Influences of past climate variations on forest disturbance in Patagonia

MUNDO, I.A.; MORALES, M.; CASTELLER, A.; VILLALBA, R.

Valdivia, Chile

Simposio; II International symposium, “Reconstructing Climate Variations in South America and the Antarctic Peninsula over the last 2000 years”; 2010

Centro de Ingeniería de la Innovación y Facultad de Ciencias Forestales y Recursos Naturales

Climate influences ecosystems by modulating the frequency, magnitude, and spatial scales of natural disturbances. Many studies have documented the importance of disturbances in the dynamics of Patagonian forests.  We report the influence of climatic variations on three types of disturbances (avalanches, insect outbreaks and fires) affecting the Nothofagus pumilio and Araucaria araucana forests in Patagonia, Argentina. Tree-ring based avalanche chronologies from nine avalanche tracks adjacent to Lago del Desierto, Santa Cruz, southern Patagonia, indicate that years with large avalanche activity are significantly correlated with abundant precipitation from May to October.  These winter seasons show features typically observed during the cold phase of El Niño-Southern Oscillation.  In the same region, defoliators outbreaks have been documented for 1998-1999, 2002-2003 and 2004-2005 growing seasons.  Tree-ring chronologies from the forests affected by Ormiscodes amphimone showed abrupt growth reductions the years following the insect attacks. The reductions in tree growth related to these outbreaks are the most severe recorded during the past 100 years. Increases in outbreak frequency and intensity may be associated with unprecedented warm temperatures in the recent decades in the context of the past 400 years.  During the past three centuries, years of fire occurrence recorded in ten fire chronologies from A. araucana in northern Patagonia were concurrent with years of reduced tree growth in this species. However, fire years are not significantly correlated with temperature variations from long-term climate reconstructions in the area, suggesting that in addition to climate, humans strongly influence fire regimes in the A.araucana forests. Based on our observations, we concluded that climate changes play a major role in modulating forest disturbance regimes across Patagonia.