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Individual study: Effect of fire intensity and season on perennial grass mortality in semi-arid grasslands of Caleu-Caleu department, La Pampa, Argentina

Published source details

Pelaez D.V., Boo R.M., Mayor M.D. & Mirta D. (2001) Effect of fire on perennial grasses in central semiarid Argentina. Journal of Range Management, 54, 617-621


Fire is a major management tool of temperate grasslands in semi-arid central Argentina. This study in Caleu-Caleu department (38°45'S, 63° 45'W), southeast La Pampa province, evaluated the effect of fire intensity in different seasons of the year on mortality of Piptochaetium napostaense, Stipa tenuis and Stipa gynerioides (three important native perennial grasses in this semi-arid region) in the field, and to determine thermal death points, in the laboratory.


The field study was undertaken a 20 ha area closed to livestock grazing since 1982.
Ten plants of each grass species were exposed to low fire intensity (300-400°C), high fire intensity (500-600°C), and no fire (control) in April and December 1994, May 1995, and January 1996. Fire treatments were applied using a portable propane burner until the plant crown temperature reached the required temperature as recorded by a thermocouple placed in the centre of each tussock at the soil surface. Plants were recorded at the end of the growing season after each fire, as alive or dead.
Thermal death point was determined (in autumn and spring) using the Wright's technique (Wright 1970).



Statistically significant mortality only occurred in P.napostaense and S.tenuis after the May 1995 burns: combining both burn treatments, average mortality was for P.napostaense (55%) and S.tenuis (85%); for S.gynerioides it was only 15%.
Although not statistically significant, mortality under high fire intensity was slightly higher than the low fire intensity: overall mortality of the three grasses combined was 25% at the higher fire intensity and 14% in the lower. Average mortality for S.gynerioides was similar and consistently lower (0-20%) than the other two species for all burning dates except the January burn (high intensity 30 and low 10%; compared with zero mortality for S.tenuis and 10% for P.napostaense at the higher intensity). No mortality occurred in the controls.
The thermal death point was similar in all three species; in the autumn it was 65º C, and in summer 68º C.
Wright H.A. (1970)A method to determine heat-caused mortality in bunchgrasses. Ecol., 51, 582–587.


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