FLORISTIC CHARACTERIZATION OF IBURA NATIONAL FOREST , SERGIPE , BRAZIL CARACTERIZAÇÃO FLORÍSTICA DA FLORESTA NACIONAL DO IBURA , SERGIPE , BRASIL

The aim of this study was to obtain information on the floristic composition and dispersal syndromes of the Ibura National Forest and carry out an analysis of similarity with other floristic surveys in the state of Sergipe. For this purpose, bimonthly sampling was carried out from September 2012 to December 2014. Total of 328 species were recorded, of which 324 were angiosperms belonging to 82 families, followed by three species of ferns and lycophytes and one species of Gymnosperm. Sixty-seven new species were recorded for the state of Sergipe. The richest families in species were Fabaceae, Myrtaceae, Rubiaceae, Asteraceae, Euphorbiaceae and Malvaceae. Regarding the dispersal syndromes, the dominance of zoochoric dispersal was observed, followed by autochoric and anemochoric dispersal. Among the tree and shrub species, the zoochoric syndrome was predominant (70%), while herbaceous species showed predominance of autochoric species (49%), and climber species have a more equitable proportion among the syndromes (38% autochoric, 32% anemocoric and 30% zoochoric). The Ibura National Forest presented relatively low levels of similarity with other sites located in the Atlantic Forest, possibly influenced by its isolation and distance between fragments. As we found in the Ibura National Forest, the dominance of zoochoric species was also observed in other studies conducted in the Atlantic Forest. The results of this study indicate that the Ibura National Forest is refuge to a high diversity of plant species of the Atlantic Forest, being a fairly heterogeneous area, which is still understudied.


INTRODUCTION
The Atlantic Forest is one of the 34 global biodiversity hotspots (MITTERMEIER et al., 2004).This domain has an estimated number of 20000 species of vascular plants (PINTO et al., 2006), of which 6663 (49%) are considered to be endemic (STEHMANN et al., 2009).Originally, the Atlantic Forest extended continuously along the Brazilian coast, penetrating into eastern Paraguay and northeastern Argentina in its southern portion (TABARELLI et al., 2005), and was considered the second largest tropical rainforest in the American continent.Currently, if we include all the fragments of native forest above 3 hectares and the non-forest formations such as salt marshes and mangroves, only 15% of the Atlantic Forest remains (FUNDAÇÃO SOS MATA ATLÂNTICA, 2014), covering a variety of climatic zones and vegetation formations of the tropical to subtropical regions (TABARELLI et al., 2005).
With regard to conservation, the largest and most important remnants are usually associated with full protection conservation units, mainly located on the coast of the states of Santa Catarina, Paraná, São Paulo, Rio de Janeiro, Bahia and the mountain region of Espírito Santo, corresponding to less than 2% of the biome's area (PINTO et al., 2006).
In the state of Sergipe, it is estimated that only 9% of the original area of the Atlantic Forest remains (FUNDAÇÃO SOS MATA ATLÂNTICA; INPE, 2002).The state has only nine conservation units for the Atlantic Forest biome and not all native vegetation fragments are included in these units (SOUZA;LANDIM, 2007).
Among the conservation units of the state of Sergipe, the Serra de Itabaiana National Park (7966 ha), Santa Isabel Biological Reserve (2766 ha), and Mata do Junco Wildlife Refuge (600 ha) are noted for being among the largest units of the state (MENDES; GOMES; ALVEZ, 2010;SOUZA-ALVES et al., 2014;OLIVEIRA;LAMDIM, 2014).But the vast majority of remnants are still in private areas, such as Mata do Crasto, located in the southern region.The latter is considered the most representative and preserved fragment of Atlantic Forest of the state, covering an area of approximately 1000 ha (LANDIM et al., 2015).
Floristic studies are starting points for understanding biological ecosystems to advance our knowledge about the complex dynamic behavior of plant communities (MARANGON;SOARES;FELICIANO, 2003).Besides the species composition, the understanding of the functional structure of each forest remnant, such as of the set of dispersal syndromes (PRADO-JÚNIOR et al. 2014), is essential to define its conservation status, which is reflected, among other factors, in the complexity of animal-plant interactions ( VAN DER PIJL, 1982).
Studies of flora are considered fundamental for basing any activities regarding the use, recovery and conservation of tropical forests (RIBAS et al., 2003).This study was developed to inventor the floristic composition and characterizing the dispersal syndromes of the Ibura National Forest and assessing its similarity to other floristic surveys in the state.Considering that the Ibura National Forest does not yet have a management plan, this study could also potentially contribute to its development.

