Community-level restoration profiles in Mediterranean vegetation: nurse-based vs. traditional reforestation.
Abstract
Many restoration projects aim to transform degraded vegetation into mature native plant communities. The recovery of the structure and properties of reference native plant communities is acknowledged as a landmark of restoration, and the success of restoration practices is measured in terms of community metrics. Nurse-assisted planting has been proposed as a promising technique for the restoration of Mediterranean and arid vegetation based on its success at seedling establishment rather than on the recovery of reference community properties. We investigate the adequacy of this restoration practice by shifting the focus of restoration from the species to the community level. In contrast to previous studies in the Mediterranean region, we assessed the efficacy of several management techniques, including nurse-based planting, in the recovery of the structure and properties of mature native reference communities. In a burned area of southern Spain, we applied widely used community analysis tools (rarefaction and species accumulation curves, Chao 2 richness estimator, species evenness and beta diversity) to compare the profiles of a reference native community and the community achieved through different management practices: traditional planting, nurse-based planting and controls where natural regeneration was allowed to occur. Our results showed that post-fire establishment of planted seedlings was higher under the canopy of nurses than in open ground. More importantly, nurse-based restoration increased the species richness and evenness of tall-shrubs and trees as well as the life-form diversity, with the restored community approaching the reference community in terms of both composition and structure of the bank of juveniles. Synthesis and applications. We conclude that in contrast to traditional reforestation, where diversity is constrained by the elimination of pioneer and regenerated tall-shrubs, nurse-based restoration contributes to accelerated recovery of important community structure and properties. Thus, it should be used preferentially over traditional reforestation in Mediterranean mountains where restoration of native communities, and not merely tree establishment, is dictated under current habitat directives.