UAV-based fine-scale monitoring reveals species-specific riparian responses to environmental changes

Riparian forests, although covering less than 1 % of Europe's land area, play a crucial role in maintaining biodiversity and providing key ecosystem services such as bank stabilization, nutrient retention, and stream temperature regulation. Despite their importance, many floodplains remain degraded due to historical land-use change, hydrological regulation, urbanization, biological invasions, and climate change. Reliable, spatially explicit indicators are needed to assess riparian vegetation condition and support adaptive management. This study introduces an integrated approach that combines high-resolution unmanned aerial vehicle (UAV) multispectral imagery with meteorological data, offering one of the first detailed assessments of seasonal riparian vegetation dynamics in Central Europe. Four UAV surveys (May–September 2022) conducted along the Silnica River in central Poland were used to derive NDVI, NDRE, and MTCI indices, which were related to topographic wetness and LiDAR-derived canopy metrics. Results revealed distinct functional differences among vegetation groups. NDVI effectively captured biomass accumulation, NDRE reflected longer-term physiological responses, and MTCI was most sensitive to post-drought chlorophyll recovery. Invasive species showed consistently high NDVI but lower NDRE and MTCI, indicating structural robustness but lower physiological efficiency. Unlike medium-resolution satellite imagery, where heterogeneous canopies produce mixed spectral signals and spatial averaging that mask functional variability, UAV-based monitoring captures these dynamics at ecologically meaningful scales. The integration of spectral and meteorological information demonstrates the potential of UAV platforms to generate fine-scale, repeatable indicators for early stress detection, invasive species monitoring, and adaptive management of riparian ecosystems under changing climate conditions. • UAV multispectral imagery tracked riparian vegetation dynamics at fine scale. • Invasive species showed high NDVI but reduced chlorophyll under cold stress. • Native species were slower in biomass growth but physiologically more stable. • Short-term rainfall strongly influenced spectral responses in native and non-native. • Integrating indices supports riparian monitoring and climate adaptation.