Knowledge for a Better Conservation: Syntaxonomic Review of Caribbean Pine Forests (Cuba, Hispaniola)

A phytosociological review is carried out of the pine forest formations on the islands of Cuba and Hispaniola (Caribbean), due to the diversity of soils and environments. We collected 10 plant associations belonging to the class Byrsonimo-Pinetea caribaea growing on siliceous, calcareous and sandy substrates and 21 associations on special, serpentine and ophite substrates and on ultramafic rocks belonging to the class Caseario crassinervis-Pinetea cubensis, exclusive to Cuba; while the association of pine forests on serpentines in Hispaniola is included in the class Phyllantho orbicularis-Neobracetea valenzuelanae with a Caribbean distribution. The comparative phytosociological and statistical study reveals phytosociological anomalies in the inclusion of various syntaxa, and in the description of other syntaxa according to the International Code of Phytosociological Nomenclature (ICPN). We therefore propose a change in status for several of the subassociations described: subass. ilicetosum repandae: syn. var. con Ilex repanda; subass. schmidtottietosum shaferi: syn. var. with Schmidtottia shaferi; subass. acrosynanthetosum trachyphylli: syn. var. with Acrosynanthus trachyphyllus; subass. psychotrietosum grandis: var. con Psychotria grandis; subass. notodonetosum roigii: syn. var. with Notodon roigii. We also propose a nomen novum: jaquinietosum oxhyphyllae Reyes & Acosta 2012 ex Cano et al. hoc loco.


Introduction
From the bioclimatic standpoint, the thermotype in the Antilles ranges from the infratropical to the supratropical (the latter only in Hispaniola) [1]. The temperature in 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. This study of Cuban pine forests is conducted in the infra-, thermo-and mesotropical thermoptypes and in rainy environments with rainfalls of between 1300-2000 mm. The ombrotype ranges from the lower subhumid to the upper humid, in agreement with Rivas-Martínez et al. [2] and Cano et al. [3] on the island of Hispaniola, in sites with a dominance of broadleaved forest; however, in areas with steep slopes or special substrates where there is a water deficit, the pine forest should be considered edaphoxerophilous [4][5][6]. tilles biogeographic province is created for Puerto Rico and the Lesser Antilles. The island of Hispaniola is considered a biogeographical province with two biogeographical subprovinces: the Central subprovince (Central sector) with acid substrates and over 500 endemic species, and the Caribbean-Atlantic subprovince with basic substrates and six biogeographic sectors with 19 district areas, which are subsequently studied by Cano Ortiz et al. [11]. For the biogeographic study we have taken into consideration several factors, the geology of the territory, endemic species, distribution and origin of the flora, as well as the existing plant communities and their catenal contacts. [8][9][10] Solid knowledge about flora and vegetation provides a valuable basis for the implementation of biodiversity management and conservation measures [12][13][14]. The gaps of knowledge, both in native and alien species, are still today the subject of interest by numerous scholars around the world [15][16][17][18]. If flora checklists provide new, complete and updated information about the presence of plant taxa in a given geographic area at small or large scale, syntaxonomical studies allow to review, improve and update knowledge on species composition of different plant communities that occupy several habitats in the world.
Pine forests are habitats widespread in the world, very important for providing ecosystem services and for their ecological role [19]. If some of them are well known and studied under different points of view, others less. It is the case of the Caribbean pine forests of Cuba and Hispaniola For the study of the pine forests in the Caribbean, the phytosociological method was used, since the existing studies in Hispaniola and Cuba are of this type. Thus we highlight the different plant associations, which constitute habitats of special protection due to the high rate of endemism.
