Effects of warming and rainfall variation on grass phenology and regenerative responses in mesic grassland

• There were apparent shifts in the phenological events but no changes in the density of buds per tiller. • The relative allocation to either vegetative or sexual reproduction was not affected. • Grass bud banks are adaptable and can modify their regenerative responses according to the timing of climatic events. • Grass species phenology in South African mesic grasslands are sensitive to climate change effects in the short term. Phenological changes can alter grassland community structures by influencing interspecific interactions, population dynamics, individual species migration or extinction, and the fitness of those species on a local scale. In this study, the combined effect of rainfall variation (drought (50 %), ambient rainfall (100 %), and wet (150 %)) and temperature (warmed and ambient) manipulation on the phenology of grass species vis-a-vis their regenerative responses from bud bank s in a mesic grassland was conducted at the Ukulinga Research Farm, University of KwaZulu-Natal, Pietermaritzburg, KwaZulu-Natal. The warming treatment was applied using open-topped warming chambers, and the rainfall treatment was applied using rainout shelters to intercept 50 % of the ambient rainfall. The intercepted rainfall was piped onto the neighbouring plot to increase rainfall by 50 %. This resulted in six treatment combinations, replicated three times and arranged in a split-plot randomized block design. Across the two years of treatment application, the study examined species phenological responses and bud bank density per vegetative and reproductive tiller per tuft. The phenological events were examined to determine the sensitivity of timing and duration of budding and flowering to experimental warming and rainfall manipulation. Generalized linear models were used to analyze whether shifts in these phenological events intensified or stabilized changes in the density of buds per tiller and their relative allocation to either vegetative or sexual reproduction. Drought delayed the timing of budding and flowering and shortened the duration ( p < 0.05). There was no effect on the total number of buds per vegetative tiller per tuft compared to the reproductive tillers. Warming advanced the budding timing and extended the budding duration ( p < 0.05). Thus, the response of timing and duration of budding and flowering of these studied grass species was sensitive to short-term effects under the ambient and manipulated temperature and moisture regimes in this study. There were apparent shifts in the phenological events but no changes in the density of buds per tiller and their relative allocation to either vegetative or sexual reproduction. These findings show that grass bud banks are adaptable and can modify their regenerative responses according to the timing of climatic events. The study also suggests that some aspects of grass species phenology in South African mesic grasslands are sensitive to climate change effects in the short term.