such as Agave, Opuntia, Stenocereus and Cephalocereus. Other important species include Alvaradoa amorphoides, Bursera simaruba, Ceiba acuminate, Bursera bipinnata, Bursera excels, Cochlospermum vitifolium, Haematoxylon brasiletto, Piscidia piscipula, Swietenia humilis, Acacia collinsii and Pseudobombax ellipticum. Pine–oak forests exist in the northwest of the park in the highest altitudes, covering about . They are part of the same type of forest found in the Soyaló region it is adjacent to. They are found at an altitude of 1,200 masl and above in areas that receive precipitation of about 1500 mm annually. The most common species is the oak Quercus acutifolia (syn. Quercus conspersa), often found mixed with the two kinds of rainforest found in the park. Air plants are common here as well as bromeliads, orchids and plants from the Maxillaria, Lycaste, Cattleya and Laelia groups. Grassland is not naturally occurring but rather exists due to human activities such as farming and livestock raising. It is seen on the north and south sides of the canyon and is usually associated with secondary vegetation such as Tecoma stans, Gliricidia sepium, Plumeria rubra and Acacia collinsii, occupying an area of in the park. Wildlife Throughout the history of the area, especially since it was definitively explored in the 1960s, the area's wildlife diversity has been severely negatively impacted by human encroachment in the form of settlements, agriculture and hunting. However, since the federal park was established in the 1980s, wildlife diversity has increased. In 1986, the federal Secretaría de Agricultura y Recursos Hidráulicos (SARH) reported a total of ninety species of vertebrates divided into four species of fish, one amphibian, 14 reptiles, 26 birds and 40 mammals. A 2005 study indicates 308 species with four species of fish, 15 amphibians, 195 birds, and 53 mammals. Between these two, there have been a number of other studies which also show the growth of the number of wildlife species in the park. Information about fish species is scarce but at least four protected species have been detected. According to a CONANP study in 2007, there are 12 species of reptile here under protection, including the river crocodile (Crocodylus acutus), and one threatened species, the Yucatán banded gecko (Coleonyx elegans). Birds are the most common type of animal in the park, with about 195 species documented. Six of these species are threatened and 17 are subject to special protection. One threatened bird species in the park is