*These authors contributed equally to the paper.
A field test of the stress-gradient hypothesis along an aridity gradient
Article first published online: 18 MAY 2011
© 2011 International Association for Vegetation Science
Journal of Vegetation Science
Volume 22, Issue 5, pages 818–827, October 2011
How to Cite
Armas, C., Rodríguez-Echeverría, S. and Pugnaire, F. I. (2011), A field test of the stress-gradient hypothesis along an aridity gradient. Journal of Vegetation Science, 22: 818–827. doi: 10.1111/j.1654-1103.2011.01301.x
Co-ordinating Editor: Martin Zobel
Armas, C. (corresponding author, firstname.lastname@example.org) & Pugnaire, F.I. (email@example.com): Estación Experimental de Zonas Áridas, Consejo Superior de Investigaciones Científicas, Carretera de Sacramento s/n, E-04120 La Cañada de San Urbano, Almería. Spain Rodríguez-Echeverría, S. (firstname.lastname@example.org): CFE - Centro de Ecologia Funcional, Departamento de Ciências da Vida, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal.
- Issue published online: 1 SEP 2011
- Article first published online: 18 MAY 2011
- Received 4 December 2010, Accepted 15 April 2011
- Species richness
Aims: The stress-gradient hypothesis (SGH) predicts how plant interactions change along environmental stress gradients. We tested the SGH in an aridity gradient, where support for the hypothesis and the specific shape of its response curve is controversial.
Location: Almería, Cáceres and Coimbra, three sites in the Iberian Peninsula that encompass the most arid and wet habitats in the distribution range of a nurse shrub species –Retama sphaerocarpa L. (Boiss) – in Europe.
Methods: We analysed the effect of Retama on its understorey plant community and measured the biomass and species richness beneath Retama and in gaps. We estimated the frequency (changes in species richness), importance and intensity of the Retama effects, and derived the severity–interaction relationship pattern, analysing how these interaction indices changed along this aridity gradient.
Results and conclusions: The intensity and frequency of facilitation by Retama increased monotonically with increasing environmental severity, and the importance tended to have a similar pattern, overall supporting the SGH. Our data did not support predictions from recent revisions of the SGH, which may not apply to whole plant communities like those studied here or when interactions are highly asymmetrical. Facilitation by Retama influenced community composition and species richness to the point that a significant fraction of species found at the most arid end of the gradient were only able to survive beneath the nurse shrub, whereas some of these species were able to thrive in gaps at more mesic sites, highlighting the ecological relevance of facilitation by nurse species in mediterranean environments, especially in the driest sites.