title: Synergy of extreme drought and shrub invasion reduce ecosystem functioning and resilience in water-limited climates.
abstract: Extreme drought events and plant invasions are major drivers of global change that can critically affect ecosystem functioning and alter ecosystem-atmosphere exchange. Invaders are expanding worldwide and extreme drought events are projected to increase in frequency and intensity. However, very little is known on how these drivers may interact to affect the functioning and resilience of ecosystems to extreme events. Using a manipulative shrub removal experiment and the co-occurrence of an extreme drought event (2011/2012) in a Mediterranean woodland, we show that native shrub invasion and extreme drought synergistically reduced ecosystem transpiration and the resilience of key-stone oak tree species. Ecosystem transpiration was dominated by the water use of the invasive shrub Cistus ladanifer, which further increased after the extreme drought event. Meanwhile, the transpiration of key-stone tree species decreased, indicating a competitive advantage in favour of the invader. Our results suggest that in Mediterranean-type climates the invasion of water spending species and projected recurrent extreme drought events may synergistically cause critical drought tolerance thresholds of key-stone tree species to be surpassed, corroborating observed higher tree mortality in the invaded ecosystems. Ultimately, this may shift seasonally water limited ecosystems into less desirable alternative states dominated by water spending invasive shrubs.
authors.affiliation: Agroecosystem Research, BayCEER, University Bayreuth, Universitätsstr. 30, 95447 Bayreuth, Germany.|CEF, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Caldeira
authors.affiliation: CEF, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal.
authors.forename: Xavier
authors.initials: X
authors.lastname: Lecomte
authors.affiliation: CEF, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal.|Instituto Nacional de Investigação Agrária e Veterinária I.P., Quinta do Marquês, Av, da República, 2780-159 Oeiras, Portugal.
authors.forename: Teresa S
authors.initials: TS
authors.lastname: David
authors.affiliation: Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB, United Kingdom.|Institute for Geophysics and Meteorology, University of Cologne, Pohlingstr. 3, 50969 Cologne, Germany.
authors.forename: Joaquim G
authors.initials: JG
authors.lastname: Pinto
authors.affiliation: CEABN-Inbio, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal.
authors.forename: Miguel N
authors.initials: MN
authors.lastname: Bugalho
authors.affiliation: Agroecosystem Research, BayCEER, University Bayreuth, Universitätsstr. 30, 95447 Bayreuth, Germany.|Institute of Ecosystem Physiology, University Freiburg, Georges-Köhler-Allee 53/54, 79110 Freiburg, Germany.
authors.forename: Christiane
authors.initials: C
authors.lastname: Werner
mesh_terms: D002980:Climate; D055864:Droughts; D017753:Ecosystem; D018526:Plant Transpiration / Q000502:physiology; D057685:Plant Weeds / Q000502:physiology*; D029963:Quercus / Q000502:physiology*; D013045:Species Specificity; D013312:Stress, Physiological / Q000502:physiology; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water