Location and General Description
Up to the middle of the 20th century, the ecoregion of the dry tropical forest of Central America extended in a continuous strip from the Pacific Coast of southwestern Mexico (southern Chiapas), through Guatemala, El Salvador, Honduras and Nicaragua to northwestern Costa Rica. The dry forest previously formed a continuous strip in lowland and premontane areas from 0-800 m elevation along the Central American Pacific Coast from southern Chiapas to Guanacaste. In addition, there are multiple fragments of dry forest from this ecoregion scattered in low altitude areas removed from the coast and even some relatively large fragments in interior lowland areas close to the Caribbean Sea in Honduras. In the Pacific strip area, the dry forest could also be found at higher elevations along the mountain system up to 2,000 m. The fact that this ecoregion extends along a large stretch of the Pacific Coast of Central America means that the confluence of flora and fauna from similar ecoregions of North and South America would be important. The climate of the region is tropical with a prolonged dry season of 5 to 8 months, with average annual precipitation between 1,000 and, 2000 mm and a generally bimodal pattern of rainfall, with a shorter and a longer dry period. Given that the prevailing winds in the ecoregion blow from the northeast or east to the southwest or south and most of the ecoregion has mountain systems running from northwest to southeast, the Pacific side of Central America receives a lesser amount of rain than the Caribbean side. These dry forests can be found in a wide variety of soils (Bullock et al. 1995).
A low stature semi-deciduous forest with two tree stories characterizes this dry forest, although there are variations in terms of structure and composition. Depending on water conditions, the trees of the canopy can measure about 30 m tall and usually have fine, compound leaves that they lose seasonally. Most belong to the leguminosae superfamily, many of which are associated with nitrogen-fixing bacteria and various species of ants. The trees in the lower story usually include more evergreen species and members of the Rubiaceae family. Mostly deciduous trees compose the canopy. Common trees in the southern part of the ecoregion include Bombacopsis quinatum, Calycophyllum candidissimum, Casearia arguata, Chomelia spinosa, Croton reflexifolius, Enterolobium cyclocarpum, Eugenia salmensis, Erythroxylon havanense, Eugenis salmensis, Guazuma ulmifolia, Jacuqinia pungens, Tabebuia ochracea, T. rosea, Thouinidium decandrum, Trichilia colimana, and Zanthoxylum setulosum (Hartshorn 1983). Underneath the canopy, thorny trees make up the understory of the forest. Also common are woody lianas and epiphytes. The small fragments of dry forest that remain contain species that are endangered and at risk of extinction such as black laurel (Cordia gerascanthum), "cristobal" Platymiscium parviflorum and P. pinnatum, "Tempisque" Syderoxylon capiri, Swietenia humilis and mahogany (S. macrophylla), "lignum vitae" (Guaiacum sanctum), "cocobolo" Dalbergia retusa, "ronrón" Astronium graveolens. Other interesting, unique or rare plants in the region are "guachipelín blanco" Myrospermum frutescens, brazilwood (Haematoxylon brasiletto), "tamarindo de monte" Lysiloma divaricatum, Cedrela odorata and Bombacopsis quinatum (Dinerstein et al. 1995; Bullock 1995; Jiménez et al. 1997).
The dry forest on the Pacific Coast of Central America corresponds to an ecoregion of biological interest because elements of both South and North America are mixed This ecoregion also contains a large percentage of endemic flora and fauna. At least 50 plant species are endemic to the region (Bullock 1995) such as Myrospermum. A Costa Rican endemic is Rehdera found in the northern Guanacaste Province (Gentry 1995). Many plant species have evolved to survive in these forests. During the dry season, for example, many species lose their leaves and drop their fruits, allowing them to limit evapotranspiration. There are also numerous adaptation examples of succulent sclerophyllous species with photosynthetic stalks or bark, short and synchronous flowering periods, and large deep roots all. This can be considered an ecosystem intimately associated with the human species for at least the last 11,000 years (Bullock 1995). As a result the ecosystem has suffered anthropogenic disturbances for considerable time. It has some vegetation in semi-arid zones and on lands with special geologic conditions and thus some endemic vegetation can be found, such as high-density stands of Quercus oleoides, and Crescentia alata. Although it is a seasonal environment, there are some fungi that have adapted to the dryness and high temperatures. New records of bryophytes and pteridophytes have emerged in Costa Rica. There are still entire groups of plants and fungi in the biological environment that remain unknown (WWF et al. 1999).
Considered a Central American area of interest by Harcourt et al. (1996) due to the endemism of its avifauna, this area also includes part of the wet forests of the Pacific adjacent to the dry forests outside of this ecoregion. According to Stattersfield et al. (1998) this ecoregion falls within the North Central American Pacific slope Endemic Bird Area with four restricted range species three of which are endemic including the white-bellied chachalaca (Ortalis leucogastra), the blue-tailed hummingbird (Amazilia cyanura) and the giant wren (Campylorhynchus chiapensis). The Pacific parakeet (Aratinga strenua) although not endemic this ecoregion is part of its restricted range (Stattersfield 1998).
