The conservation ecology ofIris rossii Baker (Iridaceae), a threatened plant in rural Japan

Abstract

Spatial distribution, size structure and reproductive activities of a population ofIris rossii were examined in managed secondary grassland with scattered pines and hardwoods. Size structure and fecundity patterns among individuals were different between the three sites, which were an open area, under pine canopy, and under hardwood canopy. Growth and reproductive parameters of the species were significantly different at each site. In the open area, mean shoot number of individuals was 9.17, and it was 6.37 under the pine canopy and 5.63 under the hardwood canopy. Fruit set ratio was 26.8% in the open area, 21.1% under the 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 seedlings occurred under hardwood canopy. Most of the individuals distributed in the sites where the height of herbaceous layer was low. These results suggest thatI. rossii can not grow in the closed, especially hardwood, canopies or tall herbaceous layer. Therefore, human interventions such as annual mowing for the restriction of the growth of dominant grasses and tree saplings are essential for the persistence of the population of the species.