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 analyse s 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-Puer to Suarez (Brazil/Bolivia) southward to Resistencia-Corrientes in nort hern Argentina, and eastward to the upper Uruguay River valley system in Argentinian Misiones and Brazilian Santa Catarina, and thus includi ng most of eastern Paraguay and the west bank of the Paraguay River; a nd the Piedmont nucleus, which extends from Santa Cruz de la Sierra in Boliva to Tucuman and the sierras of east Catamarca in northwestern A rgentina. Distribution maps are presented for over 70 taxa that show t his kind of distribution pattern or its modifications. Most of the sea sonal woodland species of this affinity are notable by their absence f rom the cerrado vegetation of central Brazil, although some occur on c alcareous outcrops in the general cerrados area, and they also avoid t he Chaco of northern Argentina. It is proposed that these fragmentary and mostly disjunct distributional patterns are vestiges of a once ext ensive and largely contiguous seasonal woodland formation, which may h ave reached its maximum extension during a dry-cool climatic period ca . 18,000-12,000 BP, coinciding with the contraction of the humid fores t.