The global conservation status of plants growing on cliffs and rocky outcrops

Ecosystems that occur on cliffs and rocky outcrops are home to many plants that are specially adapted to harsh environmental conditions. These habitats are seeing increased pressure from development, recreational use, and invasive species, calling for a thorough evaluation of the endangerment of the taxa inhabiting them. However, the conservation status of these taxa is not well understood preventing effective conservation prioritization and action. In this study, we examine the conservation status of vascular plant taxa associated with these ecosystems, using the International Union for Conservation of Nature (IUCN) Red List of Threatened Species assessments, and compare these to their taxonomic status (families and genera) and range (realm, country, occupancy). We have assembled data highlighting regions where cliff and rocky outcrop taxa most frequently occur (Madagascar, Brazil, Spain) and found that plants growing in these habitats may be more endangered than expected given global plant endangerment, however, risk patterns do vary. Certain groups find refuge in cliffs or rocky outcrops environments (Euphorbiaceae, 18% less endangered), while others may be facing increased risk (Cactaceae, 19% more endangered). We have also found that taxa occurring in habitats with low mean elevation or narrow elevational ranges are more endangered. To assist future research, we have developed a dashboard summarizing available data that also allows for interactive analyses based on user-defined goals. We see the need for additional research on cliff and rocky outcrop plants to enhance the Red List assessment process and support overall plant conservation efforts.