Effect of post-fire defoliation on growth of two native grasses in the Caldenal, Argentina

plant growth in semiarid rangelands may be affected by time grazing is excluded during the post-fire regeneration period. the objective of this field work was to study the effect of post-fire defoliation at different phenological stages [vegetative (early-season defoliation) and internode elongation (late-season defoliation)] on growth of piptochaetium napostaense and poa ligularis, two very important perennial native grasses in the temperate semi-arid region of central argentina (caldenal). in general, the post-fire defoliation treatments did not affect the number of green leaves on tillers of p. napostaense. early-season post-fire defoliation generally reduced the number of green leaves on tillers of p. ligularis in comparison to those in control plants. late-season defoliation, however, usually increased the number of green leaves on tillers of p. ligularis. nevertheless, very few significant (p<0.05) differences were detected within either one or the other phenological stage. height and total green length (leaves + stem + sheaths) of tillers on plants of p. napostaense and p. ligularis exposed to defoliation were lower (p<0.05) or similar (p>0.05) than values on non-defoliated plants, respectively. immediately after early- and late-season defoliation treatments, relative growth rates for tiller height and total green length were reduced (p<0.05) on plants of both species with respect to control plants. our results suggest that a one-year-period without severe defoliations after fire would be at least necessary for not risking the persistence of these perennial grasses in the caldenal community.