Biogeographical Areas of Hispaniola (Dominican Republic, Republic of Haiti)

The island of Hispaniola is located between parallels 17 and 19 N and forms part of the Greater Antilles group in the Caribbean region. It covers an area of 76,484 km2 and has the highest altitudes in the whole Caribbean region. The island consists of two countries: the Dominican Republic and the Republic of Haiti. The flora of both countries has been studied in depth by Liogier and several authors from the Dr. Rafael Ma. Moscoso National Botanical Garden in Santo Domingo; this has enabled us to examine the distribution of 1582 endemic species in 19 areas and several important endemic habitats for conservation: Lepotogono buchii‐Leptochloopsietum virgatae; Crotono astrophori‐Leptochloopsietum virgatae; Melocacto pedenalensi‐Leptochloopsietum virgatae and Solano microphylli‐Leptochloopsietum virgatae pine forests on serpentine belonging to the association Leptogono buchii‐Pinetum occidentalis and high‐mountain pine forests: Dendropemom phycnophylli‐Pinetum occidenta‐ lis and Cocotrino scopari‐Pinetum occidentalis. Some dry forest communities are of interest, including Chrysophyllo oliviformi‐Sideroxyletum salicifolii and Zamio debilis‐Metopietum tox‐ iferi. Based on the floristic analysis and the vegetation study, a biogeographical typology for the island, in which we propose 19 biogeographical areas (BA) has been established.


Introduction
The geological history underlying the formation of the island of Hispaniola [1], the great differences in altitude and the wide range of substrates, have all led to the existence of 2050 endemic species distributed across a wide variability of habitats with an endemic nature was carried out on existing geological materials, and a bioclimatic study of ombrotipos and thermotypes is presented in refs. [4,[33][34][35].

Results
The island's geological origin, the bioclimatic analysis with thermotypes ranging from the infratropical to the supratropical, with semiarid to hyperhumid ombrotypes, the origin of the flora as a result of migratory routes and the past isolation of the various sierras and mountains, all account for the large number of endemic species and habitats. The island has 1284 genera, of which 31 are endemic to Hispaniola: Zombia, Leptogonum There are a total of 5800 species according to [36], a figure that was subsequently extended by [37] to 6000 vascular species distributed in 1284 genera, with an estimated 2050 endemic species. Our study characterises the various biogeographical territories based on 1582 endemic species distributed in 19 areas (A1-A19), together with their own vegetation catenas, which we in turn break down into two subprovinces: the Central subprovince and the Caribbean-Atlantic subprovince, both clearly separate due to differences in their geological, bioclimatic, floristic and vegetation origin.
The province is characterised by a large number of endemic species, of which 114 belong to the family Melastomataceae [24]. The presence of a high number of endemic species with a widespread distribution on the island causes the application of Pearson's index to result in a low relation between areas A12 and A16 (r = 1.25), due to their different geological and floristic nature; between A16 and A13 (r = 1.17); and between A12 and A13 (r = 1.23). In this last case, the low relation between the two areas derives from the difference in the number of endemics. Although both zones have calcareous substrates, A13 has suffered greater human impact. A16 and A17 are highly separated, which is unsurprising as the Massif du Nord (A17) is a prolongation of the Central Cordillera range (A16). The frequent presence of calcareous islands and the intense human pressure in A17 is a further reason for their separation, with A17 acquiring a greater similarity with A15 (northwest Haiti).
The Jaccard analysis reveals that areas A12 and A16 have a distance of 0.9, representing a coincidence of only 10% and differences of 90%; this is also the case between A16 and A17, as this analysis corroborates that A17 has greater similarity with A15. The results of Pearson's analysis for areas A12 and A13 are similar to those obtained with the Jaccard analysis [24].

