Integrating Field Ecology and Sentinel-2-Compatible Remote Sensing for Monitoring Vegetation Succession in Natura 2000 Dry Grasslands

Dry continental grasslands (Natura 2000 habitat type 6210 – Festuco-Brometalia) are increasingly threatened by land abandonment and vegetation succession (Management Plan for the Natura 2000 Sites Potok Dolje and Vejalnica and Krč and the Goranec Significant Landscape, 2023). This paper presents initial results of an ongoing remote sensing study aimed at developing a satellite-based framework for monitoring succession in these habitats, using Natura 2000 site Vejalnica and Krč (HR2001298) and the Goranec Significant Landscape (City of Zagreb, Croatia) as calibration and validation sites. Field surveys and unmanned aerial vehicle (UAV) mapping were conducted in 2024–2025 across approximately 150 ha of (semi-)grassland areas. A modified EMBAL field protocol was applied for habitat delineation and ground-truth. UAV Red, Green, Blue (RGB) and multispectral imagery were processed to derive a canopy height model, from which four structural succession phases were defined. The study area was aligned to a 10 × 10 m grid compatible with Sentinel-2 pixels. Baseline mapping revealed strong spatial heterogeneity and widespread shrub and tree encroachment, providing a basis for modelling Sentinel-2 spectral metrics for monitoring succession phases in grassland habitats.