Large numbers of mammals live in these forests including endangered species of spider monkey (Ateles geoffroyi) which use the corridors of rivers through the dry forest (Appendix I of CITES), as well as various cats such as Felis onca, F. concolor, F. pardalis, F. wiedi and F. yaguaroundi, tapir (Tapirus bairdii), anteaters (Tamandua mexicana) and many others. Mention should be made of the aquatic fauna of the Pacific coast that, depending on the zone, is home to up to five different species of marine turtles, numerous fish, amphibians and other endangered reptiles.
In Honduras, the dry forests are very deteriorated. The principal cause has been migratory agriculture. With the country’s demographic explosion, the future is expected to bring a greater reduction in the few remaining dry forest habitat areas. Indiscriminate hunting and fishing, and trafficking in wildlife also threats this ecoregion. None of the small patches of dry forest in existence are found in protected areas (Carrillo et al. 1994; WWF et al. 1999). In Nicaragua, the Pacific Coastal area is the most populated region, with the most infrastructure and urban development. In addition, for the last 40 years large areas have been devoted to the growing of cotton, sugar cane or banana, and to a lesser extent coffee. Most of the hydrographic basins are contaminated and experience frequent droughts. Deforestation is due to the conversion of forestlands to extensive cattle-raising and migratory agriculture. In addition, forests are cleared for firewood, which represents nearly 50% of all of the country’s energy sources (Carrillo et al. 1994). However, a few remnants of dry forest remain at elevations below 500 m, with average annual precipitation of less than 1,500 mm. Some of the characteristic species are boxwood (Phyllostylon brasiliensis), lignum vitae (Guaiacum sanctum) and Haematoxylum brasiletto. Costa Rica is the country that has implemented the most conservation strategies for this ecoregion, although very little of the original habitat is protected. This forest is affected primarily by the extraction of precious woods and many agricultural activities (WWF et al. 1999).
The highest priority in the ecoregion is the need for rehabilitation, formulation of management strategies including fire control and prevention, and absolute protection of the last remaining fragments, as small as they may be. If an action plan is not established according to each country’s socioeconomic and political structures, the dry forests could be wiped out completely in a short time, leaving only tiny remnants (Bullock et al. 1995). The action plan should not only conserve but also work on the recovery of contiguous areas in the ecoregion.
Types and Severity of Threats
The threats to this highly decimated ecoregion vary in each country. In Guatemala, inadequate economic structures, large numbers of poor people with basic needs, expansion of the agricultural frontier and many other factors have an effect on the amount and rate of habitat destruction (Carrillo et al. 1994). In El Salvador, conservation of the dry forest has been difficult due to the lack of sectional planning, organization, institutional coordination, policies, legislation, and governmental financial capacity. The country’s natural resources and wildlife are highly endangered. The crimes of usurping and usufruct of state areas threaten the existence of natural areas (Carrillo et al. 1994; WWF et al. 1999). While this country once had abundant flora and fauna, the only remaining Park with dry forest is Deininger National Park covering 7.32 km2 (Janzen 1986; Sabogal 1992; WWF et al. 1999).
Justification of Ecoregion Delineation
The delineation’s for the Central American dry forests were derived from a variety of maps and other sources, and the final linework was a result of combining this data with expert opinion at a number of workshops. The linework for Costa Rica follows the Holdridge system (Tosi 1969) and is derived by lumping the tropical dry forest and tropical dry forest transition to humid life zones. The delineation’s for the dry forests of Nicaragua were derived from national vegetation and coverage maps (Inventario Nacional de Recursos Fisicos. 1966; Instituto Nicaraguense de Recursos Naturales y del Ambiente (IRENA) 1992). Within Honduras, Holdridge (1962) lize zones were again used and linework was derived by lumping lowland dry forest, lowland arid forest, and premontane dry forest. In El Salvador, the Instituto Geográfico Nacional "Ingeniero Pablo Arnoldo Guzmán" (1987) map was utilized and expert opinion helped place the lines. In Guatemala, Junio (1982) was utilized for linework and then expert opinion was consulted for the final product. Some assumptions were made based on climate and elevation to map historic ranges in areas were original habitat has long since been degraded. Linework in Mexico was based on Flores et al. (1971), and modified by expert opinion resulting from several workshops (CONABIO 1996 and 1997, INEGI 1996). Justification for the ecoregion is based on endemic bird areas (Stattersfield et al 1998) and both floristic and faunistic range limits to "dry forest" species, associations, and processes.
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Prepared by: Sandra Andraka (WWF Central America)
Reviewed by: Dr. Manuel Guariguata (CATIE)