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Natural populations of Heloniopsis orientalis C. Tanaka, a perennial herb, were examined at two sites from 1991 to 1997. This study addressed the effects of climate on leaf growth early in the growing season, as well as the rate of increase in plant biomass per year, changes in size-class structure, and mortality. Permanent quadrats were located in the Namhansanseong area of Kyonggi-do and at Maranggol in the Kangwon-do area. All correlation coefficients were significant at the 1% level, and were >0.9 for all interactions between leaf length and other properties, i.e., leaf area, leaf weight, and total weight per plant Plant size was correlated with leaf length. Early leaf growth was closely related to the Tn Index (Nuttonson´s Index), with the correlation coefficient being significant at the 1% level. At the stages of 20% and 90% of maximum leaf growth, the Tn indices were 80 and 314℃·d, respectively, at Namhansanseong; 128 and 456, respectively, at Maranggol. The annual Tn indices at 20% leaf growth did not vary much when individual locations were compared. However, the indices at 90% growth fluctuated over time. The Tn index at 10% maximum peduncle growth was around 60℃·d for both areas; at 50% growth, the indices were 170℃·day at Namhansanseong and 160℃·d at Maranggol. However, the two areas had dissimilar Tn indices at 100% peduncle growth. Rates of mean annual increase were 101% over the seven-year period at Namhansanseong, varying year by year. At Maranggol, the mean growth rate was 123% during the four years, with little annual fluctuation. Mean annual growth rates were high for small leaves and low for large leaves. Without recruitment by seedlings, population structures based on plant size were constant in the Namhansanseong area during the seven years, but they changed at Maranggol over the four-year-period. There, the mode shifted from smaller to large size classes over time, and the population structure changed to a normal distribution. At Namhansanseong and Maranggol, mean annual mortalities were 4.1% and 2.8%, respectively. The sizes of the dead plants varied in the former area, but generally were small in the latter. These results show that, for H. orientalis, the Maranggol environment was more suitable for sustaining the population than that in the Namhansanseong area.
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