The West Indies

Alberto Areces-Mallea

The Caribbean islands form an archipelago of over 1000 islands of considerable range in size, altitude, soil types and environmental niches. Exposed land surfaces cover a distance of 2700 km from Barbados on the east, to the western tip of Cuba, while the distance from Grenada in the Lesser Antilles to the northern tip of the Bahamas is 1900 km. The islands range in size from Cuba, with 114,500 km2 and a vascular flora of over 6000 species, to islets of small rocks of a few square metres and a flora of a dozen species.

The diversity of the West Indies is seen in such factors as altitude of the islands, temperature range, soil types, and units of vegetation on each island. Hispaniola has the greatest range in altitude where the Enriquillo Basin is 30 m below sea level and Pico Duarte reaches 3000 m. Volcanic peaks in the Lesser Antilles range from 900 m to approximately 1500 m. The major part of the land surface within the archipelago is below 300 m in altitude.

The average (mean) temperatures of the area at elevations of less than 90 m range from 24.9" (Havana) to 26.1 °C (Dominica). Neither annual nor daily variations in temperature are great. Day-length range is nearly two hours greater in Nassau in the north than it is in Trinidad just south of the area under consideration. With respect to rainfall, many areas of the West Indies receive less than 1000 mm of annual precipitation, while rainfall exceeding 5000 mm has been suggested for several areas. Sometimes there are six or seven months of reduced rainfall occurring as two dry periods, while many mountain areas show no months of rainfall of less than 100 mm. Succulents and low spiny shrub vegetation are characteristic of coastal areas with seasonally higher temperatures and rainfall under 700 mm, often falling in one short annual period.

The West Indies show a variety of soil types which offer a relatively large number of ecological niches. There are siliceous savannas in western Cuba and on the north coast of Puerto Rico. The central portion of Cuba has a nearly uninterrupted serpentine savanna. Areas of gypsum and salt concentrations, often in bands, occur in Hispaniola. A belt of aluminous lateritic soil extends through most of the island of Jamaica and occurs also in

Cactus scrub with Stenocereus hystrix and Pilosocerus royenii with Plumeria obtusa in the foreground, Mona Island, Puerto Rico.

The West Indies Cactus

the southern peninsula of Hispaniola; areas of volcanic activity occur in the Lesser Antilles. Outcrops of limestone as sedimentary rock or elevated coral reefs are abundant, and areas of intrusive igneous rock could be added to the chart as additional specialised habitats. The vegetation of the various soil types is often distinctive in composition or habit and is frequently high in endemic species. In general, geologic and edaphic features combine with climate and topographic factors such as high relief and alternation of lowlands and mountains, to determine the unique characteristics of the plant communities and the floristic diversity of each individual, isolated island.

The Caribbean Islands have a natural vegetation consisting of lowland and montane tropical forest, evergreen thicket, savanna, cactus-thorn scrub, marsh or swamp, mangrove, beach, and riverine communities. The total flora of the region consists of about 13,000 vascular plant species with around 6550 regional endemic species. About half of the endemics occur only in Cuba.

Institutional bases for the study of the West Indian flora locally are patchy and most of them are limited in physical resources and capabilities. Fortunately, interest is growing and there is current activity in, for example, Cuba, Dominican Republic, Puerto Rico, St. Lucia, and Barbados. In recent years, Floras covering both flowering plants and ferns have been published for the Bahamas, Islands, Jamaica, and the Lesser Antilles. A flowering plant Flora for Hispaniola is well advanced in production, although the Cactaceae has not yet been covered. New Floras of Cuba and Puerto Rico are being prepared. There is no current guide to the succulents of the West Indies.

A general Flora, to include all cryptogamic and phanerogamic groups, is proposed for the Greater Antilles under the direction of The New York Botanical Garden. Most of the current research on floristics in Cuba and Hispaniola is published in those islands, but for other territories, investigations and publication are institutionally based in North America and Europe.

