The influence of changes in the degree and frequency of disturbance on the annual salt marsh plant (<i>Suaeda maritima, Artemisia fukudo</i>) communities in estuarine tidal flats: A case study of the Kushida River in Mie Prefecture, Japan

Abstract

In this study, we examined the influence of changes in the degree and frequency of disturbance in estuarine tidal flats on the annual salt marsh plant communities (Suaeda maritima, Artemisia fukudo) in Mie Prefecture, Japan. Suaeda maritima and Artemisia fukudo communities occur in the branch river of the Kushida River. Although the areas occupied by these communities were very small in 2006, the Suaeda maritima community expanded significantly to 3609 m2 in 2008, and the Artemisia fukudo community expanded significantly to 2726 m2 in 2008 and 10,396 m2 in 2010. Before the onset of the investigation period in 2006, the overflow warning water level (3.5 m) and the flood fighting corps standby water level (3.0 m) each occurred on one day in August 2004 and October 2004, respectively; at those times, the water volume exceeded 1000 m3·s-1 and 1500 m3·s-1, respectively. We suggest that because much of the estuarine tidal flat erodes when the water volume exceeds 1000 m3·s&#451, the establishment of the Suaeda maritima and Artemisia fukudo communities is delayed until sufficient substrate is formed by the deposition of new sediment. In contrast, a water level of 2 - 3 m was observed on one day each in 2005, 2007 and 2009, with average water volumes of 488.5, 566.4 and 690.1 m3·s-1, respectively. We suggest that following the repeated disturbances caused by water levels of 1 - 3 m and flow volumes of 500 - 700 m3·s-1 over the bare ground exposed after flooding and erosion, Suaeda maritima is a pioneer species that colonizes on bare ground deposited by sediment transported from upstream and the sea during high tides, and following the same level of disturbance, Artemisia fukudo is secondary colonizer that has germinated and grown on the sediment deposited on the Suaeda maritima community.