To investigate optimum silvicultural methods for the maximization of biomass production in intensively cultured short rotation forests of Populus alba × Populus glandulosa, trees with different stand density (1, 000, 2, 000, 3. 000 and 4, 000 trees/㏊) and rotation period (5 and 10 years) were planted at both high and low fertility sites in Dadae Ri, Chungwoon Myun, Yangpyung Gun, Gyunggi Do, Korean, in 1975. The effects of the treatments on biomass production and stand structure of the species were studied in 1979 and 1984. The results of the studies are summarized as follows : 1. Soil conditions at the beginning and ending year of the studies were compared with each other. In 1975, such chemical properties as mineral contents were lower in high fertility sites than those in low fertility sites. However, in 1984, such chemical properties as organic matter content, total nitrogen content, :end mineral content, etc., were higher and such physical properties as the stratification of soil strata and particle structures (single granular to granular) were better than those in low fertility sites. 2. Light conditions at sites of different stand density were analyzed. Reduction rate of the quantity of Photosynthetic Photon Flux Density (PPFD) in low stand density (1, 000 trees/㏊) was very big compared with that in bare land. The quantity (Y) of spectral irradiation of PPFD was linearly and negatively correlated to stand density lX) . Their relationships were presented with the equation, Y=270.5-0.04 X (r=-0.999). The rates of PPFD quantity in the stands with the density of 1,000 and 4.000 trees/㏊ to that in bare land were 19.5% and 9.3%, respectively. Reflection rate (5.6%) of incident light to the leases of the species was similar to transmission rate (5.1%) of it. 3. Residual rates of trees in high fertility sites were relatively lower than those in low fertility, however, their difference was not statistically significant, In high fertility sites, trees showed better growth in height and diameter (1400 and single tree volume (250-3100 than that in Low fertility sites. Stand density that showed the best growth in height was 2,000 and 3,000 trees; ha for high and low fertility sites, respectively. growth in diameter at breast height ;DBH) for 10 years was negatively correlated and stand volume was positively correlated to stand density of the sites. Trees in different stand density showed no statistically significant difference in DBH 4. In the stands primarily harvested 5 Years after afforestation, the numbers of stump sprouts per tree was 3.5 5.5 regardless of site fertility and stand density. The numbers of root sprouts per tree were higher in low ferility and low density stands than those in high fertility and high density stands. Residual rates of the sprouts were 90% and 95% of the number of trees planted in 1975 and that of the stump sprouts, respectively. 5. The growth in Neigh, DBH, and single tree volume in 5 year-old coppice stands was 80%, 80%, and 50% of that in 5 year-old planted stands, respectively. Although the growth in stand volume per hectare increased in accordance with the stand density, increasing rates in coppice stands were far lower than those in planted stands. 6. Biomass production in 10 year-old stands was estimated by site fertility, stand density, and by the parts of trees. The function of log Y = a-b log D²H was considered to be the best fit, w6.ere Y is estimated by weight biomass, D is DBH, and H is the height of trees. Biomass production in high fertility stands (38. 7-94.9 mt/㏊) was 120-140 higher than that in low fertility stands (17.1-39.5 mt/㏊) and stand density was positively correlated to it. While 60-79% of total biomass is distributed to stems and branches of trees, 0.4-4.1% and 18.7-35.9% of it is distributed to leaves and root parts, respectively. In under-ground distribution of biomass, the majority (about 80%) of total weight of roots is distributed to the depth within 30cm