Beta Diversity Is Better—Microhabitat Diversity and Multiplet Diversity Offer Novel Insights into Plant Coexistence in Grassland Restoration

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Quantifying within-community variability and understanding the related assembly rules are important in developing and assessing grassland restoration. Beta diversity has great potential, revealing mechanisms behind community-level changes in succession. Here, we introduce two simple beta diversity indices: Microhabitat Diversity is the Shannon diversity of patches formed by the locally dominant species, and Multiplet Diversity is the Shannon diversity of subordinate species richness categories detected at a fine scale. Using null models, we tested the biotic filtering effects of dominants on the distribution of subordinates. Based on long-term vegetation monitoring data, we tested the utility of these models in grassland restoration. Sites sown with seed mixture and developing spontaneously were compared and used as test data for exploring the proposed indices. Microhabitat Diversity was larger at spontaneously developing sites, and its local maxima reflected reorganization in the mosaic structure of the community. Species richness categories with zero or one subordinate species were typical in sown grassland, while small 5 cm × 5 cm microsites where 2, 3, or 4 subordinate species co-occured were more frequent in spontaneous succession. Contrary to expectation, a slight convergence of beta diversity measures was revealed after 15 years of succession between passive and active restorations. Microhabitat Diversity and Multiplet Diversity are simple indices that complement existing methods and provide new insights into grassland restoration.