Vegetation and moisture signatures of lameiros in transboundary Mediterranean headwater basins: a multi-scale remote sensing assessment

Lameiros, traditional man-made valley-bottom wet meadows, are relevant agroecosystem features within mountain headwater catchments of the northwestern Iberian Peninsula, hypothesised to act as sediment disconnectivity elements and moisture reservoirs. This study assesses whether their valley-bottom position translates into a distinct, remotely detectable vegetation and moisture signature, and whether this signature is further modulated by land-use status and hydrological setting.

Two paired transboundary headwater catchments (B.08 and B.13, Montesinho Natural Park, NE Portugal/NW Spain) were classified into headwater, hillslope and valley-bottom units using a Topographic Position Index (TPI) derived from a merged Portuguese–Spanish LiDAR DEM. Vegetation and moisture conditions were characterised through five Sentinel-2-derived spectral indices (NDVI, EVI, NDMI, SAVI, NDRE), extracted as zonal statistics across 756 sub-catchments for a cloud-free 2020 reference scene. The 99 mapped lameiros, all confined to the valley bottom, were further stratified by management status (active/abandoned) and watercourse presence (with/without), and compared using non-parametric statistical tests.

Most spectral indices (NDVI, EVI, SAVI, NDRE) increased consistently along the headwater–hillslope–valley-bottom gradient (e.g., mean NDVI rising from 0.26 to 0.34), while NDMI showed a comparable overall trend with a marginal dip at hillslope positions. These patterns confirm that valley bottoms occupied by lameiros sustain denser and moister vegetation cover than the surrounding geomorphic units. Active lameiros with a watercourse consistently showed the highest values across all five indices (NDVI = 0.56), whereas abandoned lameiros without a watercourse showed the lowest (NDVI = 0.46), consistent with a spectral signature of eco-hydrological degradation associated with land abandonment and reduced hydrological connectivity.

These findings, integrated into a broader multivariate framework linking vegetation indices to sediment connectivity (AIC) and fire severity metrics (dNBR) from earlier stages of the same research, show that satellite-derived indicators can capture fine-scale differences in ecological condition among lameiros. This supports the use of freely available multispectral imagery as a scalable monitoring tool to inform the conservation of these threatened Mediterranean mountain agroecosystems.