How Diverse are the Mountain karst Forests of Mexico?

Tropical forests on karstic relief (karst forest) are among the most species-rich biomes. These forests play pivotal roles as global climate regulators and for human wellbeing. Their long-term conservation could be central to global climate mitigation and biodiversity conservation. In Mexico, karst landscapes occupy 20% of the total surface and are distributed mainly in the southeast of the country, along the eastern slope, and in the Yucatan Peninsula. Within each of these areas, the following types of karst occur: coastal karst, plain karst, hill karst, and low-, medium and high-mountain karst. Mountain karst forests cover 2.07% of Mexicos surface and are covered by tropical rainforests, montane cloud forests, and tropical deciduous forests. It is probably one of the most diverse biomes in Mexico. However, the Mountain karst forest of Mexico has received little attention, and very little is known about it. Here, we evaluate the vascular plant species richness within the mountain karst forests of Mexico. We assembled the first, largest and most comprehensive datasets of Mexican, mountain karst forest species, from different public databases (CONABIO, GBIF, IBdata-UNAM), which included a critical review of all data. The families, genera and species present within the mountain karst forest of Mexico were compiled. Taxa that best characterize the forest of Mexico were identified based on their spatial correlation to this biome. Also, the conservation status of each of them was determined. We explored biodiversity patterns, identifying areas with the highest species richness, endemism centers, and areas of relatively low sampling intensity. We found that within the mountain karst forest of Mexico there are representatives of 11,771 vascular plant species (253 families and 2,254 genera), ca. 50 % of the Mexican flora. We identified 372 species endemic to these forests. According to preliminary IUCN red list criteria, 2,477 species are under some category of conservation risk, of which 456 (3.8 %) are endangered. Most of the Mexican karst forests have been extensively explored and six allopatric, species-rich areas were identified. Compared to other regions in the world, the mountain karst forest of Mexico is one of the most diverse biomes. It contains more species than some entire montane systems in Mexico such as Sierra Madre Oriental, and Sierra Madre del Sur. Also, the mountain karst forest of Mexico is most diverse than similar forests of South America and Asia, even if considering the effect of different sampling areas. The fact that mountain karst forest is covered by some of the most species-rich Mexican forests, in addition to being embedded in areas of high biotic diversity in Mexico, probably contributes to its great floristic diversity. Thus, the mountain karst forest of Mexico is an important source of diversity and shelters a large percentage of the Mexican flora.