Forest Decline in Northern Patagonia: The Role of Climatic Variability

Abstract

Forest decline is driven by several factors interacting in complex ways,and it is often exacerbated by climate, adding complexity to the process andmaking it more difficult to identify the causing factors. The long-term perspectiveprovided by tree rings has proven to be successful for disentangling the causes offorest decline worldwide. We present recent dendroecological studies developed todetermine the influences of climatic variation on the radial growth patterns anddeath of trees in declining Austrocedrus chilensis and Nothofagus pumilio forestsin northern Patagonia, Argentina. These results were used to distinguish betweenpossible causes and interactions of abiotic and biotic stress factors versus standdynamics processes in the development of the forest declines. For our study forests,we found complex interactions between abiotic and biotic factors acting at differentspatial and temporal scales that predispose trees, then incite and contribute to thedevelopment of the symptoms leading to their subsequent death. We summarizeour findings in a conceptual model presenting forest decline as a spiral of processesdriven by interactions between abiotic and biotic stress factors that predispose, inciteand contribute to stand-level decline in these forests. Our framework formalizesan alternate hypothesis to single causal agents of decline in Patagonian forests byemphasizing the role and importance of climatic variability as a driver of decline.