dense forests (Polisel et al. 2014; Lopes et al. 2015) showed more expressive species richness in the understory than Cambarazal forest. According to Table 3, the f diversity index in the Cambarazal forest understory was greater than that of Brazilian cerrado (Soares et al. 2015), gallery forests (Silva et al. 2004) and dry forests (Pereira et al. 2002; Gandhi and Sundarapandian 2014); however, it was smaller than that of terra firme (Oliveira and Amaral 2004), semideciduous seasonal (Meira Neto and Martins 2003; Coelho et al. 2011; Barroso et al. 2014) and ombrophilous dense forests (Polisel et al. 2014; Lopes et al. 2015). According to Nascimento and Nunes da Cunha (1989) and Arieira and Nunes da Cunha (2006), the low species diversity in Cambarazal forest is linked to flood, which is a limiting factor for the establishment of plant species (Junk et al. 1989).
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Arieira and Nunes da Cunha (2006) sampled the Cambarazal forest canopy and founded lower diversity (H ‘ = 2.1 to 2.9) than that in the understory in the current study (H ‘ = 3.15); thus, evidencing that the understory provided 28 unique species. Gentry and Emmons (1987) stated that the understory diversity pattern differed from the pattern presented by the canopy species, because it responded to different abiotic factors such as light, nutrient and water availability, wind and temperature (Denslow et al. 1990). The result by Barddal et al. (2004) for the understory in mixed ombrophylous forest corroborates the statement above. Gentry and Dodson (1987) reinforced the importance of including understory communities in floristic analyses, although these synusiae remain neglected. Monospecific forests are not among the most species-rich communities (Hart et al. 1989; Nascimento and Nunes da Cunha 1989; Nascimento et al. 1997; Marimon and Felfili 2000; Arieira and Nunes da Cunha 2006). In addition, the flooded forests in Pantanal are not species-rich (Nunes da Cunha and Junk 2001); thus, it is necessary conducting understory studies to help better understanding the diversity of these communities. Pinho et al. (2011) and Pinho and Marini (2014) emphasized that the Cambarazal forest is very importance for wetland bird conservation; it is the key habitat of many nesting-bird species. According to these authors, the highest richness and abundance of bird species are recorded in the dry season, because of the food availability in the understory. They selected the mature Cambarazal forest to prior protection.