Zacatonal

Category: Grassland, Tundra, and Human Biomes.

Geographic Location: North America.

Summary: Found high above the tree line on Mexico’s tallest peaks, this ecoregion is dominated by the alpine bunch grasslands—zacates amacollados in Spanish—that give the region its name.

The Zacatonal ecoregion is made up of small, isolated patches of high alpine grasslands and shrublands occurring above the natural treeline on mountains in Mexico. This name of this ecoregion is a derivation of the Spanish word for grass: zacate. Grasses, such as plants from the genera Fetusca, Calamogrostis, Muhlenbergia, and Stipa, are the dominant vegetation of the ecoregion. Although these grassy patches are neither extensive in size nor widespread, the Zacatonal biome is a hot spot for biodiversity, home to many endemic (not found elsewhere) species of plants, birds, and mammals.

Zacatonal grass occurs in enclaves among pine-oak forests of the Trans-Mexican Volcanic Belt, at elevations of 3,600–8,200 feet (1,100–2,500 meters), and in even higher elevations above the natural treeline. The Trans-Mexican Volcanic Belt stretches across south-central Mexico for about 560 miles (900 kilometers), from Jalisco on the west coast to Veracruz on the east coast. It is a band of volcanic peaks, some of which are the highest in Mexico. Some of the volcanoes are active and some are dormant. Zacatonal can be found on volcanic mountains here, such as Pico de Orizaba, Iztaccihuatl, Popocatépetl, Nevado de Toluca, Nevado de Colima, Malinche, and Ajusco.

At the elevations where Zacatonal is found, the climate is subhumid continental; however, there are climatic changes at higher altitudes. Temperatures usually range from 36 to 41 degrees F (2 to 5 degrees C). On average, there are 24 to 31 inches (60 to 80 centimeters) of precipitation per year, much of which is snow; the snow usually does not persist for long periods. The soils on which Zacatonal occurs are volcanic in origin, can be quite deep, and tend to have high organic content.

Flora and Fauna

Biological evidence indicates that Zacatonal represents relict flora from a time during the Pleistocene, when climatic conditions were such that bunch grasslands covered much of Mexico. The volcanic activity that shaped these mountains, along with subsequent changes in the climate, made the area favorable to alpine bunch grasslands and shrublands. At present, Zacatonal occurs mainly as isolated patches within the temperate pine-oak forest.

This habitat fragmentation led to the radiation of new species. Approximately 75 percent of the plants found in Zacatonal are endemic to this ecoregion. Zacatonal is characterized by grasses and sedges such as Agrostis perennans, Calamagrostis spp., Bouteloua spp., Deschampsia elongate, Festuca spp., Fimbristylismexicana,Hilaria cenchroides, Muhlenbergia spp., Poa spp., Sporobolus spp., and Stipa spp., as well as other herbaceous plants in the Arenaria, Draba, Lupinus, and Potentilla genera.

Creeping junipers (Juniperus monticola f. compacta) can be found growing on rocky outcrops and along the banks of streams.

This ecoregion also has high levels of vertebrate diversity. More than 200 species of birds have been observed in the Zacatonal biome, more than 20 of which are endemic, including the striped sparrow (Oriturus superciliosus), several species of sedge wrens (Cistothorus platensis potosinus, C.p. potosinus, and C.p. jalapensis), the Sierra Madre sparrow (Xenospiza baileyi), the long-tailed wood-partridge (Dendrortyx macroura), and montezuma quail (Cyrtonyxmontezumae). Several of these species are threatened with extinction. A total of 85 species of migratory birds make use of Zacatonal.

Zacatonal is also home to 10 species of amphibians, 42 species of reptiles, and 48 species of mammals, including endemic mammals such as Saussure’s shrew (Sorex saussurei), the black-eared mouse (Peromyscus melanotis), and the volcano rabbit (Romerolagus diazi). Other mammals in the ecoregion include skunk, opossum, grey fox, bobcat, and notably the puma.

Human Impact

Threats to the Zacatonal ecoregion include hunting, land clearing for agriculture, overgrazing, fires, and climate change. Several of the mountains on which Zacatonal occurs are protected as national parks. Some of the threatened or endangered species occurring in this ecoregion have also been given protected status.

Given that preservation of a small area of Zacatonal could ensure the survival of hundreds of species of plants and animals, this ecoregion is important for conservation. Zacatonal also provides ecosystem services such as climate regulation and the maintenance of hydrological cycles. This is a fragile ecosystem that is unable to tolerate disturbances.

Human activity threatens this ecoregion with destruction. Habitat loss is a significant issue. Overgrazing by cattle, goats, and sheep depletes grasslands. Erosion from grazing on steep hillsides is also a significant problem. Plants are often cleared for the cultivation of food crops. Fires resulting both from negligence and arson are becoming more common. Hunting and the capture of wild birds for the exotic bird trade are further endangering some species. The effects of climate change on Zacatonal could be severe because of the high sensitivity of the grasses to temperature and moisture.

Five peaks with Zacatonal—Izta-Popo Zoquiapan, Malinche, Nevado de Colima, Nevado de Toluca, and Pico de Orizaba—are protected by the Mexican national park system. Endangered and threatened species, such as the volcano rabbit and Saussure’s shrew, are protected under Mexico’s National Commission of Protected Natural Areas.

Bibliography

Bobbink, R., G. W. Heil, and Nuri Trigo Boix, eds. Ecology and Man in Mexico’s Central Volcanoes Area. Dordrecht, Netherlands: Kluwer Academic Publishers, 2003.

Dávila, Aranda P., R. L. Saade, and J. B. Reyna. “Endemic Species of Grasses in Mexico: A Phytogeographic Approach.” Biodiversity and Conservation 13 (2004).

Delgadillo, Claudio, Jose L. V. Rios, and Patricia Dávila Aranda. “Endemism in the Mexican Flora: A Comparative Study in Three Plant Groups.” Annals of the Missouri Botanical Garden 90, no. 1 (2003).

Ramamoorthy, T. P., A. Lot, and J. Fa, eds. Biological Diversity of Mexico: Origins and Distribution. New York: Oxford University Press, 1993.

"Zacatonal Transvolcánico y de la Sierra Madre." NatureServe, 6 Jun. 2022, explorer.natureserve.org/Taxon/ELEMENT‗GLOBAL.2.722146/Zacatonal‗Transvolc%C3%A1nico‗y‗de‗la‗Sierra‗Madre. Accessed 8 Aug. 2022.