Botanical nursing by a dwarf shrub as a nature-based approach to plant biodiversity conservation in the Nepal Himalayas

Plant-plant positive interactions are among the main drivers of plant community structure, especially in stressful environments. While the ecological dynamics of facilitation are increasingly understood, studies evaluating the importance of nurse plants in preserving phylogenetic diversity and protecting species of medicinal value and conservation concern are still limited. Here, we investigated the nurse effects of a Himalayan endemic shrub, Berberis angulosa, in promoting taxonomic richness, composition and phylogenetic diversity of overall and highly valued species in the high-elevation mountain landscape of Langtang National Park, Nepal. Using pair-wise sampling design, we recorded plant communities within the patches of Berberis shrubs and in open gaps at three altitudinal belts. Compared to adjacent open areas, Berberis patches were found to harbor compositionally distinct and phylogenetically diverse plant communities with significantly higher average overall and human-valued species richness. Relative interaction indices showed clear patterns along elevation gradient with the strongest facilitation observed at highest elevation. Similarly, Net Relatedness Indices (NRI) were significantly different between nursed vs open habitats for both overall and human-valued species, with lower mean NRI within Berberis patches indicating higher phylogenetic diversity of communities within the nursed habitats. Facilitation by Berberis enhanced community-level richness by 40% (39 species; total = 97), including 19 human-valued species ([~]36%; total = 53) that occurred exclusively within shrub canopies. Many medicinal, endemic and conservation priority species were either shrub specialists or had significant association with Berberis patches, illustrating the protective role of the nurse shrub. Our results demonstrate that the facilitative effect of Berberis is not only crucial in maintaining plant communities with diverse evolutionary histories but also equally contributing to local beta and landscape-scale gamma biodiversity, sustaining valuable ecosystem services and benefits to human communities in the Himalayas. These findings suggest that appropriate management of such nurse plants may constitute a nature-based approach to biodiversity conservation, that should be considered in policies for sustainability, resilience and ecosystem functioning in this and similar alpine systems.