Abstract
Vegetation surveys with portable point positioning GPS devices were carried out for a specific alien plant, Ludwigia grandiflora subsp. hexapetala, at 132 communities on the shore of Lake Biwa from 2015 to 2016. The relationship between significant wave height and ground level where the alien plant grew was studied using a database of wind speed, wind direction, and effective fetch at six observation stations around Lake Biwa. The main results are as follows: 1) Ludwigia grandiflora subsp. hexapetala was not observed at communities with significant wave height was greater than 18 cm, 2) Ludwigia grandiflora subsp. hexapetala was observed at 55 communities. They were classified into four groups on the basis of the ground level where the alien plant was observed. The submerged type was found in 20 communities (from Biwako Surface Level (B.S.L.) -150 to -50 cm) . The emerged type was found in 14 communities (from B.S.L. -90 to -30 cm) . The ecotone type was found in 15 communities (from B.S.L. -50 to -30 cm) , and the land type was found in six communities (from B.S.L. -30 to -10 cm) , 3) The average significant wave height was 5.5 cm, 9.4 cm, and 13.2 cm, respectively, for submerged, emerged, and ecotone types. The significant wave height might be one of the factors governing the ground level at which the alien plant grows.
