EFFECTS OF FOUR DECADES OF FIRE MANIPULATION ON WOODY VEGETATION STRUCTURE IN SAVANNA

TLDR

The amount of carbon stored in savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. The study examined how woody plant structure responds to long‑term experimental burning in savannas. A randomized block design with 192 seven‑hectare plots across four savanna ecosystems tested fire exclusion, burn season, and frequency. Results show that woody plant density is largely insensitive to fire, yet the proportion of small trees shifts markedly with fire regime, leading to structural changes that could alter carbon balance, while biomass responses differ among savannas, indicating demographic resilience but structural responsiveness.

Abstract

The amount of carbon stored in savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. We analyzed the structural response of woody plants to long-term experimental burning in savannas. The experiment uses a randomized block design to examine fire exclusion and the season and frequency of burn in 192 7-ha experimental plots located in four different savanna ecosystems. Although previous studies would lead us to expect tree density to respond to the fire regime, our results, obtained from four different savanna ecosystems, suggest that the density of woody individuals was unresponsive to fire. The relative dominance of small trees was, however, highly responsive to fire regime. The observed shift in the structure of tree populations has potentially large impacts on the carbon balance. However, the response of tree biomass to fire of the different savannas studied were different, making it difficult to generalize about the extent to which fire can be used to manipulate carbon sequestration in savannas. This study provides evidence that savannas are demographically resilient to fire, but structurally responsive.