Tree-rings as an indicator of environmental-stress: Past and present climate impacts on water, forests and people
by
Ricardo Villalba
Departamento de Dendrocronología e Historia Ambiental, IANIGLA-CONICET, C.C. 330, (5500) Mendoza, Argentina.
Coauthors: Raquel Gil Montero, Mariano S. Morales, Mariano Masiokas and Salvador Cali1.

This presentation illustrates the use of tree-ring indices as indicators of physical, biological and socio-economic stress in subtropical and temperate regions of South America.

Tree-ring based temperature reconstructions for northern and southern Patagonia show substantial inter-centennial changes and point out how unusually warm climate conditions during the 20th century have been in the context of the past 400 years. Recent surveys of environmental changes indicate that the anomalous climate of the past century has affected both the biotic and abiotic components of the landscape in the Southern Andes. Due to the steeper precipitation and temperature gradients imposed by the local mountains, the physical and biological systems in the Southern Andes are particularly sensitive to relatively minor changes in climate., the Loss of glacier volume in the Southern Andes started after the last Neoglacial advance (14-19th centuries) and continued in several stages of increasing rates during the 20th century, particularly in the past decades. Melting of ground ice has markedly accelerated since the mid-1970s, concurrent with large-scale atmospheric changes related to the Pacific Decadal Oscillation.

Dendroecological analyses suggest that some tree species in northern Patagonia are already responding to the anomalous climate during the 20th century. Increased numbers of mortality events and lightning-ignited fires are the responses to warmer summers, consistent with the persistence of atmospheric circulation modes that might have been unusual in the previous centuries.

In the absence of traditional indicators of socioeconomic stress in the Puna of Jujuy, Northwestern Argentina, we have been used tree-ring indices from moisture sensitive trees as a proxy for droughts and their related economic stresses. Examining the relationship between population mortality and ring-width indices allows inferences to be drawn about the relative importance of environmental and sociopolitical factors in determining human mortality patterns that contributed to the depopulation of this area in the late 19th century.

The case studies reviewed in this presentation represent attempts to link local-scale physical, biological and socioeconomic processes in the Andes with current and past variations in large-scale atmospheric conditions. New research devoted to establishing linkages between climate variations, physical-biological systems, and human activities in the Southern Andes is strongly advised.

Date received: February 10, 2005