2010 Volume 1 Pages 33-42
Penthorum chinense (Saxifragaceae) is a wetland species whose conservation status is ranked as 'nearly threatened (NT)' in the national red data book of Japan. To determine ecological characteristics of its habitats as the basis for future restoration work, we studied microtopography and plant communities of two natural sites in Kanagawa prefecture, where the species grows in retarding basins. The highest frequency and dominance of P. chinense was recorded in the quadrates located at the water level of 0-20 cm below the ground. Such sites have likely experienced frequent flooding disturbances. In addition, we conducted artificial growth experiments to compare vegetative growth and sexual reproduction of P. chinense under different water-level conditions (i.e., 0 cm, 20 cm, and 40 cm below the ground) and competing vegetation (presence and absence). Penthorum chinense exhibited the most vigorous growth and capsule production when water level was set at 0 and 20 cm below the ground. In contrast, individuals planted at the water level of 40 cm exhibited the much lower production of capsules than those at the 0 and 20 cm levels regardless presence or absence of competing vegetation. With competing vegetation, growth and seedling establishment of P. chinense were extremely suppressed at the 40 cm-level due to the shades created by the perennial tall herbs. We concluded that P. chinense grows best under natural conditions at the open sites where water level was 0-20 cm below the ground and that potential competing species, such as perennial tall herbs, were likely disturbed by frequent flooding. Preservation and restoration of such sites are important for conservation of P. chinense.