FLORISTIC COMPOSITION AND SIMILARITY OF A CAATINGA FOREST AREA, BAHIA, BRAZIL

The present study evaluated floristic composition, similarity and the phytogeographic structuring framework of Caatinga in the Contendas do Sincora National Forest. The climate of the region is BSwh', with annual precipitation of 500 to 700 mm and altitude between 300 and 400 m. The soil is eutrophic red-yellow ultisol. Floristic similarity was established by the unweighted pair group method with arithmetic mean. Fifty-one (51) taxa were found distributed in 20 families. The families with the largest number of genera and species were Fabaceae and Euphorbiaceae. The classification for this physiognomy was Woody Savanna-Steppe. Floristic similarity revealed a tendency of grouping between fragments of the same state and ecoregion. Despite the history of exploitation, the floristic composition was as expected for Caatinga areas. The similarity analysis revealed that the area in question does not have a similar floristic identity to the other Caatinga areas analyzed.


INTRODUCTION
Savannas have small or medium-sized trees (3 to 10 m high), generally spaced and with wide, low-spreading crowns (IBGE, 2012). According to the same publication, the term Savanna was coined by Fernández de Oviedo y Valdés, designating Venezuela's tree-lined woodlands, and later introduced by Spanish naturalists on the African continent. The Savanna-Steppe, which has several subgroups, is the name that best defines the Brazilian vegetation types of the northeastern semi-arid regions, known as Caatinga.
According to Velloso et al. (2002), the Caatinga is subdivided into eight ecoregions: the Campo Maior Complex, the Ibiapaba-Araripe Complex, the Sertaneja Setentrional Depression, the Borborema Plateau, the Sertaneja Meridional Depression, the São Francisco Dunes, the Chapada Diamantina Complex and the Raso da Catarina. Each ecoregion has different vegetation characteristics influenced by soil types, water availability, altitude and site relief.
The Caatinga is a unique ecosystem in the world with a significant number of rare and endemic taxa (FERRAZ et al., 2013;PEREIRA JÚNIOR et al., 2014;FERNANDES & QUEIROZ, 2018) and occupies approximately 10% of the Brazilian territory (GUERRA et al., 2014).
Despite its uniqueness it is one of the least studied biomes in the country. According to Silva et al. (2015), the Amazon and the Atlantic Forest receive many researchers among the biomes present in the country considering their high riches and international interest in these areas. The Cerrado has a very high number of publications compared to those already mentioned, while the Caatinga has less than 5% of the number of publications that each of these biomes has. The Chapada Diamantina region and the South region (Mata Atlântica) in Bahia are regions which concentrate the largest number of publications, even though the Caatinga is present in more than half of the state.
The present study was motivated by the existence of this information gap regarding this important Brazilian biome, especially regarding the state of Bahia. Thus, this work aimed to perform a floristic survey, to establish the phytogeographic structuring framework and perform a floristic similarity analysis of a Caatinga tree fragment located in the Contendas do Sincorá National Forest, southwestern Bahia state.

