Veredas ( Mauritia Flexuosa palm swamps ) in the southeast Brazilian savanna : Floristic and structural peculiarities and conservation status

The Mauritia flexuosa L. f. (Arecaceae) palm swamps (known as veredas in Brazil) are 
hygrophilous communities associated with hydromorphic soils in areas of headwaters, and 
feature special importance for water and biodiversity maintenance in the Cerrado biome. 
In northern Minas Gerais, the veredas have more complex structure and floristic composition 
in comparison with the veredas located in other parts of central Brazil, in the same biome. 
However, these areas are less studied and suffering various environmental impacts, 
which can uncharacterize them even before they are properly known. In the present work, 
a literature review was carried out, in which the age and the development of vegetation in 
the veredas of central Brazil and north of Minas Gerais were addressed. The conservation 
status and the importance of these areas for the biome were also discussed. Hence it was 
concluded that the veredas of the north of Minas Gerais are older than the veredas of 
central Brazil, suggesting that they are in a more advanced stage of ecological succession. 
However, many factors can influence the floristic composition and structure of these plant 
communities, requiring further studies involving ecological processes in veredas in order 
to elucidate those matters. 
Keywords: vegetational structure, ecological succession, palynological analysis.


Introduction
The Cerrado biome (Brazilian Savanna) is identified as one of the richest world's ecosystems, covering 21% of the country (about 2 million km²) and has more than 55,000 cataloged species plants, with a total of 5% of the world's biodiversity (Padovesi-Fonseca et al., 2015).The high biodiversity is mainly related to its connection with other Brazilian biomes, thereby generating biogeographic zones of tension (Azevedo et al., 2014).In addition, biodiversity is also due to its great environmental heterogeneity, the variation of soil and its characteristics (chemical composition, depth, type of drainage), favoring the diversity of environments and supporting various vegetation types that alternate in the landscape (Klink and Machado, 2005).Most facies of the Cerrado biome present xerophytic vegetation, ranging from open areas such as grassland formations to closed formations as the cerradão (Ribeiro and Walter, 2008).
Despite the predominance of well-drained soils in the phytophysiognomy, the Cerrado also features wetlands, as the palm swamps (with Mauritia flexuosa L. f.), which are known as veredas in Brazil (Resende et al., 2013;Padovesi-Fonseca et al., 2015), with a floristic and structural complexity in contrast to the usual open formations (Rull and Montoya, 2014).Veredas are hygrophilous communities associated with hydromorphic or peat soil in headwater areas, where there are high water table (Guimarães et al., 2002;Ribeiro and Walter, 2008).In these environments, the floristic richness is favored by a gradient of humidity related to changes in soil drainage.The border zone is the driest area that occurs surrounding the vereda.The central portion or background of vereda is a saturated area near the stream, where M. flexuosa can be found (Ribeiro and Walter, 2008).The moisture gradient thus permits the establishment of species with different ecological requirements, ranging from flooded experts, generalist species, and species common at the dry soils (Kurtz et al., 2013).Thus, veredas have several species associated with distinct water saturation regimes, and large number of endemic species, which are more vulnerable to extinction (Rosolen et al., 2015).
The veredas have a great environmental importance, especially in the northern region of Minas Gerais, which has a semiarid climate with marked seasonality and drought period of approximately eight months, or more (Neves, 2011).In the dry season, the veredas may represent the only sources of water, food and shelter for the associated species and the humans who inhabit these surroundings (Neves, 2011;Silva and Maillard, 2011;Resende et al., 2013).This happens in detriment of the fact that veredas act as great reservoirs: peat soil stocks the water which is released over time, making the rivers and streams downstream become perennial, mitigating the ef-fects of flooding and minimizing erosion (Moss, 2012).Peats also function as a filter, removing pollutants and agricultural inputs in the water seeping from dry areas to the vereda (Moss, 2012).
In Brazil, several authors characterize the veredas as a savanna formation (Ribeiro and Walter, 2008), a mostly grassy field, where the forest cover ranges from 5-10% of the territory (Meirelles et al., 2002;Resende et al., 2013).The Brazilian Forest Code defines veredas as a "savanna vegetation type found in hydromorphic soils, with palm tree Mauritia flexuosa without forming canopy, among clusters of shrub and herbaceous species" (Brasil, 2012).This classification where the veredas appears as a grassy field in the presence of M. flexuosa palms is prevalent and observed in the studies in central region of Brazil, in Goiás (Resende et al., 2013), in the Distrito Federal (Meirelles et al., 2002) and the region of Triângulo Mineiro (Minas Gerais State) (Araújo et al., 2002;Guimarães et al., 2002;Oliveira et al., 2009;Ramos et al., 2014;Rosolen et al., 2015).
