PATTERNS OF SPECIES DISTRIBUTIONS IN THE DRY SEASONAL FORESTS OF SOUTH-AMERICA

Studies of the distributions of species of seasonal woodland habitats in South America by means of dot-mapping and phytosociological analyses indicate the presence of three nodal areas: the Caatingas nucleus of arid northeastern Brazil; the Misiones nucleus, comprising a roughly right-angled triangular area enclosed by lines connecting Corumba-Puerto Suarez (Brazil/Bolivia) southward to Resistencia-Corrientes in northern Argentina, and eastward to the upper Uruguay River valley system in Argentinian Misiones and Brazilian Santa Catarina, and thus including most of eastern Paraguay and the west bank of the Paraguay River; and the Piedmont nucleus, which extends from Santa Cruz de la Sierra in Boliva to Tucuman and the sierras of east Catamarca in northwestern Argentina. Distribution maps are presented for over 70 taxa that show this kind of distribution pattern or its modifications. Most of the seasonal woodland species of this affinity are notable by their absence from the cerrado vegetation of central Brazil, although some occur on calcareous outcrops in the general cerrados area, and they also avoid the Chaco of northern Argentina. It is proposed that these fragmentary and mostly disjunct distributional patterns are vestiges of a once extensive and largely contiguous seasonal woodland formation, which may have reached its maximum extension during a dry-cool climatic period ca. 18,000-12,000 BP, coinciding with the contraction of the humid forest.