Analysis of biogeographical territories (sectors) and areas (districts) (BT, BA)
The Central Cordillera is characterised by a predominance of siliceous materials and a tropical rainy and tropical pluviseasonal macrobioclimate on the summits, occasionally tropical xeric at the base. All this has led to the development of a particular endemic flora with 451 different endemic species and vegetation units [11]. This biogeographical territory (BT) contains a single area, A16, Central-Eastern, occupying the Central Cordillera (Dominican Republic), and dominated by siliceous materials with slight inclusions of serpentines in the easternmost area, representing the transition to the Yamasense biogeographical unit. The thermotype ranges between the infra and supratropical, and the dominant ombrotype is humid-hyperhumid. The penetration of the trade winds causes the presence of both broadleaf rainforest and cloud forest towards the mid-mountain, with a dominance of species from the genera Prestoea, Magnolia, Didymopanax, Cyathea; while the high-mountain areas beyond the reach of the trade winds are home to Pinus occidentalis, a forest belonging to the endemic habitat Dendropemon phycnophylli-Pinetum occidentalis Cano, Veloz & Cano-Ortiz 2011, alternating with hemicryptophytic communities of Danthonia domingensis Figure 1.
BT-2. 1. The Bahoruco-Hottense district includes two areas or districts (A12 and A13). The Sierra de Bahoruco and its continuation in the Massif de la Selle and de la Hotte in Haiti have a similar geological origin and frequently suffer the impact of Caribbean hurricanes. The ombrotype in these territories ranges from subhumid to hyperhumid, leading to a predominance of broadleaf cloud forest, sierran palm forests of Prestoea montana, cloud forest of Magnolia and Didymopanax, and-in the supratropical thermotype on the summits-a pine forest of P. occidentalis, belonging to the association Coccotrino Scopari-Pinetum occidentalis Cano, Veloz & Cano-Ortiz 2011. The general vegetation catena characterising this biogeographical territory is therefore conditioned whether it is a dry forest, broadleaf forest, cloud forest or high-mountain pine forest. In addition, due to its high rate of endemic species, this biogeographical territory is of interest for conservation. We are unaware of the existence of Podocarpus aristulatus Parl. and Ocotea wrightii (Meisn.) Mez in the Bahoruco-Hottense sector; and this BT thus reveals significant differences when compared with the Neiba-Matheux-North-western sector. The relation between the two areas (A12 and A13) in this BT is low, as they present a certain number of different endemic species with an r = 1.23 Figure 2.
BA-A12. The Bahoruco-La Selle district occupies calcareous mountain ranges with an occasionally supratropical thermotype. There is a broadleaf cloud forest of M. hamorii and D. tremulus,  In basal zones such as the Procurrente de Barahona, Ceitillan and Pedernales, the ombrotype is semiarid and the thermotype is infratropical. There is a predominantly dry forest, with a floristic composition comprising Lomandra hystrix, P. polygonus, Ceratocystis moniliformis, Antillesoma antillarum, Coriandria caribaea and Melocactus pedernalensis, in whose clearings there is a hemicryptophytic and endemic community of Melocaptoa pedernalensis-Leptochloopsietum virgatae Cano, et al. [24,25]. In coastal areas, it is worth highlighting the presence of mangrove forests of R. mangle, L. racemosa and A. germinans, enriched towards drier areas with C. erectus. In these territories, the mangrove forest alternates with halophilous communities of S. portulacastrum. This area has a high rate of endemic species, with 693 endemic plants.
BA-A13. The Hottense district is characterised by calcareous substrates whose geological origin is similar to that of La Selle and Bahoruco. It is located at the end of the southwest peninsula (Haiti), and has 171 endemic plants, but in lesser numbers than in the Bahoruco-La Selle area. However, this biogeographical unit is home to the endemic genus Hottea, which is distributed throughout the biogeographical units A12, A13 and A14; the highest numbers of endemic species in this genus are found in A13. This biogeographical unit has a thermotype that ranges between the infra and mesotropical, and the ombrotype is dry in the basal areas to humid on the summits of La Hotte.

