Southern Pacific Dry Forests

The lesser long-nosed bat has a wide-spread range of subpopulations throughout Central and North America. Typically, the lesser long-nosed bat will roost in old mines and caves nearby the base of mountains in groups of thousands. One roost in Mexico was identified to have over 100,000 bats. This species is relatively small (8 cm) but has a long tongue adapted to gathering nectar from the dry forest flowers; it also feeds on fruits and insects. It is a characteristic species of the Southern Pacific Mexico Dry Forests, and very important for the pollination of night blooming cactus such as the emblematic saguaro and organ pipe cactus. These bats will hover above the flowers to gather the nectar, and in the process became covered in pollen.

The Southern Pacific Dry Forests ecoregion is located on the southeastern slopes of the Sierra Madre del Sur Mountains, which give way to a narrow fringe of coastal plains on which the dry forests of this ecoregion are found. The elevation ranges from sea-level to 1,400 m. The climate is tropical dry, with precipitation levels of 800 mm/year after a length dry season. 

The forests grow mostly on shallow, well-drained soils derived from limestone. Dominant plant species include Lysiloma divaricatum (a hardwood “quebracho” or “axe breaker” tree species) and the flowering plants torchwood copal and Bursera excelsa (another copal). Often these are found in association with Ceiba aesculifolia trees (reaching up to 25 m), Comocladia enleriana flowering plants, and Trichilia Americana trees identified by their exfoliated bark. 

The dry forests of southern Pacific Mexico constitute a narrow belt of vegetation along the coast and have a unique assemblage of species, including many endemic. The plant genera Acacia (shrub and tree groups), Ipomoea (flowering plant groups), and Euphorbia (flowering plant groups) have more endemic species in these forests than anywhere else in Mexico. 

Beyond vegetation, the butterfly family Papilionidae has 11 endemic species within this ecoregion. It is the richest area for spiders in Mexico with 311 species and also has greatest diversity of scorpions in Mexico. It is also one of the only areas where the Mexican bearded lizard (one of the only two venomous lizards in the world) can be found. Characteristic fauna includes lesser long-nosed and greater bulldog bats, coati, Buller’s pocket gopher, green and black iguanas, elegant quail, and the red-crowned ant tanager. 

The only remaining intact dry forest occurs along the coast of the state of Michoacán, an area with very difficult access, making agriculture and other land exploitation opportunities unappealing. Despite the biological importance of this region and its critical condition in the face of outstanding threats, only two protected areas have been established, one along the coast of the state of Oaxaca and the other in Guerrero. Another eight areas have been proposed for protection. Several Important Bird Areas have also been identified here, including Sierra Norte, Sierra de Miahuatlan, and La Sepultura.

Over several centuries, the deciduous forests of the Mexican Pacific have been severely exploited and disturbed. Agricultural expansion, primarily for fruit and coffee plantations have replaced vast expanses of forest. This impacts native biodiversity directly through habitat loss and indirectly through erosion and soil loss. Major threats of today include sheep farming and developmental pressures from increasing tourism. Illegal hunting is an additional threat, severely reducing the populations of green and black iguanas.

The priority conservation actions for the next decade are to: 1) encourage resource-based management integration in agricultural and animal farming practices; 2) increase the number of protected areas prioritizing the dry forests in the state of Michoacán; and 3) regulate development processes as tourism increases infrastructure.

Citations 

1. Valero, A. Schipper, J. Allnut, T. 2019. Southern North America: Southern Mexico. https://www.worldwildlife.org/ecoregions/nt0230 Accessed March 13, 2019.
2. Challenger, A. 1998. Utilización y conservación de los ecosistemas terrestres de México. Pasado, presente y futuro. Conabio, IBUNAM y Agrupación Sierra Madre, México.
3. Arriaga, L., J. M. Espinoza, C. Aguilar, E. Martínez, L. Gómez, and E. Loa (coordinadores). 2000. Regiones terrestres prioritarias de México. Escala de trabajo 1:1 000 000. Comisión Nacional para el Conocimiento y uso de la Biodiversidad. México.
4. Medellín, R. 2016. Leptonycteris yerbabuenae. The IUCN Red List of Threatened Species 2016: e.T136659A21988965. http://dx.doi.org/10.2305/IUCN.UK.2016 1.RLTS.T136659A21988965.en. Accessed March 13, 2019