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

VILLALBA R.; BLAZINA, A.; MASIOKAS M.; RODRIGUEZ CATON, M.; CALÍ, S.; MORALES, M.; SRUR, A.; RIPALTA A.; MUNDO I A

Mendoza

Conferencia; Ameridendro 2016 Third American Dendrochronology Conference; 2016

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 of climatic 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 3 to 6 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. Since these dry-mesic N. pumilio sites will face more severe droughts in the 21st century, as suggested by future climate scenarios, the areas affected by forest decline would increase substantially.