Characteristics Of Tree Knot And Wound Healing After Pruning Of Fraxinus Mandshurica Plantation

The knot is a kind of wood defects,and the number of dead knot and the discoloration of knot are important indexes to evaluate wood grade.Pruning is an important management measure to reduce wood knot and improve wood quality.The effect of pruning is closely related to pruning intensity.Fraxinus mandshurica is an important and precious tree in northeast China.However little is know about the discoloration of knot and effects of pruning on the knot healing.This study selected 49-year-old,20-year-old and 15-year-old Fraxinus mandshurica plantation forest stand to analyze the knot characteristics under the condition of natural pruning and the wound healing process after pruning.The following.results were obtained:(1)Under the condition of natural pruning,the average occlusion time of Fraxinus mandshurica knot was 6.7 years,and about 91%of the knots occluded within 3-11 years.All knots had discolored,and the average discoloration length was 30.9mm.About 93%of the knots' discoloration length was less than 60.0mm.The occlusion time of the knot in the southwest was significantly higher than that in the northeast(p<0.05),but there is no significant difference with that in the southeast and northwest(p>0.05).The occlusion time and discoloration length of the knot increased significantly with the increase of knot height while knot was located below 10.0m(p<0.05).The occlusion time and discoloration length of the knot increased with the increase of the knot diameter,the radius of dead knot and the total radius of knot.When the knot diameter and the dead knot radius exceeded than 15.0mm and 30.0mm respectively,discoloration length of the knot increased significantly.With the increase of knot insertion angle,the discoloration length of the knot decreased significantly(p<0.05).The smaller the insertion angle of the knot,the larger the knot diameter and the radius of the dead knot(p<0.05).In addition,the occlusion time of knot was negatively correlated with stem diameter growth rate during knot occlusion.(2)The knot lifetime increased with the increase of knot insertion height when knot was located below 15.0m,and was also positively correlated with DIBD(distance from birth to death of the knot).The occlusion time of knot was positively correlated with DIOT(distance from death to occlusion of the knot),and increased with the increase of the knot lifetime(p<0.05).(3)The growth of DBH under the condition of 40%-50%pruning intensity was better than that of CK.The wound healing effect of 15-year-old Fraxinus mandshurica was better under 40%pruning intensity,while the wound healing rate of 20-year-old Fraxinus mandshurica was faster under 50%pruning intensity.The smaller the wound diameter and the higher the wound position,the faster the wound healing after pruning.The tree DBH was positively correlated with the wound healing rate.In addition,6 and 16 months after pruning,the wound healing effect of 15-year-old Fraxinus mandshurica was better than that of 20-year-old Fraxinus mandshurica.In conclusion,we recommended that the branch diameter should not exceed 15.0mm when pruning,and the pruning intensity should be controlled between 40%and 50%in order to reduce discoloration risk of the knot and improve the wound healing rate.