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

Abstract

Summary 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. 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. Size‐structured matrix models were constructed separately for each fire treatment, incorporating demographic and fire parameters estimated from field data. 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. 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.