Dry matter production, population structure and environmental conditions of the spring ephemeralErythronium japonicum growing in various habitats differing in sunlight exposure in cool temperate Japan

Phenology, dry matter production, population structure and environmental conditions were examined in Erythronium japonicum Decne plants growing on the floor of a deciduous broad-leaved Quercus mongolica forest (Q.m. stand), an evergreen coniferous Cryptomeria japonica plantation (C. j. stand) and bare ground left for 3 years after the clearing of a forest composed of young Q. mongolica and Pinus densiflora trees (bare stand) in the cool temperate zone of Japan. The average population density of the plants growing at the Q.m. stand was much higher than that observed at the bare stand, whereas the average number of flowering plants at the former stand was less than half of that at the latter. The population density and number of flowering plants growing at the C. j. stand were both less than 30% of those at the Q. m. stand. The number of seedlings at the Q. m. stand was much more than that at the bare and C. j. stands. Their survivorship rate over 1 year at the former stand also seems to be significantly higher than those at the other stands. Their above ground and below ground parts at the bare stand were exposed to more severe heat and water stress than those at the other two stands. The net production per leaf area of the plants growing at the Q. m. stand was two and six times larger than those at the bare and C. j. stands, respectively. The plants at the bare stand did not use the available solar radiation as efficiently for dry matter production through photosynthesis as those growing at the Q. m. stand, whereas those at the C. j. stand are strongly restricted in their photosynthetic process by the significantly limited light condition on the floor of the evergreen coniferous plantation. The differences in the number of plants reaching sexual maturity, the density and structure of the population and the net production between their three habitats are discussed here from the standpoint of differences in environmental conditions.