ABSTRACTFacilitation by legume nurse plants increase understorey diversity and support diverse ecological communities. In turn, biodiversity shapes ecological networks and supports ecosystem functioning. However, whether and how facilitation and increased biodiversity jointly influence community structure and ecosystem functioning remains unclear.We performed a field experiment disentangling the relative contribution of nurse plants and increasing understorey plant diversity in driving pollination interactions to quantify the direct and indirect contribution of facilitation and diversity to ecosystem functioning. This includes analysing pollinator communities in the following treatment combinations: (i) absence and presence of nurse plants, and (ii) understorey richness with none, one and three plant species.Facilitation by legume nurse plants and understorey diversity synergistically increase pollinator diversity. Our findings reflect diverse assemblages in which complementarity and cooperation among different plants result in no costs for individual species but benefits for the functioning of the community and the ecosystem. Drivers of network change are associated with increasing frequency of visits and non-additive changes in pollinator community composition and pollination niches.Synthesis Plant–plant facilitative systems, where a nurse shrub increases understorey plant diversity, positively influences mutualistic networks via both direct nurse effects and indirect plant diversity effects. Supporting such nurse systems is crucial not only for plant diversity but also for ecosystem functioning and services.
Litter quality and microtopography as key drivers to topsoil properties and understorey plant diversity in ancient broadleaved forests on decalcified marl