BT-2.2.
The Neiba-Matheux-North-western sector has four districts (A14, A15, A17 and A19). It is floristically characterised by the presence of 90 endemic species such as Guettarda oxyphylla Urb. and Chionanthus dictyophyllus (Urb.) Stearn, with its own vegetation catenas ranging from the dry to the subhumid and cloudy, with pine forests of P. occidentalis on the summits. Two of the areas in this biogeographical territory (A14 and A15) have a relation r = 0.93, indicating major floristic differences between both biogeographical units Figure 3.
BA-A14. The Neiba-Matheux district covers the calcareous mountain ranges of Neiba, Matheux and Noires with an altitude of 1793 m and a dry, subhumid-humid ombrotype and an infra, thermo and mesotropical thermotype, which is occasionally supratropical in the Massif des Montagnes Noires. It is home to a rare broadleaf forest of P. aristulatus, a cloud forest of P. montana and a forest of D. tremulus which is enriched with P. aristulatus, O. wrightii, Persea krugii Mez and Brunellia comocladifolia H. & B. In the highest sites in the Neiba range, it is still possible to find pine forests of P. ocidentalis on calcareous substrates over a limited extension. This area reveals a certain influence of the Central province due to the presence of P. aristulatus, which is also located near Valle Nuevo (Central Cordillera) and the absence of M. hamorii; the presence of the pine forest of P. occidentalis connects it with Bahoruco. There are 27 endemic species exclusive to this area.

BA-A15
. This district is located in the northwest of the Republic of Haiti and also has a predominance of carbonated rocks. These territories are exposed to the trade winds from the Atlantic. However, as they contain no major elevations-the maximum altitude of around 840 m-the dominant ombrotype is subhumid. West-facing areas connecting with Gonaive and Hene Bay have a dry ombrotype, as this is an area of shade, and a thermotype ranging between infra and mesotropical. The floristic character is based on the presence of 59 endemic species.
BA-A17. The Central-Western district occupies the whole of the Massif du Nord in Haiti. This mountain is a prolongation of the Central Cordillera. In this case, there is also a dominance of siliceous materials with the inclusion of basic substrates; the thermotype is infra to mesotropical, and the ombrotype ranges from subhumid to humid. We collected fewer endemic species (60) in this biogeographical unit than in the Central-Eastern unit (A16), as these areas are highly altered, as is generally the case in the whole of the Republic of Haiti, which has suffered widespread deforestation throughout its history.
BA-A19. The Tortuga Island district is calcareous in nature and located in the north of Haiti, at a maximum altitude of 378 m so the trade winds only reach the highest areas. The vast majority of the territory has a dry ombrotype, occasionally becoming subhumid-humid. The relation of A19 with the nearest areas-A3 and A15-is r = 1.02 and r = 0.89. In spite of its small size, the presence of the monotypical genus Tortuella abietifolia Urb. & Ekman and 15 exclusive endemic species justifies its consideration as a biogeographical unit in itself.

