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..CARIBBEAN ISLANDS
REGIONAL OVERVIEW

CARIBBEAN ISLANDS

Introduction
Geology
Total land area:
c. 240,000 km².
Number of islands:
115 + c. 3400 rocky islets and cays.
Altitude:
-40 m (Lago de Enriquillo) to 3087 m (Pico Duarte), both in Hispaniola.
Climate
Population (1991): 35,000,000.
Natural Vegetation: Lowland and montane tropical forest, evergreen thicket, savanna, cactus/thorn scrub, mangrove and riverine communities.
Flora
Number of vascular plants:
c. 13,000 species.
Number of single island endemics:
6550 species.
Number of genera:
c. 2500.
Number of endemic genera:
205.
Number of vascular plant families:
186 (excluding ferns).
Number of endemic families:
1 (Goetzeaceae).
Useful plants
Factors causing loss of biodiversity
Conservation
Centres of Plant Diversity and Endemism
References

Introduction

The Caribbean islands, with their spectacular land- and seascapes, and diverse flora and fauna have been, like many tropical islands, under European influence a little over 500 years. In that time they have been ruthlessly exploited for forest lumber, firewood, agricultural produce and minerals, mostly for the benefit of people who have never lived on them. They were stolen from the original inhabitants, fought over, bartered, bought, sold, colonized and eventually settled by people of African, Asiatic and European descent while the indigenous Amerindians were eliminated.

This history is similar to those of the Indian and Pacific Oceans, which have comparable islands derived from fragmented continents, ancient or active volcanoes, or living coral. The main distinguishing feature, outside the uniformity of coconut or sugar-cane plantations and contrasting with urban and resort developments, is the native flora which has evolved in each major tropical island cluster on independent lines.

All islands falling within the area of latitudes 10-27°N and longitudes 59-85°W are considered here, with Bermuda mentioned in context. The location, land-surface area and greatest altitude of the principal islands or island groups are given in Table 38. They are arranged from north to south in geographical units with some political adjustment for convenience of reference. Each entry includes a brief note on the number of islands or off-shore islets in the group.

The area of ocean encompassing the islands, excluding Bermuda, is nearly 5 million km². The total area of land is approximately 240,000 km², a ratio of sea:land of about 20:1. This ratio does not imply uniformity of dispersal nor size; on the contrary the locations, groupings and areas of the islands are very uneven. In all respects, whether considering physical or biological attributes, the key-word is diversity. The complexity makes it difficult to state reliably how many islands there are, but, allowing for the availability and accuracy of sources and some interpretation of definitions, it can be said that there are about 100 permanently inhabited islands and another 50 or so major vegetated cays (keys) and rocky islets with names that appear on maps at scales of 1:50,000 or smaller and in some gazetteers and atlases; in addition, several thousand low sandy or rocky cays, mostly in the northern half of the region, are recorded on larger-scale maps and Admiralty Charts. Distances between islands vary greatly, but none, except Bermuda, is more than 200 km from its nearest neighbour.

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Geology

The oldest land areas of the modern Caribbean are at the extreme ends of the arc of islands in Cuba and Trinidad. Jurassic rocks have been identified in Cuba suggesting continental relationships and there are geological links between that island and Yucatán. Some biological distribution patterns support the hypothesis of a Cretaceous land-mass occupying the position of the Caribbean Sea (Weyl 1965) indicating direct links between northern South America and the Greater Antilles avoiding Central America (Stearn 1971).

More recently, renewed interest in plate tectonic research has led to some less speculative biogeographical conclusions. Jamaica was completely submerged between the mid-Eocene and early mid-Miocene and has at other times comprised several small islands. It is believed that, since its last emergence, Jamaica has had no connection with any other island nor a land-bridge to the continental mainland (Buskirk 1985). Hispaniola (Haiti and the Dominican Republic) and Puerto Rico were continuous in the late Eocene and early Oligocene, but, since their separation, Hispaniola has been repeatedly divided and rejoined during the Pleistocene, at the level of the Cul de Sac - Enriquillo Valley, creating at times two islands of unequal size.

The Greater Antillean islands have all had a somewhat similar geological history but they differ from one another in the distribution, form and erosion patterns of the limestones deposited during several phases of submergence and uplift through the Tertiary period and Pleistocene. The richness of the flora of Cuba is explained, in part, by the wide range of soils derived from limestones, serpentine, dolomite, basalt, granite, diorite, gabbro, sandstone and slate (Borhidi 1991).

The Atlantic Plain of North America, including Florida and the Bahamas, was submerged until the Oligocene and has been much affected since by periodic changes in sea-level. Apart from sporadic unions between islands now separated by shallow seas, as within the Bahamas, Virgin Islands or Grenadines (as groups), the other islands have always been separate from one another. The Virgin Islands are peaks of a drowned mountain range created by volcanic activity in the Cretaceous.

The northern part of the Lesser Antilles comprises two more or less parallel arcs of islands. The irregular outer arc stretches from Anguilla to Antigua, the "Limestone Caribbees" (Harris 1965), and extends to include Grande-Terre of Guadeloupe, La Désirade and Marie Galante at the southernmost end. The complex geological history is represented by volcanic and sedimentary strata of Oligocene age, ranging to Pleistocene coral limestone and alluvium.

The inner arc of the Lesser Antilles is much longer, reaching from Saba in the north to Basse-Terre of Guadeloupe and on through the Windward Islands to Grenada. Formation of these exclusively volcanic islands began in the Eocene and still continues (Martin-Kaye 1963).

Trinidad belongs structurally to northern South America and a land connection with Venezuela existed almost into historical times. The general similarity with the coastal cordillera is seen in the mountainous ridges of metamorphosed sedimentary rocks of lower Cretaceous age with their igneous intrusions. At lower elevations the central plain of Trinidad combines erosion products from the nearby hills and exposed lacustrine sediments. The relationships of Tobago are less obvious but some connection with the Paria Peninsula, possibly even including faraway Barbados, should not be ruled out.

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Climate

The latitude and western Atlantic position indicate warm moist conditions determined by easterly or north-easterly trade winds and the intertropical convergence. Rainfall and temperature data are given by most of the authors referred to in Table 38.

Rainfall depends on topography, ranging from less than 600 mm along leeward coasts in rain-shadow to over 5000 mm on windward slopes of mountains. Most inland areas have annual rainfall within the 1500-2000 mm per annum range. All climates in the region are seasonal with, at sea-level in most years, at least one dry month when rainfall is less than 100 mm. The main dry period is usually between January and April; there may be a second dry period in more southerly latitudes in July to September.

A serious deficiency in climatic data is the lack of rainfall records for higher altitudes. Moisture conditions are usually more uniform due to the formation of cloud around mountain peaks, but they are sometimes excessive. Sastre (1978, 1979a) and Sastre and Portecop (1985) have recorded maximum annual rainfall on the upper windward slopes, at altitudes of c. 1450 m, of the volcanic peaks of Guadeloupe and Martinique of the order of 8000-10,000 mm.

The temperature regime is equable as befits intertropical oceanic islands. At sea-level, temperature in February, which is often the coolest and driest month, rarely falls to 12°C. Rainy seasons are usually warmer, but maxima rarely reach 33°C. Overall averages at sea-level are mostly in the range 25-27°C.

With rare occurrences in Grenada and Tobago, and even rarer ones in Trinidad, hurricanes may from time to time devastate other islands (see Factors causing loss of biodiversity). The tracks pass mostly from south-east to north-west across the region.

