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Island group in the southeast Caribbean

In contrast to the Leeward Islands that form the north half of the Lesser Antilles, the Windward Islands are characterized by a sharp relief, high annual rainfall, large areas of wet forest, and only small areas of dry, scrub habitat. This Xeric Scrub Ecoregion, due to its limited area and proximity to coastal areas, is particularly susceptible to human-caused alteration and disturbance. Areas such as Barbados and the western coast of Dominica suffer from a relatively high population and extensive agricultural development; circumstances that bring associated problems such as introduced exotics and habitat alteration. Notable endemics in this ecoregion are the Grenada dove (Leptotila wellsi) and several reptiles characteristic of dry, low elevation xeric scrub habitat. Most conservation focus is on the more elevated forest areas of the Windward Islands however, it is perhaps this ecoregion that is suffering the most direct pressure from population growth and development.

  • Scientific Code
    (NT1317)
  • Ecoregion Category
    Neotropical
  • Size
    400 square miles
  • Status
    Vulnerable
  • Habitats

Description
Location and General Description
This ecoregion represents the drier, low elevation, areas of islands in the Caribbean’s Windward Islands and Barbados to the east. Specifically, Xeric Scrub habitat can be found on all of Barbados, and coastal portions of Trinidad, Grenada, St. Lucia, Martinique, and Dominica.

The Windward Islands extend south from 15° 45' to 11° 45' N and from 60° 45' to 62° 00' W (Rand McNally 1988). They are west of Barbados and northwest of Trinidad and Tobago. From south to north, the islands are: Grenada, the Grenadines, St. Vincent, St. Lucia, Martinique, and Dominica.

The Windward Islands lie within the trade wind belt and lie upwind, in terms of the prevailing south-easterly wind, of the Leeward Islands. The rainy season occurs in summer and fall. Hurricanes and tropical storms pass over the islands during this period. The interior highlands of the larger islands also receive rainfall in the drier winter months and additional amounts in the summer months (Walsh 1985). Annual rainfall in the interior highlands ranges from 10,000 mm in Dominica to 3,750 mm for the lower elevation mountains in Grenada. Coastal areas that comprise much of the Xeric Scrub habitat receive lesser amounts ranging from 1,000 mm on Dominica to 1,600 mm at the southern end of St. Vincent.

The Windward Islands form a volcanic island arc. Lava flows, ash, and pyroclastic deposits ranging from Miocene to recent in age are the principal bedrock found in these islands. Some limestones are interspersed between the volcanic layers (Fairbridge 1975). In general, Grenada, the Grenadines, and St. Vincent are composed of basalts and basaltic andesites. Typically, lava flows outcrop on the steeper slopes and ash underlies the gentler slopes (Walsh, 1985). St. Lucia, Martinique, and Dominica are predominantly composed of acid andesite and dacitic rocks. Pyroclastic flow deposits, volcanoclastics, and lava domes are typical for these islands (CCA 1991a). Characteristic soils in the ecoregion are alluvial and shoal while montmorillonitic clay is commonly found on the western slope of Dominica (CCA 1991b).

The vegetation of this ecoregion is seral in character with an adaptation to xeric conditions and low soil fertility. The extent and development of vegetation along the beaches depends on the width and elevation of the beach and the extent of interference by man (Stoffers 1993). Commonly found are Lonchocarpus pentaphyllus, Pisonia fragrans, Haematoxylon campechianum, Myrsia atrifolia, Chrysophyllum argenteum, Erythroxylum ovatum and two types of cactus (Opuntia dilenii, Pilosocereus royeni) (Carrington 1998). In Barbados, sugar cane (Saccharum officinarum) cultivation dominates with plantations occupying nearly 28% of the land area. In the Windward Islands, xeric scrub occurs most in areas with high coastal population densities and concomitant agricultural development. As a result, this ecoregion is particularly susceptible to human-caused alteration and degradation.

Biodiversity Features
Due to the high proportion of tropical forest on the Windward Islands, there is high floral and faunal diversity. However, relatively little is unique to the small proportion of xeric scrub habitat found in this part of the Lesser Antilles. The most important plant component of this Ecoregion is the several species of Cactaceae which act as important resources for local fauna.

Barbados has the greatest amount of faunal endemism in this ecoregion owed partly to its relatively large area. The tree lizard (Anolis extremus) is one of these. It is ubiquitous and has adapted well to human presence. Other endemic lizards include Kentropyx borckiana and Phyllodactylus pulcher (Malhotra & Thorpe 1999). The single endemic colubrid (Liophis perfuscus) has a very restricted distribution in the hilly, extreme east central portion of the island which is relatively mongoose free and not affected by sugar cane production (Censky & Kaiser 1999). It has been suggested however, that this species is likely extinct (Malhotra & Thorpe 1999). Crocodiles are not native to the Lesser Antilles. Caiman crocodylus, a Central and South American species, is apparently an occasional vagrant to the Grenadines (Schwartz & Henderson 1991).