BT-2.3.
The Azua-San Juán-Hoya Enriquillo-Port au Prince-Artiobonite-Gonaivës sector (A9, A10, A11 and A18) covers all the low-lying areas in the south of the Dominican Republic and west of Haiti. These territories are differentiated from the Procurrente de Barahona as they have soft deposit materials, despite their similar infra and thermotropical thermotype and semiarid-dry ombrotype. However, in this case, there is an occasional presence of the subhumid ombrotype on the heights of the Sierra Martín García, which represents a small island surrounded by dry forest, distinguishing this area from the previous one. Although most of the territory is dominated by dry forest, there is an occasional presence of broadleaf forest on the summits of Martín García. Unlike in Bahoruco and Neiba, there are no formations of P. occidentalis. The dry forest in this biogeographical unit is dominated by the species P. polygonus, L. hystrix, A. antillarum, Mimosa diplotricha C. Wright ex Sauvalle, Brya buxifolia (Murr.) Urb., N. paniculada, Thouinia domingensis Urb. & Radlk., Solanum microphyllum (Lam.) G. Don., Coccotrinax spissa Bailey, A. skleroxyla, Scolosanthus triacanthus (Spreng.) DC., C. moniliformis, M. lemairei and C. caribaea. In view of the differences in flora, vegetation, geology, ombrotype and thermotype, these areas should be treated as specific biogeographical territories. In all cases, the relations between the four areas proposed have a value of r in Pearson's index of equal to or less than 1, as they share very few endemic species.
BA-A9. The Azua-Sán Juán-Hoya Herniquillo district is an area that extends from Bani and Azua towards the Sán Juan river valley as far as the border with Haiti, where it becomes what is known as the Central Plain in Haiti, with higher elevations. The Cordillera Central in the Sierra de Neiba is separated through the Sán Juán valley. These semiarid-dry territories border the Sierra de Neiba along the south, and extend along Lake Herniquillo to Jimani and Malpaso. From a geological point of view, there is a predominance of soft materials of a Quaternary nature with gypsum islands in the areas near Herniquillo Lake. There is a constant infra and thermotropical thermotype and a semiarid-dry ombrotype. This district has 85 endemic species, some as emblematic as N. paniculada, M. lemairei, Acacia barahonesis Urb. and Zanthoxylum azuense (Urb. & Ekm.) Jiménez, which give the territory its distinctive character. This area is characterised by the presence of habitats such as the association Solano microphylli-Leptochloopsietum virgatae Cano, et al. [24,25]  with maximum altitudes of 1210 m. This district (A10) has calcareous clayey substrates, a thermotropical thermotype and a dry ombrotype, and differs from the semiarid-dry forest in unit A9. This difference is evidenced in the values of Pearson's index-r = 0.91-as the Central Plain in Haiti has higher rainfall, and in its eight endemic species: Bumelia picardae Urb., Carpodiptera hexaptera Urb. & Ekm, Dorstenia flagellifera Urb. & Ekman, Malpighia aquifolia L., Malpighia setosa Spreng., Phenax pauciflorus Urb., Plumeria paulinae Urb. and Thouinidium pinnatum (Turp.) Radlk.

BA-A11.
The Port au Prince-Arbiobonite-Gonaives district is past Jimini (Dominican Republic), approaching the border with Haiti and entering the plain of Port au Prince, where the materials continue to be soft and Quaternary in origin. The thermotype is infra and thermotropical, and the ombrotype is semiarid-dry due to the lack of rain, as these are areas of shadow. The Sierras de Bahoruco, La Selle and Neiba act as a barrier in the south, and those of Matheux, Noires and the Central Cordillera do the same in the northeast. The altitudes range between 0 and 100 m. These are areas with scarcely any natural vegetation as they are used for agriculture; the semiarid-dry character of the territory is prolonged the length of the northern fringe of the Massif de la Selle and de la Hotte, from Port au Prince bay to Gran Caimite, an island that is also part of this biogeographical unit. The territory extends to the southwest of  There are frequent serpentines, which can also be found in the province of Dabajón in the Cibao Valley, leading to the widespread presence of a dry spiny forest and a pine forest. The thermotype for this BT ranges from infra to thermotropical and the ombrotype is semiarid to subhumid; however, due to the type of substrate-serpentines and perforated coralline limestones-the territory behaves as dry. All this causes the predominance of a dry forest. This biogeographical unit has particular vegetation associations and catenas. The general vegetation catena is the dry and semi-deciduous forest of M. toxiferum, S. mahagonii and C. diversifolia. It has a large number of endemic species, distributed in the three biogeographical areas. The relation between the areas in this BT is: r = 0.95 for A3-A7, r = 0.97 for A3-A8 and r = 1.01 for A7-A8 Figure 5.  [29]. Along with this dry forest it is frequent to find habitats of Leptochloopsis virgate and Crotono astrophori-Leptochloopsietum virgatae Cano, et al. [24,25], and mangrove forests of Rhabdadenio biflori-Laguncularietum racemosae Cano et al. [27].
In serpenticolous territories, there is a pine forest or community of P. occidentales, Calliandra haematomma (Benth.) Benth., Tabebuia  The Eastern Caribbean area occupies the whole of the coastal plain overlooking the Caribbean Sea. Its coralline origin causes the substrate to be highly porous, and although the rainfall is over 800 mm, the territory acts as dry. There is a strong floristic similarity between these territories in the Cibao Valley and the areas in the southwest, and to a lesser degree between this area and that of Yamasá. There are also differences between the flora, habitats and uses of the territory and the dry areas in the southwest, as the territories on the eastern coastal plain are essentially used for the cultivation of sugarcane and coconut. These eastern plains must therefore be treated as specific biogeographical areas. There are 60 endemic species of flora, some of which have problems of conservation, as is the case of P. quisqueyana. In terms of vegetation, it has its own characteristic plant communities depending on the substrate. The dry forest occurs when the soil is thin and porous, but if the soil is deep, these dry phytocoenoses  BA-A8. The Yamasá district is a complex geomorphological unit occupying the Sierra Prieta and Yamasa ranges. It has siliceous, limestone and serpentine substrates, the last of which cause the appearance of endemic serpenticolous communities with a spiny character. This is a xerophytic high shrubland, and throughout the Quaternary era, this territory served as a route for the passage of species between the xeric areas in the Cibao Valley and the Eastern Coastal Plain and the xeric areas in the southwest. These floristic peculiarities are related to the origin of the territory, which is why different connection forces can be established with the neighbouring territories in the various statistical studies on the rates of endemic species. Although these considerations might suggest a wide biogeographical territory, the absence of its own vegetation catenas, the fact it has a xerophytic vegetation and has served as a migratory route between the biogeographical area of the Eastern Caribbean and the Cibao Valley all lead us to propose this as a highly original biogeographical area Figure 7.

