Facilitation of plant species richness and endangered species by a tussock grass in a moist tall grassland revealed using hierarchical Bayesian analysis
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Using hierarchical Bayesian analysis, we tested the hypothesis that a perennial tussock grass, Ischaemum aristatum var. glaucum, facilitates the species diversity of vegetation and the regeneration of individual native vascular plants in Ukishima Marsh, a moist tall grassland of eastern Japan. We analyzed microscale distribution patterns of sympatric plant species in response to ground height. Both the species richness of the whole plant assemblage and the occurrence of many native vascular plants, including two endangered species, were positively correlated with ground elevation, which was directly mediated by I. aristatum var. glaucum tussocks and/or the occurrence of mosses on tussocks. Susceptibility to late spring inundation of microsites on the tussocks was significantly lower than that on bare ground. These results suggest that the facilitation by I. aristatum var. glaucum contributes to maintaining the high species richness of the marsh. Consideration of the facilitation among native vascular plants is necessary for establishing sound conservation plans of wetland vegetation.