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Widespread crown condition decline, food web disruption, and amplified tree mortality with increased climate change-type drought

  1. Josep Peñuelasa,2
  1. aGlobal Ecology Unit, Centre for Ecological Research and Forestry Applications-Centre for Advanced Studies of Blanes-Spanish National Research Council, Autonomous University of Barcelona, 08193 Bellaterra, Catalonia, Spain;
  2. bCommunity Ecology and Conservation Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands;
  3. cDepartment of Animal Biology, Plant Biology and Ecology, Autonomous University of Barcelona, 08193 Bellaterra, Catalonia, Spain;
  4. dDepartment of Geography, Autonomous University of Barcelona, 08193 Bellaterra, Catalonia, Spain; and
  5. eNational Service for the Protection of Forests, Spanish Ministry of the Environment and Rural and Marine Affairs, 28071 Madrid, Spain

  1. Edited by Harold A. Mooney, Stanford University, Stanford, CA, and approved December 15, 2010 (received for review July 17, 2010)

  2. ↵1J.C. and M.C. contributed equally to this work.

Abstract

Climate change is progressively increasing severe drought events in the Northern Hemisphere, causing regional tree die-off events and contributing to the global reduction of the carbon sink efficiency of forests. There is a critical lack of integrated community-wide assessments of drought-induced responses in forests at the macroecological scale, including defoliation, mortality, and food web responses. Here we report a generalized increase in crown defoliation in southern European forests occurring during 1987–2007. Forest tree species have consistently and significantly altered their crown leaf structures, with increased percentages of defoliation in the drier parts of their distributions in response to increased water deficit. We assessed the demographic responses of trees associated with increased defoliation in southern European forests, specifically in the Iberian Peninsula region. We found that defoliation trends are paralleled by significant increases in tree mortality rates in drier areas that are related to tree density and temperature effects. Furthermore, we show that severe drought impacts are associated with sudden changes in insect and fungal defoliation dynamics, creating long-term disruptive effects of drought on food webs. Our results reveal a complex geographical mosaic of species-specific responses to climate change–driven drought pressures on the Iberian Peninsula, with an overwhelmingly predominant trend toward increased drought damage.

Footnotes

  • 2To whom correspondence may be addressed. E-mail: josep.penuelas{at}uab.cat or jofre.carnicer{at}creaf.uab.cat.

  • Author contributions: J.C. and J.P. designed research; J.C., M.C., M.N., X.P., and J.P. performed research; J.C., M.C., M.N., X.P., and G.S. contributed new reagents/analytic tools; J.C., M.C., M.N., X.P., and J.P. analyzed data; and J.C., M.C., and J.P. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1010070108/-/DCSupplemental.

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