Droughts as triggers of Nothofagus pumilio growth decline in northern Patagonia, Argentina

RICARDO VILLALBA; CATÓN, MILAGROS RODRIGUEZ

Berlin

Conferencia; Conference and Workshop Climate Impacts on Glaciers and Biosphere in Fuego-Patagonia; 2017

Instituto Antártico Chileno (INACH, Chile) y Humboldt-Universität zu Berlin Geographisches Institut Klimageographie

Understanding the influence of climatic variations on forest decline is a major challenge for scientists investigating global changes. Although reductions in tree growth have previously been associated with forest decline, comprehensive efforts to understand these relationships are rare. Based on ring-width variations, we determine the influence ofclimatic fluctuations on the onset and temporal evolution of Nothofagus pumilio growth decline in the Patagonian Andes. We sampled 11 sites showing crown dieback symptoms.Regional patterns of Basal Area Increment (BAI) were derived from 294 Nothofagus trees in a 500-km latitudinal transect along the forest-steppe ecotone in northern Patagonia. Two BAI patterns show sustained negative trends over the last three to six decades. Tipping points in growth trends are associated with two extreme dry-warm climate events in spring summer of 1942-1943 / 1943-1944 / 1944-1945 and 1978-1979. Both severe droughts were preceded by up to 10 years of wet periods that promoted above-average tree growth. We concluded that severe droughts occurring after wet periods trigger the decline of large, dominant N. pumilio trees with high rates of growth. The coincidence between major changes in regional growth with two of the most severe droughts in the instrumental records shows that climatic variations over northern Patagonia synchronize the onset of forest decline at a regional scale. As these dry-mesic N. pumilio sites will face more severe droughts in the 21st century as suggested by future climate scenarios, the areas affectedby forest decline would increase substantially.