The endemic Mediterranean dwarf palm boosts the recolonization of old-fields: Implications for restoration.

Understanding the mechanisms underlying the recolonization of old-fields is critical to promote the recovery of the ecosystem functioning, particularly in regions where agricultural abandonment has increased in the last 60 years. Given that seed arrival and seedling survival often limit the recolonization process by woody species in many Mediterranean habitats, the 'perching' and 'nursing' effects exerted by some pioneer species could be crucial for the restoration of such abandoned lands. We examined the role of an endemic Mediterranean palm (Chamaerops humilis) on the recolonization of old-fields by woody species in southern Iberian Peninsula. We chose three independent old-fields differing in their shrub encroachment levels. To identify potential facilitation by C. humilis, we used a spatially-explicit approach and analyzed its spatial associations with ten common woody species (e.g. Asparagus spp., Daphne gnidium, Olea europaea var. sylvestris, Pyrus bourgaeana). We detected positive spatial associations between C. humilis and woody species at small-scale (1-5 m) in the three plots. Most of such small-scale associations were linked to the bird-dispersal of woody species. Nonetheless, there were marked differences among plots in spatial associations between C. humilis and woody plants, being Asparagus spp. the only species positively associated with C. humilis within the three studied old-fields. These species-specific differences were likely related to variations among old-fields in encroachment level and the legacy of human management. Such small-scales spatial associations between C. humilis and woody species across Iberian old-fields were linked to the perching and nursing effects exerted by the palm. We emphasize the strong potential of this pioneer Mediterranean palm for the restoration of native ecosystems and the recovery of ecosystems services.