Abstract
The study of the forest in rainy environments of the Dominican Republic reveals the presence of four types of vegetation formations, clearly differentiated from each other in terms of their floristic and biogeographical composition, and also significantly different from the rainforests of Cuba. This leads us to propose two new alliances and four plant associations located in northern mountain areas exposed to moisture-laden winds from the Atlantic: All. Rondeletio ochraceae-Clusion roseae (Ass. Cyatheo furfuracei-Prestoetum motanae; Ass. Ormosio krugii-Prestoetum montanae); and All. Rondeletio ochraceae-Didymopanion tremuli (Ass. Hyeronimo montanae-Magnolietum pallescentis; Hyeronimo dominguensis-Magnolietum hamorii). Due to human activity, some areas are very poorly conserved, as evidenced by the diversity index and the presence of endemic tree and plant elements. The worst conserved in terms of the relationship between characteristic plants vegetation (cloud forest) in areas with high rainfall in the Dominican Republic, along with its floristic diversity and state of conservation. Thanks to this study it has been possible to significantly increase the botanical knowledge of this important habitat.
Introduction
The territory of the Dominican Republic (DR), with an extension of 48,198 km2 including the small adjacent islands, accounts for over two thirds of the territory of Hispaniola, an island located between parallels 17-19°N in the group of the Greater Antilles. Most previous botanical studies have concentrated predominantly on the flora –for example the work of [1] in the Sierra de Bahoruco– and highlight the abundant rainfall of up to 4,000 mm and the very high rate of endemic species. There are also other studies by several authors on the cloud forest in the Cordillera Central, Septentrional and Oriental ranges [2–17]. All these works, together with previous studies carried out by ourselves [18–29] have enabled us to undertake the present work. All the aforementioned studies focus attention on the knowledge of the flora, with only passing references to the vegetation. The main aim of this work is to determine the forest vegetation (cloud forest) in areas with high rainfall in the Dominican Republic, along with its floristic diversity and conservation status.
Material and methods
The island of Hispaniola, with an area of 76,484 km2, and Cuba, Jamaica and Puerto Rico are the largest islands in the Caribbean region. The geological origin of the mountains on the island dates from the Cretaceous and Oligocene-Miocene era with the exception of the intramountain valleys formed during the Quaternary period due to the deposit of materials [30]. There is a predominance of calcareous materials with a karstic character, marbles, limestones and Quaternary deposit materials, and a large central nucleus of siliceous materials with serpentine outcrops [19–21]. The island has a mountainous relief with several mountain chains such as the Oriental, Central and Septentrional ranges, and sierras such as Bahoruco and Niebla. The northwest-southwest orientation of the mountains and the prevailing direction of the Atlantic winds explains the existence of a permanent sea of clouds, which gives rise to high rainfall on north-northeast-facing slopes.
This study is focused on the humid-hyper-humid forests in the Dominican Republic (DR) on the island of Hispaniola. Vegetation samples were taken in areas of high rainfall such as the Cordillera Central and Oriental ranges and the Sierra de Bahoruco, selecting sampling plots with an area of 500-2000 m2. Due to the scarcity of vegetation studies, we analysed the works of [31–35] in territories of Cuba. For the dynamic-catenal landscape study we took into account the criteria of [36–37]. An Excel© table was created with 483 rows (species) x 12 columns (tables containing 67 relevés) (Table 1). A statistical treatment (clustering) was applied to separate the communities described for Cuba from those of Hispaniola. The statistical treatment was done by adapting the Van der Maarel conversion [38] and substituting the abundance-dominance indexes with synthetic indexes with the following equivalence: I = 3, II = 4, III = 5, IV = 6, V = 7. Once the indexes were converted, a cluster analysis was applied using the Jaccard distance marking the distance between the associations studied. After separating the forests in the Dominican Republic (DR) from those of Cuba based on the Jaccard distance, an Excel© table was created with the vegetation relevés from the DR, and a Euclidean distance cluster analysis and a DCA were applied to obtain the different types of forests present in the DR. A CCA was done to determine the influence of environmental factors (temperature and rainfall) on the distribution of these forests, followed by a study of the diversity and conservation status.
