Abstract
Cerrado vegetation covers about 33% of the total area of the state of Piauí, northeastern Brazil, where there are also large areas of transition and contact with other vegetation types. Although the Piauí cerrados are a direct northern prolongation of the central core area, they are considered marginal by almost all authors. There are few previous records of their woody flora. This paper presents a floristic list of woody species based on the survey of 11 localities and updating of two already published lists. The climate belongs to Thornthwaite's subhumid category due to Piauí's position between the semiarid northeastern domain and the superhumid Amazon. The annual total rainfall is similar to that of the major part of the Brazilian cerrado area, but the rainy season is shorter. The soils differ from most cerrado soils in containing a greater proportion of concretions and plinthite with generally lighter colours, which may be interpreted as indicating large fluctuations of the water-table during pedogenesis. There are also widespread indications of seasonal high water-table showing that many of the Piauí cerrados probably belong to Sarmiento's hyperseasonal savannah category. A total of 60 families is represented by 307 woody taxa (including 14 family indet., four genera indet. and 80 species indet.). The lowest floristic diversity (richness) occurred in pure cerrado, the greatest in transition and contact areas.O cerrado do Piauí, nordeste do Brasil, cobre cerca de 33% da área do estado e apresenta extensas áreas de transição e contato com outros tipos de vegetação. É um prolongamento setentrional do cerrado central, mas é considerado marginal. Sua flora lenhosa é pouco conhecida. Este trabalho apresenta uma lista florística lenhosa baseada em 11 levantamentos de campo e atualização de duas listas já publicadas. Os climas são subúmidos de Thornthwaite, em decorrência de sua localização entre o domínio semi-árido nordestino e o superúmido amazônico. O total anual de chuva é semelhante ao do resto do cerrado, mas a estação chuvosa é bem mais curta. Os solos são diferentes dos do restante dos cerrados, apresentando concreções, plintita e cores claras, indicando grandes flutuações do lençol freático durante a pedogênese. As grandes flutuações estacionais do lençol freático implicam em que boa parte do cerrado piauiense possa ser classificada como savana hiperestacional de Sarmiento. Apresenta-se um total de 60 famílias conhecidas e 308 táxons lenhosos (14 desconhecidos no nível de família, 4 desconhecidos no nível de gênero e 80 desconhecidos no nível de espécie). A menor diversidade (riqueza) florística ocorreu no domínio puro do cerrado; as maiores ocorreram nas áreas de transição.
Highlights
The state of Piaui is located in the northeastern region of Brazil (Fig. 1) and has a total area of 25,093,400ha of which about 33.3% (8,349,759ha) is covered by cerrado vegetation sensu lato, and 14.0% (3,507,107ha) represents transition and contact areas of cerrado with other types of vegetation: caatinga, carrasco, dry deciduous forest, seasonal subdeciduous forest, Orbignya palm forest, riparian forest and grasslands (CEPRO, 1992)
The cerrado area in the state of Piaui is a direct continuation of that of the core area on the Central Plateau of Brazil, it is generally considered marginal (e.g. Rizzini, 1963) since it is located at the northern extreme of the distribution area of the biome
Rizzini (1976) produced a preliminary list of 61 species of angiosperms based on a single field survey and an examination of herbarium material, but Barroso & Guimaraes (1980) and Castro (1984) reported intensive field surveys
Summary
The state of Piaui is located in the northeastern region of Brazil (Fig. 1) and has a total area of 25,093,400ha of which about 33.3% (8,349,759ha) is covered by cerrado vegetation sensu lato, and 14.0% (3,507,107ha) represents transition and contact areas of cerrado with other types of vegetation: caatinga (dry thorn woodland and shrubland), carrasco (dry cerrado-caatinga transition), dry deciduous forest, seasonal subdeciduous forest, Orbignya palm forest, riparian forest and grasslands (CEPRO, 1992). Cerrado constitutes the second most extensive type of vegetation in the state; its area is only exceeded by that of the caatinga. The cerrado area in the state of Piaui is a direct continuation of that of the core area on the Central Plateau of Brazil, it is generally considered marginal The present paper communicates the results of surveys of some representative areas in the state
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