Precipitation variability and landslide occurrence in a subtropical mountain ecosystem of NW Argentina

Landslides are common on the steep slopes of the subtropical montane forests in Northwestern (NW) Argentina (Yungas). Instrumental and tree-ring records from this region indicate that rainfall has increased during the second half of the 20th century and there has also been an increase in landslide events. We used dendroecological techniques to date the occurrence of landslides during the past 50 years and examine the relationships with regional precipitation trends. Alnus acuminata H.B.K. is the dominant species in the upper montane forest and colonizes the bare areas exposed by landslides. Landslide dating was based on the identification of suppression-release patterns in ring-width series from trees growing along the landslide scarps, in combination with age determination of trees growing on the landslide failure or depositional surfaces. We cored A. acuminata in three areas that span the latitudinal range of the montane forest in NW Argentina: Los Sosa (27°S), Hualinchay (26°S) and Yala (24°S). The results show that landslide occurrence (and therefore probability) is more frequent during summers with abundant rainfall. As General Circulation Models for subtropical South America predict an increase in summer precipitation during the 21st century, increased precipitation could induce changes in landslide regime that would lead to important environmental changes in these montane ecosystems.