Results
The results of the analysis of Jaccard distances (Fig 1) applied to six plant communities in Cuba and six in the DR, show that the six communities described in Cuba by [31–35], C1-C6 (Table 1, 35 relevés), can be broken down into the community C1 and the group G1 (C2,C3,C4,C5,C6). C1 is differentiated from the rest in terms of its floristic, structural and ecological composition, as this is a pinewood of Pinus maestrensis Bise growing in rainy environments but on highly oligotrophic soils, in common with the other communities in group G1, which is floristically significantly different from group G2. There are very significant floristic differences between Cuba and the DR (Tables 2 and 3), with 173 species present in the samplings in the DR but not in Cuba, whereas the samplings in Cuba reveal 139 plants that are absent from the DR. In group G2, which contains 32 of our own relevés and those one of [9–10], (DR7, DR8, DR9, DR10, DR11, DR12), the communities DR7, DR11 and DR12 can be seen to form a group for the DR representing different types of forests; these formations are a series of plant communities in very rainy environments in the Dominican Republic (DR) located in the Sierra de Bahoruco and the Cordillera Central and Oriental ranges, with rainfall of over 2,000 mm. Group G2 is broken down into two subgroups of plant communities –DR7-DR11-DR12 and DR8-DR9-DR10– which is plausible, as the first three correspond to areas with acid substrates and rainy environments in the Cordillera Central range, whereas the second subgroup contains communities growing on different kinds of substrates and in hyper-humid environments. We therefore focus on the analysis of 17 of our own samplings to which we apply a Euclidean distance cluster analysis and an ordination analysis, both of which perfectly separate the sampling groups.
Phytosociological study
The statistical analysis of the samplings from the DR reveals the existence of four forest plant associations (Fig 2): As1) Hyeronimo montanae-Magnolietum pallescentis nova hoc loco (S1 Table rel. DR1, DR2, DR4, DR5, DR6; typus rel. DR4), growing at altitudes of between 1,300 and 1,500 metres on siliceous substrates in the Cordillera Central range (central biogeographical district), and in rainy environments with a humid ombrotype and a mesotropical thermotype [16,23,39,40]. These forests contact in hyper-humid areas with forests of Prestoea montana (sGrah.) Nichol, and have a high floristic diversity with 21 trees, eight climbing species and five epiphytes, and a high rate of endemisms (14 species). As2) Cyatheo furfuracei-Prestoetum montanae nova hoc loco (S2 Table rel. DR3, DR7, DR8, DR9, DR10; typus rel. DR3), a plant community dominated by Prestoea montana, always found in hyper-humid environments, generally in very rainy and shady gorges, contacting with the previous association towards areas that are somewhat less rainy and more exposed to sun and wind. It also has a high diversity, with 40 tree and 25 epiphyte species. Due to the catenal contact between both associations, As1 and As2 present a series of common species; they are therefore statistically close (Figs 3 and 4). As3) Hyeronimo dominguensis-Magnolietum hamorii nova hoc loco (S3 Table rel. DR11, DR12, DR13, DR14; typus rel. DR11) represents forests of Magnolia in the Sierra de Bahoruco, which develop on calcareous substrates in humid environments at altitudes of around 1,200-1,300 metres in a humid ombrotype and a mesotropical thermotype, with a high number of tree (25) and epiphyte (14) species. As4) Ormosio krugii-Prestoetum montanae nova hoc loco (S4 Table rel. DR15, DR16, DR17; typus rel. DR16), an association characterised by a high diversity of trees (27 species), and a lower number of endemic species than the previous associations. The four associations present a clear floristic and biogeographical differentiation (Fig 5, Table 4) [41,42].
Conservation status of the associations
The analysis of the floristic diversity of the relevés shows a predominance of Shannon_T diversity (total diversity) over the diversity of non-endemic and endemic species, except in the samplings DR15, DR16 and DR17, where there is a coincidence between Shannon_T and Shannon_Ne due to the low rate of endemic species, with only two species: Bactris plumeriana and Clidemia umbellata. The diversity rate for characteristic species (Shannon_Ca) tends to be high compared to companion species (Shannon_Co), except in DR3 which has a value for Shannon_Co = 1.099 (Table 5).
In the comparative analysis of the diversity between the four associations using the average diversity values for each relevé, it can be seen that association As4 has a Shannon_E =0 due to an almost total lack of endemic species. This association also has low values for total diversity and non-endemic species, with 44.2% trees, 22.9% shrubs, 13.1% climbing plants and 16.3% herbs; whereas the other associations have a greater diversity. The Shannon_Ca value is higher than Shannon_Co in the four associations except for As3; however, the values are similar due to a tendency to ingression by companion species from neighbouring communities (Table 6, Fig 6).
