Studies On The Growth And Crown Structure Of Poplar Plantations In West Liaoning Province

In this paper, the growth, above-ground biomass, crown structure (including first-order branches, crown form and leaf area distribution) were studied in the 9-year-old poplar stands of various clones, various densities in the west region of Liaoning Province.The difference of growth between the ten clones is significant. The close study on the four selected clones that grow fast (No. 47), intermediately (No. 64 and No. 48) and slowly (No. 51) shows they have same growth pattern, but the amount is different. The fast-growing colnes take longer time to reach quantitive maturity. The amount of the above-ground biomass is relevant to the speed of growth, the allocation among the organs is nearly same. The proportions of the stem biomass to the above-ground biomass are about 75%, the proportions of branches are about 20% and the proportion of foliage are about 5%, but the amount of foliage biomass is not relevant to the the speed of growth. The studies on the crown structure of the four clones show the upper parts of the crown profiles are almost same but the lower parts are different. The sizes of the crowns are proportional to the leaf area. The two factors that affect the leaf growth efficiency are the branch inclination and the vertical distrubution of the leaf area. The crown with small branch inclination in the upper and middle parts of the crown and leaf area distributed lower has the lower leaf efficency.The studies on the poplar stands of various densities show that the growth of the 9-year-old No. 64 poplar is significantly different among the 8 densities, but as to the 9-year-old Zhaolin-6 poplar, the difference among the 8 densities is not significant. Higher density stands reach quatitive maturity earlier than lower density stands, the annual stem volume produced by unit land area of higher density stand is larger than that of lower density stands. Along with increasing of the density, the amount of above-ground biomass of one plant decreases, so is the amount of biomass of stem, branch and foliage, but the proportions of the stem biomass to the above-ground biomass increase and the proportions of the branch decrease. The proportions of the foliage decrease slightly in No. 64 poplar stands and increase slightly in Zhaolin-6 poplar stands. The branches become shorter, thinner and less. The change of branch inclinations is not obvious. Though the leaf area of one plant decreases drastically but the stand LAI increases, the stand of medium density has the biggest stand volume increment. The distribution of the leaf area shifts upwards, the crown depth where the leaf area distribution density is maxium decrease and the portion of leaf area above this crown depth diminishes. The whole-tree leaf efficiency is highest in the stand of medium density.