Plant species richness and composition under different disturbance regimes in marginal grasslands of a Japanese terraced paddy field landscape

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AbstractQuestionHow are the patterns of species richness and composition in marginal semi‐natural grassland habitats maintained by different disturbance regimes characterized by location and agricultural management practice?LocationA terraced paddy field landscape in southeastern Niigata Prefecture, Japan (37°06′N, 138°49′E).MethodsWe recorded species occurrence within five 1 m × 1 m quadrats at each survey site from four different habitat types: paddy levees (Levee); slopes between paddies and farm roads (i.e. entrance slopes of paddy fields; Slope_Road); slopes between paddies (Slope_Paddy); and slopes between paddies and adjacent woodlands (Slope_Woodland). We compared species composition among the habitat types using non‐metric multidimensional scaling (NMDS). We then classified plant functional groups (PFG) based on four response traits: growth form, life span, plant height and flowering season, and compared richness patterns of PFG among the habitat types using analysis of covariance.ResultsThe estimated total richness was over 220 species in Slope_Paddy, Slope_Woodland, and Slope_Road, including more than 35 grassland species in each habitat type. Species composition at Levee habitat was significantly different from that at the other three habitat types as revealed by the NMDS axis 1 scores. The NMDS axis 2 scores for Levee and Slope_Road habitats were significantly different from those for Slope_Paddy and Slope_Woodland habitats. Species richness patterns along with the ten PFGs investigated in this study were also significantly different among the habitat types. Levee and Slope_Road habitats were characterized by a number of annual species, whereas tall perennial forbs, especially pteridophytes, characterized Slope_Paddy and Slope_Woodland habitats.ConclusionsWhile some species occurred in all four habitats, habitat specialists characterized by specific PFG responded to different disturbance regimes in each habitat type. The four types of marginal semi‐natural grassland play different roles as habitats for a variety of herbaceous species, including typical semi‐natural grassland species. These habitats make up the complex landscape mosaics of terraced paddy fields and contribute to the overall biodiversity of these landscapes at the regional scale.