Discussion
In all cases there is a high diversity of trees, among which it is particularly worth noting the endemics Magnolia pallescens Urb. & Ekm., Hyeronima montana A. Liogier, Magnolia hamorii Howard, Hyeronima domingensis Urb., Malpighia macracantha Ekm. & Nied., and Bactris plumeriana Mart. These are therefore plant communities with an endemic character that require protection measures. Although all four associations are of great interest to conservation, the two best conserved associations have the highest rate of endemics, and are precisely the ones located in the Bahoruco-Hottense and central biogeographical sectors [18,20] which concurs with the floristic studies of [1,3,11,43]. However, the areas exposed to greater environmental impact, as is the case of biogeographical sectors such as the Cordillera Oriental range which are subjected to significant human pressure, have less floristic diversity and a lower number of endemic species. No significant differences can be seen between the relevés in the Shannon diversity index, whose values range between DR3 with indexes of Sh = 2.451, and DR12 with higher values of Sh = 3.972 (Table 5); this does not imply that DR3 is poorly conserved [27], but simply that there is an almost complete predominance of the faithful species Prestoea montana, which has a high cover and very few companion species. However, relevé DR12 contains many individuals with low cover and a high rate of companion species. The low rate of endemisms in As4 represented by relevés DR15, DR16, DR17 in the Cordillera Oriental range is the result of significant anthropic action owing to population density.
The four associations described are included in the phytosociological classes Weinmannio-Cyrilletea Knapp 1964 and Ocoteo-Magnolietea Borhidi and Muñiz, in Borhidi et al. 1979. Due to the high floristic and biogeographical differentiation between Hispaniola and Cuba (Tables 2 and 3), these associations cannot be included in any of the alliances described for the island of Cuba. We therefore propose two new alliances: all. Rondeletio ochraceae-Clusion roseae, in which the alliance species are Rondeletia ochracea, Turpinia occidentalis, Clusia rosea, Mikania cordifolia, Alchornea latifolia, and Cyatheo furfuracei-Prestoetum motanae is the type association; and all. Rondeletio ochraceae-Didymopanion tremuli, with the species Rondeletia ochracea, Didymopanax tremulus, Psychotria guadalupensis, and Hyeronimo montanae-Magnolietum pallescentis as the type association. All these results are according to [44]
Conclusions
This study in the Dominican Republic reveals the existence of different types of rainforest that are clearly differentiated by their floristic, biogeographical and bioclimatic composition. This broadleaved forest or rainforest is frequent in the Sierra de Bahoruco and the Cordillera Central, Septentrional and Oriental ranges due to the increased rainfall in these areas caused by the impact of moisture-laden Atlantic winds. Differences in soil and biogeography have conditioned a rich and different flora. The Cordillera Central range –geologically the oldest, and with a siliceous character– is home to rainforests of Magnolia pallescens and forests of Prestoea montana (As1 and As2) in humid-hyper-humid areas; whereas the associations As3 in Bahoruco and As4 in the Cordillera Oriental range also develop in humid environments but on soil substrates. This leads us to propose four new syntaxa with the rank of association and two new alliances.
Syntaxonomical checklist for the cloud forest of Hispaniola
Weinmannio-Cyrilletea Knapp 1964
Weinmannio-Cyrilletalia Knapp 1964
Rondeletio ochraceae-Clusion roseae Cano, Cano-Ortiz & Veloz all. nova hoc loco
Cyatheo furfuracei-Prestoetum motanae Cano, Cano-Ortiz & Veloz ass. nova hoc loco
Ormosio krugii-Prestoetum montanae Cano, Cano-Ortiz & Veloz ass. nova hoc loco
Ocoteo-Magnolietea Borhidi and Muñiz in Borhdi et al. 1979
Ocoteo-Magnolietalia Muñiz in Borhdi et al. 1979
Rondeletio ochraceae-Didymopanion tremuli Cano, Cano-Ortiz & Veloz all. nova hoc loco
Hyeronimo montanae-Magnolietum pallescentis Cano, Cano-Ortiz & Veloz ass. nova hoc loco
Hyeronimo dominguensis-Magnolietum hamorii Cano, Cano-Ortiz & Veloz ass. nova hoc loco
Acknowledgments
We are very grateful to Ms Pru Brooke Turner (MA Cantab.) for the English translation of this article. This manuscript has been released as a Pre-Print at: Biorxiv 543892; doi: https://doi.org/10.1101/5438922019.