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Population

The original Amerindian inhabitants, Caribs and Arawaks, have long since ceased to influence or modify the land and vegetation of the Antilles. Fewer than 2000 Caribs live today in a reserve in Dominica and fewer than 3% of these are of pure race. In any case, the original Amerindians had very little influence on the environment in comparison with Europeans, who invaded from the time of Columbus, and the Africans and Asians brought by Europeans, originally as slaves or indentured plantation workers. The modification of the West Indian landscape has taken almost 500 years to reach its present condition.

The population of the Caribbean islands in 1991 was estimated to be 35 million (FAO 1990), projected to rise to about 40 million by the year 2000, and to nearly 60 million by 2025. It is difficult to make a reliable overall forecast because the rates of increase vary considerably from island to island depending on internal social and economic factors and international political links which affect emigration. Life expectancy ranges from 51 in Haiti to 74 in Puerto Rico.

In general, although all island-totals are increasing, the incremental rates and the proportions of populations economically active in agriculture have fallen over the past decade. These trends reflect increase in mechanization and efficiency on farms and in importations of foods replacing local produce, combined with migration to towns and coastal tourist resorts. Higher growth-rates are associated with larger rural populations and relatively smaller movements away from agricultural pursuits, as in Jamaica, Haiti and the Dominican Republic. The totals of people living in agricultural communities actually rose in Jamaica and Haiti (by 7.5%) during the decade, this trend matching several of the poorer Central American republics, where, however, numbers of those actually economically active on the land also fell.

There are 16 urban centres in the Caribbean with over 100,000 inhabitants: Bahamas - Grand Bahama, Nassau; Cuba - Habana, Camaguey, Santiago de Cuba, Guantanamo; Jamaica - Kingston, Montego Bay; Haiti - Port-au-Prince; Dominican Republic - Santo Domingo, Santiago de los Caballeros; Puerto Rico - San Juan; Guadeloupe - Pointe-à-Pitre; Martinique Fort-de-France; Barbados - Bridgetown; Trinidad - Port-of-Spain.

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Vegetation

The following descriptions of natural communities cover the range of vegetation types in the Caribbean. Further information on Caribbean vegetation may be found in the references accompanying Table 38. Topography, climate and edaphic features combine to determine the unique characteristics of the communities and the floristic diversity of each individual island. Determining those characteristics which are most in need of safeguarding requires analysis of each island; inference and extrapolation of data from other islands or similar mainland sites are rarely valid. Coastal and low-elevation communities have in general the greatest uniformity; the more inland and elevated communities have the highest diversity.

Coastal communities

The most common formation along the thousands of miles of coastline is the open pioneer vegetation of upper beaches and maritime rocks. Some differences depend on whether the substrate is of volcanic, coral-limestone or alluvial origin, or whether the rainfall is low or high. Most seashores have lower rainfall than the immediate hinterland, but, because of the continuous high humidity, woody vegetation is almost always evergreen. Floristic individuality is low among coastal pioneer communities and many species have an amphi-Atlantic or even pantropical distribution.

Cactus scrub, evergreen bushland and dry evergreen thicket occupy well drained, usually rocky, substrates. Succulents and low spiny shrub vegetation is characteristic of coastal areas with seasonally higher temperatures and rainfall under 700 mm, often falling in one short annual period. Unique floras of endemic cacti, other succulents and spiny shrubs exist along the leeward coasts of the larger islands. These places have mostly been spared from agricultural development on account of their infertility and lengthy droughts, but they may have been severely damaged by cutting for firewood and charcoal; resort development and gathering of cacti for horticultural use are contemporary risk factors.

Any forests which might have grown close to the sea have been long since removed, especially if they were near the first points of entry and settlement. Some undisturbed patches of marsh forest in the Negril area of Jamaica existed immediately inland from the strand in the early 1960s. They comprised mature examples of buttonwood (Conocarpus erectus) and Tabebuia angustata, both up to 25 m, accompanied by large woody climbers, such as Dalbergia brownei, and endemic epiphytes, such as Hohenbergia negrilensis. Standard Flora descriptions of buttonwood refer to a shrub or tree up to 7 m. This vegetation was eliminated very soon after a major road was built along the west coast of the island to enable easy access and tourist development.

Sand dunes are rare in the tropics (Morton 1957) because the beach sand scarcely becomes dry enough and the onshore winds strong enough to move it. Flattish particles of algal (Halimeda) or shell sand may offer broad surfaces to the wind but these are usually strongly cohesive in damp salty conditions. Dunes form in the Caribbean in Barbados (Gooding 1947), Aruba (Stoffers 1956) and Barbuda (Harris 1965). Given the rarity of these sites and their ecological interest, their vulnerability as natural accumulations of graded sand should be recognized.

Raised coral beaches, as for example along the north and south coasts of Jamaica, and in Cuba and southern Hispaniola, support a low suffruticose vegetation adapted to withstand wind, salt spray and high insolation. The rock pavements exemplify the harshest aspects of karst limestone, to which plants respond by becoming dwarfed and acquiring strongly rooted perennial stocks. Individuals of buttonwood here may flower and fruit at a height of 15 cm.

Mangrove, lagoon and riverine formations

In estuaries or sublittoral lagoons of low coastlines, mangroves are, or have been, extensive; many have been destroyed in recent years by reclamation and pollution. Lagoons and quiet coves with mangroves have suffered through competition for beach space, moorings and resort development. Mangroves are unhappy partners with human habitation on account of the unpleasant odour of the anaerobic muddy substrate and the mosquitoes which infest them, but, in relation to coastal resources, they have significant geomorphological and biological functions. They are dynamic communities showing diverse vegetational facies, as for example in the Cayman Islands (Brunt in Proctor 1984). Recent studies in Puerto Rico (Jiménez, Martinez, and Luis 1985), Guadeloupe (Renard 1976), Dominica (James 1980) and St Lucia (Portecop and Benito-Espinal 1986) emphasize their importance and the protection imperative. Mangrove swamps and sublittoral lagoons are fragile because of their sensitivity to any alteration of drainage systems. Early recognition of adverse change may save a valuable asset; an example may be cited of the Caroni Swamp in Trinidad where exploitation was recognized (Bacon 1970) and public awareness led eventually to designation as a National Park and legislated management (Thelen and Faizool 1979, 1980a).

Some mangroves have been reduced through the natural silting up of streams entering lagoons or the sea. Open barren saline areas (salinas) have resulted. These are frequent along the dipping south coast of Jamaica where their formation may have been accelerated through erosive cultivation methods on large sugar-cane plantations nearby. Adjacent to other coastlines are brackish or freshwater permanent swamps dominated by palms, tall grasses and sedges, as in Cuba (Cienaga Zapata), Jamaica (Black River Morass) and Trinidad (Nariva Swamp).

Because of the relatively small size of the islands compared with continental areas, rivers are short and have rather simple systems. Ponds and lakes are few but there are many streams and torrents especially in the higher wetter places; in limestone country the streams often flow underground. Some rivers have been dammed for water-supply and hydroelectric developments. Such developments frequently coincide with rugged terrain of scenic beauty and floristic richness which may be put at risk.