Study area
Before the creation of the Ibura National Forest (FLONA Ibura), this area was used to support the development of livestock farming in the state of Sergipe (Horto Ibura) and later to support recovery projects of degraded areas.It was transformed into a sustainable conservation unit by September 2005.
The Ibura National Forest (10º83'86.0"W, 37º13'42.0"S) covers an area of approximately 145 ha and is located in the municipality of Nossa Senhora do Socorro, in the state of Sergipe.It is classified as semideciduous forest, at medium and advanced stages of regeneration, associated with mangroves (Figure 1) (BRASIL, 2005).In general, the vegetation of the Ibura National Forest is quite peculiar, having a history of deforestation for eucalyptus plantation, introduction of exotic species and anthropic pressure.It presents four main vegetation types: (i) a preserved forest area (on the margins of the BR101 highway) with a canopy in an advanced state of succession when compared to the other subareas; (ii) an area under regeneration, with an understory in secondary succession stage mixed with an old abandoned eucalyptus plantation; (iii) a mangrove area along the margins of Cotinguiba River, with a small spot on the east margin of the BR101 highway ; (iv) an open area, characterized by sparse grasses and shrubs.Several trails were also found surrounding the area and inside it, some of which were approximately 5m wide.

Floristic survey
To study the vegetation structure and composition of a particular type of vegetation, it is important that the sample is representative, namely that the procedures and methods used for forest measurement are compatible with the vegetation, and cover a significant portion of its flora.Initially, a visit for recognition of the area was conducted.This led to the choice of a method for obtaining data on floristic characterization that included random sampling along the edge of the forest and along existing trails inside the forest.Sampling was carried out twice a month, from September 2012 to December 2015.
The collected material was pressed in the field, according to Martins-da- Silva et al. (2014) and identified through specialized literature, assistance from experts, and comparisons to preexisting herbarium specimens.It was subsequently deposited in the Herbarium ASE -Federal University of Sergipe.

Analyses
From the Jaccard similarity index, a cluster analysis was performed using the unweighted pair group method with arithmetic mean (UPGMA).As some of the studies that were used for the comparison did not sampled herbaceous species of Atlantic Forest (SOUZA-ALVES et al., 2014;VICENTE et al., 2005;OLIVEIRA et al., 2013;LANDIM et al., 2015) and Caatinga (SILVA; PRATA; MELLO, 2013;FONSECA, 1991;FERREIRA, 2011;NOGUEIRA-JÚNIOR, 2011;MACHADO;PRATA;MELLO, 2012), in this analysis only tree and shrub species were considered.The analyses were performed using the program PAST (HAMMER; HARPER; RYAN, 2001).The composition of tree and shrub species at the Ibura National Forest were compared with other floristic studies in the state of Sergipe carried out both in the Atlantic Forest and in the Caatinga (Table 1).

RESULTS
The study area presented a total of 328 species, of which 324 were Angiosperms belonging to 82 families; three were species of ferns from three families and one was a Gymnosperm.Of this total, the 11 families with the greatest species richness were Fabaceae (standing out with 50 species in 30 genera), followed by Myrtaceae (20 species in 7 genera), Rubiaceae (15 species in 11 genera), Asteraceae (14 species in 14 genera), Euphorbiaceae (13 species in 9 genera), Malvaceae (12 species in 8 genera), and Orchidaceae (12 species in 12 genera).These families comprised approximately 26% of the species found (Appendix 1).
Among the 324 species of Angiosperms sampled in the Ibura National Forest, 286 are native species, 14 exotic species, 18 naturalized species and six cultivated species (Appendix 1).Among the native species, 22 are endemic to the Atlantic Forest and to the northeast of Brazil (Caatinga and Cerrado), according to the classification of the List of the Brazilian Flora (LSBF; http://floradobrasil.jbrj.gov.br/).
Comparing the floristic composition with inventories already carried out in the state, the similarity showed two large clusters, the first belongs to the Atlantic Forest (AF) (11-24%) and the other to the Caatinga (CA) (18-41%).Species richness of the Ibura National Forest, grouped with other studies located on the site of the Atlantic Forest (AF), however they presented relatively low similarity levels (11-19%).The site that showed the highest similarity to the Ibura National Forest was the Piauitinga River Basin (4), municipality of Salgado, (with 19%) and Serra de Itabaiana PN (5) (with 15%) (Figure 3; Table 1).

