The Branching Characteristics And Short-term Response Of Tripl Oid Populus Tomentosa Plantation To Pruning

Triploid Populus tomentosa is a fast growing and high yield Poplar Variety with independent intellectual property rights in China.Because of the characteristics of fast growing,high yield,high quality and high efficiency,it has become the main timber tree species in North China.At present,the Triploid Populus tomentosa is widely cultivated in northern China.But according to statistics,the average productivity of forest land is only 14 m3·hm-2·yl,far below the potential productivity of 40 m3·hm-2·y-1 years above.The reason is that there is no good way to cultivate.In view of the extensive management of poplar plantation,the problem of low wood yield and quality,this paper studies characteristics and effects of branch pruning of Triploid Populus tomentosa on growth and physiology,in order to provide theoretical and technical support for the scientific canopy management of Populus tomentosa plantation.Based on the determination of the branching characteristics of 30 Populus tomentosa,including the branch diameter,branch length,branch number,branch angle,azimuth and other indicators,the branching characteristics and canopy structure were analyzed.Secondly,the treatment of different pruning intensity(CK,severe pruning,mild pruning)was carried out by completely randomized block experiment design,and the tree growth(height,DBH,crown width)and physiological characteristics(sap flow,net photosynthetic efficiency etc.)was determinated,The results showed that:(1)The triploid Populus tomentosa branch mainly distributed in the branching between 50°-70°.It is the 49%of all branches.There was a significant effect of canopy position on the branch angle of the first branch(P<0.05),with the decrease of the canopy,the average branching angle increased.The branch of the first azimuth is more than 90°-180°,while the branch of 270°-360° angle is relatively small.The relative branch depth of second branch of Populus tomentosa was larger in the 0.3-0.6 range,it is 67.65%.That is,the branches and roots of the first branch of the second branch are relatively small.The probability of the first branch to grow 2-3 second branches was the highest,it is 37.61%.There was no significant effect of canopy position on shoot diameter ratio(P>0.05).The diameter ratio of the middle branch was the highest,with an average of 0.454.With the increase of the number of branches,the average branch length of the first grade branches of Populus tomentosa gradually increased.(3)In the whole growth season,pruning treatments could not significantly increase the DBH growth of triploid Populus tomentosa(P>0.05),but in mid May to mid June,the DBH of mild pruning was significantly greater than severe pruning and control treatment(P=0.024).Pruning on tree height growth is not significantly affected(P>0.05).Pruning can reduce the triploid central trunk diameter growth,but different treatments had no significant effect(P=0.3).(4)Pruning significantly decreased the leaf area index of three triploid(P=0.014),and the maximum control was significantly higher than that of mild pruning,The leaf area index of severe and mild pruning pruning is close.Pruning had no effect on the sap flow rate of triploid Populus tomentosa.In the whole growth season,sap flow rate of no pruning is relatively large.Therefore,from the results of this study,mild pruning is reasonable pruning intensity.But the tree growth cycle is longer,it is difficult to make a comprehensive evaluation in a short period of time.It is necessary for long-term observation after treatment tree pruning and using various indicators in larger scale comprehensive measure.