The influence of fire on the demography of a dominant grass species of West African savannas, Hyparrhenia diplandra

Abstract

1 Effects of fire on the demography of a population of a long-lived perennial tussock grass, Hyparrhenia diplandra, were investigated in a West African savanna that normally burns annually, Seedling growth, survival and fecundity were recorded in burned and unburned plots during 3 years for a first cohort and during 1 year for a second cohort initiated 1 year later. 2 Seedling growth and survival rates were significantly higher in unburned plots, with larger seedlings surviving burning better. Regardless of treatment/fire regime, seedlings grew faster when located further from the nearest tuft, but differences between clones showed that growth rate also had a genetic basis in this apomictic species. Adult survival was always high, but exclusion of fire increased size, and therefore age, at maturity. Fire therefore affects life-history traits in this grass species of fire-prone environments. 3 Size-structured matrix models were constructed separately for each fire treatment, incorporating demographic and fire parameters estimated from field data. 4 The asymptotic population growth rate was higher in the unburned model (λ = 1.23) than in the burned one (λ = 1.07), indicating that the population of H. diplandra expanded quickly in the absence of fire. 5 Overall, results indicate that annual burning limits population growth rate. Less frequent, but still regular fires may allow establishment while preventing the accumulation of litter and accelerating nutrient recycling; thus lead to more stable populations than in the total absence of fire.