On the northern or windward face of the mountains, there is a predominance of broadleaved or rainforest of Magnolia, Prestoea, Ocotea, Podocarpus, Cyathea (Ocoteo-Cyrilletea racemiflorae Borhidi 1996) [20], while the pine forest is on the Caribbean or leeward face at low altitudes above the sea of clouds. The genus Pinus comes from North America and reached the Greater Antilles via the Florida migratory route. Cuba [21 ,22] and López Almirall [23], we maintain the taxon P. maestrensis Bisse. Some authors also cite P. occidentalis var. cubensis in Cuba. In Hispaniola there is a dominance of P. occidentalis (endemic) and in a disperse manner P. caribaea. Only P. caribaea is located in Puerto Rico, where it forms different types of forest. Other plant communities developing exclusively in Hispaniola are the hemicryptophyte grass scrublands in the supratropical bioclimatic belt, dominated by Danthonia domingensis Hack. & Pilg., a plant that is endemic to the Cordillera Central and that coexists with the endemic plant Deschampsia domingensis Hitchcock & Ekman, occupying the open areas left by the pine forest of P. occidentalis, described by Cano et al. [24] as Dendropemom phycnophylli-Pinetum occidentalis Cano, Velóz, & Cano-Ortiz 2011. Several researchers have studied the In the syntaxonomic review carried out, we have taken into consideration the syntaxa described by various authors, with a range of association, subassociation, variants and subvariants. We started from 18 associations (180 inventories), for the islands of Cuba and Hispaniola. However, Reyes & Acosta [27] accept 21 syntaxa with association rank, 11 subassociations and 22 variants and subvariants, although they didn't provide inventories of all syntaxa. In this review, we accept for Cuba 31 associations described by various authors and that comply with the ICPN [36], 8 subassociations and 4 variants. For Hispaniola we only have 3 associations described by us in previous works.
In both cases, pine forests occupy large areas of Cuba and Hispaniola, with human actions that cause a decrease of these ecosystems in areas of the Caribbean and elsewhere on the planet [43,44]. If we add to this phenomenon changes in rainfalls and temperatures due to climate change [45,46], we obtain plant communities that substitute these forests, some of these being invasive communities. It is the case of Prosopis juliflora (Sw.) DC. that it is invasive in much of the world [47]. However, the resilience of Pinus species is high [48]. These pine forests located on different types of substrates, represent habitats of interest due to their high rate of endemic species, either because they are located on special substrates or because of the mountain effect, since the mountains present an increase in endemics when climbing in altitude [24,49].
We include two orders and six alliances with ten plant associations in the class Byrsonimo crassifoliae-Pinetea caribaeae. The forests of Pinus occidentalis on the island of Hispaniola have a different biogeographical distribution and floristic composition from that of the pine forests of Cuba; for this reason, they form separate groups in the DECORANA statistical analyses (Figure 3). In Hispaniola, Cano et al. [24] described three plant associations for three different environments. Coccotrino scopari-Pinetum occidentalis (CP) growth on calcareous substrates in the Sierra de Bahoruco. Dendropemon phycnophylli-Pinetum occidentalis (DP) covers large extensions on siliceous substrates in the Cordillera Central, with both associations growing at altitudes above the sea of clouds. Finally, Leptogono buchi-Pinetum occidentalis (LP), located on serpentines in the northeast of the island of Hispaniola (Dajabón). The alliance Rondeletio christii-Pinion occidentalis was described for these pine forests on serpentines on the island of Hispaniola, and assigned to the order Ariadno shaferi-Phyllanthetalia orbicularis Borhidi & Muñiz in Borhidi 1996 and to the class Phyllantho orbicularis-Neobracetea valenzuelanae Borhidi & Muñiz in Borhidi 1996, representing sclerophyllous heaths in submontane areas in western Cuba. These plant communities on serpentines on the island of Hispaniola were not included by their authors in the class Caseario crassinervis-Pinetea cubensis Borhidi & Muñiz in Borhidi 1996, due to their marked floristic difference from Cuban serpentinicolous vegetation, as can be seen in the synthetic table we provide (Appendix A, Table A1). There are significant ecological, biogeographical and floristic differences between the three pine forest associations described for the island of Hispaniola, and which clearly separate the three syntaxa, as can be seen in the table prepared with the typus (Appendix A, Table A2).

