Climate influences on forest dynamics in the Patagonian Andes, Argentina

ANA M. SRUR, MARIANO M. AMOROSO, ALEJANDRO CASTELLER, MARIANO S. MORALES, IGNACIO A. MUNDO, MILAGROS R. RODRÍGUEZ CATÓN, M. LAURA SUAREZ Y RICARDO VILLALBA

Mountain Forests in a Changing World Realizing values, addressing challenges

FAO/MPS and SDC

Año: 2011; p. 65 - 65

Patagonean forests are probably experiencing the warmest period of the last millennium; precipitation has also significantly decreased in recent decades. These changes have introduced substantial variations in the rate of forest growth and in the frequency, magnitude, and spatial scale of natural disturbances at regional scales. Several long-lived tree species living in the region are suitable for reconstructing past disturbances at an annual resolution, making it possible to understand these relationships using long-term series of both climate and disturbance. Across the Patagonian Andes, drought events are one of the major factors influencing dynamics of the extensive Austrocedrus chilensis, Nothofagus dombeyi and N. pumilio forests in northern Patagonia. These events have been associated not only with episodic tree mortality but also have triggered forest decline at the regional scale. Increasing summer temperatures appear to be the major cause for changes in the growth and mortality patterns in southern Patagonia?s N. pumilio forests during the 20th century. An abrupt increase in mortality rates at the xeric forest-steppe border coincided with more frequent dry-warm events over the last three decades. Higher temperatures have also significantly influenced the frequency, intensity and magnitude of Ormiscodes amphimone outbreaks in these forests. Trees affected by this moth exhibited complete defoliation and an abrupt reduction in growth in the years following insect attacks in 1998, 2003, and 2005. In the upper-elevation N. pumilio forests, avalanches are a major forest disturbance. The frequency and intensity of avalanches have been related to regional variations in winter precipitation during the 20th century. In years with large avalanche activity, the atmospheric circulation patterns showed features typically associated with the cold phase of the El Niño-Southern Oscillation. Climate model simulations suggest that even warmer and drier conditions will prevail over the Patagonian Andes during the 21st century. Consequently, both the number of climate-induced disturbance events and the area affected by forest decline can be expected to increase in the near future.