Indeed, Ribeiro andWalter (2008), andGuimarães et al. (2002) reported that, with the growth of vegetation, the veredas may have dense hygrophilous vegetation associated, forming islands of woody vegetation amid the savanna plains, as it happens in the veredas in northern Minas Gerais.In an attempt to fit these areas on a ranking system that classifies their forest physiognomy, the veredas of the northern Minas Gerais were classified by some authors as flooded riparian forests, gallery forests or simply riparian forests (Silva and Maillard, 2011;Gaya, 2014).However, the main defining feature of the veredas environment is the strong presence of the M. flexuosa palm, associated with the peat and hydromorphic soil (Guimarães et al., 2002;Ribeiro and Walter, 2008;Bahia et al., 2009a), which is observed in the veredas of the region.
For the purpose of making scientific comparisons, guiding public policy and environmental management (Gaya, 2014) or even to guide projects for environmental restoration, there is a need to have uniformity in the terminologies used for characterization and classification of phytoecological units.However, there is a lack of scientific studies for this purpose in the veredas system, and even works related to the characterization of vegetation are scarce (Araújo et al., 2013;Rosolen et al., 2015).Veredas areas suffer various environmental impacts, culminating in their mischaracterization and degradation (Guimarães et al., 2002;Bahia et al., 2009a), even before species composition, structure and provided ecological services are known.Therefore, this study aims to conduct a literature review on the veredas (M.flexuosa palm swamps) of the northern Minas Gerais, inferring about the processes that determine the floristic and structural differentiation and discussing their importance and conservation status.

Considerations about vegetation and floristic peculiarities in veredas
Studies about the vegetation of veredas are scarce (Silva and Maillard, 2011;Araújo et al., 2013), making it difficult to classify these systems consistently.In Brazil, most works about vegetation on veredas indicate the occurrence of herbaceous and grasses formations with Poaceae, Cyperaceae and Asteraceae as the most abundant families (Guimarães et al., 2002;Meirelles et al., 2002;Oliveira et al., 2009;Araújo et al., 2013;Resende et al., 2013), although an exception is represented by studies conducted on the veredas of the north of Minas Gerais State, which have differentiated floristic composition with forest formations dominated by individual trees, especially Annonaceae, Anacardiaceae, Cecropiaceae and Fabaceae (Bahia et al, 2009a.;Gaya, 2014).Silva and Maillard (2011) highlighted the structural complexity inherent to this type of vegetal formation and indicated that the criteria used to classify these environments are incipient, mainly by the lack of studies aimed to characterize the vegetation of veredas and their development.
Because of their occurrence on hydromorphic soils, the veredas show floristic and structural peculiarities distinct from surrounding formations (Teixeira and Assis, 2005).In these areas, the waterlogged soil gives a swampy environmental aspect, and the varying levels of water saturation in the soil determine the environmental heterogeneity (Gaya, 2014), which can provide greater variety of habitats, and consequently more complex flora.Studies in the Venezuelan Amazon (Rull and Montoya, 2014) and Peru (Endress et al., 2013) showed veredas as forest systems of high floristic and structural complexity, different from those veredas with more open formations that usually occur in the Cerrado.However, the studies applied in the north of Minas Gerais showed the veredas not only as a shrub-grassy formations, but as hygrophilous forest formations with abundant occurrence of tree species characteristics of wetlands (Bahia et al., 2009a;Lorente and Meyer, 2010;Araújo et al., 2013;Gaya, 2014).
Due to their floristic composition and distinct physiognomic structure, the veredas are classified by Araújo et al. (2002) as a "vegetation complex".Although other authors classify the veredas as "forests of flooded gallery" or "gallery forests", Gaya (2014) points out that the veredas of north Minas Gerais "do not fit, in part, to the sub-type of gallery forest (flooded) proposed by Ribeiro and Walter (1998)".It has been noticed that veredas are formed by two layers, i.e., woody and herbaceous strata, which percentages vary over time (Ribeiro and Walter, 2008).Thus, richness and dominance of shrub and herbaceous components decrease and the tree component gains expressiveness as the succession process progresses (Bahia et al., 2009b).