Discussion
Borhidi [13,14] includes the alliances Acoelorrapho-Pinion tropicalis Samek in Borhidi et al. 1979, Blechno serrulati-Acoelorraphion wrightii Hadac and Hadacová 1971, Neomazaeo-Pinion caribaeae Borhidi 1991, and for Hispaniola Cano et al. [24] propose the alliance Ilici tuerckheimi-Pinion occidentalis Cano et al. 2011, which contains two of the abovementioned associations CP and DP. The associations published by Samek [50,51] for the island of Pinos, (PAP) Paepalantho seslerioidis-Pinetum tropicalis and Roigello-Pinetum tropicalis (Samek 1969) Borhidi 1996, were compiled by Borhidi [22,37] and included in the alliance Acoelorrapho-Pinion tropicalis. In our analysis the association Byrsonimo pinetorum-Pinetum tropicalis-caribaeae (BYP) published by Borhidi [22] is perfectly separated from the previous ones, which is to be expected as it was published for rainier sites in western Cuba and included in the alliance Blechno serrulati-Acoelorraphion wrightii. This same author published the alliance Neomazaeo-Pinion caribaeae for the pine forests on rocky serpentine substrates in the Sierra de Cajalbana, where he includes three associations published by Samek [51], although two of them with a new name. Agavo cajalbanensi-Pinetum caribaeae, Guettardo-Pinetum caribaeae and Neomazeo-Pinetum caribaeae are associations that are typified by Borhidi based on the relevés of Samek. Borhidi [22,37] published the alliance Pachyantho poiretii-Pinion caribaeae for the mixed forests of Pinus caribaea and Quercus oleoides subsp. sagraeana, subordinating it to the order Pinetalia tropicalis-caribaeae. He creates for this alliance the association Querco-Pinetum caribaeae for slates and sandstones in the Sierra de los Organos and the Sierra del Rosario. Due to its mixed forest characteristics, this alliance must be included in the order Pinetalia occidentalis-maestrensis. The alliance Cyrillo nipensis-Pinion cubensis described for rainy environments on ferritic soils and serpentines in northeast Cuba, with the association Cyrillo nipensis-Pinetum cubensis described in Toa River, Sierra de Maguey and Cupeyal, have been included in the order Podocarpo-Sloanetalia curatellifoliae Borhidi & Muñiz in Borhidi 1996, which consists of epiphyte-rich vegetation in rainy environments. Based on its floristic and physiognomic characteristics, this alliance  should be in the order Pinetalia occidentalis-maestrensis, which also includes the alliance Pinion maestrensis, with the association Clethro cubensis-Pinetum maestrensis described for oligotrophic soils in the rainy mountains of the Sierra Maestra; this association is clearly differentiated from the rest of the syntaxa in the study due to its floristic, ecological and biogeographical composition. All the relevés, including the typus, are separated in an independent group, as can be seen in the general cluster in Figure 2.
All the Cuban pine forests growing on ultramafic, serpentine, serpentinised peridotites and ferritic acid soils were included by Borhidi et al. [35] and Borhidi [22,37] in the class Caseario crassinervis-Pinetea cubensis Borhidi & Muñiz in Borhidi 1996, representing pine forests growing on ferritic acid soils derived from serpentines and very rich in endemisms. The order Pinetalia cubensis Borhidi & Muñiz in Borhidi 1996 is created for this class, and includes the alliances Andropogono-Pinion cubensis to group the montane mesophilic pine forests growing on serpentine laterites, and Guettardo ferrugineae-Pinion cubensis to include the xeric pine forests on serpentines in eastern Cuba. The first alliance initially proposed by Borhidi comprised the associations Rhynchosporo cernuae-Pinetum cubensis Borhidi 1996 for decapitated ferritic substrates in Sierra de Nipe, and Shafero-Pinetum cubensis Borhidi & Muñiz 1996 for Sierra de Maguey. The following associations have been proposed for the second alliance Anemio coriaceae-Pinetum cubensis (ACP), Euphorbio helenae-Pinetum cubensis (EHP), (ASP): Agavo shaferi-Pinetum cubensis (ASP) and Dracaeno-Pinetum cubensis (DCP), which were typified by Borhidi [22]. In our analysis these last four associations are grouped in the cluster, separated from the rest of the associations published by Reyes & Acosta [27], which denotes the strength of this alliance. These last authors do not recognise the alliance Andropogono-Pinion cubensis, which is recognised by Galán de Mera & Orellana [52], but they do accept the alliance Guettardo ferrugineae-Pinion cubensis, for which they propose various suballiances: Caseario crassinervis-Pinenion cubensis, Garcinio-Pinenion cubensis, Dracaeno cubensis-Pinenion. They include in these suballiances several new associations and the four associations mentioned previously ACP, EHP, ASP, and DCP. The suballiance Dracaeno cubensis-Pinenion cubensis Reyes in Reyes & Acosta 2012 is incorrect in virtue of article 27 [36], as it actually corresponds to a status novo under article 51 [36], and hence should be cited as Dracaeno cubensis-Pinenion cubensis (Borhidi 1991 [35] and Borhidi [22,37] had previously described the alliance Cyrillo nipensis-Pinion cubensis with the association Cyrillo nipensis-Pinetum cubensis Borhidi & Muñiz 1991 for the serpentine substrates in eastern Cuba. The suballiance proposed by Reyes and Acosta should be synonymized to the one described by Borhidi (art. 2b [36]).
