Effect of post-fire defoliation on bud viability and plant mortality of Piptochaetium napostaense (Speg.) Hack. and Poa ligularis Ness

The objective of this work was to evaluate the effects of post-fire defoliation on axillary bud viability and mortality of Piptochaetium napostaense (Speg.) Hack. and Poa ligularis Nees. at different phenological stages. Both species are cool-season perennial native grasses highly preferred by cattle in the semi-arid region of central Argentina. The following treatments were established for each species: no defoliation (control), early-season defoliation (vegetative stage) and late-season defoliation (internode elongation stage). Ten plants were assigned randomly to each treatment. Fire treatment was applied at the end of the annual growing cycle of both species. Our results would suggest that early-season defoliation during the first year after fire might reduce axillary bud viability in P. napostaense and P. ligularis. In addition, P. napostaense was more susceptible to early-season defoliation than P. ligularis. Post-fire defoliation, principally early-season defoliation, might increase plant mortality in P. napostaense, but it does not seem to affect P. ligularis. Therefore, a period with no grazing after fire might be the key factor to protect axillary buds, and subsequently permit the re-establishment of the photosynthetic canopy through the production of new tillers, favouring mainly the persistence of P. napostaense in the community.