Geodiversity Hotspots: Concept, Method and Cartographic Application for Geoconservation Purposes at a Regional Scale

As a parallel to the "biodiversity hotspot" concept used in conservation biology, "geodiversity hotspots" can be defined as geographic areas that harbor very high levels of geodiversity while being threatened by human activities. Identifying geodiversity hotspots may offer a powerful way to set geoconservation priorities, but numerical methods integrating both geodiversity values and threats are still lacking. Here we propose for the first time an integrated approach using GIS and geoprocessing to map geodiversity hotspots at a regional scale, with a cartographic application to the Ceará State (Northeastern Brazil). The method is based on the quantification and mapping of two numerical indices: a geodiversity index (GI) and a threat index (TI). On one hand, the GI is calculated as the sum of four sub-indexes representing the main components of geodiversity, i.e., geological diversity (rocks, minerals, fossils), geomorphodiversity (topography and landforms), pedodiversity (soils and palaeosoils) and hydrodiversity (surface and underground waters). On the other hand, the TI is calculated as the sum of three sub-indexes including the level of environmental protection, the degree of land degradation and the type of land use. Mapping and delineation of geodiversity hotspots are automatically obtained from a combination of GI and TI, i.e., in areas where higher geodiversity indexes coincide with higher threat indexes. In the study area, results show the spatial delimitation of five geodiversity hotspots, including the Araripe basin (to the South), partly recognized as a UNESCO Global Geopark since 2006, and the Fortaleza metropolitan region (to the North), both faced with severe threats to geodiversity. In addition to a tool for geoconservation, geodiversity hotspots could also provide useful support for biodiversity research and action programs, given the structural and functional links between geodiversity and biodiversity.