The four large rivers in the region are the Río Cauto in eastern Cuba, the Artibonite in Haiti, and the Río Yaque del Norte and Río Yaque del Sur in the Dominican Republic; they are between 150 and 200 km long. The Río Cauto is bordered in the lowland parts by swamps and gallery forests on rich black alluvial soils. The forests are characterized by the presence of Roystonea palms, a single canopy of partly deciduous trees to c. 20 m, and moisture-loving lianas. Removal of the gallery forest results in savanna with varying complements of tall grasses, sedges and palms of the genera Copernicia or Sabal. The original vegetation along the Río Yaque del Norte and Río Yaque del Sur has almost all been lost.

The shorter but floristically diverse Black River of Jamaica flows into a sunken landscape where it is associated with an extensive morass. The complex of communities here includes many facets of strictly aquatic vegetation both in flowing and still water. Herbaceous swamps comprise large grasses (Phragmites), sedges (Cladium, Cyperus giganteus and Fuirena) and other monocotyledons, such as Typha, Alpinia, Sagittaria, Crinum and Thalia. Marsh forest was once dominated by species of Symphonia, Terminalia, Hibiscus elatus, Grias cauliflora (the only West Indian representative of Lecythidaceae), and the endemic morass royal palm Roystonea princeps. Cutting of the trees followed by burning has produced a fire subclimax savanna with extensive areas of the sedge Cladium jamaicense and bull thatch palm Sabal jamaicensis. The riparian forest, which existed alongside the river further inland, comprised a number of rare and unusual trees and woody vines. It has now been virtually eliminated. The bignoniaceous Tanaecium jaroba and the endemic Combretum robinsonii are large lianas ecologically reminiscent of Amazonian riverine forests.

Forests and woodlands

The natural vegetation of the Antilles is essentially woody except where there is very low rainfall or the land becomes waterlogged during wet weather. The forest formation-types depend on temperature, related to altitude, and the amount and periodicity of rainfall. Different authors have classified the vegetation variously, frequently using non-comparable criteria to define the chosen categories. Some of the systems are physiognomic (Hodge 1941; Stehlé 1945-1946; Howard 1974, 1979; Cuba 1989) and others employ a more detailed analysis of floristic and phytosociological data (Beard 1944, 1946, 1949, 1955; Borhidi 1991). Where geological, geographical, climatic, edaphic, structural (life form) or taxonomic elements have been called upon in diverse arbitrary combinations, comparisons and logical ecological correlations are difficult. There is, as yet, no ideal classification of the vegetation based on plant data alone.

The most luxuriant forests are those at low elevations, up to c. 300 m altitude. Beard (1955) referred to these as seasonal forest, prefixed by the adjectives evergreen, semi-evergreen or deciduous, related to the behaviour of trees in places experiencing an increasing number of dry months. Lowland rain forest in its optimum evergreen non-seasonal expression does not occur in the Caribbean islands.

The 'climax' forests have different species of dominant trees with distinctive associated subordinate floras in each of the major island groups, related to high levels of intra-regional endemism (see Flora). The lowlands were easily accessible and ideal for pioneer development. Much, sometimes virtually all, of the original forest was replaced by plantations during the early days of colonization. As Beard (1949) pointed out "in practice to-day, natural forest and woodland is only found in areas which are too inaccessible or too unfavourable for cultivation".

On rugged terrain, such as the extensive karst limestone hills of the Greater Antilles, forests and woodland persist, although much has been cut for timber or fuelwood. Drier facies with rainfall under 1500 mm are particularly prone to this form of degradation (Kapos 1986). Generally, sites with easterly aspects backed by mountains have higher rainfall and carry more luxuriant forests (Dominica - Hodge 1954; Jamaica - Kelly 1986).

Various types of montane rain forest and lower montane rain forest have been described (Ciferri 1936; Beard 1942, 1949; Stehlé 1945; Asprey and Robbins 1953; Grubb and Tanner 1976; Tanner 1977, 1986). Although there have been clearances for crops such as coffee, vegetables, flowers and coniferous forestry, or in the past for quinine and tea, steeper slopes may still carry relatively less disturbed woodland than places at lower altitudes. Peaks often have a low vegetation of gnarled trees and shrubs, in some places referred to as elfin woodland, which is a response to strong wind, high insolation, minimal soil and low nutrient status (Howard 1968). Frost is a rare occurrence; water butts on the summit of Blue Mountain Peak (2256 m) in Jamaica may sometimes be found to have a thin film of ice on the surface in the early morning. The highest peak of the Caribbean islands is Pico Duarte (3087 m) in the west Cordillera Central of the Dominican Republic.

Accurate figures for the present forest cover for the Antillean islands are difficult to establish. Table 40 is compiled from data published by the FAO (1988) and other sources. Some sources do not distinguish between natural, managed or plantation forests and may not record recent felling or changes of composition through active management. Particular forestry policies may lead to reports of expanded areas of forest which might even comprise monocultures of exotic species.

Savannas

The savannas of Cuba have been described and discussed by Borhidi and Herrera (1977) and Borhidi (1991). They comprise a formation-type which is very well represented there. Concepts of what constitutes savanna range from semi-desert, on rocky soils experiencing rainfall of 300-600 mm per annum with 9-10 dry months, to artificial pastures in areas of much higher rainfall with shorter dry seasons. The latter exist mostly where original woodland has been removed and an herbaceous vegetation has become stabilized by repeated wood-cutting, fire and grazing. Estimates of how much of Cuba was savanna at the time of the first Spanish settlers vary from 5 to 30% or more of the land. None of these islands ever carried herds of grazing animals like the savannas of Africa, but the pre-Hispanic inhabitants may well have set fire to natural grassy areas alongside rivers and on marshes during dry weather.

A narrower concept of natural savanna was defined by Beard (1946, 1953) as edaphic. Seasonal, but not necessarily extremely dry, climatic conditions result in actual drought during periods of low rainfall and physiological drought due to impeded drainage and waterlogging during periods of high rainfall. Both situations are inimical to the growth of trees. These savannas are level and usually have sandy topsoils with impervious subsoil horizons. They occur in Cuba, Jamaica, Puerto Rico and Trinidad and are renowned for their local floristic diversity in contrast to derived savannas characterized by the presence of significant proportions of widespread adventive and exotic weeds.

In Cuba there are many endemic palms and their distribution is closely related to soil type. In areas of shallow infertile serpentine latosols many local endemics have evolved. Silica sands support short grass and sedge savanna with palms and sometimes with pines. Savanna vegetation with pines is reminiscent of physiographically comparable areas of open pine forests (pine barrens) in the Bahamas (Correll and Correll 1982) and Florida. The Bahamas, low oolite calcareous islands, have natural vegetation differing in floristic composition on the more fertile "blacklands" and the less fertile "whitelands". These Bahamian communities resemble more the glades and hammocks of Florida than the savannas of Cuba or Trinidad; strangely, the natural pinelands are confined to Grand Bahama, Abaco, New Providence and Andros, and disjunctly the Caicos Islands.

Siliceous soils are responsible for much individuality in the floras of Cuba and the Isla de la Juventud. Otherwise they are strictly localized in the Antilles. Two small sandy savannas exist in Jamaica and there is another at Bayamon in Puerto Rico, but the best known in the English-speaking islands are those of Trinidad (Beard 1946; Richardson 1963). The Aripo, Piarco, Mausica and Omeara Savannas occupy a series of low flattish dissected terraces derived from mainly siliceous erosion products of the Northern Range. In the last 30 years or so, the Mausica, Omeara and Piarco Savannas have been lost to housing, industrial, airport and water-supply developments. Only the Aripo Savannas remain and they have now been designated as areas protected for environmental conservation and scientific research (Thelen and Faizool 1980b). The sites of several endemic species will be preserved but some rare plants may have been lost on the other savannas.

