Phenology Studies in Mediterranean Ecosystems: Assessing the Impact of Temporal and Spatial Resolution

Satellite-based characterization of vegetation phenology in structurally complex Mediterranean ecosystems remains challenging because of the contrasting spatial and temporal properties of remote sensing platforms. This study evaluates how differences between sensors, including spatial and temporal resolution, influence phenological parameter extraction from NDVI time series in a cork oak woodland in central Portugal. NDVI time series from Landsat 8/9, Sentinel-2, and a ground-based spectrometer (FloX) were processed in TIMESAT to extract six phenological metrics across three vegetation types (cork oak, herbaceous vegetation, and open woodland) over three growing seasons (2022–2025). Landsat 8/9 and Sentinel-2 agreed closely for herbaceous vegetation and open woodland, whereas differences concentrated in cork oak, where Sentinel-2 estimated a start of season 161 days earlier in Year 1 and an end of season 33 to 61 days later in Years 2 and 3. Sentinel-2 retrieved higher amplitude and seasonal integral values in all vegetation types and years. Compared with FloX, satellite end of season and peak timing for cork oak were later in all years (by 72–198 and 87–203 days, respectively), whereas deviations for herbaceous vegetation were 15 days or less. These findings support multi-scale phenological characterization of Mediterranean montados and offer a baseline for future multisensor assessments of dry-land ecosystems.