Population Structure and Flowering Phenology of Euchresta japonica in University Forest in Chiba,The University of Tokyo

IntroductionEuchresta japonica is an evergreen Leguminosae shrub. Its distribution is limited to Southern China, Cheju Island of Korea and the warm temperate forests of Japan. In Japan, it is distributed mainly in the evergreen broadleaf forests along the Pacific Coast, from Kyushu to the northern limit of Ibaraki Prefecture. Recently, its number is degreasing rapidly, and is anxious for extinction. So we try to conserve this species through the investigations on its population structure and breeding systems.Distribution, vegetation of habitat, individual size, flowering phenology, visiting insects and seed dispersal were studied at University forest in Chiba the University of Tokyo. Here we report about population structure, flowering phenology, visiting insects.Material and MethodThree plots sized 2*2m~10*10m in accordance with their growth area were set. Individual height and remaining rachis after blooming were recorded. Blooming situation was observed at an interval of once for a week from July 3, 2003 till July 24 when all the flowers fell in four plots, and the number of buds, the number of the flower, which was in bloom on the investigation day, the state of each flower, and the number of the fruits were recorded. A observation stand was installed at the side of a plot and action of the insect which visited the flower, a flower-visiting equity volume, and the staying period in a plot were recorded on the timetable on July 16, 17, and 18.Result and discussionStructure of individual size: Mode of the plant height was at 5~9cm on a histogram and individuals higher than 10 was gradually decrease toward 40cm. The size of flowering individuals was over 10cm.Flowering phenology: Each flower has bloomed toward the upper part from under of inflorescence, and although the life of one flower was about 3~4 days. Blooming is continued for about two weeks. There was a peak of blooming flower rate at every plot. It is found that there is a character of synchronization of blooming with surrounding individuals. The rate of fruition is about 10%. However, it can be said that Euchresata japonca has the strategy that it have germinate few seed certainly by high germination rate, with 80% or more by germination test.Flower-visiting insect: Six species (except ants) of visiting insects were identified .Halictidae spp., Colletes pateratus, Bombus diversus diversus, Leptura ochraceofasciata, Artogeia melete, and Nonarthra cyaneum.