Using plant functional distances to select species for restoration of mining sites.
Plant facilitation, an ecological interaction that benefits at least one species without harming the other, is increasingly used as a restoration tool. To restore degraded habitats under a facilitation framework, practitioners must correctly select both the benefactor (nurse) and the beneficiary (facilitated) species. Based on community assembly and species coexistence theory, we propose selecting plant species that largely differ in a suite of functional traits so that competition is minimized and facilitation maximized due to functional complementarity. To apply this guideline in a pilot restoration experiment performed in metalliferous mine tailings in South-Eastern Spain, we first built the plant-plant facilitative interaction network naturally occurring in a set of 12 tailings. After characterizing each species with 20 morphological and physiological traits, we verified that facilitative interactions were predominantly established between functionally distant species. Then, we designed a sowing experiment combining 50 nurse-facilitated species pairs separated by a wide range of functional distances. The success of seedling establishment significantly increased with the functional distance between the nurse and the facilitated plant species. Synthesis and applications. We encourage the use of ecological facilitation together with trait-based species selection to design restoration programmes based on the principle of increasing functional distance between target species. This method may not only promote the restoration of the plant cover but also impact paramount ecosystem functions, thus being an efficient low-cost restoration practice in abiotically stressful ecosystems.