Plant Settlement Patterns and Their Effects on Breeding Sites of Little Terns (Sterna albifrons) on Sand Bars on Ganwol Lake

We analyzed soil characteristics, soil seed banks, and plant communities in a small islet inGanwol Lake from May 2005 to August 2006 to examine the forces driving plant settlement on sand bars andthe effects of plant settlement patterns on nesting sites of little terns (Sterna albifrons). The soil nutrientscontents in a site where the feces of wintering birds accumulate (N: 15.4 mg/kg, P: 10.5 mg/kg, LOI: 0.51%,pH: 6.8) and a site where organic sediments accumulate (N: 20.7 mg/kg, P: 16.4 mg/kg, LOI: 0.40%, pH: 6.6)were much higher those of a control site which was not affected by bird feces and organic sediments (N: 4.1mg/kg, P: 5.4 mg/kg, LOI: 0.41%, pH: 6.7). However, a seed bank was formed only on the site withaccumulated organic sediments. Plant settlement was accelerated by feces from wintering birds and organicsediment accumulation on sand bars in Ganwol Lake. The percentage of area disturbed by human activitiesincreased from 0.2% in May 2005 to 13.9% in August 2006, and the percentage of annual communitiesincreased from 27.5% to 43.3%, but the percentage of open area decreased from 55.2% to 28.0% from May2005 to August 2006. These increases in disturbed area and annual communities decreased the open areafor breeding of little terns. The enlargement of P. communis and T. angustata communities was suppressedby irregular flooding. These results provide useful information for the management of little tern breeding sitesfor conservation purposes.