Abstract
Plant growth in semiarid rangelands may be affect - ed 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 ligu- laris, 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) than values on non-defoliated plants, respectively. Immediately after early- and late-season defo- liation 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 Calde- nal community.
Highlights
A high capacity for new tiller formation and high growth rates of these tillers after foliage removal contribute to determine a rapid photosynthetic canopy re-establishment, and allow perennial grasses to tolerate defoliation and maintain their status in the community (Becker et al, 1997)
After early-season defoliation in 2005, tillers of defoliated plants of P. ligularis appeared to have a lower number of green leaves than those on control plants; no statistical differences (p>0.05) were detected (Fig. 1C)
In general post-fire defoliation did not affect the number of green leaves on tillers of P. napostaense, except immediately after the early-season defoliation treatment effected in 2006 (Figs. 1A and 1B)
Summary
A high capacity for new tiller formation and high growth rates of these tillers after foliage removal contribute to determine a rapid photosynthetic canopy re-establishment, and allow perennial grasses to tolerate defoliation and maintain their status in the community (Becker et al, 1997). Removal of biomass and photosynthetic tissue by either grazing or fire may reduce perennial grass growth (Bullock, 1998; Peláez et al, 2003). Number and size of leaves, and tiller height are growth components that may contribute to re-establishment of a photosynthetic surface area. If post-fire defoliation has a negative effect on one or more of these growth components, rapid re-establishment of a green canopy might be limited. Length of the resting period after fire might affect perennial grass growth
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