Influence of rainfall and grazing on belowground biomass dynamics in a dry tropical savanna

Abstract

Root biomass and its variation with time and soil depth were studied in ungrazed and grazed treatments, in a seasonally dry tropical savanna. A greater proportion of belowground biomass was located in the 0-10 cm soil depth in the rainy season compared with the summer season. In contrast, in the 10 - 50 cm soil profile, belowground biomass was greater in summer than in the rainy season. Peak belowground biomass in ungrazed savanna was not correlated to the rainfall in the early part of the rainy season, but it was correlated to total rainfall received in the later part of rainy season. Apparently the belowground component responds quickly to the rainfall events and generates growth pulses in the aboveground vegetation. Peak canopy biomass increased rapidly with the increase in peak belowground biomass and then plateaued, indicating a greater potential for accumulation of biomass belowground than aboveground. Grazing reduced belowground biomass by 41-55%. Maximum reduction occurred in the heavily grazed savanna. Peak belowground biomass was inversely related to grazing intensity.