Prioritizing ecological values with Sequential Hierarchical Intersection Layers (SHIL): a case study from a Mediterranean biodiversity hotspot

Biodiversity loss is accelerating globally, driven by land-use change, habitat degradation, and climate stressors, emphasizing the importance of aligning conservation efforts with national, European, and global biodiversity frameworks. In regions like the Mediterranean, characterized by high ecological value and vulnerability, effective prioritization depends on methods that are not only robust but also accessible and transferable to practitioners. This study introduces the Sequential Hierarchical Intersection Layers (SHIL) method, a spatially explicit, scalable, and replicable GIS-based framework for ecosystem prioritization. Compared to other existing prioritization tools, SHIL provides an intuitive and transparent workflow suitable for practitioners without extensive programming expertise or specialized training. The framework generates individual ecological indices for each dataset via intersection with a chosen subdivision layer, through a stepwise workflow and customizable weighting schemes. The integration of multiple ecological datasets into a composite prioritization score (CEVI) enables systematic identification of conservation priorities. Applied to Sicily, a Mediterranean biodiversity hotspot, SHIL revealed ecological strongholds in inland and mountainous provinces, while also detecting critical corridors and isolated habitat systems, demonstrating its ability to capture complex spatial patterns. While careful consideration is required in defining the weighting scheme, SHIL offers an accessible, adaptable, and reproducible alternative to more technically demanding prioritization tools. By providing a transparent, modular, and scalable framework, SHIL supports conservation planning, habitat restoration and ecological network management in Sicily, and is transferable to other regions facing similar conservation challenges.