Tree mortality and summer droughts in Nothofagus pumilio forests in the southern Patagonian Andes, Argentina

RICARDO VILLALBA; MARÍA SOL MONTEPELUSO

Mendoza

Conferencia; Ameridendro 2016, Third American Dendrochronology Conference; 2016

Laboratorio de Dendrocronología del IANIGLA del CCTMendoza

Increasein the frequency, duration and severity of droughts associated with climatechange are modifying the composition, structure and biogeographic distributionof forests in many regions of the world. The occurrence of a recent and extensive treemortality event in the Nothofaguspumilio forests, southern Patagonia, Argentina, providesan opportunity to advance in the study of therelationships between tree mortality events, episodic droughts andregional climate variability. At a N. pumilio stand affected by the 2011-2012drought, health conditions of each individual in the canopy was recorded. Atree ring chronology (AD 1818-2014) developedfrom 40 trees in the stand was used to establish the death date of trees using visual andstatistical (COFECHA program) cross-dating techniques. Our results indicatethat from 40 trees sampled on the plot, 25 individuals (63%) presented total canopy mortality, whereas the remaining 15 trees(37%) were alive or with varying degrees of mortality. Based on morphological characteristics, the25 dead trees were classified into three categories: recently dead trees(2 trees with bark and well-preserved small branches), long-time ago dead trees (4 trees without barkand no small branches) and composite dead trees (19 trees with bark showing partof the canopy simultaneouslywith and without small branches).From the 15 alive trees, 10 trees (67%) show healthy crowns, whereas the 5 remaining trees (33%) show partial dead crowns (previousconcurrent with composite mortality). Tree-ring dating of recent and compositemortalities indicates that more than 90% of trees died in 2011. Some of theseindividuals had over 150years. These results suggest the occurrence of anunprecedented N. pumilio mortality episode related to the severe spring-summerdrought during the 2011-2012 in Santa Cruz, Argentina.