The St Joseph Savanna, also in Trinidad, shares some species with the others but the habitat is a steep hillside. Thus, the factor of impeded drainage is replaced by the factor of shallow infertile soil; there are also more frequent fires. This vegetation is fairly typical Byrsonima-Curatella (Chaparro-Savanna Serrette) savanna, but there are local endemic and rare herbaceous species in the community. The Erin Savannas of the south of Trinidad have an intermediate ecological status between the "Aripo" and "St Joseph" types. All the savannas of Trinidad have their counterparts in Venezuela but the similarity of the floristic composition remains to be confirmed.

The colloquial understanding of the word "savanna" or "savannah" in the Caribbean is often in connection with a piece of flat land from which woody vegetation has been cleared; such places are frequently close to habitations and are used for recreation.

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Flora

There are an estimated 13,000 native vascular plant species in the region. Table 41 includes flora statistics for 32 territories in descending order of the total number of vascular plant species recorded from them. The table provides counts of indigenous and naturalized species separately and, within these, phanerogams (seed plants) and pteridophytes (ferns and fern-allies) are also reported separately. The numbers of indigenous phanerogams and pteridophyta which are endemic are given in further separate columns (being already included in the totals of those categories), and the percentages are calculated accordingly. There is a small number of gymnosperms in most of the floras and these have been included numerically with the flowering plants.

The quality and availability of sources of the flora statistics in Table 41 is extremely variable but for most of the islands the information is relatively complete and up-to-date. Some of the data have been augmented and revised from more recent monographs or herbarium studies. Counts for the ferns of the Lesser Antilles have been taken from The Flora of the Lesser Antilles, volume 2 (Proctor in Howard 1977); for seed-plants, the same Flora (Howard 1974-1989) has been used, augmented and confirmed from other publications, independent local contributions and herbarium studies. Some islands such as Antigua, Grenada and St Lucia have never had an independent list published, while comprehensive works covering St Vincent and Trinidad and Tobago are long overdue for revision. References to published Floras are given in the bibliography to this overview.

Institutional bases for the study of Caribbean 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 Cuba, Dominican Republic, Puerto Rico, St Lucia, Barbados, and Trinidad and Tobago. In recent years Floras, covering both flowering plants and ferns, have been published for Bahamas, Cayman Islands, Jamaica and the Lesser Antilles; a fern volume for Puerto Rico has recently appeared and a flowering plant Flora for Hispaniola is well advanced in production. 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, Hispaniola, and Trinidad and Tobago is published in those islands but, for other territories, investigations and publication are institutionally based in North America and Europe.

Naturalized species

The distinction of species which are indigenous from those which have been introduced and have become naturalized is important from the point of view of conservation. The recognition of truly rare or threatened taxa is particularly necessary, especially if the threats might lead to global extinction. This is not to say that all plants restricted to small or clearly circumscribed areas are at risk, nor that every exotic introduction or widely dispersed species is thereby safe. One of the rarest orchids of Jamaica is not endemic there; it is known also from a few distant and scattered localities in South America. If possible, the status of each species in a territory should be assessed on its own merits because the potential of any introduction to become naturalized is unpredictable. In a complex of archipelagos extending over a latitudinal range of nearly 30°, local conditions favour the establishment of adventives differentially. Some introductions naturalize readily in some places and not in others. For example, Para rubber (Hevea brasiliensis) is totally at ease with conditions in Trinidad and reproduces there by means of vigorous seedlings, but this occurs only rarely in Jamaica. Introduced species known only in cultivation have been omitted from the flora statistics in this overview. Worldwide species, fully integrated in Caribbean floras, and not obviously or historically known to be of exotic derivation, are treated as native. The widespread seashore species and many synanthropic plants belong to this category.

The Caribbean species of mahogany (Swietenia mahagoni) is only truly native in southern Florida, Bahamas, Cayman Islands, Cuba, Jamaica and Hispaniola. It was much exploited in the early colonial era and is not now found in Jamaican forests (Howard and Proctor 1957). Well grown trees have become rare in the forests of Cuba where the species was once an important component of lowland karstic semi-deciduous woodlands; they are, however, not rare in Hispaniola. Because of its value, this species was introduced elsewhere and has now become naturalized. Watts (1978) has described the site-characteristics, structure and floristics of mahogany woodlots on coral limestone in Barbados. The accompanying ground cover that has developed is overwhelmingly of forest plants native to Barbados and adjacent islands and some native trees have also regenerated. These artificial but ecologically harmonious communities were regarded by the author as indicating the nature of the island's original forest cover, and were seen as refuge sites with a high potential conservation status.

Naturalized species have become fully integrated into some of the autochthonous island communities and in these situations exotic trees such as mango (Mangifera indica) or breadfruit (Artocarpus altilis) do not stand out as ecologically incompatible with the indigenous ones. Thus, floristically mixed communities have been created providing habitats for native birds, mammals and other animals, as well as indigenous epiphytes, parasites and climbers. Such artificial vegetation is regarded by many people as "natural".

Some species which do not seem to be fully integrated into the primeval vegetation were possibly introduced or moved into new areas, or even from island to island, pre-Columbian times. The blue mahoe (Hibiscus elatus) could have been brought to Jamaica from Cuba by the Arawaks to be used for bark rope (Adams 1971). Hodge and Taylor (1957) suggested that the Island Caribs might have brought the larouman (or tirite) Ischnosiphon arouma from Trinidad or mainland South America to Dominica and Guadeloupe for use in basket-making.

One of the most interesting features of the collective statistics of the island floras is the observation that, whereas the naturalized flora of a small heavily exploited island like Barbados amounts, with 150 species, to c. 30% of the total, the absolute number of naturalized species increases much more slowly in relation to the size of the island than does the native flora. It then seems to reach a steady ceiling, in these examples, of not over 400 species. This means that Jamaica, Hispaniola and Cuba have 14%, 8% and 6% respectively of naturalized species - in inverse sequence to the sizes of these islands.

The total land area of the Lesser Antilles is c. 6500 km², and the total count of vascular plants for the archipelago is 2713. Of these, the number of naturalized species is 374, i.e. nearly 14%. There is no simple explanation for there being a standard limit on the number of naturalized species, and it is not suggested at this stage that there is a common pool of available exotic plants waiting for suitable niches to occur. Common elements in the patterns of human occupation of hitherto unexploited lands may result in correlated responses by vigorous and versatile plants and possibly there is only a limited number of such taxa which can adventively fill the gaps created by alteration or removal of native vegetation. A comprehensive list of all the species of these opportunistic floras occurring in a wide range of tropical situations would enable this question to be answered. A few remarks on the benefits or threats from naturalized species are made in the section later on Factors causing loss of biodiversity - Invasive exotics.

Endemism

The concept of endemism can be applied at three levels of dispersal, namely: (1) Continental - taxa extending to Florida, Central America or northern South America, (2) Antillean - taxa not extending, as far as known, beyond the Caribbean islands, and (3) Greater or Lesser Antillean groups, separately and exclusively. These divisions reflect the main events and trends of the flora history of the Neotropics.