BT-2.5.
The areas in the north of the island include five biogeographical districts (A1, A2, A4, A5 and A6) comprising the Northern Cordillera, the Samaná Pensinsula and the Eastern Cordillera, the last of which includes Los Haitises. The dominant materials are limestones or coralline rocks, although on the Atlantic coast to the north of the Northern Cordillera, there are islands of serpentines (Puerto Plata and Gaspar Hernández). Although the value of the It/Itc is mitigated by the effects of the trade winds, the thermotype continues to be infra, thermo and mesotropical; the ombrotype in this case ranges between the subhumid in the basal areas and the hyperhumid in territories more exposed to the trade winds. The macrobioclimate is tropical Caribbean-Mesoamerican Pluvial, and there are therefore no dry sites. The spiny forest occurs only in places with serpentines, as the territory acts as dry. The diversity of substrates, the bioclimate and the different dating of the areas accounts for the presence of 154 endemic species.
This territory has a predominance of ombrophilous forest with a rainy character due to the intense influence of the trade winds. This produces a dominance of a broadleaf evergreen forest with well-conserved formations of P. montana in Loma Diego de Ocampo, forests of M. abbottii to the northeast of the Northern Cordillera and, in somewhat less rainy areas, mahogany forests of S. mahagoni and C. diversifolia. In addition to the differences in flora and habitats with the rest of the territories, this biogeographical unit lacks the pine forests of P. occidentalis, typical of Bahoruco, Neiba and the Central province. In swampy freshwater areas, there are frequent coastal forests of Pterocarpus officinalis Jacq., and mangrove forests of L. racemosa, A. germinans and Rhyzophora mangle L., and to a lesser extent C. erectus. In all cases, the relation between the proposed biogeographical units has a Pearson's index of equal to or less than 1, and in some situations, the value of r is very low-r = 0.73 for A2-A4 and r = 0.81 for A4-A6indicating a high degree of similarity between the two units   buchii [28]. In the rest of the territory, the potential forest consists of Swieteania mahagoni and C. diversifolia. An important feature in this area is the presence of the Gran Estero, developed in the last 400-500 years from deposits of materials from the Northern Cordillera. This area is subject to frequent flooding, and is home to a forest of P. officinalis belonging to the association Roystoneo hispaniolanae-Pterocarpetum officinalis Cano, Veloz, Cano-Ortiz & Esteban 2009. It represents the outer edge of the mangrove forests of R. mangle that are typical in the broad channels and in Samaná Bay [23].
BA-A4. The Samaná Peninsula was isolated from the rest of the territory until 300-400 years ago. It constitutes a geomorphological unit dominated by karstic and limestone materials, with schists and marbles. The thermotype is infratropical and the ombrotype is subhumid-humid. The presence of escarpments (cliffs) has led to the installation of edaphoxerophilous communities that must be considered as dry forest, owing to the pre- BA-A5. The Eastern Cordillera is the oldest range in this biogeographical territory, and has a frequent presence of limestone, karstic landscapes, tufas, alluvial deposits and foothills. It serves as a separation from the great eastern coastal plain, with sporadic intrusions of Palaeozoic slates and basalts. The thermotype ranges from infra to mesotropical; the macrobioclimate is rainy and the ombrotype is subhumid to hyperhumid. The subhumid forest with a semi-deciduous character represents the transition between the dry and ombrophilous

