Assessment of the Ecological Vulnerability of the Forest Ecosystem in the Pardinho River Basin, RS, Brazil, Associated with the Risk of Biological Invasion by Hovenia dulcis Thunb

Riparian forests, transitional ecosystems between terrestrial and aquatic environments, are vital for habitats and ecosystem services but are highly vulnerable to human-induced stressors like land use changes, deforestation, urbanization, damming, grazing, mining, and invasive species introduction. This study developed an Ecological Vulnerability Index for the riparian vegetation of the Pardinho River, RS, focusing on the risk of invasion by Hovenia dulcis (Japanese raisin tree). Using a Geographic Information System, key parameters were weighted: Land Use and Occupation (0.623), Soil (0.213), Normalized Difference Vegetation Index (0.108), and Slope (0.056). These were combined to create a digital Risk Map for H. dulcis invasion, categorized as Very High (8.8%), High (18.7%), Moderate (20.0%), Low (28.1%), and Very Low (24.4%). Very High and High-risk areas cover 27.5% of the study area, indicating significant vulnerability. Field surveys in 40 phytosociological plots (100 m² each) validated land-use classification and assessed the arboreal community. The Shannon diversity index (H’) was 3.45, and the Pielou evenness index (J’) was 0.78, reflecting moderate species richness and evenness. However, 15 exotic species were identified, with H. dulcis showing high Absolute Density (272.5 ind. ha⁻¹), Relative Density (9.846%), and Importance Value Index (9.239%), posing a major threat. The Ecological Vulnerability Index effectively identified priority areas for managing invasive species in the Permanent Preservation Areas of the Pardinho River, supporting sustainable ecosystem management.