THE CONSERVATION ECOLOGY OF IRIS-ROSSII BAKER (IRIDACEAE), A THREATENED PLANT IN RURAL JAPAN

Spatial distribution, size structure and reproductive activities of a population of Iris rossii were examined in managed secondary grassland with scattered pines and hardwoods. Size structure and fecundity patt erns among individuals were different between the three sites, which w ere an open area, under pine canopy, and under hardwood canopy. Growth and reproductive parameters of the species were significantly differe nt at each site. In the open area, mean shoot number of individuals wa s 9.17, and it was 6.37 under the pine canopy and 5.63 under the hardw ood canopy, Fruit set ratio was 26.8% in the open area, 21.1% under th e pine canopy and 12.1% under the hardwood canopy, Six seedlings were found in the open area and one under the pine canopy, while no seedlin gs occurred under hardwood canopy, Most of the individuals distributed in the sites where the height of herbaceous layer was low, These resu lts suggest that I, rossii can not grow in the closed, especially hard wood, canopies or tall herbaceous layer, Therefore, human intervention s such as annual mowing for the restriction of the growth of dominant grasses and tree saplings are essential for the persistence of the pop ulation of the species.