Reyes & Acosta [27] include 21 syntaxa with association rank, for which they propose eight new pine forest associations, one new status, and one new combination, in addition to nine new subassociations and two new combinations. The statistical analysis and the synthetic tables for the 180 relevés corresponding to the associations and subassociations included in the different suballiances and alliances show no substantial differences in some cases. The relevés in the association Anthaenantio-Pinetum cubensis created as a new combination, and for which two new combinations are in turn created with the rank of subassociation euphorbietosum and subassociation grisebachianthetosum nipensis, form a clearly characterized and homogeneous group. In this case the association has been typified: Samek's relevé 39 [53,54] is adopted as the type for euphorbietosum, and for the subassociation grisebachianthetosum nipensis, the type relevé of the cluster (141ANP) is relevé 4 Table 14 of Reyes & Acosta [27]. Unfortunately, this last subassociation is incorrectly named, as the taxon Grisebachianthus nipensis also belongs to the type relevé of the association ARP, which leads to misinterpretation according to articles 26 [36], as it is a syntaxon that only presents the endemisms Lobelia oxyphylla and Jacquinia robusta as differential in regard to the rest of the type. We therefore propose: jaquinietosum robustae subass. nova. The association Arthrostylidio-Pinetum cubensis represents a homogeneous group in the cluster in Figure 2 together with the subassociations annonetosum sclerophyllae and xylosnetosum buxifolii, which does not occur in the DECORANA ordination analyses. An analysis of the synthetic table shows floristic differences between ANP and ARP; however, the Jaccard distance is similar between both associations. The type of the association ARP and the types of its two subassociations show a close Jaccard distance given the similarity between the three syntaxa, and particularly between the type for the association and the type for the subassociation annonetosum sclerophyllae; however floristic differences can be seen in the table of type relevés, which together with the different ecology they present allows us to maintain both subassociations. The association Panico-Pinetum cubensis (PP) has been described for the altiplano in the Sierra de Nipe. The cluster analysis for the relevés forms a very homogeneous group, in which the association is differentiated from the subassociation lyonetossum affinis. However, in the Detrended Correspondence Analysis (DCA) the relevés tend to be intermixed with those of ANP and ARP, which is to be expected as they have a certain floristic similarity with these associations, and the Jaccard distance is similar between them (  this association, its authors describe two subassociations in addition to the type subassociation: ilicetosum repandae and schmidtottietosum shaferi. The ordination analysis for the general cluster in Figure 2 shows a group with all the relevés corresponding to CSP, with two subgroups, one of which contains the typus relevé of the association (75CSP) corresponding to relevé 8 Table 4 Reyes & Acosta [27]; the other subgroup contains the typus for the two subassociations. Both type relevés are floristically and ecologically very close, and appear to be more a case of ecotones with neighboring associations, as stated by their authors for the subassociation ilicetosum repandae in regard to the contact with the submontane tropical and subtropical moist forest, as it happens in Hispaniola [20]. Schmidtottietosum shaferi has been characterized by species with a broad distribution, all of which are native, and which have even been used as characteristic plants for both subassociations with the rank of genus, without specifying the species. Schmidtottia shaferi has been used as a characteristic for the suballiance Cyrillo nipensis-Pinenion cubensis, and also gives the name to the subassociation. Schmidtottia shaferi belongs to various associations (Tables  A1 and A2), and has been used to name Schmidtottio shaferi-Pinetum cubensis, an association that is very close to the previous