MATERIALS AND METHODS
The study was carried out at the Contendas do Sincorá National Forest (Flona), situated on the BA-026 highway, km 22, in the municipality of Contendas do Sincorá, with geographic coordinates (UTM) 271468, 8460009 (headquarters), in the southwest of Bahia State (Figure 1). The Extrema farm was bought by a mining company aiming to extract timber for coal production. As the results were below expectations, it was sold to a second mining company that had the same objective. Once again production was considered low and the farm was ceded to IBAMA in exchange for forest replacement credits in 1997. Flona was officially created by Presidential Decree, without number, of September 21, 1999.
According to MMA (2006), the relief unit is called Peripheral and Interplanaltic Depressions. No major structural deformation was found in the area such as displacement, pushing or even fracture failures. This fact was determinant for the low water availability of its groundwater. The predominant formation in the buffer zone is sandy, which is east of the unit, with an altitude ranging from 300 m to 400 m and dominated by siliciclastic and bimodal igneous rocks.
The climate of the region is BSwh' (Köppen Classification), warm, semi-arid, with annual precipitation of 500 to 700 mm. The rainy season occurs between November and January, with an average temperature of 23°C and a relative humidity of 60 to 80% (LIMA & LIMA, 1999).
Flona is inserted in the Chapada Diamantina Complex ecoregion, with part of the Sertaneja Meridional Depression (VELLOSO et al., 2002). The vegetation is predominantly Caatinga forest, with Cerrado and dry forest species. It is an ecotone between the Cerrado, Caatinga and Atlantic forest biomes, with difficult delimitation due to their interpenetration (LIMA & LIMA, 1999).
The floristic composition was obtained through a phytosociological survey that covered an area of 10,400 m², in addition to eventual fertile material collections. Only individuals of tree size with a diameter at breast height equal to or greater than 5 cm were sampled. This inclusion criterion aimed to restrict the research to individuals of arboreal size, since the objective was to analised the potential use for the caatinga area in question, in order to propose sustainable uses of the resource. Identification of the collected material was performed by consulting the specialized bibliography (Flora Brasiliensis, Flora from Bahia, Flora from Sergipe, Flora Neotropica, QUEIROZ, 2009, among others) and comparing it with specimens from the UESB herbarium in Vitória da Conquista (HUESBVC). The classification of botanical families was performed following the system APG IV (2016).
Floristic similarity relationships were performed between the study area and 19 other surveys in Caatinga (Savana-Steppe) from different states (Table 1). It is noteworthy that, for this analysis, only tree size species were used.  Este é um artigo publicado em acesso aberto sob uma licença Creative Commons Climate, soil type, altitude and rainfall characteristics were also evaluated ( Table 2).  The unweighted pair group method with arithmetic mean (UPGMA) and the Bray-Curtis similarity coefficient (1957) were used. Only individuals classified at species level were considered. The calculations were performed using Fitopac 2.1 software (SHEPHERD, 2010). The cut-off line for group identification was performed using the methodology proposed by Mojena (1977). Milligan & Cooper (1985) suggested the value of 1.25 for the constant "Φ".
It is important to highlight that the presence of A. pyrifolium is mainly due to its adaptability to the environment. It occurs in northeastern Brazil and northern Minas Gerais, ranging from shrubbery in dry caatinga areas, to arboreal in forest caatinga. The species adapts well to locations with long drought and stony shallow soils  and usually occurs at altitudes below 332 m (LEITE et al., 2015), constituting similar characteristics to the area of this survey. Leite et al. (2015) listed M. ophthalmocentra and M. tenuiflora as pioneers, occurring in previously degraded regions and in the middle regeneration stage. The area importantly underwent periods of vegetation exploitation before being transformed into Flona, which corroborates the information of the authors mentioned above.
According to Ferraz et al. (2014), the good adaptation of A. urundeuva to an area is an indication that early species (with greater dispersal and establishment capacity) are giving way to those with higher competitive capacity. This fact demonstrates that the area is regenerating from the impact suffered during the wood extraction for coal production.
The Burseraceae family presented only the C. leptophloeos species. This was also recorded by Lemos & Meguro (2015) in the state of Ceará, in a tree stratum with individuals higher than five meters. Guerra et al. (2014) found the species in an anthropized area in Rio Grande do Norte. According to Sanquetta et al. (2014), the species showed a high adaptability to both soil and water deficit in a study conducted in Brumado (BA), which is characteristic of the region.
It is worth mentioning the presence of H. selachidentatus and Leucochloron limae which were classified as "almost threatened" on the endangered species red list (MMA 2014) and Syagrus coronata and S. tuberosa, immune to cutting (State Law 13908, 2018).
The physiognomic classification that best fit the study area was Forested Savanna-Steppe (IBGE, 2012), due to its floristic composition (Table 3) and its structure. This subgroup is highlighted by S. tuberosa, C. leptophloeos and A. pyrifolium, as well as others of the Mimosa genus. Its structure is formed by two strata: one superior and sparse arboreal, and the other inferior grassywoody, with relevant phytophysiognomic importance.
Six groups were found regarding floristic similarity (Figure 2). The cut-off line for group formation was 0.88. There was a tendency to cluster between studies in the same state. The exceptions were Farias & Castro (2004) in the municipality of Campo Maior (PI), Lima & Lima (1999) and present study in Contendas do Sincorá (BA) and Sanquetta et al. (2014) in Brumado (BA). The survey carried out by Farias & Castro (2004) in the municipality of Campo Maior (PI) presents very different soil type, climate, altitude and annual precipitation from the Serra da Capivara National Park (LEMOS, 2004;LEMOS & RODAL, 2002), as can be observed in Table 2. It is noteworthy that the work by Lima & Lima (1999) carried out in Contendas do Sincorá (BA) was conducted in 1990. The wood exploitation history in the area until 1997 (the year it was assigned to IBAMA) may be the explanation for the low similarity with the present study. It was found that five of the six created groups exclusively unite an ecoregion: the first, the second and the fifth united the experiments carried out in the Sertaneja Meridional Depression, the third in the Ibiapaba-Araripe Complex, and the sixth in the Campo Maior Complex. The fourth group brought together the Raso da Catarina and Sertaneja Meridional Depression, all in the state of Bahia. In this case, the similar altitude and precipitation found in the surveys were determinant.
The minimum distance found was 0.33 between surveys conducted in the municipalities of Juvenília and Montalvânia, Minas Gerais (SANTOS et al., 2007) (Figure 2). The work carried out in Contendas do Sincorá-BA (LIMA & LIMA, 1999), did not form a group with the present study, although they were performed in the same area (Figure 1). This indicates that the area no longer had its original characteristics soon after the wood extraction for charcoal production (when the first study was carried out), since it is still in its middle regeneration stage about 20 years after the exploitation.
The cophenetic correlation was 0.85, indicating that the data provided by the dendrogram were well representative. According to Shepherd (2010), values below 0.7 indicate that the representation of the dendrogram was not satisfactory.

CONCLUSION
Despite the exploitation history, floristic composition was expected for Caatinga areas. Due to its floristic composition and physiognomic structure, the physiognomic classification for this physiognomy was Forested Savanna-Steppe.
The similarity analysis revealed that the Contendas do Sincorá National Forest does not have a similar floristic identity to the other Caatinga areas analyzed, including those of Bahia.

ACKNOWLEDGEMENTS
The present authors would like to express their thanks to Contendas do Sincorá National Forest for the authorization to perform this study.