Discussion
The island of Hispaniola is characterised by its abrupt differences in altitude-from 0 to 3175 m on Pico Duarte in the Central Cordillera- [38], the wide diversity of substrates and a pluviometric gradient that ranges from 400 to 4600 mm [35]. These three parameters, in combination with the isolation to which the various territories have been subjected, are key factors in explaining the existence of the current vegetation. For the study of this vegetation, we have established several large areas based on rainfall and temperature-dry, subhumid, humidhyperhumid areas and high-mountain zones-as highlighted in [22,23]. The bioclimatic analysis reveals the presence of several macrobioclimates on Hispaniola: tropical xeric, tropical pluviseasonal and tropical pluvial; all of which are reflected in different vegetation units: dry forest, subhumid broadleaf forest, cloud forest and high-mountain forest (pine forest) [35].

Distribution analysis of endemic species
The study of the 19 areas in Hispaniola shows a wide distribution of endemic species, but with three nuclei of particular interest due to their high rate of endemic plants, as highlighted by the comparative treatment between the total number of endemic species present in an area and the endemic species that are exclusive to this area. There are a total of 2094 endemic species in the 19 areas, of which 1162 are exclusive. The difference between 2094 − 1162 = 932, confirming the high number of endemic species distributed all over the island. The highest concentrations are found in areas A12, A16, A13 (Table 1), whereas the rest of the areas have a lower number of endemic species, with a slight increase in areas A4 and A9. These areas continue to be of interest as they contain endemic species that are exclusive to the territory, and even endemic genera, as occurs in A18 and A19 (Figure 11). Table 1. Comparative analysis of the total endemic species in each area with the number of endemic species exclusive to that area.
Relationship between the relation of endemic taxa (total number) to exclusive endemic taxa per study area 20 Figure 11. Ratio of total endemic species in each area to endemic species exclusive to that area.

Conclusions
Hispaniola has recently been elevated by us to the rank of biogeographical province [2,22,24], having previously been treated with the rank of biogeographical sector [4] and included in the province of the Antilles. In previous studies, we raised it to the rank of superprovince of the Central-Eastern Antilles and included Hispaniola in it, which along with a group of small neighbouring islands-Beata, Saona, Gonave and Tortuga-constitute the province of Hispaniola. In the current study, we propose a biogeographical typology with the rank of district for both countries (Dominican Republic and Republic of Haiti) in the biogeographical province of Hispaniola, in which we establish five biogeographical territories (sectors) and 19 areas (districts), in the Caribbean-Mesoamerican region. This proposal is based on geological, climatic and bioclimatic aspects and on studies of the flora and vegetation.
The high number of genera and endemic species in areas A12, A13 and A16 justifies their proposed designation as being of special interest for conservation.