The tree and shrub flora in savanna riparian forest in northeastern Brazil : update to Uruçuí-Una Ecological Station , Piauí State , Brazil

Floristic surveys are the basis of phytodiversity knowledge and when carried out in protected areas add value because they can generate incentives for conservation and subsidies for management plans. With the objective to contribute to flora knowledge in Piaui State, Brazil, a floristic study was developed in the riparian forest Uruçuí-Una Ecological Station. This station has a 135.122,29 ha area and is in Baixa Grande do Ribeiro municipality, Piauí, in Northeast of Brazil. The area is in Cerrado’s phytogeographical domain, with riparian forest along the river Uruçuí-Preto, which borders part of its area. The survey was conducted from samples collected of woody vascular plants in an area of approximately 4.5 ha on the left bank of Uruçuí-Preto River. The samples collected were properly herborized, taxonomically identified, and stored in herbaria Graziela Barroso (TEPB) and Delta do Parnaíba (HDELTA). The study resulted in 90 species, 71 genus, and 37 families. Except for Tilesia baccata species, Asteraceae naturalized, all species are native to Brazil, and 21.50% are also endemic in Brazil and 6.45% endemic in Cerrado. Most species, i.e 78.49% were not evaluated for the extinction risk, while 15.05% are classified in the Little Worrying category and only, Bowdichia virgilioides is in the condition of Near Threatened. This study contributes significantly to the scientific literature as it is the second floristic survey presented for this conservation unit since 1984, and the first study carried out in the riparian forest in this protected area of the Brazilian Cerrado.


Introduction
The Cerrado is considered to be a biodiversity richest savannah in the world and a global critical point on conservation priorities (Franke, et al., 2018) and is the second major phytogeographical domain Brazil, occupying an area of about two million square kilometers which corresponds to 25% of the national territory and has strong dynamics that varies with seasonal and anthropism, the latter mainly due to the production of grain (Resende & Guimarães, 2007;Sano, et al., 2007;Dias, 2008).
In addition, it is one of the Brazilian domains most anthropized by human activity (Beuchle, et al., 2015). In recent decades, public policies in Brazil have encouraged agriculture, livestock farming and exotic monoculture plantations in its territory (Morandi, et al., 2020). Its distribution area covers all regions of Brazil as well as occurring in disjoint areas of Caatinga and Amazon Rainforest (Resende & Guimarães, 2007).
Formed by a mosaic of different types, the Cerrado biome has high species richness, endemism, and very heterogeneous formation (Ferreira, et al., 2017), with different species of phytogeographic domains. In Piauí and Maranhão the Cerrado sensu lato is presented in the form of the following phytophysiognomies: dirty field cerrado, field cerrado, cerrado sensu stricto and cerradão (Castro & Martins, 1999). The cerrado sensu stricto can be divided into four subtypes depending on the density of the tree-shrub component and local environmental conditions: dense cerrado, typical cerrado locally called cerrado típico, thin cerrado, and rocky outcrop cerrado locally called "cerrado rupestre" (Ribeiro & Walter, 2008). Some conservation units in the state of Piauí, were created not only to protect the biodiversity of the Cerrado, but also the water sources and its sources. Due to human activities, some riparian species have become vulnerable, and have considerably reduced their numbers in the wild, mostly preserved in these protected areas.
To establish the categories of vulnerability for the species were created the criteria of species classification list endangered according to the IUCN (International Union for Conservation of Nature) (Martinelli & Moraes, 2013). Although little studied species of economic importance as Virola surinamensis Warb. (Lobão, et al., 2013) and Bowdichia virgilioides Kunth were found in riparian forest (Matos & Felfili, 2010) and cerrado sensu stricto (Lindoso, et al., 2010) in 'Sete Cidades' National Park, PI and are in vulnerable and almost threatened categories, respectively. To conserve these species in their environment they created rules for actions for the conservation of endangered species (Martinelli & Moraes, 2013). Many of the species that are cited in the red list are also endemic (14.79%). Development, v. 9, n. 10, e9589109264, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.9264 5 Current data presented for an overview of the brazilian diversity, indicated 11,973 species of angiosperm endemic to Brazil, with significant differences between the phytogeographical domains. In this context, the Cerrado is emerging on the national scene as the second hot spot in endemic species of angiosperm (35.1%), followed by the Atlantic Forest (49.5%). To the state of Piauí have been 1,992 species of angiosperm, with 1.5% of endemic species (BFG, 2015).
The contributions of this study are related to the survey and presentation of the floristic richness of an important biogeographic region, with little literary framework. Finally, we assume that we will provide important perspectives for understanding the floristic structure and composition of these plant formations, which may serve as essential subsidies for management actions, forest restoration and regeneration of plant communities. The singularity of vegetation types reinforces the importance of considering each floristic identity as a potential support to conservation planning, restoration, and other ecosystem interventions (Luiz & Alves, 2016;Guimarães, et al., 2019;Fernandes, et al., 2020). The main novelty of our study is that the floristic survey presented is the second most complete survey on the floristics of the Uruçuí-Una Ecological Station, since 1984, with the publication of the Castro (1984) study published in the National Botanical Congress, held in the Rio Grande do Sul, Brazil.
In order to increase knowledge of the floristic composition, vulnerability and endemism of riparian forests in the state of Piauí, there was a survey of the tree and shrubbytree flora, present on the left side (direction upstream to downstream) the Uruçuí-Preto River, located on the edge of the Uruçuí-Una Ecological Station, southeast of Piauí, Brazil.

