DIOECY IN THE CERRADO VEGETATION OF CENTRAL BRAZIL

Occurrence of dioecy in Cerrado, Neotropical savanna region in Central Brazil, is analyzed here. Frequency of dioecious species and their ph enological and morphological characteristics were studied for a cerrad o woody community near Brasilia, and a broader comparative survey was done using phytosociological data for different cerrado areas and vege tation physiognomies. Nine dioecious species were found in the studied community (15% of the species in the area), most with simple open flo wers visited by small insects. Flowering phenology differed from speci es to species including long, sparse flowering and cornucopian strateg ies. Distance between flowering individuals varied from 13 to 70 m. Ge nder related differences in spatial distribution and in height or circ umference were tested for three of the species and significant departu re from random was found only for Rapanea guianensis. The regional sur vey showed frequencies of dioecy higher in denser woodlands and forest than in open cerrado areas. Most species presented small promiscuous flowers, probably associated to pollination by small insects, and fles hy fruits. Among the species occurring in the cerrado areas one could separate a group of dioecious shrubs and treelets really adapt ed to c errado environment and another group of evergreen forest species which occur only in denser woodlands, the cerradao. Differences in the freq uency of dioecy seems to be related to the occurrence of this latter g roup and the appearance of cerradao.