Post-fire Vegetation dynamics in Three Rangelands of Northeastern Patagonia, Argentina

ROSTAGNO, CESAR MARIO, DEFOSSÉ, GUILLERMO Y DEL VALLE, HÉCTOR

Rangeland Ecology and Management (ex JRM)

Society for Range Management

Lugar: Lawrence, Kansas, USA; Año: 2006 vol. 59 p. 163 - 170

1550-7424

In many rangeland ecosystems, the role of fire on vegetation dynamics has been object of detailed studies. In Argentina, and especially in Patagonia, the knowledge of how fire changes vegetation is scarce. In three areas affected by wildfires on different dates (1988, 1994 and 1998), we determined the structure of the vegetation (plant cover, density and biomass) and compare it with that of nearby unburned areas. Based upon these data, we present a qualitative state-and- transition model of this rangeland. For the sites burned in 1988 and 1994, aerial biomass, density and cover of perennial grasses were significantly greater (P £ 0.05) for burned than for unburned areas. For the site burned in 1998, although there were no significant differences in perennial grass biomass and cover, density was significantly greater compared to the unburned area. Total shrub cover was significantly lower (P £ 0.05) in burned than in the unburned areas, attaining 49.7%, 15.0% and 5.5% of that of the unburned areas for the sites burned in 1988, 1994 and 1998, respectively. Similar to cover, density for most shrubby species was significantly higher in the unburned than in the burned areas for the three sites. Grazing and fires of different intensities, combined with variable rainfall, makes the prediction of postfire vegetation changes difficult. However, it can be generalized that fire changed the vegetation from shrub-dominated steppes, a persistent state in northeastern Patagonia, into a grass-dominated, transient state. This change has persisted for more than 10 years after a fire event. From the perspective of sheep raising the significant postfire increase in perennial grass biomass represents a substantial improvement in the condition of these rangelands. However, repeated fires would be necessary to control the sprouting shrubs and maintain the grass-dominated state.