Table 41 includes, for the large islands and many of the small ones, figures for the numbers of endemic species of phanerogams and pteridophytes. Each entry is accompanied by a calculated percentage of species endemism based on the indigenous total. Where the number of naturalized species is known, it seems to be more realistic to consider the native flora in its own right. The effect has been to present the endemism rate at a somewhat higher figure than that usually given (Borhidi 1991: 216).

Of the estimated 13,000 native vascular plant species in the region, about half are single island endemics. About half of these occur in Cuba. Some analyses of inter-island and multiple-island endemism have been made (Howard 1974; Borhidi 1991).

Endemic families
The Caribbean islands have 186 families of native seed plants. A clearly distinct endemic status for any one of them is difficult to maintain. Until recently Picrodendraceae (Picrodendron, 3 spp.) was upheld, but this taxon is now considered to belong to Euphorbiaceae. Goetzeaceae represents a group of 4 local genera but possibly with a Mexican element involved. This small group is considered by some authors to be intrinsically solanaceous (Mabberley 1987).

Goetzeaceae  
· Coeloneurum 1 sp., Hispaniola
· Espadaea 1 sp., Cuba
· Goetzea 2 spp., Hispaniola, Puerto Rico
· Henoonia 3 spp., Cuba

Endemic genera
There are about 2500 genera of seed plants in the Caribbean. These include 204 endemic flowering plants and one endemic gymnosperm (Microcycas). All the endemic genera are confined to the Greater Antilles (see Table 42). Of these, 118 are restricted to single islands. The endemic genera are classified in 53 families of which 19 families have one each, 14 have two and 20 have three or more of such genera (see Table 43). The number of species comprising the endemic genera is 766, about 12% of the total of endemic species and about 6% of all species found in the Caribbean islands. Thus, about 88% of the endemic species belong to non-endemic genera.

Comparison of the representation of endemic with non-endemic genera, and the distribution of the latter, leads to the conclusion that indigenous Antillean floras were recruited from pre-existing continental taxa. Northern migrations from Central America to the Greater Antilles took place largely independently of movements from South America to the more recent volcanic islands of the Lesser Antilles. Some of the most striking speciations have taken place locally in cosmopolitan genera like Ipomoea, Solanum and Panicum, and pantropical Psychotria (Adams 1990). Non-endemic genera, such as Rondeletia (Rubiaceae) and Eugenia (Myrtaceae), may be responsible for larger numbers of endemic species in the islands than are the endemic genera.

Endemic species
Comparison of Tables 38 and 41 reveals that all islands less than 2000 km² in area have fewer than 3% of endemics, while islands taken as groups, like Bermuda, Bahamas, Cayman Islands and Southern Netherlands Antilles, have slightly higher rates even if the combined area is quite small. Large single islands, over 8000 km², have much higher rates.

The number of single-island endemic species of vascular plants for the whole of the Caribbean is 6550, nearly half of them from Cuba (3224) and slightly fewer (3004) from Hispaniola, Jamaica and Puerto Rico taken together. The remaining single-island endemic species inhabit smaller islands, of which there are many and in which the endemic element in any one of them is negligible. Special habitats, such as exposed volcanic peaks and sulphur springs, where there are special floras, tend to have species which occur on more than one island. No accurate estimate has been made of the number of species endemic to the region as a whole.

Large islands have more endemic species than they have rare or threatened ones. This is presumably because the products of evolution have multiplied in more spacious niches and migrated relatively less often to neighbouring islands. Small islands tend to have fewer endemic species than they have rare or threatened ones. For the Lesser Antilles, nearly 70% of all endemism is spread to two or more islands in the archipelago (Table 44). Only the woody element, comprising distinctive climax forests, shows significant single-island endemism there; roughly 40% of arborescent endemic species are restricted to one island. Endemism in the Lesser Antilles has an overall rate of c. 12% and it is strongly associated with the forests of the wetter higher topography of the volcanic islands.

An independent count of Lesser Antillean endemic species (H. Synge 1991, pers. comm.) has a grand total of 327 species and 9 varieties. Genera with two or more endemic species are listed in Table 45. Ongoing exploration and taxonomic revision will produce revised statistics. A striking example of the consequences is in the recent discovery of the Barbados mastic Mastichodendron sloaneanum (Box and Philipson 1951) previously thought to be extinct. It has proved to be not different from the widespread West Indian mastic Sideroxylon foetidissimum (Howard 1989; Carrington 1991).

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Useful plants

A summary of indigenous species with existing use and future development potential is presented in the various parts of Table 46. An asterisk denotes endemic status.

The natural ranges of Caribbean species, other than those known for certain to be endemic, are often obscure. Situations may change as taxonomic revisions are undertaken. For example, West Indian mahogany (Swietenia mahagoni) has only recently been accepted as specifically distinct from all of its continental mainland congeners and is, therefore, now considered to be an endemic species in the region.

A number of potential ornamental species, including shrubs (e.g. Gesneria spp., Lisianthius spp., Portlandia spp.), trees (e.g. Charianthus fadyenii, Thespesia grandiflora), cacti (e.g. Rhodocactus cubensis), epiphytes (e.g. many bromeliads and orchids), climbers (e.g. Passiflora spp., Solandra spp.) and ferns, all endemic, exist but are too numerous to be listed comprehensively here.

Naturally occurring food plants are extremely few. Whereas the native birds consume many, if not all, kinds of fruit with a fleshy pericarp and are the usual agents for the dispersal of the seeds, only a few of these species of trees and shrubs are used to any extent by people; some of these are listed in Table 46. Several berry-type fruits, acceptable to birds, are toxic to humans, for example the drupes of Metopium brownii, the burnwood of Jamaica.

Species which are used for both medicinal and culinary purposes have not been repeated in Table 46, parts 2 and 3.

Most medicinal plants in current use are widely dispersed, as Table 46, part 3, shows. Although admittedly not exhaustive, the list in Table 46 includes no species restricted to the Antilles. The notion is often voiced that native Caribbean flora might yield new medicinal plants and that forests should be conserved pending searches for them. This is fairly unrealistic because the use of "bush" for medicine is so general in the region that, at one time or another, everything is likely to have been tried. Empirical properties are well known and the higher priority is for these species to be tested systematically. Very few known medicinal plants are uncommon and many are ubiquitous weeds. If a new discovery were made in a rare local species, it would at once stand in danger of being over-exploited or possibly wiped out. Rare medicinal plants will only survive in cultivation. The people best fitted to do this are the local practitioners who already grow their own herbs, such as Chenopodium ambrosioides or Aristolochia trilobata, a tradition which should never be allowed to die out.

The same remarks as made above about the sustainability of medicinal plants also apply to craft materials which may only occur in the wild. In fact, many craft materials are obtained from common and readily available crops, such as coconut or maize, or from widespread introduced ornamentals or shade trees, such as flamboyant (Delonix regia) or red bead tree (Adenanthera pavonina). Other materials, used nowadays, include synthetic manufactured items like plastic sheeting and nylon cord. A healthy craft industry could be based on the added value of the skill of the crafts people rather than on any special merit of local raw materials.

The increased use of imported items could, on balance, result in the conservation of native species of plants. The depletion of natural populations of rare trees, such as Ormosia jamaicensis which is known to have been felled to obtain the beautiful seeds more easily, could be accelerated by the impaired reproductive potential caused by removing seeds and leaving the survivors to take their chance in natural competition. The seeds germinate readily in garden conditions and the tree grows vigorously in cultivation. Most carving and turning woods, like blue mahoe, Hibiscus elatus grow well enough in plantations to meet all demands.

