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 and making it more difficult to identify the causing factors. The long-term perspective provided by tree rings has proven to be successful for disentangling the causes of forest decline worldwide. We present recent dendroecological studies developed to determine the influences of climatic variation on the radial growth patterns and death of trees in declining Austrocedrus chilensis and Nothofagus pumilio forests in northern Patagonia, Argentina. These results were used to distinguish between possible causes and interactions of abiotic and biotic stress factors versus stand dynamics processes in the development of the forest declines. For our study forests, we found complex interactions between abiotic and biotic factors acting at different spatial and temporal scales that predispose trees, then incite and contribute to the development of the symptoms leading to their subsequent death. We summarize our findings in a conceptual model presenting forest decline as a spiral of processes driven by interactions between abiotic and biotic stress factors that predispose, incite and contribute to stand-level decline in these forests. Our framework formalizes an alternate hypothesis to single causal agents of decline in Patagonian forests by emphasizing the role and importance of climatic variability as a driver of decline.