Recent decadal drought reverts warming-triggered growth enhancement in contrasting climates in the southern Andes tree line

Fajardo A, Gazol A, Mayr C, Camarero JJ (2019)

Publication Type: Journal article

Publication year: 2019

Journal

Journal of Biogeography Wiley-Blackwell

DOI: 10.1111/jbi.13580

Abstract

Aims: Rising temperature and declining summer precipitation due to the 1970s-climate shift in southern South America have reduced forest productivity at dry sites. Here, we worked with the most widespread Southern Hemisphere tree line species, Nothofagus pumilio, across contrasting climatic conditions and determined whether rising atmospheric CO2 concentrations as well as warmer and drier climatic conditions provoked by the 70s-climatic shift have been causing systematic changes in tree line growth rates and intrinsic water-use efficiency (iWUE). Location: 36–54°S, southern Andes. Time period: 1950–2010. Major taxa studied: Nothofagus pumilio. Methods: We worked at five disparate climatic tree line locations, spanning 18 degrees of latitude; at each location, we sampled trees at four different elevations, including tree line elevation. We quantified the variation in annual tree-ring width (TRW) as a function of climate, elevation, tree age, size, annual CO2 concentrations and location, using linear mixed-effects models and interpreted TRW trends in relation to iWUE and isotope (δ13C and δ18O) signalling. Results: Across locations, the patterns of tree line growth occurring in the 1980–2010 period exhibited a clear and significant negative trend, in contrast to the previous 1950–1980 period. We found an increase in iWUE and δ18O across time and locations. Given that an increase in δ18O indicates a decrease in stomatal conductance, we assert that drought-induced stomatal closure appears to be causing the reduction in growth. Main conclusions: We show unequivocal evidence that warmer and drier summer conditions translated into a decrease in growth rates along the elevational tree line of the southern Andes, reverting previous growth improvements linked to climate warming. An improvement in iWUE at all locations is most likely explained by decreased stomatal conductance given the rising δ18O signal. An iWUE–growth decoupling may act as an ecological strategy to respond to drought.

Authors with CRIS profile

Christoph Mayr Institut für Geographie

Involved external institutions

Instituto Pirenaico de Ecología ES Spain (ES) Centro de Investigación en Ecosistemas de la Patagonia CL Chile (CL)

How to cite

APA:

Fajardo, A., Gazol, A., Mayr, C., & Camarero, J.J. (2019). Recent decadal drought reverts warming-triggered growth enhancement in contrasting climates in the southern Andes tree line. Journal of Biogeography. https://doi.org/10.1111/jbi.13580

MLA:

Fajardo, Alex, et al. "Recent decadal drought reverts warming-triggered growth enhancement in contrasting climates in the southern Andes tree line." Journal of Biogeography (2019).

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