one in terms of its floristic similarity, as can be seen in the various ordinations we performed and in the table of typus. For this last association, Schmidtottio shaferi-Pinetum cubensis, the authors propose the subassociations shaferetosum platyphyllae and acrosynanthetosum trachyphylli; both form a compact subgroup separated from the type association. It is evident that the subassociation acrosynanthetosum trachyphylli represents an ecotone contact with Acrosynantho trachyphylli-Pinetum cubensis, an association described in the ophiolitic complex in western Cuba and with high rainfall, for which, in addition to the type subassociation, its authors describe the subassociations ossaeetosum shaferi and psychotrietosum grandis. Both subassociations form a subgroup separated from the typus of the association (see table on the comparative analysis of typus); the subassociation ossaeetosum shaferi is characterised by the endemisms Gesneria wrightii Urb., Ilex hypaneura Loes. and Ossaea shaferi Britton & P.Wils. (syn.= Miconia jashaferi Majure & Judd.) However, the subassociation psychotrietosum grandis presents the following species as differentials of the association of native species with a broad distribution: Palicourea dominguensis, Pimenta odiolens, Psichotria grandis, Purdiaea parvifolia and Vanilla bicolor. This subassociation is really a catenal contact with the broadleaved forests and should therefore have been treated as a variant. In the case of Protio fraganti-Pinetum cubensis described for the extreme northwest of the municipality of Baracoa, this is a pine forest whose authors claim is located at low altitudes in islands of ultramafic substrates, contacting at higher altitudes with the tropical and subtropical moist forest. This is therefore an edaphoxeric and thermotropical pine forest located on sites with steep slopes. The general cluster shows that the association (type relevé 111PFP), corresponding to relevé 4 Table 111 Reyes & Acosta [27], forms a subgroup with the subassociation myricetosum, whereas the subassociation notodonetosum roigii constitutes an independent subgroup. However, Notodon roigii has been used exclusively as a differential species; this is a native plant with a broad distribution. The subassociation myricetosum presents the following endemisms as differential species for the type of the association: Calycogonium cristalensis Urb., Chiococca cubensis Urb., Purdiaea ekmamii Vict. and P. stenopetala Griseb. Finally, as in previous cases the relevés for the association Phyllantho mirifico-Pinetum cubensis represent a homogeneous group in the general cluster, separating into subgroups the relevés corresponding to the association from those of the subassociation pitcairnietosum cubensis; this separation can be observed in the comparative analysis of the typus for the syntaxa. Therefore, to avoid confusion we propose a change of status for the following subassociations: we propose a change from the subassociation to variant rank for subass. ilicetosum repandae Reyes [36]).

Conclusions
All the Caribbean pine forests are included in 4 orders and 12 alliances, with a total of 34 plant associations. The high diversity of syntaxa is due to the special characteristics of the territory, as these are islands with a high rate of endemisms and numerous different substrates. Siliceous, basic, and neutral substrates, and ophite, andesite and serpentine rocks are very frequent, leading to a wide range of different soil types. All this is favoured by the special orography of the islands, as there are steep slopes with gradients between 30 and 60°. The analysis of the studies by several authors and by ourselves reveals a high number of syntaxa with the rank of association and subassociation, and ecological and geographic variants. In this work we update several syntaxa based on the nomenclature of the ICPN [36] in order to avoid possible nomenclatural conflicts, and we include all the associations described until now. Finally, we propose the following syntaxonomic checklist for all the Caribbean pine forests.

Status DP CP LP CLP PAP BYP QUP ACP EHP ASP DCP PP CSP SP AP PFP ANP ARP PHP
Pinus cubensis