The only bird endemic to the Windward Islands Xeric Scrub Ecoregion is the Grenada dove (Leptotila wellsi) that can be found in mature dry scrub lowlands and hillsides. It appears to favor a mixture of closed canopy, dense scrub and large areas of bare ground that can be found along the southern coast of Granada (Raffaele et al. 1998). All nonvolant mammals found in the Windward islands are previously introduced by Amerindian or European settlers. Rodents, feral goats, pigs and opossums have had a major impact on native vegetation and fauna. There are no remaining endemic rodents in the Lesser Antilles (Woods 1985). The introduction of the mongoose, originally introduced to control rodents and pit vipers (Bothrops), more than any other single factor, is correlated with the extirpation or extinction of reptile populations in the West Indies and particularly the small islands of the Lesser Antilles (Schwartz & Henderson 1991).

Current Status
The small size and limited resources of the Windward Islands of the Lesser Antilles, in relation to the human populations, have created serious problems of resource depletion and exploitation. Many of the Windward Islands are characterized by rugged topography that significantly constrains human settlements and agricultural development. As a result, human populations are highest in coastal areas. Several of these areas are comprised of Xeric Scrub habitat and fall within this Ecoregion. A typical example is Dominica where 70% of the island’s population lives on the flatter, western (leeward) side of the island (CCA 1991b).

Types and Severity of Threats
The two most prominent threats to this Ecoregion are the loss of natural habitat and the introduction of exotic species. These areas have suffered a long history of environmental degradation, chief among them the cultivation of tobacco and sugar-cane. Barbados is perhaps the most extreme example having been under cultivation for nearly 300 years, leaving little natural vegetation (Malhotra & Thorpe 1999). A more recent threat, with the advent of the tourism industry, is the construction of hotels and related infrastructure at the expense of natural habitats. Introduced animals continue to have a profound effect on the native fauna of all of the Lesser Antilles. The mongoose (Herpestes auropunctatus), feral cats, and in some locations rats (Rattus spp.), continue to prey on numerous lizard and snake species while domestic goats have a significant effect on vegetation, particularly on small xeric areas.

Justification of Ecoregion Delineation
This xeric scrub ecoregion of the Windward Islands was designated according to various CCA survey reports (1980). In order to maintain our broad scale coverage we lumped their classifications of "cactus scrub terrestrial life zones" from all of the Windward Island which contained this habitat type. Littoral vegetation was also included, when bordering cactus scrub formations.

References
Caribbean Conservation Association (CCA). 1991a. St. Vincent and the Grenadines: Environmental Profile. St. Michael, Barbados.

Caribbean Conservation Association (CCA). 1991b. Dominica: Environmental Profile. St. Michael, Barbados.

Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: St. Vincent, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.

Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: Grenada, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.

Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: St. Vincent, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.

Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: St. Lucia, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.

Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: Grenadines, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.

Caribbean Conservation Association. 1980. Survey of conservation priorities in the Lesser Antilles: Barbados, Preliminary Data Atlas. Eastern Caribbean Natural Area Management Program, Caribbean Conservation Association, the University of Michigan and the United Nations.

Censky E. J. and H. Kaiser. 1999. The Lesser Antillean fauna. In B. I. Crother, editor, Caribbean amphibians and reptiles. p. 181-221. Academic Press, London.

Carrington, S. 1998. Wild plants of the eastern Caribbean. Macmillan Education LTD. London.

Fairbridge, R.W. 1975. Windward Islands. In R.W. Fairbridge, editor, The Encyclopedia of World Regional Geology, Part 1: Western Hemisphere, p. 667. Stroudburg, Dowden, Hutchinson and Ross.

Lacereda, L.D. 1994. Conservation and sustainable utilization of mangrove forests in Latin America and Africa regions. Part 1, Latin America. Mangrove Ecosystems Technical Reports. Vol. 2. International Society for Mangrove Ecosystems. International Tropical Timber Organization.

Malhotra, A. and R. S. Thorpe. 1999. Reptiles and amphibians of the Eastern Caribbean. Macmillan Education LTD, London.

Portecop, J. 1975. Carte ecologique de la Martinique. Map 1:75,000. Centre Universitaire Antilles, Guyane, Martinique.

Raffaele H., J. Wiley, O. Garrido, A. Keith, J. Raffaele. 1998. A guide to the birds of the West Indies. Princeton University Press, Princeton.

Rand McNally 1988. World atlas of nations. Rand McNally. New York.

Schwartz, A. and R. W. Henderson. 1991. Amphibians and reptiles of the West Indies: descriptions, distributions, and natural history. Univ. Florida Press, Gainesville, FL.

Stoffers, A. L. 1993. Dry coastal ecosystems of the West Indies. In E. van der Maarel, editors, Ecosystems of the world 2B: dry coastal ecosystems Africa, America, Asia and Oceania. Elsevier Science Publishers, B.V., Amsterdam.

Walsh, R.P.D. 1985. The influence of climate, lithology, and time drainage density and relief development in the volcanic terrain of the Windward Islands. In I. Douglas and T. Spencer, editors, Environmental change and tropical geomorphology, p. 93-122. Allen and Unwin London.

Woods, C. A. 1985. Endemic rodents of the West Indies: the end of a splendid isolation. Proceedings from a workshop of the IUCN/SSC Rodent Specialist Group, #4. p. 11-19.

Prepared by: Sean Armstrong
Reviewed by: In process

 

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