Branch Development Of Mytilaria Laosensis Plantations In Response To Planting Density

Mytilaria laosensis Lecomte is one of the indigenous broad-leaved tree species of South Subtropical Region in China with the characteristics of growth fast and straight standing tree shape.Branches in the lower stem tend to lose nutrients and were dead gradually,but dead branches were more difficult to fall off from the stem so that more knot was formed and wood quality was affected.Here the effect of different planting density on branch development was examined in an eight-year-old plantation of M.laosensis with five planting densities.Branch quantity?number,proportion?,morphology?diameter,length and angle of primary branch?,position?height and orientation?and branch statues?dead or live?were investigated for 80standard trees and 60 dominant or co-dominant trees after the growth of each tree was measured.One-way analysis of variance?ANOVA?and Duncan's multiple range tests were conducted to explore that different planting density on branch development.It can provide theoretical basis for the improvement of timber quality of M.laosensis.The main results are as follows:?1?The results showed that height of the first dead branch was not significantly affected by planting density.Height of the first living branch increased significantly with the decreasing planting density.Number of dead branches of both standard trees and dominant or co-dominant trees was not controlled by density,but the dead branch rate increased with the increase of density.Living branch number was negatively affected by planting density.?2?The branch diameter,branch length and branch angle under the stem of 9 m of the standard trees of Mytilaria laosensis decreased significantly with the increasing planting density.Branch diameter was reduced to a minimum value of 14.78 mm with the density of2500 stems ha^-1.Branches of low densities(833 and 625 stems ha^-1)were the longest The range of branch angle was roughly 52?57°.The branch diameter and branch length of dead branches of dominant or co-dominant trees under the stem of 12 m decreased with the increasing planting density,which was basically consistent with the results of standard trees.While branch diameter of living branches was not significantly affected by planting density.The proportion of branches in the same density and different branch diameter ranges showed a single peak shape.Both the standard trees and dominant or co-dominant trees all have more branches in the branch diameter range of 10?19.9 mm,branch diameter greater than 40 mm have the lowest branch number.Branch angle of both dead and living branches were all negatively related with planting density.?3?In addition,the same density in the horizontal direction for standard stems,the branch diameter,branch length,branch angle and branch number of different orientation were increased first with the increasing position angle.It has reached the maximum value in a better illumination conditions in the range of position angle?0?90°or 316?360°?.The variation of the branch diameter,branch length and branch angle of dominant or co-dominant trees with the orientation was basically consistent with those of standard trees.Although branch number appears to decrease first and then increase with the increasing azimuth angle,the difference was not significant.In the vertical direction,for standard trees,branch number increased first with increasing relative position.After that,there was no significant changes.Branch diameter and branch length were correlated positively with the increasing height,reached the maximum value at a height of 8m and then there was no significant changes.Branch angle decreased from bottom to top in the vertical direction.Branch diameter,branch length and branch number of the dominant or co-dominant trees were all in positively significant correlation to the branch height below twelve meters.Branch height had significant effect on branch angle.Branch angle decreased with the increasing branch height.Branch diameter was significantly affected by planting density so that the branch diameter can be inhibited by high planting density(2500 stems ha^-1).There existed no remarkable difference in number of total branches and dead branches among five planting densities.Therefore,non-knot timber of Mytilaria laosensis can not be cultivated with density to control the branch number.However,by selecting the appropriate planting density,the knot size can be controlled by control the branch diameter.Considering the input costs and the market value of timber of Mytilaria laosensis,it was concluded that suitable planting density should be selected according to the cultivation purpose.The approach of cultivation for the target-tree was studied,The method which planting Mytilaria laosensis with non-knot timber by artificial pruning could improved the timber value of Mytilaria laosensis.It is necessary to carry out artificial pruning for only dominant or co-dominant trees in the juvenile stage.It was beneficial for improving the timber quality from the most valuable section of the stem.