Past and Present in the Ecological Connectivity of Protected Areas Through Land Cover and Graph-Based Metrics.

Habitat reduction is significantly threatening biodiversity, making ecological connectivity which facilitates species movement across habitat patches, essential for human impacts mitigation, promoting genetic exchange, and enabling colonization of new areas. Ecological connectivity in the River Lérez Basin (Galicia, NW Spain), including three Natura 2000 sites: River Lérez, Serra do Cando, and Serra do Candán, was assessed. Land cover maps for the years 2013 and 2023 were created using Landsat 8-9 images and the random forest machine learning method. Hardwood forest habitat patches and ecological corridors were identified. Betweenness Centrality (BC) metric, along with other global structural connectivity indices such as Integral Connectivity Index (IIC), Connectivity Probability (CP), and Equivalent Connectivity (EC), were calculated. iNaturalist records were then downloaded to observe how the distribution of records resembled that of habitat and corridors for 2023. Some indices, such as the splitting patch index (SPLIT), effective meshsize (EM), edge length (EL), and edge density (ED), were also calculated at the patch level. Results showed that the area of hardwoods increased by 2.16% across the basin. The spatial patch patterns were similar in both years. Additionally, hardwood structural connectivity appeared to have improved over the study period, with IIC rising in 20.00%, PC increase by 16.67-18.92%, and EC 8.04-8.68%. However, some patches from 2013 had higher BC values due to the loss of certain connections. iNaturalist record distribution showed similarities with habitat patch and path distribution, with a lower average distance (406.06 m) compared to random points (854.12 m) for 2023. The patch indices indicated a reduction in fragmentation, with SPLIT decreasing by 53.95%, EM and EL increasing by 173.66% and 14.21%, respectively, while ED decreased by 9.29%. The integration of satellite imagery has been proven effective for generating land cover data for connectivity analysis. It also demonstrates that indices and graph-based approaches offer a data-efficient alternative to traditional models. Furthermore, the incorporation of citizen science platforms, despite some biases, complements technical methods by providing real-world insights into species distribution. This combination is considered a promising approach for future research.