Facilitation by a dwarf shrub enhances plant diversity of human-valued species at high elevations in the Himalayas of Nepal

Abstract Facilitation is a global phenomenon that occurs when one species promotes the growth, survival, or reproduction of another species, mostly in stressful environments. However, the importance of facilitation by shrubs in maintaining plant community diversity is not well evaluated in the Himalayas, especially for the richness and conservation of medicinal and human-valued species. Therefore, we aimed to explore the facilitative role of a dwarf shrub species, Berberis angulosa, in maintaining plant composition and richness of human-valued species in the Langtang valley of Nepal's Himalayas. We censused plant species in open patches and beneath Berberis during monsoon and post-monsoon (dry) seasons at three elevations. Total species richness and richness of human-valued species were significantly higher inside the Berberis canopy than in gaps; the former being 39% and the latter 46% greater under shrubs than in open sites. Facilitation by Berberis shrubs promoted plant community diversity irrespective of season and elevation; however, higher differences in mean species richness for both total plant species and human-valued species during the dry season and at high elevation indicated increased facilitation intensity under more stressful conditions. The facilitative effect of Berberis shrubs increased, combining both seasons, overall plant diversity by 19% (total=105), and human-valued species by 16% (total=56). Our results show the importance of facilitation by nurse shrubs in structuring plant communities and protecting medicinal and socio-ecologically important plants, thus enriching ecosystem services in the Himalayas. These results suggest nurse plant species should be incorporated into conservation policies and management strategies for effective biodiversity conservation and sustainability, especially in the face of climate change.