DISCUSSION
The families with greater richness of species found at the Ibura National Forest (Fabaceae, Myrtaceae, Rubiaceae, Asteraceae and Euphorbiaceae) are similar to those found in other surveys conducted in the Atlantic Forest of the state of Sergipe (VICENTE et al., 2005;SANTOS, 2011;MENDES;GOMES;ALVEZ, 2010;SOUZA-ALVES et al., 2014;LANDIM et al., 2015).The Ibura National Forest is also distinguished by the high species richness of native and endemic species in the state, even within a smaller area, when compared to the previously mentioned studies.
About 24% of the native species found in FLONA Ibura (79 spp.) are considered new records for the state of Sergipe.This set of new records for the state can be divided into four categories, according to their distribution areas known: (i) Swartzia dipetala (Fabaceae) LANDIM et al. (2015) found 321 species, 129 of these being considered new occurrences for the Atlantic Forest of the state.It is important to note that this scenario has changed in recent years with the result of recent publications, where the number of species occurring in the state has been gradually updated, as well as records of ocurrence.
The presence of endemic species, as well as those in the "near threatened" category, emphasizes the importance of existing conservation units and reinforces the urgency of protecting new areas of vegetation in the state (ANDERSON, 1994;MAURER, 1994).
The high number of exotic species in FLONA (Table 2) can be connected to local historical factors such as the removal of native vegetation for eucalyptus plantation and anthropogenic actions carried out in the vicinity and in the study area.The introduction of exotic species can also be related to the former use of the space.Data on exotic species are worrying, since we have no studies in the area to find out whether they are causing damages or are bringing benefits to the native species.
Similar to the results found in the Ibura National Forest, the dominance of zoochoric species was also observed in other studies conducted in the Atlantic Forest (REYS et al., 2005;MOREIRA;QUEIROZ;PIGOZZO, 2009;OLIVEIRA et al., 2011;MOURA;DUARTE;LEMOS, 2011).The dominance of zoochoric species in rainforests is favored by the precipitation factor, enabling the development of edible fruits, favoring the dispersal by fauna (HOWE;SMALLWOOD, 1982).Within this group, the morphological variations and strategies to attract the disperser vary between species, nutrients and the amount of seeds, which contribute to the establishment of plant populations (PIZO, 2002).
The species cluster showed two main locations (CA and FA) for the two biomes that occur in the state, showing that species are key factors in the characterization of both.The species composition of the analyzed fragments showed relatively low levels of similarity, even those belonging to the same biome or those that are considerably close to each other.Furthermore, this low similarity is probably being influenced by the distance between fragments, and historical levels of degradation.FAHRIG (2003) mentions that the isolation of areas causes loss of species richness, decreases interaction, limits the population distribution, abundance, dispersion and, genetic exchanges.
The results of this study indicate that the Ibura National Forest is a refuge to a high diversity of plant species of the Atlantic Forest, being a fairly heterogeneous area, still under studied.The data reinforce the need and importance of conservation units for the preservation of regional biodiversity and highlight the need of a management plan and analysis of the exotic species in the area.

Figure 1 .
Figure 1.Location of the study area, Ibura National Forest, in the municipality of Nossa Senhora do Socorro, state of Sergipe, Brazil.

Figure 3 .
Figure 3. Cluster analysis based on the Jaccard florisitic similarity index of tree and shrub species in the state of Sergipe.Numerical codes are the same as those in Table 2. Legend: AF = Atlantic Forest; CA = Caatinga.

Table 1 .
Data used in the Cluster analysis, based on floristic similarity (Jaccard index) of sites sampled in Sergipe, Brazil.