The succulent flora

The succulent flora of the West Indies consists mainly of plants in the Agavaceae, Apocynaceae, Cactaceae, Euphorbiaceae, Moraceae, Portulacaceae, and Vitaceae. Also included here are marginally succulent species such as the West Indian Bombacaceae, a Sterculiaceae (Hildegardia) with a bulky, greenish trunk, all Dorstenia (Moraceae), and many of the native Euphorbiaceae with somewhat thick stems or leaves more fleshy or thicker than normal. However, no Burseraceae, Begoniaceae, Piperaceae, Rubiaceae, Urticaceae, aroids, or orchids other than the succulent vinelike Vanilla, well represented in the dry areas, are considered. Out of 324 so defined succulent plant species recorded here for the West Indies*, 243 (75 per cent) are endemic. Succulents comprise about 2.5 per cent of the total number of flowering plants of this region. The remaining 81 species (25 per cent) extend to continental landmasses in North, Central, and South America, and even sometimes to the Old World tropics and/or subtropics. This latter group is not of primary conservation concern. It is made up of many species occurring along the seashore, some within beach areas, coastal salt marshes, dunes or flats, and others on maritime rock exposures.

The families containing succulent plants in the West Indies are listed in Table 1 of Annex 14 with the number of succulent species in each genus and an indication of endemic taxa. No subspecific taxa are considered due to the yet insufficient knowledge of the Caribbean flora. New succulent species continue to be discovered (Areces-Mallea 1992, 1993) and, despite the level of botanical and horticultural interest in the group, the taxonomic status of a number of West Indian succulents remains poorly known. The non-endemic succulent species native to the West Indies are listed in Table 2 of Annex 14, whereas the endemics are shown in Table 3 of Annex 14 with their geographic distribution, regional or restricted, and an evaluation of their conservation status.

Stebbins (1952) pointed out that a dry environment stimulates speciation. The ecological and chorological study of most of West Indian endemics provides evidence for this phenomenon. In general the largest number and highest density of endemics may be observed in the arid zones (coastal areas, semi-deserts) and in the physiologically dry habitats (serpentines, limestone karsts, siliceous sands). Endemic succulent taxa are most commonly found within coastal plant communities. Cactus scrub, evergreen bushland and dry evergreen thicket occupy well drained, usually rocky, substrates. Relatively extensive semi-desert vegetation — unique flora of endemic cacti, other succulents, and spiny shrubs exist along the leeward coasts of the larger islands. The vegetation types where most of the cacti and succulents listed in Tables 1 and 3 of Annex 14 occur are described here.

I. Coastal formations

1) Sandy beaches — Herbaceous and shrubby vegetation of the tropical sandy sea shores, commonly distinguished by two main associations: a) an open pioneering community formed of creeping lianes and stoloniferous grasses (Cakile lanceolata and Blutaparon vermiculare are often associates), and b) a less open community, the next successional stage, with Sesuvium portulacastrum, Chamaesyce mesembrianthemij'olia and Argusia On low sandy shores, seaside prairies, and sandy meadows Borrichia arborescens and Scaevola plumieri might be abundant. Suriana maritima is more often found in littoral thickets in the transition of the meadows toward strand vegetation.

Sandy beach communities are common, though of limited extent on the West Indian islands, when compared with the rocky or coralline coastal associations.

* In this account including the Florida cays (only their endemic species, not found in the mainland of Florida) but excluding Aruba, Bonaire, Curaçao, Trinidad, Tobago, Margarita, and 100 other small islands adjacent to Venezuela, which are phytogeographically part of northern South America.

Undisturbed beach areas are increasingly difficult to find; most of the sandy shore areas have been heavily damaged or destroyed. Fortunately, most of the genera and species involved are of wide geographic distribution.

2) Strand littoral scrub and low forest— Inland from the coastal beach, dunes may be built up consisting solely of sand or of sand deposited on a rocky substratum. The sea-grape Coccolobauvifera is the classic component of such strand areas. Although the monodominancy of sea-grape stands is an essential characteristic found all over the West Indian islands, there are also differences with respect to the floristic composition of these associations in different locations. The community of sea-grape and Opuntia dillenii is relatively common on dry coastal areas, where the sand dunes are situated on shallow coral reefs or low banks. In the larger cays of northern Cuba Opuntia millspaughii may also be present. Selenicereus spp. are common climbers on the sea-grape. Other associated succulent species found occasionally are Scaevola plumieri, Suriana maritima, and Argugia gnaphallodes. The strand littoral scrub and low forest are still common on the sandv shores and on the first seaward dunes of the low limestone rocky shores of the Antilles, Bahamas, and Florida.