Development stages and their relationship with the structure and floristic composition in veredas of north of Minas Gerais
When comparing the studies with vegetation of veredas in north of Minas Gerais State and other veredas in Central Brazil, the veredas in north of Minas Gerais present floristic and structural peculiarities that distinguish them from one another, allowing inferences about their development stages.On a pollen analysis from vereda in Buritizeiro, north of Minas Gerais, through palinomorph identification and radiocarbon dating, Lorente et al. (2010) reconstructed two palynological zones that feature the paleoenvironment and paleoclimatic conditions of the study area.Between 13,120 and 11,640 years Before Present (BP), the studied area was characterized by a drier climate than the current field areas with open canopy, similar to Campo Limpo areas, currently taking place in Cerrado.The M. flexuosa pollen grains occurred first in 11,640 years BP, but had increased expressiveness between 6,000 and 1,500 years BP.This period was characterized by the increase of pollen grains from arboreal elements and the registration of new shrub and herbaceous and arboreal taxa, suggesting that the vereda is established only after 6,000 years BP, under more hot and humid climatic conditions (Lorente et al., 2010).A floristic inventory in the same study area found a dense vegetation, with characteristic species of hygrophilous forest (Gaya, 2014).Also in Buritizeiro, north of Minas Gerais, and in the same sub-basin of the vereda studied by Gaya (2014), Cassino (2011) conducted a pollen analysis of sediments collected in a vereda.This author identified M. flexuosa pollen between 11,190 years BP (interpolated age) and up to 10,130 years BP when the vereda started to develop, but with the change of the hot and humid climate into a cold climate over time, the area was changed to a swamp.According to Cassino (2001), the vereda turned to develop and expanded between 8,330 years and 6,320 years BP, when the weather was again hot and humid, results corroborated by the study of Lorente et al. (2010).
In palynological studies on veredas in Cromínia, Goiás State, Salgado-Labouriau et al. (1997) showed the appearance of veredas around 4,000 years BP, and the authors reported that the veredas have narrow spots of hygrophilous vegetation along the watercourses today.In Águas Emendadas, in the Distrito Federal, Barberi et al. (2000) showed the appearance of veredas around 1,600 years BP, and cited the palm M. flexuosa as the sole tree species occurring in the study area.Meirelles et al. (2002) also showed the shrub and herbaceous character of veredas in Distrito Federal.In turn, Cassino (2011) pointed out that the semimoist climatic conditions found between 11,190 years and 6320 years BP in the vereda studied in Buritizeiro differ from semi-arid conditions found in the veredas of Distrito Federal and Goiás State.These semi-moist and warm conditions were conducive to the development of M. flexuosa palm, and therefore, the veredas.Cassino (2011) emphasized that in Minas Gerais State (city of Buritizeiro), the period of cold and dry climate was much shorter than the veredas in Goiás State and Distrito Federal.Bahia et al. (2009a), in a floristic and phytosociological study of tree community on veredas of the Environmental Protection Area (APA) Pandeiros, north of Minas Gerais State, sampled two veredas at different stages of conservation.These veredas have dense hygrophilous vegetation, a structure similar to other veredas from north of Minas Gerais.
Through the palynological studies metioned above, it is clear that the formation of the veredas of the north of Minas Gerais is older than the veredas studied in the Distrito Federal and Goiás.Despite the lack of studies on the vegetation of these veredas, we can infer that, due to biggest rise time, the northern veredas of Minas Gerais are in a more advanced stage of development.Nonetheless, the variation of vegetal cover can be a reflex of productivity gap between the areas, of the human disturbance or by the influence exerted by the vegetation domains since that the veredas of north of Minas Gerais are in an ecotonal area (Azevedo et al., 2014).Hence, more researches regarding ecological processes in veredas seem to be necessary in order to clarify these issues.

Veredas in the north of Minas Gerais: status and implications for conservation
Due to the ecological, landscape and social importance of the veredas, they are considered as Areas for Permanent Preservation (APP) by the State and Federal Laws (Bahia et al., 2009b).According to the New Forest Code (Federal Law number 12,651 / 12), the protection in veredas occurs from the marginal strip in horizontal projection, with a minimum width of 50 meters from the permanently swamp and drenched space (Brasil, 2012).By State Law number 9372 of December / 1986, Article 1 and the law 9682 of October / 1988(Minas Gerais, 1988), the veredas of the São Francisco River Valley are considered to be of common interest and permanent preservation, constituting ecological reserves where the limit of preservation range is 80 meters.The State Law number 9,372/86 stresses further that "drainage, landfills, deforestation, use of fire, hunting, fishing, agricultural and industrial activities, settlements and other forms of human activities, which may cause instability to the ecosystem, are forbidden in veredas and their buffer strips".The law emphasizes that "livestock activities, use of water for watering livestock and domestic consumption, journey, leisure and research are allowed if not occasioning significant changes in natural conditions" (Minas Gerais, 1988).
