Located between the Neotropical biogeographical region, the El Cielo Biosphere Reserve is situated in in the southern part of the Mexican state of Tamaulipas within the Sierra de Cucharas, a mountain range derived from the large Sierra Madre range. It is one of the most ecologically rich and diverse places of Mexico. It comprises 14 vegetation types, dominated by the tropical sclerophyllous forest.
The reserve protects the northernmost extension of tropical forest and cloud forest in Mexico. It has an area of 144,530 hectares (357,100 acres) (558 square miles) made up mostly of steep mountains rising from about 200 metres (660 ft) to a maximum altitude of more than 2,300 meters (7,500 ft).
The conservation of the ecosystems of El Cielo is essential: they host a number of threatened plants and animal species as the oso negro (Ursus americanus), jaguaroundi (Herpailurus yagouaroundi), tigrillo (Leopardus wiedii), jaguar (Pantera onca), ocelote (Leopardus pardalis), and cabeza de viejo (Eira barbara).
The local population of 6,208 inhabitants (1999), dispersed in 47 communities, are mainly engaged in seasonal agriculture as maize, beans, pumpkin and fruits crops, hunting and forestry exploitation.
The El Cielo Biosphere Reserve includes various transition ecosystems with characteristic temperate zone elements. The main aim is to protect the vegetation of the montane cloud forest because of its wealth of species and scant extension in the country (1%). Other types of vegetation are the sub-deciduous tropical forest, the pine-oak forests and the xerophyte shrubland containing threatened or endangered endemic species.
Six species of cats, none abundant, are found in the biosphere: jaguar, mountain lion, ocelot, margay, jaguarundi, and bobcat. A small population of black bears is present. At least 255 species of birds are resident in the biosphere preserve and more than 175 migratory species have been recorded. Both birds and mammals are a mixture of temperate and tropical species
The mammals in the Biosphere Reserve include Eira barbara, Panthera onca, Leopardus pardalis, Leopardus wiedii, Herpailurus yagouaroundi, Ursus americanus, Bassariscus astutus, Galucomis volans, and Odocoileus hemionus; among the bird species, mention may be made of Accipiter striatus, Ara militaris, Asio clamator, Atthis heloisa, Bubo virginianus, Crax rubra, Falco peregrinus, Otus asio, Oxyura dominica e Icterus graduacauda; reptiles include Phrynosoma cornutum, Gopherus berlandieri and species of the Crotalus genus. The Biosphere Reserve contains the following plant species: Ariocarpus agavoides, Astrophytum myriostigma, Ceratozamia kuesteriana, Zamia fishcheri, Magnolia schiedeana, Encyclia cochleata, Laelia anceps, Laelia speciosa, Lycaste deppei, Ferocactus hamatacactus.