A high-elevation network of Nothofagus pumilio plots for studying and monitoring the dynamics of the upper treeline in Patagonia, Argentina.

SRUR A. M.; VILLALBA R.; MORALES M.; VILLAGRA P. E.; RODRIÍGUEZ M.; RIPALTA A.; DELGADO S.; MENDOZA D.

Coyhaique Chile

Workshop; Workshop on global change in harsh environments; 2009

The Objective of this presentation is to explore the role that climatic fluctuations on short time scales (i.e., annual to decadal variations) have on Nothofagus pumilio radial growth, establishment, and mortality in Patagonia along altitudinal gradients from the lower-elevation limits to the upper treeline. In order to reach this objective we need to determine 1) to environmental variables controlling the rates of tree growth of Nothofagus pumilio at upper treeline, the climatic variables controlling  2) tree establishment, 3) tree mortality in the upper limit of the Nothofagus forests, and 4) to document biotic interactions mediated or regulated by climate changes. Based on our studies along the Argentinean Patagonian Andes, we concluded that 1. Recorded climatic changes in southern Patagonia during the 20th century have modulated the patterns of Nothofagus radial growth. Higher temperatures have increased tree growth in the upper-elevation stands. In contrast, a reduction in radial growth has been recorded at lower-elevation stands in response to increased temperatures and reduced precipitation. However, at dry sites as Canigo the pattern is different. We show that upper treeline at Canigo may be also regulated by precipitation. 2. Increased temperatures in combination with more extended growing seasons since the mid 1970s have facilitated the establishment of new individuals above the present upper-elevation Nothofagus treeline. However, there is a large variability along the precipitation gradients. Tree recruitment is more abundant in humid places where a soil is relatively well-developed. 3. An increase in tree mortality rate has been recorded during the past three decades at the lower-elevation stands in El Chalten. Higher temperatures in combination with reduced precipitations have increase water deficits in the forest-steppe ecotone and induced tree mortality. The unusually warm period starting in 1977 has favored the expansion of the forest above the upper treeline and accelerated tree mortality at the low dry forest-steppe border. 4. Warmer and longer summer since the mid 1970s has increased the insect reproductive rates and consequently the damage on the Nothofagus forests.