Floristica, espectro biologico e padrões fenologicos do cerrado sensu lato no Parque Nacional das Emas (GO) e o componente herbaceo-subarbustivo da flora do cerrado sensu lato

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

The cerrado, a savanna-like ecosystem, is the second largest vegetation type in Brazil. Among the reserves that protect it, Emas National Park (ENP) is one of the largest and best preserved. The ENP, with about 132,000 ha, is located in the Brazilian Central Plateau, southwestem Goiás State, under warm and wet tropical climate with three dry months in winter. Most of ENP s area, more than 90%, is covered by cerrado physiognomies. Until now, ali studies cattÍed out within the reserve were restricted to its fauna and fues. From November 1998 to October 1999, we cattÍed out a floristic survey in the cerrado physiognomies in ENP, when we found 601 species, belonging to 303 genera and 80 families. Among the collected species, 12 were weeds and seven, new to science. The herbaceous to woody species ratio was 3.03:1. The richest families were Asteraceae, Fabaceae, Poaceae, Myrtaceae, and Lamiaceae, which comprised 48% of the total number of species. The results obtained in this survey showed the importance of Emas National Park to the cerrado conservation, since from 8 to 20% of the species related for this vegetation type occur in the reserve. We compared the frequency distribuition of species per family obtained for the ENP flora with those obtained by other authors for the cerrado vegetation and the Cerrado Domain. We used these more general pattem as null models against which the frequency distribution of species per family in ENP was tested, characterizing thus its flora and discussing some phytogeographical pattems. The frequency distribution of genus and family sizes was highy skewed to the smaliest class, with a higher number of monospecific genera and families. The distribution of species per family in ENP was significandy different from those obtained in the Cerrado Domain and in the herbaceous and woody components of the cerrado flora. The herbaceous component of ENP flora was charactetÍZed by the overproportion of Myrtaceae and underproportion of Orchidaceae and Lythraceae, and the woody component, by the overproportion of Myrtaceae and Nyctaginaceae. When compared with oudying cerrado sites, the ENP was quite distinct, not only on species level, but also on family levei. Based on the floristic list obtained in the cerrado physiognomies in ENP, we constructed the life form spectrum of its flora, following Raunkiaer s system. The main life-form classes were hemicryptophytes and phanerophytes, which accounted, respectively, for 49.92% and 24.79% of the total number of species. When compared with Raunkiaer s normal spectrum, the ENP spectrum was significandy different, due especially by the overproportion of hemicryptophytes. Other cerrado sites presented also higher proportions of hemicryptophytes and phanerophytes, although their relative importance vaned according to the prevailing physiognomies. When compared with life-form spectra from other vegetation types, the cerrado sites formed a distinct group, with eigenvalues doser to those of the hemicryptophytes and phanerophytes. The cerrado sites distinguished themselves from the savanna sites by their under-representation of therophytes. Even if sometimes criticized in its application on tropical communities, Raunkiaer s system was useful to characterize the cerrado floras and to separate it from other vegetation types. In the cerrado, as in other savannas, the phenological pattems are dosely linked to the climatic seasonality. The flowering and fruiting pattems of the community were analysed in relation to dispersal syndromes, comparing the herbaceous and the woody components. The herbaceous component was characterized by an overproportion of autochorous species, and the woody component, by an overproportion of zoochorous species. There was a striking seasonality in the community-wide pattem of flowering and fruiting, although they were different between the herbaceous and the woody components. W oody species flowered mainly during late dry and early wet seasons, whereas herbaceous species flowered generally during late wet season. At the dry season, when their diaspores could be dispersed more efficiendy, the proportion of fruiting anemo and autochorous fruits was higher. During the rainy season, when their fruits could be kept attractive for longer time, the number of fruiting zoochorous species reached its peak. Even if frequendy neglected, the herbaceous component of the cerrado flora is richer than the much more studied woody component. We tried to compile a checklist of the herbaceous species that occur in the cerrado, using life-form class as criterion of inclusion. All non-phanerophytes species were assumed to belong to the herbaceous component. We listed 2,856 species, a figure higher than the lower limit of a previous estimation. The richest families were Asteraceae, Fabaceae, Poaceae, Lamiaceae, Euphorbiaceae, Rubiaceae, and Orchidaceae, which accounted for 53.47% of the total number of species. The distribution of family sizes in the cerrado as a whole can be used to compare and characterize the herbaceous component in cerrado sites. The richest genera were Hyptis, Vernonia, Chamaecrista, Paspalum, and Mimosa, all belonging to one of the best represented families. Our checklist is probably an underestimation of the actual number of species in the herbaceous component of the cerrrado flora, due to the few surveys currendy available in which the herbaceous species had also been sampled. Future studies dealing with the cerrado vegetation can no longer ignore the herbaceous component, which is richer and more vulnerable than the woody component

ASSUNTO(S)

savanas cerrados fenologia

ACESSO AO ARTIGO

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