METHODS

1 Study sites and grasslands The data were obtained at 484 grassland permanent quadrats in 28 grasslands in 17 sites. These grasslands cover from sub-arctic zone to warm temperate zone in Japan (Fig. 1). Furthermore, these grasslands cover major artificial and semi-natural (including Miscanthus grassland and Zoysia grassland) grasslands.in Japan. We showed detail data for each site in Table S1 and for each grassland in Table S2 (in Supporting Information pdf). Fig. 1. Distribution of 17 sites over Japan It is shown that the number after a site name has two or more investigated grasslands at each site (refer to Table S2) 2 Field method A Permanent Quadrats Twelve or twenty quadrats were established in each grassland excluded some grasslands. At each grassland, we conducted survey at almost the same season in every census year (see Table S2). Census season was from late spring to autumn. Each quadrat size was 1 m2 (1m × 1m). B Data collection We measured in each quadrat as follows: Plant coverage (%): Total area which live plants occupy in each quadrat Community height (cm): Mean height of plant community in each quadrat Number of species: Number of vascular plants occupies emerged in each quadrat C (coverage) *: Coverage of each plant species in each quadrat L (plant length): Maximum plant length of each plant species in each quadrat *Coverage was measured with one of two styles. One was percentage cover (%) and the other was the cover-abundance scale modified Braun-Blanquet (Table 1.) 3 Taxonomy and Systematics Most botanical identifications were made in the field and recorded in Japanese common names (in the original data basese). Scientific names followed Ohwi and Kitagawa (1992) at first. If we cannot specify in it, we followed Japanese Soc. of Grassland Sci. (2000), Shimizu (2003) and Shimizu et al. (2008). A large majority of plants were identified to species-level including subspecies and varieties. For some species, the minimum identification level varied. For example, it was identified to genus-level (ex. Taraxacum sp.) or family (ex. Gramineae sp.) only. Furthermore, Bryophyte plants recorded as Bryophyta sp. If it was not able to be identified, we recorded as unknown sp.