Long-term effects of resin tapping on growth and modelling of mature Masson pine (Pinus massoniana)

Masson pine (Pinus massoniana) is essential for timber and resin production in China. This study evaluates the effects of resin tapping on the growth of mature Masson pine in southern China, aiming to develop predictive models for DBH and volume in tapped trees. Eighteen analytic trees were analyzed to assess the impact of resin tapping on radial growth, tree height growth, volume growth, and changes in the experimental form factor. Both linear and nonlinear models described the relationships between root diameter, DBH, tree height, and volume for tapped and untapped trees. Long-term resin tapping significantly inhibited DBH growth without affecting root diameter, diameter at 3.6 m, radius at 1.3 m on the non-tapped side, total height, or annual height growth. However, it reduced total and annual volume growth. The form factor increased with years of resin tapping. The model (DBH = a + b·XD0.1+c·XD0.12+d·XD0.13+e·H) predicted DBH more accurately than other models.The volume model (V = a·(XD0.1+DBH)b×Hc) outperformed traditional models, which included only DBH or root diameter and tree height, in estimating volume. Using growth data from tapped trees and the aforementioned predictive models of untapped trees, the impact of resin tapping on DBH and volume growth of Masson pine can be more accurately quantified.