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

PELÁEZ, D.V.; BÓO, R.M.; MAYOR, M.D.; ELIA, O.R.; MARTÍNEZ, S.A.

PHYTON - INTERNATIONAL JOURNAL OF EXPERIMENTAL BOTANY BA ARGENTINA

FUNDACION ROMULO RAGGIO

Año: 2009 vol. 78 p. 4 - 11

0031-9457

Plant growth in semiarid rangelands may be affected by the length of 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.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.