ORIGINAL PAPER Facilitation of the non-native annual plant Mesembryanthemum crystallinum (Aizoaceae) by the endemic cactus Eulychnia acida (Cactaceae) in the Atacama Desert Jaime Madrigal-Gonza ´lez • Alex P. Cea • Leticia A. Sa ´nchez-Ferna ´ndez • Karina P. Martı ´nez-Tillerı ´a • Juan E. Caldero ´n • Julio R. Gutie ´rrez Received: 19 August 2011 / Accepted: 26 November 2012 / Published online: 4 December 2012 Ó Springer Science+Business Media Dordrecht 2012 Abstract The Atacama Desert is one of the most stressful environments worldwide and represents a strong barrier for the establishment of native and non- native plants. In this study, we report the establish- ment of a non-native annual plant through facilitation by a native endemic cactus in a relatively undisturbed coastal area in north-central Chile. Soil collected under Eulychnia acida contained more available nutrients (N, P and K), water, and soluble salts than soils collected away from E. acida. Co-occurrence analyses showed a strong positive spatial association (facilitation) between the native cactus E. acida and the non-native annual, Mesembryanthemum crystall- inum. The aboveground biomass of M. crystallinum individuals was 4-fold higher under the influence of E. acida. Native halophytes occasionally shared the cactus understory with the non-native species, but dominant native shrubs and perennial herbs did not co-occur with the cactus at scales of 1 and 4 m 2 . All these results support facilitation of the native cactus on the non-native herb. The combination of direct and indirect positive effects could explain the assembly of the non-native annual plant in these undisturbed areas of the Atacama Desert and have major implications on M. crystallinum capacity to colonize new areas. Keywords Facilitation Á Mesembryanthemum crystallinum Á Eulychnia acida Á Saline soils Á Atacama Desert Á Direct and indirect interactions Introduction How non-native species invade new areas is a central issue in ecology and conservation biology (Lodge 1993; Kolar and Lodge 2001). Competition in the recipient community (i.e., ecological resistance) and abiotic stresses (i.e., physical environment) have been traditionally proposed as major controls of non-native species establishment (Case 1990; D’Antonio 1993; Alpert et al. 2000; Corbin and D’Antonio 2004). However, non-native species may be facilitated by resident species (Simberloff and Von Holle 1999; Badano et al. 2007; Bulleri et al. 2008). Under abiotic stress, facilitation is thought to be important in structuring plant communities, as ameliorated abiotic Electronic supplementary material The online version of this article (doi:10.1007/s10530-012-0382-y) contains supplementary material, which is available to authorized users. J. Madrigal-Gonza ´lez (&) Á A. P. Cea Á L. A. Sa ´nchez-Ferna ´ndez Á K. P. Martı ´nez-Tillerı ´a Á J. E. Caldero ´n Á J. R. Gutie ´rrez Instituto de Ecologı ´a y Biodiversidad (IEB), Universidad de La Serena, Casilla 599, La Serena, Chile e-mail: ecojmg@hotmail.com A. P. Cea Á K. P. Martı ´nez-Tillerı ´a Á J. R. Gutie ´rrez Universidad de La Serena, La Serena, Chile J. R. Gutie ´rrez Centro de Estudios Avanzados en Zonas A ´ ridas (CEAZA), Universidad de La Serena, La Serena, Chile 123 Biol Invasions (2013) 15:1439–1447 DOI 10.1007/s10530-012-0382-y