Environmental Characterization of the Study Area
The Uruçuí-Una Ecological Station (U-UES) is located 8º50'S and 44º10'W in the state of Piauí, covering the municipalities of Baixa Grande do Ribeiro and Santa Filomena.
The vegetation in the U-UES is made up of some physiognomic types of Cerrado phytogeographical domain. In the cerrado sensu stricto type occurs abundance of grasses interspersed with small to medium sized trees. The riparian forests are found along the main rivers, the Uruçuí-Preto and Riozinho, located respectively on the outskirts of the eastern and western U-UES and for which converge numerous streams of small, forming the woodlands.

Results
The present study found 90 species, 71 genera and 37 families, and eight were not identified taxonomically by lack of reproductive material, thus generating 82 taxon identified to species level. These species were distributed according to the habit in trees (64.51%) and shrubs (34.40%).
In Figure 2 we present the graph of the floristic wealth found in the U-UES study area.

Discussion and Final Considerations
Floristic surveys in many different riparian vegetation of Brazil, indicate Leguminosae as the most representative taxon (Ribeiro & Walter 2008;Souza & Rodal, 2010;Matos & Felfili, 2010;Mendonça, 2012;Santos-Filho, et al., 2013;Silva, et al., 2013). Surely this family stands out because it is cosmopolitan, with many species being present in almost all terrestrial environments. Part of their adaptive success can be explained by fixing microbiota nitrogen, which form nodular root associations, enabling them to colonize environments poor in this element (Queiroz, 2009). However, in flood riparian forests there is a tendency to lower species richness for this taxon, as shown in other studies to the Piauí cerrado, as in flooded sections of the 'Sete Cidades' National Park (7CNP), PI (Matos & Felfili, 2010) and in the study area. Matos & Felfili (2010) conducted a study in 7CNP, specifically focusing on the arboreal vegetation of riparian forests, indicating high wealth specific to Leguminoseae (14), (7) and Anacardiaceae (4). Cabacinha & Fontes (2014) make indication of the same families, among others, to the Alto Araguaia Basin. These taxon are also present for the riparian forest of the U-UES.
The floristic richness of the Cerrado is due not only to its physiognomy diversity, but also its geographical position in the Americas (Mendonça, et al., 2008), which allows a wide contact with the Amazon Rainforest (Maracahipes, et al., 2015), the Caatinga (Castro, et al., 2014), the Atlantic Forest (Françoso, et al., 2016) and the Pantanal (Mendonça, et al., 2008).
Taxons as Orchidaceae, Myrtaceae, Rubiaceae, Melastomataceae and Euphorbiaceae are widely represented in the Cerrado, and the Atlantic Forest and Amazon Rainforest .
Regarding generic representativity, Matos & Felfili (2010) cite the genera Hirtella L., Licania Aubl. and Myrcia DC. ex Guill. for riparian forest 7CNP while Cabacinha and Fontes (2014) make indication of the same genera, among others, to the Alto Araguaia Basin. These kinds of higher specific representations are present with certain frequency and are important for forest formations of the Cerrado domain (Mendonça, et al., 2008). Except for Myrcia, these taxons are also present for the Riparian Forest of the U-UES.
Regarding the specific representation, Cabacinha & Fontes (2014) cite Gallery forest of Alto Araguaia basin (GO), indicating the occurrence of the species: Astronium fraxinifolium, Bowdichia virgilioides, Connarus suberosus, Diospyros sericea, Machaerium Research, Society and Development, v. 9, n. 10, e9589109264, 2020 (CC BY 4. Corroborating the above information, there was strong influence of other phytogeographic areas for study area because of the 90 taxon shown in Table 1, 83.33% also occur in the Amazon, 70% in the Caatinga, 52.22% in Atlantic forest, with a low correlation to the Pantanal (14.44%). Regarding the Amazon, Chaunochiton kappleri was indicated to date only for this area, also occurring in the study area.
