IDENTIFICATION OF CONSERVATION MEASURES TO PROTECT THE JAPANESE ENDANGERED PLANT-SPECIES ASTER KANTOENSIS

To identify the factors responsible for degrading the habitat of the e ndangered plant species Aster kantoensis, as well as the vulnerable li fe stage where this occurs, we carried out sowing experiments. Two nat ural habitats were simulated, being situated along the floodplains of the Tama River in central Japan. Seeds collected from a natural habita t were sown in two apparently suitable locations (Tomoda and Ishida si tes). Germination, survival, growth, and seed production were subseque ntly monitored from 1993 through to 1997. The Tomoda site was a gravel bar in floodplains formed by flooding in 1991, while the Ishida site (two plots) was one gravel bar where several plants were growing spars ely and another where a population had become extinct in 1992. Seed co horts completed their life cycle within 3 years at the Ishida site and within 5 years at the Tomoda site. Monitored parameters at Ishida wer e substantially lower than those at Tomoda. In addition, estimates of population growth indicated an increase at Tomoda and a rapid decrease at Ishida. However, degradation of habitats seemed to occur at Tomoda over the monitored periods. In view of our results, we conclude that natural germination of about 0.13% is needed for increasing population size. The major factors for decreasing population size are believed t o be the lack of safe sites for germination and seedling establishment in old habitats (> 10 years). Conservation measures are suggested bas ed on these findings.