Abstract
The production of knot-free and high-quality wood can be a vital issue in silviculture and forest management. In this study, knot properties, branch occlusion, and wood discoloration were investigated in an 11-year-old Mytilaria laosensis plantation in Guangxi, China, to examine the effectiveness of natural pruning in reducing knot-related defects. A total of 1513 occluded branches from 20 trees were sampled and dissected. Occluded branches were most common at heights of 2–6 m, and the mean diameter of the occluded branches gradually increased with height from the base to 6 m. Linear and generalized linear mixed-effect models were developed to reveal the relationship between branch occlusion and discoloration. The mortality of branches was highest in the third and fourth year and it took roughly three to six years to occlude. The mixed-models indicated that the branch occlusion time was positively correlated with the occluded branch diameter and dead branch stub length, and negatively correlated with the stem radial increment during branch occlusion. Branch discoloration was positively correlated with the occluded branch diameter and branch occlusion time, and was negatively correlated with the branch angle. The probability of wood discoloration also increased with the branch occlusion time. Our findings contribute to a better understanding of the spatiotemporal allocation and internal characteristics of occluded branches, and provide a reference for growing high-quality M. laosensis wood.
Highlights
Regulating the development of tree crowns and their branches is an important method of forest management to promote tree growth
The mean occluded branch diameter showed an increasing trend for this part of the tree. This revealed that the most serious problem with the timber quality of M. laosensis is the knot size and amount, where knots have been identified as an important timber downgrading defect [24]
Our model showed that discoloration length (DL) was positively correlated with the occlusion time (OT) and occluded branch diameter (OBD), and was negatively correlated with exsertion angle (EA), which was consistent with previous studies [14,19]
Summary
Regulating the development of tree crowns and their branches is an important method of forest management to promote tree growth. Silvicultural interventions such as pruning and thinning are commonly applied to improve timber quality and tree growth [1,2]. Branch development can result in knot-related defects on the wood. Knot-related defects mainly result from the decaying portion of knots caused by fungal infections, and greatly affect the appearance, quality, and mechanical properties of the wood [6,7,8], which are important indices in timber grading evaluation. Exploring methods for minimizing the occurrence of dead knot-related defects has become an essential research topic
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