Precipitation variations and tree growth in the semi-arid Chaco region of South America
The semi-arid Chaco is one of the most extensive forest formations in South America and has been subjected to high deforestation rates since the 1970s. At present, the main ecological, social and production problem in the region is the variation in water availability, a complex situation that combines a negative water balance and flood events. In this work, we studied the spatial and temporal variability of precipitation patterns, using rainfall instrumental records and tree rings of Schinopsis lorentzii, in three sites in the semi-arid Chaco region of Argentina. We cross-dated annual rings and compared tree growth with local and regional climatic variables, including rainfall and temperature. We found that interannual variability of precipitation is not homogeneous across the region, but shows a differential east-to-west distribution of moisture. Variability in tree-ring width responded positively to climatic signals related to water availability and inversely to temperature, mainly during the period of greatest water deficit and the onset of the growth period. The three chronologies displayed an increase in interannual values and a significant change in growth variability from the 1950s, consistent with an increase in the magnitude and variability of precipitation in the last decades.
The analysis involving gridded regional climatic variables revealed the differential predominance of the large-scale moisture sources that enter the region. The results obtained in this study enabled us to disentangle the roles of the different sources of moisture, their spatial and temporal variability, and their impact on the tropical dry ecosystems of the Chaco region.