造林密度对三倍体白杨杂种无性系胸径和树皮厚度的影响

三倍体杨树具有突出的营养生长优势，研究造林密度对三倍体毛白杨杂种无性系径向生长的影响规律，可为三倍体毛白杨工业用材林营建和经营管理提供理论指导。以定植于河北威县的11年生三倍体白杨杂种无性系（B301、B331和S86）以及二倍体毛白杨对照无性系1316密度试验林为研究对象，研究造林密度（2 490、1 665、1 110、825、615、495株/hm²和405株/hm²）对三倍体白杨杂种无性系胸径和树皮厚度的影响。结果表明，造林密度和无性系以及造林密度与无性系间的交互效应均对三倍体白杨杂种无性系的胸径生长具有极显著的影响，以495株/hm²造林密度条件下三倍体白杨杂种无性系S86的胸径生长量最大，平均胸径达25.1 cm；三倍体白杨杂种无性系B301、S86的胸径生长量显著大于无性系B331和二倍体对照毛白杨无性系1316；无性系对11年生三倍体白杨杂种无性系的树皮厚度具有极显著的影响，造林密度对11年生三倍体白杨杂种无性系的树皮厚度具有显著的影响。三倍体白杨杂种无性系B301、B331、S86以及二倍体对照毛白杨无性系1316内部个体间胸径与树皮厚度均呈现正相关，说明树皮厚度随着胸径生长量的增大而增厚。研究结果对于认识造林密度对杨树径向生长的影响和指导三倍体白杨良种无性系的推广具有重要意义。

Effects of Spacing on the Diameter at Breast Height and Bark Thickness of Triploid Hybrid Clones in White Poplar

Triploid Populus has been proved to have outstanding advantages in vegetative growth over diploids.The study on the effect of spacing on radial growth in triploid hybrid clones of Poulus tomentosa will provide theoretical guidance for the construction and management of triploid Populus plantations.In the present study,effects of spacing(2490,1665,1110,825,615,495,and 405 trees/hm 2)on diameter at breast height(DBH)and bark thickness(BT)were examined by taking 11-year-old triploid hybrid clones(B301,B331 and S86)as research objects and diploid clone 1316 of P.tomentosa as the control in Wei Country,Hebei Province.The results indicated that spacing and clone and spacing×clone interaction had highly significant influences on DBH.The largest growth in DBH(25.1 cm)of triploid hybrid clone S86 planted with 495 trees/hm 2 was observed.The growth in DBH of triploid hybrid clones B301 and S86 was much higher than that of triploid hybrid clone B331 and diploid clone 1316(control)of P.tomentosa.Clonal effect had highly significant effects on BT.Spacing had significant effects on BT.However,positive correlations between DBH and BT in triploid hybrid clones B301,B331,S86 and diploid clone 1316 were observed,suggesting that BT increased as the growth of DBH increased.Our findings will help to understand the effects of spacing on the radial growth and generalize the improved triploid clones of P.tomentosa.