Post-burn reproduction of woody plants in a neotropical savanna: the relative importance of sexual and vegetative reproduction.
Abstract
Burning typically occurs at intervals of 1 to 3 years in the Brazilian cerrado, a rate that exceeds the precolonization fire regime. To determine if woody plants of the cerrado successfully reproduce within the short span of time between burns, experimental burns were used to quantify the effects of fire on sexual and vegetative reproduction of six species of resprouting trees and shrubs. Four of the six species reproduce vegetatively by producing root suckers. For three of these species, Rourea induta, Myrsine guianensis and Roupala montana, sucker production was seven to 15 times greater in burned plots than in unburned controls. Fire had a negative impact on sexual reproduction. Fire caused an immediate reduction in sexual reproductive success by destroying developing reproductive structures and seeds. Additionally, five of the six study species exhibited overall reductions in seed production in the years following fire. Fire had this effect by reducing the individual size of all species and, for three species (Miconia albicans, Myrsine guianensis and R. montana), by reducing size-specific reproductive output. Only the tree Piptocarpha rotundifolia exhibited increased seed production following burning. Fire caused substantial mortality to both seedlings and suckers. Suckers were larger than seedlings and experienced lower mortality rates for two of three species. Fire-induced mortality of seedlings varied greatly among species, ranging from 33% to 100%. It is concluded that vegetative reproduction is much more successful than sexual reproduction under the high fire frequency typical of current fire regimes, and that current fire regimes must be causing a shift in species composition, favouring species capable of vegetative reproduction.