ANALYSIS OF THE FLORISTIC COMPOSITION OF THE BRAZILIAN CERRADO VEGETATION III: COMPARISON OF THE WOODY VEGETATION OF 376 AREAS

摘要

An analysis was made of the floristic composition of 376 areas of cerrado and Amazonian savanna, encompassing most of the area of such vegetation in Brazil. A total of 951 species of trees and large shrubs was recorded for these areas, of which 334 (35%) occurred at only a single locality (unicates). The core cerrado area and its outliers were studied in 315 areas, and 914 species were recorded. However, only 300 species occurred at more than eight of the sites (i.e.≥2.5% of the total) and only 38 speeies at ≥50%, while the remaining 614 species, including 309 unicates, are very rare. About 300 species, therefore, dominate the core cerrado area; this number is expanded to 350 if the southern Sao Paulo cerrados are included. Alpha diversity, the number of tree species occurring in a single community, is often high, with more than 100 species of trees and shrubs growing together. We noted particular 'hotspots' in the drainage of the rivers Araguaia, Tocantins and Xingu, but high diversity figures occur in many other areas of the cerrado core, and also in Sao Paulo state. On the other hand, the disjunct Amazonian savannas, with the exception of Alter do Chao (Para) and one site at Humaita (Amazonas), represent a low diversity vegetation in which 117 species of trees and large shrubs were recorded in the 58 sites analysed. Of these, 77 are widespread species common in the core cerrados. The alpha diversity of disjunct Amazonian savannas seldom exceeds a dozen species of trees and large shrubs. The data were analysed using two techniques of multivariate analysis which we had found particularly appropriate in our previous work: (a) a divisive hierarchical classification by Two-Way Indicator Species Analysis (TWTNSPAN), and (b) an agglomeratiye hierarchical classification by UPGMA (Unweighted Pair-Groups Method using Arithmetic Averages), using the Sorensen Coefficient of Community (cc) as a measure of similarity. The results of both methods showed great similarity, demonstrating a strong geographical pattern in the distribution of the cerrado biome similar to that outlined in the preliminary scheme of our previous work. The following geographic groups were recognized: (ⅰ) A very distinctive group of southern sites in Sao Paulo, Parana and southern Minas Gerais. (ⅱ) Central and southeastern sites from the Federal District, neighbouring Goias, and southern and central Minas Gerais. (ⅲ) North and northeastern sites from Bahia, Ceara, the extreme north of Minas Gerais, Maranhao, Piaui, Tocantins, and one site in Para very close to the Tocantins border. (ⅳ) Central-western sites made up of a huge swathe running across the states of Mato Grosso do Sul, Mato Grosso, Goias, Tocantins, and into Para. (ⅴ) Widely spread sites with a strong mesotrophic character; this group is particularly well represented in Mato Grosso do Sul. (ⅵ) Far western mesotrophic sites, forming a small group in Rondonia, Mato Grosso do Sul and Mato Grosso. (ⅶ) Disjunct Amazonian sites forming a very distinct group separated from the other sites at the first division of both TWINSPAN and UPGMA.