POSTBURN REPRODUCTION OF WOODY-PLANTS IN A NEOTROPICAL SAVANNA - THE RELATIVE IMPORTANCE OF SEXUAL AND VEGETATIVE REPRODUCTION

1. Burning typically occurs at intervals of 1-3-years in the Brazilian cerrado, a rate that exceeds the precolonization fire regime. To dete rmine if woody plants of the cerrado successfully reproduce within the short span of time between burns, experimental burns were used to qua ntify the effects of fire on sexual and vegetative reproduction of six species of resprouting trees and shrubs. 2. Four of the six species r eproduce vegetatively by producing root suckers. For three of these sp ecies, Rourea induta, Myrsine guianensis and Roupala montana, sucker p roduction was seven to 15 times greater in burned plots than in unburn ed controls. 3. Fire had a negative impact on sexual reproduction. Fir e caused an immediate reduction in sexual reproductive success by dest roying developing reproductive structures and seeds. Additionally, fiv e of the six study species exhibited overall reductions in seed produc tion in the years following fire. Fire had this effect by reducing the individual size of all species and, for three species, by reducing si ze-specific reproductive output. Only the tree Piptocarpha rotundifoli a exhibited increased seed production following burning. 4. Fire cause d substantial mortality to both seedlings and suckers. Suckers were la rger than seedlings and experienced lower mortality rates for two of t hree species. Fire-induced mortality of seedlings varied greatly among species, ranging from 33% to 100%. 5. The results indicate that veget ative reproduction is much more successful than sexual reproduction un der the high fire frequency typical of current fire regimes. It is con cluded that current fire regimes must be causing a shift in species co mposition, favouring species capable of vegetative reproduction.