Start-of-season raster maps for European beech in Slovenia derived from Sentinel-2 IRECI time series, 2018–2021

This dataset contains annual GeoTIFF raster maps of start-of-season (SOS) dates for European beech (Fagus sylvatica L.) forest areas in Slovenia for 2018, 2019, 2020 and 2021. SOS was derived from dense Sentinel-2 Level-2A time series using the Inverted Red-Edge Chlorophyll Index (IRECI). Raster values represent SOS expressed as day of year (DOY). The spatial delineation of European beech areas follows the forest classification approach described in Potočnik Buhvald (2025), which used multisensor satellite image time series to monitor forest conditions in selected ecological regions of Slovenia. Sentinel-2 observations were filtered for clouds, cloud shadows and outliers, temporally interpolated, smoothed using a Savitzky–Golay filter, and processed using a relative amplitude threshold approach with α = 0.5. The code and reproducible workflow associated with the processing of Sentinel-2 time series, vegetation-index calculation, temporal smoothing, SOS extraction, statistical analyses and figure generation are available in the associated GitHub repository: https://github.com/Anapot/phenology-timeseries.