Growth Response of Trees with Different Growth Statuses to Pruning on a Pinus massoniana Lamb. Plantation

Pruning is an important technique in culturing good knot-free timber. However, to make more accurate pruning plans, it is necessary to consider the growing status of trees and set reasonable pruning intensities based on this. In a seven-year-old Pinus massoniana Lamb. plantation, we carried out pruning twice with a time interval of two years. The treatments included one unpruned treatment (CK) and five pruned treatments (from P1 to P5, representing the live branch height being kept at 68%, 55%, 60%, 55% and 45% of the tree height). CK, P1 and P2 were conducted in the first pruning in March 2019, and the remaining treatments were conducted in the second pruning in January 2021. The growth investigations were carried out in March 2019, December 2019, December 2020 and December 2021. Another investigation was carried out only for the measurement of live branch heights and crown widths in January 2021 just after the second pruning. The results showed that pruning resulted in a 15.08% to 60.62% increase in diameter growth and an 10.28% to 29.87% increase in volume growth. The stem form was also improved. Significant differences were recorded in live branch heights after green pruning but gradually recovered to the same level in two years by branch senescence. Pruning also resulted in a faster extension of the crown width with an enlarged growing space by the removal of green branches. We highlighted that trees with different growth statuses responded differently to pruning intensities: trees of weak growth statuses grew better under a light pruning intensity, while those with a strong growth status grew better under a severe pruning intensity. Overall, for the seven-year-old young mason pine plantation, keeping four rounds of branches in trees with diameters of less than 8 cm and keeping three rounds of branches in trees with diameters of more than 8 cm were appropriate measures.