Location and General Description
The Motagua valley thornscrub is one of the driest areas of Central America. Surrounded by mountains that reach up to 3,000 m on the north side and 2,000 m on the south, the valley receives less than 500mm of precipitation annually. Most of the rain falls from June to August, when the valley experiences a short, green growing season (Land 1970). The xeric climate, with its extended dry season, contrasts sharply with the bordering mountain-top cloud forests, which receive up to 10 times as much rainfall. The valley has been extensively impacted by development for irrigated agriculture in the broad central valley floor and subsistence agriculture and cattle farming elsewhere, often despite extremely steep slopes. Only about 20-30,000 hectares (10-15% of the total) remain as relatively intact natural habitat (Dix 1997); none of the ecoregion is currently in protected areas.
The Motagua valley is situated in northeastern Guatemala, along the border of Honduras, where it lies on the fracture zone of the North American and Caribbean continental plates which have been moving apart since the Cenozoic. It is among the smallest ecoregions in Mesoamerica, approximately 200,000 ha, and its composition is heavily influenced by a single large river, the Motagua River, which flows into the Atlantic Ocean. The valley is subjected to high temperatures, up to 41 C, and experiences a long dry season (Dix 1997).
Vegetation is limited by aridity and sandy soil. The flora of the Motagua valley is dominated by spiny species, particularly Opuntia cacti, Acacia, and thorny Fabaceae shrubs, except in river valleys with permanent water which support rich evergreen, riparian forests. The most abundant species include: Acacia spp., Opuntia spp., Cephalocereus maxonii, Nyctocereus guatemalensis, and Guaiacum santum (Dix 1997).
Only 75 bird species occur in the valley, with the Columbidae, Tyrannidae, Icteridae, and Fringillidae families sufficiently abundant in the upper valley to be considered characteristic (Land 1970). This valley is the only location of Russet-crowned Motmot (Momotus mexicanus) in Central America.
The integrity of all components of the Motagua valley are seriously threatened by human development. The valley floor has been almost entirely converted to irrigated cropland. Riparian habitats of the smaller feeder rivers are largely converted to a mixture of fruit trees and small patches of irrigated annuals (corn and beans). The lower, drier hillsides are used for range animals, cattle goats and sheep, while hillsides higher in the valley are also planted to coffee and cardamom (Dix 1977).
Types and Severity of Threats
No protected areas exist within the valley and current land use trends will inevitably eliminate much of the native biodiversity. However, in recognition of this threat, there is an effort by a national conservation group, Defensores de la Naturaleza, to extend the nearby Sierra de las Minas biosphere reserve into the Motagua valley. The success of that effort is critical to the future of this ecoregion (Powell, pers. obs.).
Justification of Ecoregion Delineation
This thornscrub ecoregion is limited to the Motagua Valley of Guatemala and vicinity, and is host to several endemic species. Linework follows Junio (1982), from which we lumped the following classifications: "natural grasslands in the arid sector of the Motagua River", "natural grasslands", and all enclosed or partially enclosed agricultural or cultivated classifications.
Dix, M.A. 1997. Sierra de las Minas Region and Biosphere Reserve, Guatemala. S. P. Davis, V. H.
Haywood, O. Herrera-MacBryde, J. Villa-Lobos, and A. C. Hamilton, editors. 1997. Centres of Plant Diversity-Volume 3: The Americas. WWF and IUCN. United Kingdom.
Junio, C.A. 1982. Mapa de cobertura y uso actual de la tierra Republica de Guatemala. Instituto Geográfico Nacional Guatemala, Guatemala City.
Land, H.C. 1970. Birds of Guatemala. Livingston Publishing Company. Pennsylvania. Powell, G. Personal observation.
Prepared by: George Powell and Sue Palminteri
Reviewed by: In progress