Climatic variability and climate-trend effects on north Patagonian forests: implications for conservation

KITZBERGER, T.; VEBLEN, T.T.; VILLALBA, R.; MERMOZ, M.; SUAREZ, M.L.; TERCERO BUCARDO, N.

Mendoza

Simposio; CONCORD Symposium. Climate Change – Organizing the Science for the American Cordillera; 2006

Climate is a major influence on forest dynamics both indirectly through effects on climatically related disturbances and directly through influences on tree demography. Several lines of evidence show that protected forest-steppe ecotonal areas located at c. 39-43°S in northern Patagonia are highly sensitive to interannual to decadal scale climatic variability suggesting that current and predicted climatic trends are to drastically alter forest landscape structure and composition with consequences on conservation goals. 1. Austrocedrus chilensis the main arboreal species of dry forest had during the last half century episodic establishment in relation to decadal-scale climatic episodes inducing importaant changes in the forest composition and structure. 2. Interannual variability of climate and the occurrence of extreme events had strong effects on Nothofagus dombeyi and A. chilensis adult tree mortality changing forest composition and inducing forest dieback. 3. Forest fire size and severity is high sensitive to interannual climatic variability with profound consequences on landscape structure promoting fire-adapted plant communities at the expense of putting at risk fire-sensitive forest types. 4. The frequency forest fires ignited by lightning has increased three-fold, tracking decadal increases in summer temperature after the mid-1970s increasing fire frequency in ecosystems dominated by species adapted to lower fire frequencies. 5. Post-fire climatic conditions, particularly rainfall conditions 1-2 years after the fire modify tree seedling establishment rates and thus are strongly controlling future forest composition as well as forest to shrubland conversion rates. Climatic variables that directly or indirectly modify key aspects of protected ecosystems are largely controlled by large scale climatic patterns such as position of subtropical anticyclones, southern polar votex strength, Altantic and Pacific Ocean temperature patterns. Therefore, stronger interdisciplinary research interaction between ecologists and climatologists and paleecologists is necessary for improving predictions of ecological responses to climate change necessary for the design of appropriate mitigation strategies. Keywords: fire regime, forest dynamics, tree demography, climatic variability, lightning, landscape change, dendroecology, warming experiments.