Fire-rainfall relationships in Argentine Chaco savannas

Abstract

We used dendroecological techniques to date fire scars in woody species growing in a subtropical savanna of the Argentine Chaco dry forests, and to explore the temporal trends of fire with rainfall variability at different temporal scales during the 20th century. Eight sampling sites were located along an ecotone between savanna and a dry forest, and a composite chronology was developed for a savanna, based on a total of 21 fire dates. The mean fire frequency was 0.18 fires year-1 and the mean fire interval was 3.3 years. The period post 1971 (which had 22% more rainfall) experienced a fire frequency more than two times higher than the period 1925-1970 (p<0.05). Decadal fire frequency was correlated to 10-years moving average rainfall (R2=0.58). Superposed Epoch Analysis showed that fires occur during years of above-average rainfall, and extensive fires tend to follow two years of above-average rainfall, all these associations being statistically significant. These results indicate a climatic control of fire regime, associated to enhanced fine fuels production during years of high rainfall, and imply that regional increase in rainfall associated to global changes in atmospheric circulation are affecting local ecosystems by significantly changing their disturbance regime.