Índice de vulnerabilidade ecológica do ecossistema florestal da Bacia Hidrográfica do Rio Pardinho, RS, Brasil, associada ao risco de invasão biológica pela espécie Hovenia Dulcis Thunb. : subsídios à gestão ambiental sustentável.

Abstract

Ecological Vulnerability (EV) is characterized as a critical assessment of the ability of ecosystems to resist disturbances and changes caused by anthropic or natural factors. Understanding and evaluating EV is fundamental to implementing effective conservation and environmental management measures, promoting the sustainability of ecosystems and mitigating negative impacts. The spread of invasive exotic plants is a factor of great relevance to EV. When introduced into a new environment, they cause damage to the local ecosystem, competing with native species for light, water and nutrients, which can lead to the decline of native populations and loss of biodiversity. In this context, this research aimed to develop an Ecological Vulnerability Index of the forest ecosystem of the Pardinho River Hydrographic Basin, RS, Brazil, associated with the risk of biological invasion by the species Hovenia dulcis (Japanese raisin tree), aiming to provide subsidies for river basin management. The research began with the development of a systematic literature review to identify the different EV assessment methods, and the main impacts of invasive plants on the ecosystem. Subsequently, a combination of methodologies was used, employing the use of RGB images obtained by Drone and the construction of rectified orthomosaics to validate the images obtained from the CBERS-4A satellite, and processed in the QGIS software to confirm the identification of the invasive species H. dulcis in the urban forest area of the Green Belt (GB) in the Municipality of Santa Cruz do Sul. Furthermore, a study of the GB tree community was carried out, where 72 random sample plots of 100 m² each were arranged. The results indicated that the GB plant community presented a high species richness, 108 taxa, distributed in 39 botanical families. Regarding the community structure, the calculated indices of Shannon (H') = 3.65 and Pielou Evenness (J') = 78%, demonstrate that the plant community has a high species diversity, expressed through species richness and a homogeneous distribution of relative abundances, favoring biodiversity conservation. H. dulcis highlights as the invasive alien species with the highest number of individuals sampled (146), being the species within the community with the highest Relative Density - DeR (9.14) and the second highest in Relative Frequency - FeR (5. 10%), Coverage Value Index - CVI (8.85%) and Importance Value Index - IVI (7.60%). Regarding the processing of satellite images, the results indicated that H. dulcis occupies 86.44 hectares of the forest area, being well distributed and corroborating the phytosociological data obtained in the field. These results demonstrated high accuracy in the methodology for detecting invasive plants and suggest the urgent need for control and eradication measures. Finally, an Ecological Vulnerability map of the arboreal vegetation in the Pardinho permanent protection areas to the invasion of the species H. dulcis was prepared. Thus, to create the map of use and occupation by the invader, multispectral images of 8 x 8 m pixels were used together with the 2 x 2 panchromatic images from the CBERS-4A satellite. Geospatial soil data, the Normalized Difference Vegetation Index and Slope were also used, which were combined through Hierarchical Analysis of the data. These data were compared with results based on the phytosociological study. The results demonstrate that the methodology was efficient in detecting the invasive species and creating a thematic invasion risk map. Field data confirm and demonstrate the presence and occupation of the invasive H. dulcis in the riverside ecosystem of the Pardinho River Basin, and highlight the importance of urgent monitoring and control measures for this species, which presented the second highest IVI (9.24%), and also the second highest Absolute Density - DeA (272.5 in. ha-1), and the second highest DeR (9.846%) within the tree community. This work provides a methodology applicable to other Atlantic Forest remnants that present this serious environmental problem.