3) Saline flats — The vegetation of the salines is comprised of leaf-succulent dwarf shrubs, annual or perennial succulents, and grasses of high osmotic tension. This belt of salt vegetation is developed on the inland side of the mangrove-zone, in the areas flooded only twice a year by the high equinoctial tides, where the salt tends to concentrate by evaporation, and allows the development of herbaceous flats with Balis maritima, Salicornia spp., and Suaeda spp. Other succulents occurring in the saline prairie vegetation, mostly at the edge of the supratidal belt, are Heliotropium curassavicum and Blutaparon

They are all of wide geographic distribution, and no endemic taxa occur in these communities. Due to its environmental requirements this saltwort vegetation is not extensive, nor very abundant in the Caribbean islands. However patches and belts up to one kilometer wide may be locally common in Cuba.

4) Rock pavement vegetation — This orophilous halophytic vegetation of the supratidal rocky shores, is conditioned by the influence of salt spray, the unprotected exposure and extremely poor soil conditions. The rock-pavement substratum for this type of vegetation occurs on uplifted coral reefs as benches. It dominates entire cays of such origin or occurs in outcrops between sandy or low muddy beaches. There is a well-recognised pioneer association of creeping or prostrate leafsucculent plants such as Sesuvium spp., Trianthema portulacastrum and Lithophila muscoides, and another association with Borrichia arborescens, Chamaesyce mesembrianthemifolia and Opuntia dillenii. This community that grows on the inland side is characterised by more dense growth. In Puerto Rico and the Virgin Islands Opuntia repens may be also present, and on Mona Island (Puerto Rico) there is a spectacular dominance of Mammillaria nivosa within this type of vegetation. In contrast to sandy and saline vegetations, which are primarily of pan-tropical character, the vegetation of coastal rock pavements is mainly of Antillean and Caribbean distribution.

II. Coastal-lowland formations

1) Dry limestone shrubwoods — This dense vegetation cornposed of thorny, sclerophyllous, small-leaved trees and shrubs occurs on bare rocks of dry limestone terraces usually on the inland side of the coastal rock pavement vegetation, and on the lowland karstic 'dogtooth' formations. The 2-3 m high shrubs and the emergent individuals or groups of 5-6 m 'rod-like' associated trees are best developed under climatic conditions consisting of two dry seasons per year which together amount to about seven or eight dry months. Columnar or tree-shaped cacti may occur under a loose canopy layer or intermingled with shrubs in denser communities. They are often seen at the edges of cliffs and exposed rock surfaces together with globular cacti.

The dry limestone shrubwood, also known as thorn scrub, is considered to be the most common and characteristic lowland formation of the West Indies. Sometimes restricted to the coast, it may also extend far

Opuntia macracantha, Guantânamo, Cuba. Vulnerable.

inland in many of the Caribbean islands. Spectacular coastal benches with dry shrubwoods occur at the eastern end of Cuba arround Punta Maisi, and a series of uplifted coastal benches are found on the southern coast of Hispaniola extending inland to considerable altitude. In Maisi it is common to see Melocactus acunai in thinly rock flats between microphyllous shrubs strongly modified into grotesque windswept aberrant forms. Extensive unbroken stands of this vegetation type are found in the southern terraced Cuban coast between Maisi and Cabo Cruz, with the endemic cactus species Pilosocereus brooksianus, Leptocereus maxonii, L. sylvestris, and Opuntia macracantha, and in north-eastern Cuba, where Leptocereus santamarinae and other species occur. Smaller stands of this vegetation type are found in the northern coastal zone of west Cuba, and in south-central Cuba. In Hispaniola there is also an extensive stand in areas below sea level in the Enriquillo Valley Cul-de-sac area, giving way to succulent sea coast vegetation with Melocactus lemairei, Leptocereus weingartianus, and Mammillaria prolifera, at the shores of the lake. Smaller floras of endemic cacti, other succulents, and spiny shrubs exist along the leeward coast of Jamaica and Puerto Rico, and also in the Bahamas, the Virgin Islands, and Lesser Antilles.

