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Subtropical thorn woodland |
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Subtropical dry forest |
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Dry forest in transition to humid |
The more extensive areas of this life zone are found in the Southwest of the country. A small area is observed to the southwest of Baní, crossing Arroyo Hondo, and extending westward till Calderas Bay. The borderline between dry forest and thorn woodland is found again to the east of Azua, between Hatillo and Las Charcas. A more extensive area begins around Puerto Viejo, extending to the northwest, crossing part of the Azua valley, the Yaque del Sur river to around the Enriquillo lake.
To the southeast of Pedernales, and around Cabo Rojo, another area with this life zone is observed; it is not well defined because it is on limestone and it is easy to confuse it with the dry forest.
In the Northwest, there is another small area in the foothills of the Los Aguacates mountain, close to the Cruce de Guayacanes.
In this life zone, the climatic conditions are represented by bright days most of the year and a very low annual rainfall. Trade winds cross these regions; those winds, changing direction depending on the season, do not allow that the air masses filled with water could get saturated and so rains do not fall. Most rainfalls are convective ones, and fall mainly from august to october, matching the season with higher rainfall in the Southwest. In Puerto Viejo (Azua), the mean annual total of rainfall is 455 mm.
The mean annual biotemperature could be estimated in 22.0 °C. The potential evapotranspiration could be estimated, on average, to be 130% higher than the amount of mean annual rainfall. In this life zone, the rain water rarely gets to flow by the river beds.
Lands in this life zone are flat to slightly hilly. Altitude ranges from sea level to 300 m high.
Natural vegetation consists mostly of shrubs and thorny plants. Among the main species that prevail in this formation are cacti, such as guasábara (Cylindropuntia caribaea), common in the region between Azua and the Enriquillo lake; cagüey (Neoabottia paniculata), common from the Tábara river to around Enriquillo lake; bayahonda or cambrón (Prosopis juliflora), common to all regions within this zone. Besides cacti, there are isolated Capparis spp. plants.
The land in this life zone could be used in agriculture only with irrigation, mainly those of alluvial origin. The recommended crops are those with a short vegetative cycle.
The regions within this life zone are located in different places of the country. In the Southwest, it is found in along a belt that, starting in the Enriquillo town, extends westward by the southern foothills of Sierra de Bahoruco till the Haitian border, close to Pedernales. In the northern section of the Barahona peninsula, there is another belt that goes from the Caribbean Sea coast to Jimaní, between the limit of the thorn woodland and the northern foothills of Sierra de Bahoruco. The dividing limits between the dry forest and the Subtropical humid forest are confusing in some places in the southern and eastern foothills of Sierra de Neyba and this region continues till the neighborhoods of Pedro Corto and Las Matas de Farfán. From here, the limits extend to the Southeast along the southern foothills of Cordillera Central, from Juan de Herrera, Padre las Casas, Baní, till Hato Viejo to the South of San Cristóbal. In the Southeast of the country, it goes from Cabo Engaño to San Rafael del Yuma; in the Northwest, it extends itself from Santiago to Monte Cristi, among the northern foothills of Cordillera Central and the southwestern foothills of Cordillera Septentrional.
The climatic characteristics of this life zone are bright and sunny days during the dry months and partially cloudy during the raining season and months January to March.
In the South of the country, rains occur in two well marked season; the first season corresponds to May and June, when the trade winds determine the country's more important convective rains, even if they do not correspond to the highest rainfalls in this region. The second rain season is September and October, with the highest rainfalls in the region. In the North, the situation is more variable; in some places, the main rains occur in April - June and in other places it is in September - October.
Rainfalls range from 545 mm, in Puerto Escondido, to 980 mm in Santiago de los Caballeros. On average, it rains in 51 days per year, some times as showers.
For this life zone, mean annual biotemperature is very close to 22.5 °C and it corresponds to a mean annual temperature of about 26 °C, mainly in those places close to great water masses. In places located in higher elevations, the mean annual temperature could be around 23 °C.
Potential evapotranspiration for this life zone could be estimated, on average, in 60% higher than the total annual amount of rain. Rain waters do not get to flow by rivers, except those coming from more humid life zones.
Topography in this life zone is variable, from flat close to the coast to hilly in the foothills of the mountain ranges. Altitude ranges from sea level to about 700 m.
Guayacán Click to enlarge |
The natural vegetation consists mainly of species of the family Cactaceae (cacti), shrubs and some trees. Among the main species of this life zone are baitoa (Phyllostylon brasiliense), bayahonda or cambrón (Prosopis juliflora), aroma or cambrón (Vachellia farnesiana), guayacán (Guaiacum officinale) and vera (Guaiacum sanctum). Species vary after soil quality; in some places, almácigo (Bursera simaruba) and frijolillo (Capparis spp.) prevail; meanwhile in other places the most common species are guano (Coccothrinax argentea) and some members of genus Croton (tremolina blanca - C. discolor). Uva de playa (Coccoloba uvifera) is common in soils close to the coast. In those places where the natural vegetation has been eliminated then cacti prevail, such as cayuco (Pilosocereus polygonus), alpargata (Consolea moniliformis), bombillito (Mammillaria prolifera), guasábara (Cylindropuntia caribaea), melón espinoso (Melocactus communis) and others.
Native species grow slowly in this life zone. Only where there is enough soil humidity, there could be formation of new tree stands by natural regeneration.
Agriculture without irrigation is restricted to crops with short vegetative cycles because the short rain season. However, pests and diseases are rare and the climatic conditions are appropriate for the development of agriculture.
The segregation of this transitional zone to the dry forest itself is based mainly in its climatic characteristics and its orographic location. In those places where this zone is close to the humid forest, annual rainfalls occur during 108 days. In some places, the month with the highest rainfall is May but in others is October. In transitional zones, located in higher altitudes, biotemperature could be 2 °C lower in some periods. This atmospheric phenomenon helps to keep longer the humidity, even if those places get the same amount of rain that in dry forest.
To identify this transitional zone, the palm cana (Sabal umbraculifera) is an indicative species that helps to separate this zone from the humid forest.
| Life Zones | Dry Forests | Humid Forests | Montane Forests |
