Land surface phenology for the characterization of Mediterranean permanent grasslands

Abstract

The provision of ecosystem services from Mediterranean permanent grasslands is threatened due to shifting management practices and environmental pressures. This observational study tested the hypothesis that Land Surface Phenology (LSP) parameters from high-resolution satellite data can characterize various permanent grasslands to support conservation and improvement practices. The potential of LSP derived from Sentinel-2 data in identifying the multi-layer mixed vegetation of Mediterranean grasslands, including silvopastoral systems, that were well-characterized from an agronomic and ecological perspective through field surveys, was assessed. Forty-nine polygons, representing eleven sites characterized by different grassland vegetation, soil, climate and management, were identified in Sardinia (Italy). Sentinel-2 satellite images from 2017 to 2023 were processed to derive NDVI, and LSP parameters were calculated using TIMESAT 3.3 software. The Canonical Correspondence Analysis showed a significant association (p < 0.05) between a combination of LSP metrics used as proxies of a set of relevant agronomical indicators. It was then possible to differentiate managed vs. abandoned grasslands (e.g., start and peak of the season significantly later under unmanaged grasslands, p < 0.0001), wooded grasslands vs. open grasslands(e.g., base value significantly higher in woodlands and wooded grasslands, p < 0.0001) across environmental gradients (altitude) and management practices (green-down rate significantly higher under mown than unmown areas, p < 0.0001). The LSP parameters proved to be promising proxies to characterize agronomic features (e.g., length of the growing season, earliness, forage availability, mowing and grazing intensity, unpalatable species) of Mediterranean permanent grasslands. The characterization can support management design or monitoring to detect abandonment or environmental pressures early.