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Title: Few multiyear precipitation-reduction experiments find a shift in the productivity-precipitation relationship

Author
item ESTIARTE, M - Consejo Superior De Investigaciones Cientificas (CSIC)
item VICCA, S - University Of Antwerp
item PENUELAS, JOSEP - Consejo Superior De Investigaciones Cientificas (CSIC)
item BAHN, MICHAEL - University Of Innsbruck
item BEIER, CLAUS - University Of Copenhagen
item EMMETT, BRIDGET - Centre For Ecology And Hydrology
item Fay, Philip
item HANSON, PAUL - Oak Ridge National Laboratory
item HASIBEDER, ROLAND - University Of Innsbruck
item KIGEL, J - Hebrew University
item KROEL-DULAY, GYORGY - Hungarian Academy Of Sciences
item LARSEN, KLAUS - University Of Copenhagen
item LELLEI-KOVACS, ESZTER - Hungarian Academy Of Sciences
item LIMOUSIN, JEAN-MARC - Montpellier Supagro – International Center For High Education In Agricultural Sciences
item OGAYA, ROMA - Consejo Superior De Investigaciones Cientificas (CSIC)
item OURCIVAL, JEAN-MARC - University Of Montpellier
item REINSCH, SABINE - University Of Oslo
item SALA, OSVALDO - Arizona State University
item SCHMIDT, INGER - University Of Copenhagen
item STERNBERG, MARCELO - Centre For Ecology And Hydrology
item TIELBORGER, KATJA - University Of Tubingen
item TIETEMA, ALBERT - University Of Amsterdam
item JANSSENS, IVAN - University Of Antwerp

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2016
Publication Date: 7/1/2016
Publication URL: https://handle.nal.usda.gov/10113/63146
Citation: Estiarte, M., Vicca, S., Penuelas, J., Bahn, M., Beier, C., Emmett, B.A., Fay, P.A., Hanson, P.J., Hasibeder, R., Kigel, J., Kroel-Dulay, G., Larsen, K.S., Lellei-Kovacs, E., Limousin, J., Ogaya, R., Ourcival, J., Reinsch, S., Sala, O.E., Schmidt, I.K., Sternberg, M., Tielborger, K., Tietema, A., Janssens, I.A. 2016. Few multiyear precipitation-reduction experiments find a shift in the productivity-precipitation relationship. Global Change Biology. 22:2570-2581. doi:10.1111/gcb.13269.

Interpretive Summary: Altered precipitation patterns are projected for many portions of the globe in most climate change scenarios. A crucial question for natural resources managers and policy-makers is the extent to which altered precipitation patterns may push ecosystems past ‘tipping-points’ where their structure and function change rapidly and sometimes irreversibly. Such altered ecosystems may differ from their prior states in productivity and biological diversity with important consequences for species conservation and ecosystem goods and services, including agricultural productivity. This study asked whether current ecosystem drought experiments push their systems hard enough and far enough to detect the presence of tipping points. The study analyzed eight multi-year drought experiments located in grassland, forest, and shrublands in the U.S. and Europe, to test whether the aboveground productivity in drought treatments in these experiments respond more to year-to-year precipitation variability than did the aboveground productivity of control treatments. The study found that for all but one site, drought treatments did not alter the sensitivity of aboveground precipitation to year-to-year precipitation variability, indicating that the degree of drought stress imposed in most of the experiments did not push these ecosystems past a tipping-point where their structure and function – and potentially their agricultural productivity- were sizeably altered. The study calls for more extreme drought treatments to be conducted to detect possible tipping points in a variety of ecosystems.

Technical Abstract: Precipitation is a key driver of ecosystem net primary productivity and carbon cycling. Global warming is altering precipitation patterns globally, and longer and more intense drought episodes are projected for many temperate and Mediterranean regions. The challenge of predicting the effects of altered precipitation into net primary productivity arises from a major uncertainty: the relationship between aboveground net primary productivity (ANPP) and precipitation differs if the focus is spatial, driven by the climatic variability among sites, or temporal, driven by the interannual variability within sites. In most studies, the spatial dependency of ANPP on precipitation is much stronger than the temporal dependency, indicating differences in the sensitivity to climate versus weather. The most definitive way to estimate effects of reduced precipitation is via manipulation experiments, where confounding factors are minimized. We analyzed results from eight multi-year rainfall reduction experiments to determine whether ANPP responded to drought as expected from the temporal relationship between ANPP and non-manipulated annual precipitation for each site. The global spatial pattern suggests that when a drought treatment causes fundamental changes in ecosystem functioning, that would be revealed by more pronounced declines in ANPP than what would have been expected from the temporal relationship within the current range of precipitation variability. However, we found no evidence for such change. Instead, experimental data indicate that the temporal ANPP-precipitation slope should be preferred when evaluating the performance of models, at least within the annual precipitation (AP) ranges defined by current experiments. Nonetheless, our study highlights the glaring need for new experiments with multiple drought treatment levels that elicit the changes required to identify the AP boundaries within which the temporal slope remains unaltered.