Abstract:
Reduction in rainfall is amongst the major climate change manifestation phenomena,
and will have a significant impact on grassland ecosystems. A split plot experimental design was
used to investigate the interactive effect of rainfall reduction and resting period (RP) (70 and 90 days)
on herbaceous biomass production and rainwater use efficiency in semi-arid grasslands of South
Africa. Different levels of rainfall reduction (RD) were setup as main plot treatments while resting
periods were set as sub-plot treatments. Four 0.5 m × 0.5 m quadrats were harvested in spring,
summer and autumn of 2016/17 and 2017/18 from each sub-plot to determine herbaceous species
structure, aboveground biomass production and rainwater use efficiency (RUE). Grasses were most
affected by rainfall reduction than forbs at the 30% and 60% RD levels. In contrast, the forbs were
more affected at 15% RD while the grasses showed resilience up to 15% reduction in rainfall. The RUE
was higher at 30% RD and 70 days RP in almost all three seasons, except in spring 2016/17. Our results
show that herbaceous above ground biomass showed resilience up to 15% reduction but were affected
more as the rainfall reduction exceeded 30%. The future predicted reduction in rainfall may result in
domination of forbs and increaser grass species in the grassland.