Despite the protection afforded by law, the veredas are still exploited for various purposes, and human impacts alter their biotic functions and compromise their resilience (Guimarães et al., 2002;Bahia et al., 2009a).In 1981, the Federal Government of Brazil created the National Program for Use of Irrigable Wetlands (ProVárzea) through the statute number 86,146/81, in order to promote drainage and agricultural use of floodplains by landowners (Brasil, 1981).This program has been responsible for decimating wetlands across the country, causing the degradation of several veredas in northern Minas Gerais.According to Neves (2011), some veredas in the APA Pandeiros, north of Minas Gerais State, had a loss of 50 to 99 percent of their forest cover for rice and eucalyptus plantations, besides the compromised stream flow by intense drainage of the area.Veldman et al. (2015) point out that conversion of savanna areas to tree plantations decreases plant and faunal diversity, decreases the groundwater, recharge and stream flow, and reduce soil-carbon storage.Neves (2011) evaluated the stream flow in the veredas studied by Bahia (2009a) in the basin of Pandeiros river, for a year, and noted that the preserved veredas did not suffer significant peaks in flow during the rainy season, and remain evergreen throughout the study period.The impacted veredas had irregular and intermittent flow in the dry season, and one of the impacted veredas showed no flow, even in the rainy season.
In fact, Rosolen et al. (2015) stated that the veredas are fragile ecosystems, and drainage and use of these areas for agriculture degrade vegetation, affect the hydrology, promoting erosion, and provide the change of chemical and morphological soil properties.They constitute poorly resilient ecosystems, so that human impacts may result in their degradation, preventing the performance of ecological services provided there (Guimarães et al., 2002;Resende et al., 2013).Bahia et al. (2009a) characterized the veredas in preserved and disturbed based on phytosociological, structural and compositional variations between them.The authors noted that anthropogenic disturbances have affected the composition of the tree community, promoting the loss of species, biomass reduction and changes in the natural process of vereda succession.The human impacts also affected the structure of the tree community, reducing the richness, abundance and diversity in veredas subjected to higher disturbances (Bahia et al., 2009a).
According to Silva and Maillard (2011), veredas have disproportionate importance to the area it occupies, as they take up a small area within the Cerrado biome, but represent ecological corridors, interlinking ecosystems and allowing the movement of gene flow (Bahia et al., 2009b).They are naturally fragmented systems that follow the stream flow and play the role of water source among situations of local water scarcity (Silva and Maillard, 2011;Resende et al., 2013).Several bird species land, shelter, nest and forage in these areas, as well as other species of terrestrial and aquatic fauna (Padovesi-Fonseca et al., 2015).They are also essential for stocking water for the wildlife and for the local populations (Silva and Maillard, 2011).However, ecological and social importance of the veredas have been underestimated due to the lack of studies characterizing, investigating the peculiarity and attesting the complexity and fragility of these systems.This situation is worrying, once the systems of veredas are considered as "Cradle of Waters" (Boaventura, 2007) because they have a significant role for water maintenance, and consequently, for the maintenance of biodiversity in the Cerrado biome.The scenario is even more serious in the north of Minas Gerais, semiarid region where the veredas are peculiar systems and may represent the only perennial water sources in the region, including the supply of important rivers, such as the San Francisco river (Silva and Maillard, 2011;Neves, 2011).

Conclusion
Palynological studies in the veredas of central Brazil point to a long development of the veredas in north Minas Gerais State, compared to the veredas in Goiás State and the Distrito Federal.Also, the dense hygrophilous vegetation associated with veredas in north of Minas Gerais State suggests that they were in a more advanced successional However, many factors can influence the floristic composition and structure of these plant communities, requiring further studies involving ecological processes in veredas.
Due to lack of scientific research in these areas, the criteria used to characterize the environment of veredas are incipient, and do not reach the floristic and structural complexity by the northern veredas of Minas Gerais.The lack of knowledge about these environments is a concern considering the degree of disturbance to which these areas are exposed.Although protected by law, the veredas suffer various human impacts that may result in their degradation.Also, the lack of public policies that ensure the conservation of these areas contributes to worsen this situation.Scientific studies aiming at better characterize the veredas in order to base public policies and actions for the conservation and restoration of these areas are needed, so that biodiversity and ecological services of these wetlands are not lost, even before they are known.