In the past, dyestuff and rope have been obtained from the bark of mangroves and Hibiscus elatus and H. tiliaceus (H. pernambucensis) causing great damage to the trees. There are many precedents for the importation of synthetic imported materials for use in unique local crafts, for example the Kente cloth of Ghana.

Some native plants which are sources of insecticides have not yet, or have only sparingly, been brought into cultivation. They include Dioclea mollicoma and related species, Piscidia spp. and Ryania speciosa.

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Factors causing loss of biodiversity

"Future developments in the West Indies will take place in environments which are already heavily modified, frequently degraded, and in which the natural resources are already depleted. There are no truly natural environments left in the Caribbean, only those which have survived 200-300 years of human impact" (Bacon 1985).

Natural environmental factors

Periodic earthquakes, volcanic eruptions and hurricanes are intrinsically associated with the physical instability of West Indian environments. Their occurrences have been reviewed by Tomblin (1981). Least predictable are the geological disturbances, but volcanic activity no longer affects the northern part of the region directly. Scars of the famous earthquake of 1692, which destroyed the town of Port Royal in Jamaica, are detectable where landslips still carry incompletely restored vegetation.

Volcanoes
Volcanic activity in the Lesser Antilles in this century was reviewed by Howard (1962b). The consequences of recent eruptions have been described for Guadeloupe (Howard, Portecop and Montaignac 1981; Sastre, Baudoin and Portecop 1983; Sastre 1985), Martinique (Sastre and Fiard 1986) and St Vincent (Rowley 1979). There are about 30 active or potentially active volcanoes in the Lesser Antilles but major events in this century have only taken place at the highest peaks of Guadeloupe, Martinique and St Vincent. The Antillean eruptions are characterized by the explosive emission of clouds of ash with boulders, and at times glowing avalanches ("nuées ardentes"), but not by lava flows. Falling stones and ash defoliate trees and bury shrubs and herbs; recovery occurs readily from persistent corms in plants like Heliconia, while some trees, such as breadfruit, regenerate easily from their roots. Glowing avalanches are more destructive; large volumes of gas, charged with fine ash, pebbles and boulders, flow downhill at speeds of up to 120 km/hr and temperatures within the cloud have been estimated to be of the order of 600-800°C. The force is great enough to topple walls and uproot trees, and the heat kills all living things. Following a major eruption, the vegetation returns to an appearance of normality after about 25 years (Rowley 1979).

Howard (1977) has suggested that some unusual species may have been eliminated by volcanic activity, but Sastre (1978) has shown that an endemic flora persists. If this is threatened by further volcanic activity, it is probably also at risk through tourism. Several named localities on the peaks of Guadeloupe have been recommended for protection (Sastre 1979b). The vegetation close to permanent active fumaroles and sulphur springs, as in Montserrat, Dominica and St Lucia, is specialized and limited to a few species Clusia and Pitcairnia are among the plants tolerant of sulphurous gases and hot, polluted water.

Hurricanes
There have been some disastrous hurricanes in recent years, events which have in a few hours destroyed more trees than decades of misuse of forest. These happenings are irregular but are much more frequent than geological upheavals. Jamaica is supposed to be at risk on average once every 9 years, Puerto Rico once every 10 years (Wadsworth and Englerth 1959), and Dominica once every 15 years (Neumann et al. 1978). Tobago has experienced only three in 200 years and Trinidad has no record of any event more severe than an occasional tropical storm.

The effects on plant life have been rarely recorded in as much detail as those of Hurricane David. This storm struck Dominica on 19 August 1979 and has been estimated to have been the most intense hurricane in the Caribbean during this century. Wind velocities averaged 92 km/hr, with peaks of 241 km/hr, over a minimum duration of 10.2 hr. On one-third of the island (246 km²), 5,100,000 trees were damaged (Lugo et al. 1983). The effects were seen to be greater on some species than others, but natural regeneration was rapid and this was attributed to the wetness of the localities where most damage was done. Groome (1970) studied some trees damaged by a hurricane in Grenada and found that some evergreen trees could not survive removal of all their leaves at one time, because the normal rate of replacement was too slow. It may well be that the frequency and intensity of hurricanes are environmental factors reflected in the growth characteristics of the trees and the ecology of climax forest in these islands.

The situation in Tobago seems to have been somewhat different. Hurricane Flora struck the Main Ridge Forest Reserve on 30 September 1963. This forest had been under protection for water supplies since 1765. Destruction was virtually complete: of the upper storey trees 75% were blown over and the remainder had their crowns completely removed or irreparably damaged. It was estimated that very few trees of the original canopy would reform a normal crown (Dardaine 1974). The ecological consequences were profound due to exposure of soil, drying out and erosion. The re-afforestation programme included planting of exotic species such as Pinus caribaea, Tectona (teak), Swietenia (mahogany), Araucaria and Khaya on a trial basis. It was estimated that replanting the whole of some 44.5 km² would take 18 years. Natural regeneration would surely have overtaken this programme, and it would be very revealing to have an up-to-date statement. It is possible that environmental harmony, especially of the quality needed for watershed protection, may be reached only through natural processes.

Heavy rainfall accompanies hurricanes and tropical storms, and may, especially in places where forest cover has been depleted, cause landslips on steep hillsides and result in flooding and further damage (Box 1939b). This type of environmental injury is little different from that brought about by road and reservoir construction and surface mining. Successions on the raw substrates often comprise tangled thickets of strong-stemmed gleicheniaceous ferns, colonization by woody species being slow.

Intensive studies of the regeneration of montane forest in Jamaica, following the destruction brought about by Hurricane Gilbert on 12-13 September 1988, are being carried out (Tanner 1989, pers. comm.). A collection of case studies documenting the damage to natural ecosystems and the initial recovery process from three recent hurricanes in the Caribbean has been published by Walker et al. (1991).

Human-made factors

Mining and quarrying
Threats to the landscape in the Caribbean arise mostly from mining activities. Whatever type of mining is carried out, vegetation is cleared and there is always some surface disturbance either from stripping operations or dumping of tailings.

An ancient activity was the collection of guano and phosphate from usually isolated rocky islands such as Alta Vela (Howard 1955, 1977), Navassa (Burne, Horsfield and Robinson 1974) and Redonda (Tempany 1915; Box 1939a; Howard 1962a). Goats, sheep and rats often came with the miners and persisted after the workings were abandoned, establishing an equilibrium with an altered vegetation.

Processing of bauxite to alumina produces large quantities of residual "red mud", containing excess sodium hydroxide with a pH in the range 12-13. It is totally hostile to any form of plant life. During the main years of alumina production in Jamaica from the early 1950s, this waste was pumped into mined-out pits and dammed valleys. Several years of leaching by rain and seepage led to conditions that plants could tolerate. In 1972, the oldest pond at the Kirkvine operation in Jamaica, to which no fresh residues had been added since 1957, had acquired an adventive vegetation of 166 species dominated by ferns, Compositae, grasses, and other mostly herbaceous plants. By 1975, successional changes showed primary colonizers replaced by species with different requirements and tolerances, but all were common, widespread, usually weedy species (Adams and Lawrence 1972; Adams and Ramjus 1975). Comparable mining operations, for example in Cuba and Hispaniola, produce landscapes from which natural vegetation has been removed permanently.