Regarding the vegetation type, the highlight was the cerrado sensu lato with 74.44% of the relevant species and the riparian forest 50% of species are associated with different phytogeographic domains. The Vochysia pyramidalis species and Mauritiella armata were presented exclusively only for the riparian forest, associated with phytogeographic areas: Cerrado, Caatinga, Amazon Rainforest (M. armata) and Cerrado, Caatinga, Atlantic Forest (V. pyramidalis).
The influence of the Amazon Rainforest and the Atlantic Forest in the Cerrado domain varies according to geographical location and the vegetation type. Among phytophysiognomic types of Cerrado area, the riparian forest appears to be more favorable for the species from the Amazon forest than the more open areas of the cerrado (cerrado woodland and cerradão) (Méio, et al., 2003). The cerrado sensu stricto direct interference from the surrounding vegetation, but the Atlantic Forest influencing contribute more directly, in the floristic composition of the Central Brazil's Cerrado (Françoso, et al., 2016).
Regarding the habits of species, trees (66.67%) predominated over the shrub (33.33%). In work carried out for the riparian forests of the Cerrado area, there is a predominance of arboreal habit of the shrub, herbaceous and climbing, following this order of dominance Silva Junior, et al., 2001). Other studies emphasize the dominance of only shrubs and trees habits, or the woody for sensu cerrado called (Mendonça, et al., 2008). Some authors however point out the herbaceous habit, including herbs, subshrubs, parasites, hemiparasites, lianes and geophytes palms (Mendonça, et al., 2008).
Endemism relation, it must be 22.22% of the 90 identified species are endemic to Brazil while 6.6% are endemic to the Cerrado. Hardly detected invasive species, since 99% of the species listed herein are native, except for Tilesia baccata species, Asteraceae naturalized in Brazil (Magenta, 2016).   Source: The authors (2020).
Research, Society and Development, v. 9, n. 10, e9589109264, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i10.9264 24 Specialists point out that more than 40% of woody species are endemic to this area, the number of endemic species to the Cerrado considered significant. Despite the efforts, the anthropic transformation of the Cerrado impels high losses and changes in biodiversity, mainly due to the limitations of conservation units in Brazil .
According to Castro et al. (2014) in Piauí occur transition forests, for including species of the Cerrado and Caatinga, endemic and non-endemic, occurring Atlantic and Amazonian species of wide distribution. In the same study, were cited for seasonal forests of Piauí, 39 common species found in the Amazon and Atlantic Forest, 59 for the Cerrado and Atlantic Forest and 53 for the Caatinga and Atlantic Forest. Yet they are indicated 89 species endemism to Brazil and 71 non-endemics.
Within the conservation scenario, according to the criteria of threatened species classification list of IUCN, the vast majority of species of riparian forest U-UES proved the not yet evaluated category (78.49%), while a small percentage was classified as least concern (15.05%) and only Bowdichia virgilioides proved on condition that almost threatened. With respect to this latter species, it makes up a list of species of interest to research and conservation (Martinelli & Moraes, 2013). Finally, we conclude that this floristic survey conducted for U-UES, Piauí, may be fundamental for the development of other floristic or phytosociological studies and useful for actions of conservation, protection, and restoration of riparian forests or other ecological economic purposes. In addition, the number of species that also occur in the Amazon has called our attention. Because of this, we increasingly believe that our Semi-Deciduous Seasonal Forests, even being "Riparian Forests", receive a greater influence from the Amazon Forest than from the Atlantic Forest. New studies need to be carried out for more assertive conclusions about this and other perceptions and hypotheses about riparian vegetation in the Cerrado of Piauí.