Plant Ecology

, Volume 209, Issue 1, pp 95–108 | Cite as

River confluences enhance riparian plant species diversity

  • Takeshi Osawa
  • Hiromune Mitsuhashi
  • Atushi Ushimaru


In riparian zones along the banks of streams and rivers, flooding often causes large changes in environmental conditions immediately downstream of confluences. In turn, spatial heterogeneity in flooding along rivers and streams likely affects local species diversity. Furthermore, flooding during the plant growing season can strongly affect plant survival. In this study, we hypothesized that confluences have impacts on plant species diversity, and that these impacts are larger during the plant growing season. To test this hypothesis, we measured plant species diversity and the extent of natural bare ground at 11 river confluences during two different seasons (summer and spring) within the Mukogawa River basin system, Japan. Species diversity was highest at down-confluence areas in the summer. We linked the pattern of species diversity to that of bare ground creation by floods around the confluences and to the seasonality of annual plant recruitment. The extent of bare ground was significantly greater at down-confluence areas than at up-confluence areas. The recruitment of annual species was higher in the summer than in the spring and included rapid occupancy of bare ground in the summer. We suggest that within river systems, spatial and seasonal differences in patterns of flooding function together to regulate plant species diversity.


Disturbance Flooding Spatial heterogeneity Seasonal matching Temporal matching 



We thank the staff at the Ecology Division of the Museum of Nature and Human Activities, Hyogo, and the staff at the Laboratory of Biodiversity at Kobe University for their valuable support. We also thank the Engineering Bureau of the Hyogo Prefecture Government for providing the water height data set. We also thank Drs. S. Tsuyuzaki and M. Akasaka for commenting on an earlier version of this manuscript. Two anonymous reviewers provided many valuable comments during the review process.


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Takeshi Osawa
    • 1
  • Hiromune Mitsuhashi
    • 2
  • Atushi Ushimaru
    • 1
  1. 1.Graduate School of Human Development and EnvironmentKobe UniversityKobe CityJapan
  2. 2.The Museum of Nature and Human Activities HyogoSanda CityJapan

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