Effects of temporal grassland continuity on plant diversity and species composition in geographically diverse communities

Abstract Semi-natural grasslands, which support high biodiversity, are declining worldwide, underscoring an urgent need to identify high biodiversity grasslands that should be prioritised for conservation. We previously reported that grasslands with longer temporal continuity in a single region in Japan have higher plant diversity. To confirm the generality of this finding, we targeted three regions (40 to 90 km apart) in central Japan, including the previously-studied area. We first traced vegetation changes since the 1910s to the present in and around ski-run grasslands, and then examined the effects of vegetation history on plant communities. We surveyed plant communities using transects at five to eight sites in each of three vegetation types: "old grasslands", which are estimated to have persisted for 110 to several thousand years, "new grasslands", which were created by deforestation 45 to 89 years ago, and forests adjacent to those ski runs, in each region (total, 58 sites). The number of rare grassland species and native grassland species were highest in old grasslands. Species composition differed markedly between old and new grasslands, with the beta diversity as high as nearly half of that across all three regions. Numbers of indicator species were 21 and 4 for old and new grasslands, respectively, indicating that many plant species depend on old grasslands. Indicator species that were more frequent in old grassland were perennials, had purple flower color, and tended to have well-developed rhizomes. The strong effect of vegetation history across these three regions clearly verified the high conservation priority of grasslands with long temporal continuity.