Flora and biological spectrum of a savanna enclave within the semiarid Caatinga Dominion in Ceará state, Northeastern Brazil

Abstract

Inside the Brazilian semiarid region (Caatinga Dominion), there are enclaves of vegetation from another bioma (Cerrado) that appear as scattered patches, mainly present on the tops of plateaus and in areas locally called "tabuleiros". Aiming for a better understanding of the floristic composition to support conservation strategies, a survey of the vascular flora and an analysis of the biological spectrum were conducted in the Serra do Boqueirão (southern state of Ceará, Brazilian Northeastern), an area of significant ecological and regional landscape value. Monthly botanical collections were carried out over 23 months in two distinct areas (with and without rocky outcrops – PAR and AAR), and soil samples were also collected for analysis. Species were classified in the Raunkiaer's life forms, modified according to Braun-Blanquet. The chi-square test and a detrended correspondence analysis (DCA) were performed to compare the areas, along with a similarity test to observe comparisons with other savanna areas in the Caatinga and core areas in Brazil. One hundred and seven species were identified in 92 genera and 40 families. Fabaceae (24 spp.), Malvaceae (8 spp.), and Rubiaceae (6 spp.) were the richest families. The biological spectrum showed a predominance of phanerophytes (52.3 %) and therophytes (25.2 %), forms characteristic of the tree-shrub physiognomy with annual herbs. Statistical analysis indicated that the biological spectrum differs from Raunkiaer's normal, as well as the two areas differ from each other (χ2 = 25.87, p < 0.0001). A high concentration of aluminum was observed in the area with the presence of species characteristic of the Cerrado s.s. such as Curatella americana and Qualea parviflora, and the similarity test indicated greater resemblance to Caatinga areas geographically closer to the study area. These results highlight the presence of a savanna vegetation enclave with a strong penetration of surrounding Caatinga species, emphasizing the role of historical and environmental factors of the vegetation in the area and indicating the need for conservation strategies.