Maintaining distances with the engineer: Patterns of coexistence in plant communities beyond the patch-bare dichotomy
Two-phase plant communities with an engineer conforming conspicuous patches and affecting the performance and patterns of coexisting species are the norm under stressful conditions. To unveil the mechanisms governing coexistence in these communities at multiple spatial scales, we have developed a new point-raster approach of spatial pattern analysis, which was applied to a Mediterranean high mountain grassland to show how Festuca curvifolia patches affect the local distribution of coexisting species. We recorded 22 111 individuals of 17 plant perennial species. Most coexisting species were negatively associated with F. curvifolia clumps. Nevertheless, bivariate nearest-neighbor analyses revealed that the majority of coexisting species were confined at relatively short distances from F. curvifolia borders (between 0–2 cm and up to 8 cm in some cases). Our study suggests the existence of a fine-scale effect of F. curvifolia for most species promoting coexistence through a mechanism we call ‘facilitation in the halo’. Most coexisting species are displaced to an interphase area between patches, where two opposite forces reach equilibrium: attenuated severe conditions by proximity to the F. curvifolia canopy (nutrient-rich islands) and competitive exclusion mitigated by avoiding direct contact with F. curvifolia.
We thank Carlos Díaz Palomo and Jesús López Angulo for their technical assistance in this work. We also thank the staff of the Parque Nacional de la Sierra de Guadarrama for permission to work in the field area. This research was supported by the Comunidad de Madrid as part of the project REMEDINAL 2 (CM-S2009/AMB-1783) and by the Spanish Ministry of Science and Innovation as part of the projects MOUNTAINS (CGL2012-38427) and ISLAS (CGL2009-13190-C03-02).
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