Endemic Hemicryptophyte Grasslands of the High Mountains of the Caribbean

Although there are numerous studies on the floristic composition of the Andean and Caribbean grasslands, there are limited information from a phytosociological point of view. This work therefore aims to highlight the differences in this important vegetation type in these two biodiversity hotspots to gain a better understanding of their floristic and vegetational richness. The floristic composition of Andean grasslands (Ecuador) and the island of Hispaniola is also studied. The reason for this comparative analysis of Andean and Caribbean territories is their tropical character and their bioclimatic similarities. The comparative analysis of Peruvian Andean and Colombian grasslands is based on floristic knowledge from the literature, our inventories on the island of Hispaniola, and the works of Peguero. We applied the phytosociological methodology of Braun-Blanquet and the code of phytosociological nomenclature. We performed a statistical analysis to verify the differences between both community types using the statistical packages PAST© and CAP3. The comparative analysis of Andean and Caribbean grasslands shows a clear floristic and biogeographical differentiation and reveals that the only ecological character they share is their high-mountain attribute. In the Caribbean these communities are found only on the island of Hispaniola (Dominican Republic) in the Central biogeographic sector, Central subprovince, Hispaniola province. These grasslands are exclusive to Hispaniola and have a high rate of endemics. We propose the following new syntaxa: the association Hyperico constanzae-Danthonietum domingensis, the alliance Hieracio domingensis-Deschampsion domingensis, the order Danthonietalia domingensis, and the class Deschampsio-Danthonietea domingensis. We found high biodiversity values for Andean and Caribbean areas. This is due to the intense anthropic activity on the island of Hispaniola, which has led to a high percentage of naturalized plants.


