Objective The study aims to explore the spatial and temporal distribution characteristics and discoloration law of Fraxinus mandshurica knot, and establish the predicting model of discoloration length of knot.
Method We selected 16 F. mandshurica sample trees from artificial mixed forests of 49-year-old F. mandshurica and Larix olgensis, and dissected knots with a chainsaw and measured the knot properties using a 20 × magnifying glass in the laboratory.
Result (1) The number of formed knots from 1st to 5th radial growth year accounted for the most, reaching 98.1%; the number of dead knots formed from 6th to 15th year accounted for 94.1%; the number of completely occluding knots from 11th to 20th year accounted for 73.6%. (2) 89.5% knots located below 10.0 m, and 10.5% knots located between 10.1 and 14.0 m of trunk height in the vertical distribution. (3) The discoloration length of knot increased with the increase of knot diameter. When the knot diameter was greater than 15.00 mm, the discoloration length of knot increased significantly. (4) The discoloration length of knot significantly decreased with the increase of insertion angle of knot (P < 0.05), but significantly increased with the increase of radius of dead knot and the occlusion time of knot (P < 0.05). (5) The study filtered three key factors, i.e. knot diameter (KD), total radius of knot (TRK) and occlusion time of knot (OT) , to establish a multiple regression model of the discoloration length of knot by the stepwise regression method: YDL = 1.557XKD + 0.382XTRK + 1.140XOT − 7.523. The correlation reached a significant level.
Conclusion Under the condition of natural pruning, F. mandshurica knot discolors easily. KD, TRK and OT are key factors affecting the discoloration length of knot. When the knot diameter exceeds 15.00 mm, the discoloration length of knot increases significantly. Therefore, when the branch diameter of F. mandshurica exceeds 15.00 mm, pruning should be taken in time.
DownLoad: