Aboveground biomass of functional groups in the ground layer of savannas under different fire frequencies

Abstract

Savannas with different fire histories should have differences in aboveground biomass due to varying responses of functional groups. We investigated the effects of different fire frequencies on total aboveground biomass and also the biomass of functional groups (the tussock grass Tristachya leiostachya Nees, other grasses, small woody individuals) and dry biomass in savannas subjected to annual fires, biennial fires, and protected from fire for 12 years. Total biomass in the protected area was more than twice that of the annually burned area. T. leiostachya aboveground biomass was higher in the protected area than in annually and biennially burned areas, which were not different. Biomass of other grasses was lower in the protected area, whereas woody biomass values did not differ among areas. In the biennially burned and protected areas, we found a positive relationship between T. leiostachya and dry biomass. In the annually burned area, T. leiostachya biomass was negatively correlated with the biomass of other grasses and woody individuals. This negative correlation supports the idea that frequent fires favour the former, and may indicate an outcompeting effect. Knowledge not only about biomass but especially about its functional components is necessary to understand the processes and management consequences of different burning strategies.