Location and General Description
Alvarado mangroves flourish in specific spots that are bathed by important rivers in the state of northern Veracruz and Tamaulipas, right up to the Mexico/USA border. They grow on flat terrain’s of the Gulf of Mexico coastal plains, and are influenced by the Tonala River near the border between Tabasco and Veracruz, by the Papaloapana in northern Veracruz, and by the Pánuco River near the border between Tamaulipas and Veracruz. Mangroves grow on clay soils that are deep and rich in organic matter (Rzedowski 1988). The climate is tropical subhumid with summer rains; temperature oscilations are very slight, and the levels of humidity are relatively high with between 1200mm and 2500 mm of annual rainfall.
The dominant tree species are Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa. Epiphytes are abundant, as is the fern Acrostichum aureum. These are indicators of low salinity in mangrove communities. Pachira aquatica, Hibiscus tiliaceus, and Phithecellobium belizence are common species of plants that belong to riparian associations, but nevertheless mingle with the mangroves. There are also many species of free-floating plants. As in most mangroves, herbaceous associations are not abundant in these communities, because they are intolerant of permanent flooding (Lot et al. 1993).
The Alvarado mangroves are an important migratory stop for many birds; the mangroves near El Moro de la Mancha Biological Station house 61 species of birds, of which 50% are migrant species that stop off at El Moro and then continue their route toward South America (Ortíz-Pulido et al. 1995). CONABIO has identified an terrestrial priority site in this ecoregion: Humedales del Papaloapan (Arriaga et al. 2000). This ecoregion also contains the Humedales de Alvarado important bird area (Benitez et al. 1999).They support enormous quantities of invertebrates on which many species of aquatic birds and other terrestrial vertebrates feed; thus they are natural promoters of biodiversity in aquatic environments. Mangroves near Los Tuxtlas biological station allow for the stabilization of lagoon shores (Paré et al. 1997) and provide protection. They also serve as natural storage areas for the nutrients that other species provide in the form of organic waste. Mangrove associations have long been recognized as good soil retainers (Miranda 1998; Tomlinson 1994) that allow for the continuous formation of soil to support the terrestrial communities associated with mangroves (Rzedowsky 1988).
Characteristic species of this mangrove ecoregion include birds such as the keel-billed toucan (Ramphastos sulfuratus), Townsend’s solitaire (Myadestes towsendi), bare-throated tiger heron (Tigrisoma mexicanum), tricolored heron (Egretta tricolor), reddish egret (Egretta rugescens), jabiru (Jabiru mycteria), wood stork (Mycteria americana), swallow-tailed kite (Elanoides forficatus), zone-tailed hawk (Buteo albonatus), amazon kingfisher (Chloroceryle amazona), prothonotary warbler (Protonotaria citrea). Mammals include the spider monkey (Ateles geoffroyi), nutria (Scalopus aquaticus), Gulf Coast kangaroo rat (Dipodomys compactus), and Texas pocket gopher (Geomys personatus).
Mangroves in Veracruz have been severely disturbed by human exploitation and water pollution. Some portions of mangrove habitat in Veracruz have been completely destroyed due to these pressures (Flores-Villela 1993; Gallegos 1986).
Types and Severity of Threats
The main threats to mangroves are oil extraction, water pollution, logging for agricultural purposes or for road openings, and fires. Oil affects photosynthesis, seed germination, and flowering processes. Furthermore, roadwork, drainage and fires are all associated with oil extraction, and contribute to habitat loss for many species, as well as disturbing the communities themselves. The consequences of these activities are (among others): reduction in mangrove tree size, disturbance of sedimentation and filtering processes, and in turn a reduction of primary productivity. Oil spills are a major threat to these habitats, because they can be lethal for mangroves. The mangrove roots are the main point of interaction with the environment, contributing to good water conduction and allowing entrance of small microorganisms that fix nutrients for them. Thus, pollution by hydrocarbons may be lethal for mangrove communities since these compounds may block the pores in mangrove tree roots (Gallegos 1986). Artificial drainage of mangroves for oil extraction alters the natural nutrient cycles, lowers the supply of nutrients, freshwater, and organic matter, and promotes excessive sedimentation, thus blocking natural nutrient exchange. Despite the high degree of species richness and diversity of mangroves, only one protected area has been established to ensure the permanence of aquatic habitats in Veracruz. Aquatic associations are considered an endangered habitat in Veracruz (Flores-Villela & Gerez 1994) and must therefore be adequately managed for protection.
Justification of Ecoregion Delineation
Classification and linework for all mangrove ecoregions in Latin America and the Caribbean follow the results of a mangrove ecoregion workshop (1994) and subsequent report (Olson et al. 1996).
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Prepared by: Alejandra Valero
Reviewed by: In process