological process underlying these changes. Our knowledge of these dynamics remains limited in the temperate mountains of Eastern Europe, which have experienced significant land-use shifts, especially following the collapse of the communist regime. It is noteworthy that the contribution of shrubs has not been evaluated, partly due to the difficulty of providing high-resolution mapping of shrublands. This study examines vegetation greenness dynamics in the Carpathian Mountains over the past four decades by integrating Landsat-derived NDVI time series with a customized land cover classification, based on Sentinel-2 images, specifically targeting shrublands. We detected significant positive greenness trends in 44% of pixels above 1500 m, particularly at mid-elevations (1800–2300 m) and on north-facing slopes. High-resolution mapping revealed a strong correlation between greening and shrubland cover, with Ericaceous and Juniperus-dominated plant communities exhibiting the most pronounced trends. Comparisons of historical and recent aerial photographs confirmed the increase in woody vegetation cover, suggesting that encroachment explains a disproportionate greening in shrublands. We suggest that the decline of traditional land-use, particularly extensive grazing practices, is a key driver of these ecological shifts, promoting the resurgence of previously more widespread subalpine shrublands. Our findings highlight the importance of integrating high-resolution remote sensing observations and diachronic analysis of aerial photographs to disentangle the complexity of vegetation greening in high-elevation ecosystems.