Effects Of Pruning On The Growth And Physiological Characteristics Of Fraxinus Mandshurica Rupr.plantation

Pruning is an important forest management measure to reduce wood knot and improve wood quality,and reasonable pruning intensity is the key to good pruning effect.Fraxinus mandshurica Rupr.is an important precious timber species in Northeast China.To understand the effects of different pruning intensity on the growth and physiological characteristics of F.mandshurica,the 15-year-old and 20-year-old F.mandshurica plantations were selected for pruning in Xiao Jiu Forest Farm in Shangzhi City,Heilongjiang Province and Maoershan Experimental Forest Farm of Northeast Forestry University,using four intensities of pruning branches lower than 30%,40%,50%and 60%of tree height.After pruning,the net photosynthetic rate,stomatal conductance,chlorophyll concentration,nitrogen concentration,and non-structural carbohydrate concentration(NSC)of various organs(leaves,branches,stems and roots)were measured,and the DBH growth of trees was determined.Through the comparative analysis of growth and physiological indicators,the following results are obtained:(1)The annual growth of DBH in both age forests of.mandshurica plantation with 30%-50%pruning intensity was higher than that of the control,while the 60%pruning intensity treatment showed lower annual growth of DBH than the control.The pruning intensity had no significant effect on the average DBH growth of the Fmandshurica plantation.After different intensity of pruning,the diameter growth of the trunk above the wound gradually increased with the increase of the pruning intensity,and the pruning promoted the growth of the trunk above the wound.(2)The net photosynthetic rate of the two forest ages of F.mandshurica plantations was higher than that of the control,and it gradually increased with the increase of pruning intensity at 50%and 60%pruning treatment.The net photosynthetic rate of leaves was significantly higher than that of the control.Different intensity pruning promoted the increase of leaf nitrogen concentration and stomatal conductance.The increase of nitrogen concentration and stomatal conductance caused by pruning may be the main reason for the increase of net photosynthetic rate.(3)In both ages of F.mandshurica plantation,the total non-structural carbohydrate concentration of the leaves after pruning was lower than that of the control during the vigorous growth period(July and August),and the total non-structural carbohydrate concentration of branches,trunks and roots was lower than that of the control in the end of the growing season(September)for most pruning treatments.Especially for the 20-year-old plantation,the total non-structural carbohydrate concentration of fine roots was significantly lower than that of the control during the whole growing season under 60%pruning intensity.High-intensity pruning(60%)results in insufficient supply of non-structural carbohydrate in fine roots throughout the growing season,which will limit the growth of fine roots.Overall,For the young plantation of F.mandshurica,when the pruning was carried out by using the intensity of pruning the branches lower than 30%?60%of tree height,the F.mandshurica was compensated for the adverse effects of pruning by increasing the net photosynthetic rate,resulted in breast diameter growth not being significantly affected.However,at 60%strength pruning,the total non-structural carbohydrate concentration of fine roots was significantly lower than the control throughout the growing season.Therefore,we recommend that the pruning intensity of the young F.mandshurica forest should not exceed to 50%when conducting pruning.