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. In this study, we integrated four decades of Landsat-derived NDVI time series with a customized land cover classification based on Sentinel-2 imagery to investigate greenness dynamics above 1500 m elevation in the Carpathian Mountains. The classification targeted key shrubland types using spectral indices tailored to seasonal pigment variations. We also conducted diachronic visual analysis of aerial photographs, including Cold War-era satellite images, to evaluate long-term vegetation changes. We found significant positive greenness trends in 44% of the study area, with the highest magnitude located at mid-elevations (1800–2300 m) and on north-facing slopes. High-resolution land cover mapping revealed that Ericaceous and Juniperus-dominated shrublands were the strongest contributors to greening. Visual interpretation of historical imagery confirmed widespread woody encroachment in these areas. 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.

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