Postfire Vegetation Dynamics in Three Rangelands of Northeastern Patagonia, Argentina
Abstract
In many rangeland ecosystems, the role of fire on vegetation dynamics has been the object of detailed studies. In Argentina, andespecially in Patagonia, the knowledge of how fire changes vegetation is scarce. In 3 areas affected by wildfires on different dates(in 1988, 1994, and 1998), we determined the structure of the vegetation (plant cover, density, and biomass) and compared itwith that of nearby unburned areas. Based upon these data, we present a qualitative state-and-transition model of thisrangeland. For the sites burned in 1988 and 1994, aerial biomass, density, and cover of perennial grasses were significantlygreater (P0.05) for burned than for unburned areas. For the site burned in 1998, although there were no significantdifferences in perennial grass biomass and cover, density was significantly greater compared to the unburned area. Total shrubcover was significantly lower (P0.05) in burned than in the unburned areas, attaining 49.7%, 15.0%, and 5.5% of that of theunburned areas for the sites burned in 1988, 1994, and 1998, respectively. Similar to cover, density for most shrubby species wassignificantly greater in the unburned than in the burned areas for the 3 sites. Grazing and fires of different intensities, combinedwith variable rainfall, makes the prediction of postfire vegetation changes difficult. However, it can be generalized that firechanged the vegetation from shrub-dominated steppes, a persistent state in northeastern Patagonia, into a grass-dominatedtransient state. This change has persisted for more than 10 years after a fire event. From the perspective of sheep raising, thesignificant 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.