2) Semi-desert cactus scrub — This type of open vegetation is characterised by small trees and shrubs with many succulents, mainly cacti, which are co-dominant or even dominant in both shrub and canopy layers. The most conspicuous elements of this vegetation type are the large columnar and treeshaped cacti, which are represented by local vicariant endemics in each island of the Greater Antilles and the southern Bahamas. The semi-desert vegetation in the coastal and subcoastal belts in the Caribbean islands is conditioned by an arid climate with nine to eleven dry months and 30-60 cm of annual precipitation.

In eastern Cuba the open cactus scrubs form an unbroken stretch along the coast from Guantanamo Bay to Imias. From Imias to Maisi smaller fragments occur, especially on the sand deposits of the coastal areas. Several geographically separated associations occur depending on whether the soil is rocky or sandy and on the duration of dry periods. On sandy soils Stenocereus hystrix, Opuntia dillenii, 0. hystrix, 0. militaris, and Pereskia zinniiflora are dominant, while on rocky habitats Dendrocereus nudiflorus, Pilosocereus brooksianus, Harrisia taylori, Melocactus acunae, and Agave albescens are more frequent. In the Dominican Republic and Haiti, in the Enriquillo Valley and Cul-de-sac area, there is an impressive cactus scrub with the arboreal Leptocereus paniculatus and Opuntia moniliformis. It also occurs on alternating salt rock and gypsum outcrops on the slopes of the abutting mountain ranges, and in the Azua and Bayahibe areas. In Haiti, in the north-western peninsula, there is another stand with the local endemics Opuntia

Western Cactus

Opuntia moniliformis in coastal scrubwoods, northwest Haiti.

falcata, 0. ekmanii, and 0. acaulis. A spot of this vegetation type occurs in Mona Island, Puerto Rico. Dominant cactus species in Mona are Pilosocereus royenii, Stenocereus hystrix, and Harrisia portoricensis.

3) Dry serpentine shrubwoods — The vegetation is dominated by a dense, 2-4 m high, closed shrub layer, small emergent palms, dwarf palms and 4-6 m high microphyllous evergreen trees. These dense stands usually alternate with small grassy clearings which are often transformed into dwarfgrass savannas by human interference and grazing. This vegetation type, which is well developed in Cuba along the central portion of the main island on ophiolitic rock outcrops, is rare or non-existant elsewhere in the Caribbean Islands. Unlike the dry shrubwoods on limestone in Cuba, the serpentine communities are physiognomically quite uniform despite the great differences in climate and floristic composition among the outcrops. They are also relatively devoid of cacti, with the exception of five rare Melocactus species and a unique species of endemic Escobaria, all of which are highly endangered.

Melocactus actinacanthus, M.matanzanus, and M. guitartii occur in the scrubs of western-central Cuba, while M. holguinensis, M. radoczii, and Escobaría cubensis are only found in eastern Cuba.

III. Montane formations

1) Tropical karstic forests — These are limestone-based forests composed of primarily deciduous species with seasonal flowering. They are only found on the 'mogotes' or haystack mountains of Cuba and Puerto Rico, the Cockpit Country and the John Crow Mountains in Jamaica, and on the Samana Peninsula of Hispaniola. Of these areas, only the Cuban mogotes have proven to support a noteworthy succulent flora. The mogote karstic forests have two evolutionary centres in Cuba with different floras, the oldest and richest (40 per cent endemic) in the western part of the island, and the youngest in central and eastern Cuba.

The western mogote forests occur on bare rocks of deeply eroded mountains and solitary cliffs consisting mainly of hard crystalline limestone. There is a single 4-9 m open canopy layer underneath which many smaller plants thrive thanks to the favourable light conditions. Bombacopsis cubensis, a Cuban endemic tree with barrellike trunk capable of water-storage, is present along with various species of Leptocereus with very restricted distribution patterns, including L. assurgens, L. ekmanii, L. leonii, and L. prostratus. Other cactus genera occurring in this habitat are: Harrisia, Selenicereus, Opuntia, and Rhipsalis. Agave tubulata is only found on the cliffs of the western mogotes. In the central and eastern karstic forests there is only one local species of Leptocereus, L. carinatus.

The most important areas where cacti and succulents occur in the West Indies are listed below in the section Priority Sites for Conservation.

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