Introduction
The high mountains host an endemic flora and a characteristic vegetation around the world [1][2][3][4][5], are really hotspots of biodiversity [6][7][8], and are present not only in continental lands, but in several islands too and many of them are studied from a botanical point of view [9,10].
The Antillean archipelago is formed by the islands in the Greater and Lesser Antilles, and is located between the Caribbean Sea and the Atlantic Ocean on an arc between Florida and Venezuela. The islands have a territorial extension of 299,000 km 2 , and their geological origins date from more or less 100 million years ago with the separation between Africa and America. According to some authors [11], throughout the geological eras the current islands have been shaped by three tectonic movements in the form of uplifts, subsidence and separation along faults, all of which are due to interactions between the Caribbean and the surrounding plates: Cocos, Nazca, North America and South America. The subduction of the Caribbean tectonic plate, which configured the mountains of Central America, began 25 million years ago in the Miocene era. Cuba was formed from the Mesozoic onward, specifically in the Jurassic and Cretaceous periods. The definitive separation of the Antilles from Central America occurred in the Pliocene era, leading to the establishment of essentially two migratory routes: North American route through Florida-Cuba, and the route of the Lesser Antilles from Venezuela; a third route from the Yucatán peninsula through the Caiman Islands was less important due to the distance from Central America to the Antillean arc [11].
The high mountains in Cuba that developed over millions of years were the Sierra Maestra, Sierra Escambray (Guamuhaya), Sierra Turquino at 1974 m asl, and Pico Cuba at 1972 m asl. The highest altitudes in Hispaniola are the Cordillera Central with Pico Duarte (3175 m asl), Pico del Yaque (3125 m asl) and la Rosilla (2860 m asl); the Cordillera Septentrional with Pico Diego de Ocampo (1229 m asl); other mountain ranges such as Bahoruco, Hotte and La Selle and Cordillera Oriental; and finally, in Puerto Rico the Cordillera Central with altitudes of less than 1500 m asl [12].
The Cordillera Central has a siliceous character and dates from the Cretaceous period; it represents the highest point in the whole Caribbean. The climate in all the Antilles is tropical with frequent and abundant rains on the oceanic face -sometimes exceeding 3,000 mm -and low rainfall on the Caribbean face, with up to 200 mm. The mean temperature is 24° C, and all the islands are subjected to hurricane winds with speeds of over 200 km/h [12].
The Antilles have undergone subsidence and uplifts throughout their geological history, although Cuba and Hispaniola have remained emerged while the rest of the islands sank into the sea; for this reason, these two islands became a reservoir for flora and subsequently served as dispersion centres [13].
The diversity of substrates, with a high frequency of siliceous, carbonated, ultramafic and serpentine rocks, its climate, and particularly its high-altitude orogeny, have given rise to a distinctive flora; these islands act as centres of speciation (hotspots) and have a very high rate of endemic plants: Cuba 45%; Hispaniola 36%; Jamaica 25-30%; Puerto Rico 24% and Lesser Antilles 10% [14].
Grasslands are hemicryptophyte communities located in the supratropical thermotype of Central America [15]. From the bioclimatic point of view, the thermotype in the Antilles ranges between the infra-and supratropical (the latter only in Hispaniola [16], where the temperature of the supratropical thermotype drops to 0 °C in winter. The dominant thermotypes are the infra-, thermo-and mesotropical, and the ombrotype ranges between the semiarid and the hyperhumid. The supratropical belt extends to altitudes above the sea of clouds, which causes winter temperatures to drop to 0 °C. These zones are characterised by their pluviseasonality, while the infra-, thermo-and mesotropical ombrotypes have a pluvial character. The inclusion of grassland communities in different phytosociological classes in the Andean region is due to the divergent floristic composition of the plant communities, their ecology and the biogeographic unit in which they are located [17]. Several authors have included Andean grasslands in various phytosociological classes. Izco [16] mentioned grasslands in a study on the San Francisco Reserve (Ecuador).
None of the classes cited can be extrapolated to the Caribbean as there are significant floristic, ecological and biogeographical differences; these grassland communities in Hispaniola are located on siliceous substrates in the Cordillera Central.
Grassland communities in the Andes have been studied from a floristic standpoint by several authors [18,19,[23][24][25][26][27]. Grasslands in the Antillean archipelago are located only on the island of Hispaniola, specifically in the Cordillera Central, which has been the subject of various floristic and vegetation studies as indicated above.
The island of Hispaniola is a hotspot due to the high rate of endemisms, account for 2050 out of a total of 6000 species, even compared to other well-known hot spots in the worldwide as [52][53][54][55]. This is due to its orography and diversity of climate and substrates; its ombrotype ranges from semi-arid to hyper-humid, its thermotype from infratropical to supratropical, and its substrates are siliceous, carbonate rocks and serpentines In this work we studied the flora and vegetation of the high mountains of the Caribbean, and compare them with similar Andean plant communities to highlight the differences between these two important biodiversity hotspots in order to gain a better understanding of their floristic richness. The floristic composition of the Andean scrub (Ecuador) and the scrub on the island of Hispaniola are also studied.

Comparative analysis
A comparative analysis is made between the Peruvian Andean and Colombian grasslands based on the floristic presence studies of Izco et al. [20], our own relevés collected on the island of Hispaniola, and other works of Peguero [13] in Valle Nuevo (Dominican Republic).
For the samplings carried out by us in the Central mountain range we have followed the phytosociological criteria. The plot size was chosen by previously calculating the minimum area, namely 300 m 2 [56]. In all cases the samplings were carried out in supratropical environments (Figures 1 and 2). For the abundance-dominance of the species, the work of Braun-Blanquet has been used [57].

Vegetation analysis
A study was carried out of the endemic scrub and grasslands of the Caribbean, until now exclusively located in Hispaniola.
We applied the phytosociological methodology of Braun-Blanquet [57] and the code of phytosociological nomenclature to name and describe the syntaxa [58]. A similarity analysis is carried out between areas of the Caribbean and Andean areas, through analysis of presence-absence of species and cluster. The environmental conditions have been sufficiently studied in references [14,48,51].
The statistical packages PAST (Paleontological Statistics)© [59] and CAP3 (Community Analysis Package, PISCES Conservation Ltd. IRC House, The Square, Pennington, Lymington Hants., SO41 8GN United Kingdom)© were used for this study. We applied Ana Cano-Ortiz et al.

