Environmental history and forest establishment patterns in montane grasslands of NW Argentina

CARILLA, JULIETA; GRAU, HECTOR RICARDO

Workshop; Interdisciplinary Studies on Global Climate Change and the Ecology and Management of Tropical Montane Ecosystems; 2010

The National Science Fundation

Forest-grassland dynamic is controlled by the interaction of climatic and anthropogenic factors, which act over vegetation, affecting environmental conditions and disturbance regime. In many Andean regions, forests had been replaced by grasslands as a consequence of land use. However, in some areas, this trend is currently reverting associated to socioeconomics changes that stimulate rural emigration and abandonment of pastures and agricultural areas. In addition, the increase in rainfall during the second half of the 20th century could promote opportunities for forest recovery. The objective was to analyze Podocarpus parlatorei (Podocarpaceae) establishment pattern in relation to land use history and rainfall in a disturbed valley of a subtropical montane forest. Despite decreasing grazing intensity and increasing rainfall, forests were not actively recovering over degraded grassland, likely because recurrent fires made the ecosystems resistant to forest invasion. Tree establishment in Los Toldos grasslands was spatially and temporarily associated with high livestock load and low fire frequency. In recent times, tree establishment was more active near Los Toldos town where grazing was more intense. Decrease in grazing pressure far from town was associated with an increase in fire frequency, showing that fuels (controlled by grazing and climate) rather than ignition sources were the main predictors of fire probability. Rainfall and tree establishment were negative associated. This association was indirectly, mediated by fires.