Riversides and beaches are often exploited destructively to obtain building sand and gravel and these removals may have secondary effects in the form of erosion, flooding, pollution and loss of visual amenity (Sastre and Portecop 1985). Extensive damage has occurred along the Aripo River in Trinidad posing serious problems in savanna areas and downstream by silting.

Air and water pollution
A particular aspect of these universal hazards is, in the Caribbean, smothering of vegetation by bauxite or alumina dust especially where these products are loaded onto ships (Sidrak in Hudson, c. 1973). Large quantities of soluble carbohydrates result from sugar-cane extraction. The waste, called "dunder", is disposed of into drains and rivers, and causes eutrophication downstream. This is seasonal but, combined with rural runoff and urban sewage, coastal environments come under stress, particularly around the larger islands (Wade 1976; Schroeder and Thorhaug 1980; Rodriguez 1981; Provan, Wade and Mansingh 1987).

Fire
The natural vegetation of the West Indian islands has not evolved the fire-tolerant life forms that are found throughout much of tropical Africa or continental America, so fire is comparatively more destructive in the Caribbean. The few savanna species dependent on fire for their survival in competition with larger life forms are restricted in distribution and, generally, the woodlands and forests have experienced fire as a significant ecological factor only since human exploitation gained momentum within the past 500 years. Secondary savannas such as the Maximiliana (cocorite)/Imperata thickets and glades of the Central Plain of Trinidad are maintained and expanded by fire. They represent degraded forest on land of low natural fertility.

Fire is commonly used to clear land for agriculture and settlements, to "clean" undergrowth in forests, and to encourage new growth in savannas and bushland in the dry season for pasturage. Fires are also started in the belief that they will bring rain. Often such fires are allowed to spread unchecked into neighbouring areas. Efforts to protect forests or plant trees in grassy places are often thwarted by deliberate setting of fires, even in statutory Forest Reserves.

As most Caribbean islands, except Trinidad, lack fossil fuels and have very limited development of other sources of energy, the inhabitants are strongly dependent on fuelwood and charcoal.

Agricultural development
Soon after the Columbian discovery, a process of modification of the vegetation began which continues to this day. Plants suitable for human food are of negligible occurrence in the indigenous floras of any of the islands and those that occur are also found on mainland America and probably all originated there (see Table 46, part 2). Some staples such as cassava, maize and pulses had been brought from the mainland by Arawaks and Caribs at an earlier time. Citrus, ginger and plantains were among the first useful plants to be brought by Europeans from Asia. Sugar-cane was introduced into Santo Domingo in 1516. Crops to be grown for export, including indigo, cotton and tobacco, were established in Barbados by 1640. These crops replaced native woodlands, the timber being used for building and fuel for the sugar factories.

It was soon realized that clearing of forest had an adverse effect on water supplies, either by affecting the rainfall or by allowing less retention and greater loss through evaporation. Shifting cultivation on rainy mountain sides had serious effects on stream-flow and caused silting, comparable with damage done by hurricanes. Legislation to protect water supplies goes back to 1721 in Antigua and 1791 in St Vincent (Beard 1949).

Clearing of land was greatest at the time of the Napoleonic wars. After that, erosion and the depression of sugar as a commodity caused poor and degraded areas to be abandoned and to revert to pasture; some sugar estates began to wear out and were retired to pasture. Ultimately, various types of secondary woodland grew up. The history of land-use can be inferred through the presence in the woodlands of trees such as logwood, Haematoxylum campechianum, introduced from Central America in the early 18th century, and the stone walls of ancient field boundaries overgrown with woody vegetation. After the abolition of slavery, people scattered into the hills surrounding the plantations and settled there leading to further degradation of forests.

The philosophy that natural products of the land are divine bounty to be used directly or shared with whoever is in need is prevalent in the West Indies. Such belief tends to blur refinements of property and ownership, resulting in only occasional prosecutions and even rarer convictions for illicit felling of trees or environmental vandalism. Long-term culling for charcoal and uncommon forest products causes progressive damage. Tree fern trunks are removed and cut into blocks for the cultivation of ornamental orchids. Yam and bean poles are gathered from forests and these removals are selective of size-class, so that regenerative cycles are broken.

Coppice regrowth of trees cut for poles or firewood may develop multiple trunks producing an artificial shrub-like habit (Adams 1972). Some species of Coccoloba grow like this without being cut, as do the clustering Bactris palms, but more often the presence of coppice shoots is evidence of human disturbance. Other observations, such as paucity of field and ground layer species, openness of undergrowth and leaf-litter with saprophytes, may indicate the primary or mature status of forest (Adams 1977).

Tourism
The growth of tourism in many of the islands over the past 50 years has resulted in hotel developments along coastlines having white-sand beaches. This has often meant complete change to the landscape locally, involving the removal of natural vegetation and the planting of ornamental trees, shrubs and grass for lawns and golf courses. Mosquito control and marina developments have eliminated mangroves and littoral thickets in many places. New roads have often been constructed to give access to coastal areas which previously could only be reached on foot or by sea.

The movement of people from rural areas to towns and resorts, with the lure of employment opportunities in servicing the new tourism, has coincided with the decline of export-based plantation agriculture. Increased demand for fresh fruit and vegetables has often resulted in unacceptable levels of cultivation on unsuitable land (Rojas et al. 1988).

Introduced animals
The consequences of the introduction of grazing and browsing animals to Antigua, Barbuda, and Anguilla have been described by Harris (1965). The principle that man has priority in all matters relating to his own needs and comfort takes for granted that his attendant animals may also live off the land. Cattle are often allowed to roam free and damage caused by them is usually impossible to redress. As far back as the buccaneers of the 17th century, cattle, goats and pigs had become feral on many islands. Predatory importations, as for example cats and mongoose, are destructive of other animals; several small mammals, mainly herbivores, birds and reptiles have become extinct because of them. A recent attempt to re-introduce the coney (Geocapromys brownii) into western parts of Jamaica have been unsuccessful (Wilkins 1991). Donkeys and deer (Harris 1965: 61) browse and alter the species relationships of secondary formations; introduced monkeys in Barbados, Grenada and Nevis live in balance with introduced citrus, guava and other fruit trees in artificial communities.

Other biological hazards
The worst environmental disaster to hit Bermuda in recent years has been the attack on the dominant endemic cedar trees (Juniperus bermudiana) by accidentally introduced scale insects. This has resulted in the loss of some 90% of the cedars. The infestation began in about 1943 and spread steadily. Although various attempts at biological control failed, some trees survived, apparently through resistance (Challinor and Wingate 1971).

Measures to control introduction and spread of pests and disease vectors are of paramount importance to agricultural authorities in the islands but sometimes protective practices may entail the destruction of indigenous species. Examples are the compulsory removal of malvaceous plants, such as Thespesia, on cotton-growing islands to reduce alternative hosts of insect pests. The destruction on sight of Hippobroma longiflora was at one time ordered in Haiti because it is so poisonous to stock. The systematic removal of the coastal manchioneel tree Hippomane mancinella is often undertaken near resort developments because of the caustic sap, but this tree is not usually regarded as a hazard in Barbados nor on the French islands.