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the Jaccard distance to differentiate the Andean from the Caribbean communities. For the biogeographical and bioclimatic study, we followed [60][61][62][63][64]. The nomenclature of the taxa reported is according to Global Biodiversity Information Facility (GBIF) [65] and the Flora of Hispaniola [66].
The Shannon-Wiener, Margalef and Simpson indices were used to determine the diversity of the plots studied, since they offer the best fit with the measurement of diversity when using the table of presence and absence of species. However, it was impossible to use the Pielou Evennes index as it does not fit well when only the presence and absence of species is used.
The hemicryptophytic communities inventoried by us and by Peguero in the Valle Nuevo National Park (Dominican Republic) present a high endemic richness with 138 endemic plants. These communities are located only in supratropical environments above altitudes of 2000 metres on siliceous substrates. As these are environments exclusive to the Central Cordillera in the Dominican Republic, they represent endemic habitats with a high ecological value [67].

Results and Discussion
These endemic communities of Hispaniola cannot be located in the phytosociological classes described before for the Andean and Caribbean. The similarity, cluster and PCA analyses show clear differences between Andean and Caribbean grasslands (Figures 3 and  4) -plots P1 to P10 in the Caribbean group and plots P11 to P15 in the Andean groupwith a significant floristic difference between the two groups (Tables S1 and S2, Supplementary materials). Although the analysis represented in Figure 3 is not exhaustive, it shows the significant differences between both territories. According to the Simpson, Shannon and Margalef diversity indices, this diversity is greater in the Andean plots ( Table      In our study we observe a clear difference between the Peruvian and Colombian grasslands and those of the Caribbean. Unfortunately, for the plots from Peru and Colombia we only have the reference by [24,26] on the species of the genus Danthonia in the Colombian Andes, and the floristic composition of the Andean grasslands (Ecuador) is different from on the island of Hispaniola. Izco et al. [20] report that the southern scrublands of Ecuador comprise over 33 [51].
These hemicryptophyte communities located in the clearings of the pine forest are very rich in endemic plants, as they are located in the high mountains [67]. Although climate change affects the forest of P. occidentalis, it does not seem to affect these communities. With the death of the pine, open spaces appear that allow the expansion of the "pajón" or Danthonia domingensis, as occurs in the protected natural area of Valle Nuevo (Hispaniola), although globalization is leading to an increase in human pressure and jeopardising the conservation of these communities [39]. It is evident that if climate change and human pressure continue, these fragile communities that are unique to the Caribbean will come under a certain degree of threat, since a set of naturalised (Na) species has already appeared as a result of anthropic action.
Cano et al. [50] recently published a syntaxonomical proposal for the grasslands of Hispaniola. This study reveals the existence of an endemic grassland community that is widespread throughout the supratropical thermotype in the central biogeographic sector, Central subprovince, Hispaniola province. This is an endemic community of grassland characterised by

Conclusions
The comparative analysis of Andean and Caribbean grasslands allows us to propose new syntaxa for the island of Hispaniola, as there are no phytosociological studies for these types of communities in the Caribbean. As these communities cannot be ascribed to any of the classes previously published for South America due to the major floristic and biogeographical differences between them, we propose a new class, order, alliance and association. These are endemic syntaxa that are currently restricted to the island of Hispaniola. Endemicity is due to the "insular effect": something similar occurs in other islands and peninsulas, including mountain areas, such as the Etna volcano on the island of Sicily (Italy), in which due to the above mentioned effect insular effect there are endemic taxa of interest [68]. The floristic diversity of the plots in the study reveals high values for Andean areas, with maximum Simpson, Shannon and Margalef values of 0.94, 2.89 and 5.88 (Hispaniola, Caribbean) and 0.97, 3.50 and 6.79 respectively (Andean areas). Altough this is also due to the intense anthropic activity on the island of Hispaniola, which has led to a high rate of naturalised plants -over 30% -, endangering these habitats and consequently their endemisms, the high floristic diversity is determined above all by the high percentage of endemisms and native flora as a whole.
We highlight the importance of these plant communities in the Caribbean area, since they are unique phytocoenoses in this territory; so although there is little phytosociological information available, their very significant floristic divergences, the origin of the floras and the epiontological differences are sufficient reasons for the diagnosis of new syntaxa.
Consequently, the diagnosis of new syntaxa for science will allow the protection of these habitats.