Invasive exotics
The successful naturalization of invasive exotic species in lowland areas, from which the original forest has long since been removed, may improve or diminish the environment in human terms. For example, the early introduction of guinea grass Panicum maximum was beneficial in providing cover and fodder. However, the recent invasion of Puerto Rico, Haiti, Cuba and Trinidad by the Asiatic grass Dichanthium annulatum (Andropogon annulatus) is unfortunate. This species competes successfully with guinea grass and is also one of the least palatable of pasture grasses (Goberdhan 1971). A greater disaster has been the introduction of the extremely aggressive shrub Dichrostachys cinerea from the savannas of Africa into Cuba and Marie Galante; the plant regenerates vigorously from the smallest fragments of roots. "A noxious tree that is a most aggressive invader" in the Bahamas is Melaleuca quinquenervia introduced from Australasia; Schinus terebinthifolius from Mexico is also invasive in those islands (Correll and Correll 1982).

Introductions from the Old World into the mountains of Hispaniola and Jamaica are numerous. Those which threaten native vegetation include mock orange Pittosporum undulatum from Australia in Jamaica (for example, see Data Sheet on the Blue and John Crow Mountains - CPD Site Cb10). Rose apple (Syzygium jambos) is a problem in Hispaniola and Jamaica, and already forms extensive secondary woodlands and shades out competitively most species of native shrubs and undershrubs; oddly, this species has become one of the most favoured support plants for a beautiful and uncommon local orchid Comparettia falcata in Puerto Rico (Rodriguez-Robles, Ackerman and Melendez 1990). Ginger lily Hedychium gardnerianum and its natural hybrids, and molasses grass Melinis minutiflora, the latter introduced into Jamaica about 1925 (Adams 1972), are strongly invasive and colonize disturbed areas rapidly. They appear to inhibit natural successions which might lead to the restoration of woody cover.

The local establishment of temperate herbaceous exotics in mountainous areas can also be exemplified by the situation in the Port Royal Mountains of Jamaica where in the mid-19th century many European and North American herbs were introduced accidentally with fodder imported to supplement feed for horses at a military hill station. None of these plants, which include Plantago spp., Rubus spp., Rumex spp., Stellaria media, Taraxacum officinale and several festucoid grasses, appear to pose much of a threat to indigenous flora in places which have already been developed, as footpaths and vegetable gardens, and they are not invasive.

Principles recently set out as suggestions for managing alien plants in high-altitude places (Dickson, Rodriguez and Machado 1988) are entirely worthy, but may be too exacting and expensive to implement effectively in the Caribbean region, even in a National Park system.

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Conservation

Recognition and designation of protected areas

Encouragement to conserve natural fauna and vegetation on a formal basis in the Caribbean began largely with individuals and small groups with an amateur leaning towards natural history. Effective non-governmental organizations (NGOs) with concern for the preservation of native plants and animals are few. The Trinidad Field Naturalists' Club was founded in 1891 (the addition of "and Tobago" being made in 1975). The interests of the most of the founder members were predominantly zoological. Such groups have been formed in other islands from time to time, with variable levels of activity, continuity and support (e.g. Putney 1983).

Towards the end of the last century, it became clear that natural forests should come under some form of management (Hart 1891). Forest Departments began to be set up in the English-speaking islands some 25 years later, and eventually Forest Reserves were created. Although foresters were generally interested in only a few economic trees, the office of Chief Conservator of Forests was frequently combined with the function of Game Warden and this was a potentially useful link to promote respect for plant and animal wildlife equally.

The natural consequences of more coordinated concern were that some of the Forest Reserves came, in due course, to be looked at as protected areas. This tended to lead to the preservation of vegetation for environmental reasons, besides controlling the utilization of economic species and preventing the extinction of rare ones. Since international interests and their agencies have been giving encouragement to the establishment of National Parks and other protected areas, especially in tropical countries with significant amounts of natural vegetation still remaining, governments and NGOs have responded by submitting lists of designated and proposed locations. Unfortunately, in some cases, the selections encompass areas ranging from totally artificial to natural forests and the conservation ethic has been stretched to include units which are protected merely for their capability of producing commercial lumber, some even comprising a majority of exotic species. The Jamaican authorities list 126 Forest Reserves in Category VIII, 33 of them being less than 10 ha in area (see Table 47).

A special case of an area of relict forest comprising species, rare in one island but not globally threatened, was among the earliest to receive notice; this was Turner's Hall Wood in Barbados (Gooding 1944). The impact on attitudes of the realization that a flora may be under threat in a particular island, even if the species are common elsewhere, is significant for conservation generally. Many of the Caribbean islands do not and never have had a very distinctive flora, but what there is must still be worth protecting. Neither Turner's Hall Wood nor the Mason River Savanna in central Jamaica, which has several rare endemic species (Proctor 1970), have any association with Forest Reserves and their future management depends on other support.

The historical preoccupation with forest and present-day concern for tropical rain forest might divert attention from other vegetation of equally deserving botanical merit. For these other formations in the Caribbean to be brought to proper notice, it is necessary to take a broad view of the region as a whole to determine those areas which might have rare or limited physiographical characteristics. We are aware of: the special floras of serpentine soils in Cuba and Jamaica; the restricted existence of siliceous sand savannas outside Cuba; the excessively high rainfall locations of eastern Jamaica or highest ground of the Windward Islands; the general scarcity throughout the region of bodies of fresh water. There may be hitherto undiscovered discrete geographical units where accelerated local evolution has taken place. Some of them are not necessarily remnants of large disappearing formations but rather less obvious sites of unexpected interest, for example the Harris Savanna of Jamaica, or the Grand Etang crater lake of Grenada. Perhaps because they are not very distinctive or are not under obvious threat, they may be difficult to promote as protected areas.

Besides unique geological sites, non-conformity is a clue to the possibility of finding important biological communities and, by contrast, uniform situations are unlikely to furnish them. This means that, from the terrestrial flora viewpoint, inland areas may be of greater potential botanical interest than coastal mangroves, beach thickets and salinas.

In general, expectations of permanent or even moderately ongoing protection in these islands are weak. The principal reason for this is reluctance of local governments to make commitments to long-term funding. Whereas detailed surveys to enable the recognition and demarcation of National Parks or Wildlife Sanctuaries have been financed by international agencies (e.g. for Dominica, Honychurch 1978), follow-up from the same sources has been very limited or lacking. In view of this, it is difficult to know at any one time if designated areas are fully respected or really protected.

Table 47 summarizes the designated protected areas of the Caribbean islands. A review of the protected areas system and conservation legislation in the Caribbean region is given in IUCN (1992).

Identification and population size of species at risk

Up to the end of the last century the only Flora in English was the general West Indian work of Grisebach (18591864). The initiation of Flora-writing projects for the larger islands (Jamaica in 1910; Puerto-Rico in 1923; Trinidad in 1928, etc.) produced independent awareness of whole floras, although some of these works are still incomplete or in great need of revision.

Deficiencies in the coverage of several of the Floras and the likelihood of a shortage of local personnel capable of making accurate identifications, lead to the possibility of errors of judgement in assessing claims for conservation status. One of the most difficult aims to fulfil is to estimate population size and area of dispersal of rare species. In countries where there are few people with appropriate specialized knowledge, decisions may be made on an ad hoc basis, rather than with good information and objective comparative analysis (Adams and Baksh 1981).

This overview was written by C. Dennis Adams (The Natural History Museum, Department of Botany, Cromwell Road, London SW7 5BD, U.K.)

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