Branch Occlusion and Discoloration under the Natural Pruning of Mytilaria laosensis

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.

Genetic diversity and structure among natural populations of Mytilaria laosensis (Hamamelidaceae) revealed by microsatellite markers

Mytilaria laosensis is a fast-growing tropical broadleaf tree that is extensively used for wood production and has significant ecological benefits. To investigate the genetic diversity and population structure of M. laosensis, eight major natural popu­lations in China were analyzed by using simple sequence repeat (SSR) markers. A total of 88 microsatellite-containing fragments were obtained by the method of magnetic bead enrichment, among which 26 pairs of SSR primers were scree­ned out and used to generate a total of 190 alleles among 152 individuals. The average of observed number of alleles, Shannon’s information index and polymorphism information content per locus were 18.3, 1.1577 and 0.7759, respectively, implying a high level of genetic diversity in M. laosensis popu­lations. The variation within populations accounted for 81.74 % of total variation based on analysis of molecular variance. Clus­ter analysis divided the eight populations into four groups, among which five populations from the southern parts of Guangxi province were classified as one major group. Mantel test showed that there was highly significant correlation bet­ween Euclidean genetic distance and geographic distance, suggesting that geographic isolation contribute to the high genetic diversity of M. laosensis. Together, these could provide support for the feasibility of exploration and utilization of M. laosensis in subtropical areas of East Asia including Jiangxi, Hunan and Fujian province of China.

Effects of Ozone and Drought on Biomass Allocation of Four Seedlings in South China

Seedlings ofMichelia macclurei,Cinnamomum camphora,RhodoleiachampioniiandMytilaria laosensiswere placed in open-top chambers (OTC) with three ozonic treatments including E20 (20 ppb), E40 (nature air, 40 ppb) and E160 (160 ppb) and two water treatments. Root biomass, stem biomass and leaf biomass total biomass and root/shoot ratio of four seedling types were evaluated. The results showed that there were no significant differences in impacts of ozone stress and drought stress on root, stem, leaf, and total biomass ofM. macclureiamong different treatments. The biomass ofM. laosensisdecreased with increasing ozone concentration, whereas biomass ofC. camphoraandR. championiichanged irregularly. Most of the biomass of four kind seedlings under ozone and drought intercross stresses was lower than those under ozone stress. The root/shoot ratios of four seedling species were all low. The ratios under high concentration ozone (160 ppb) were lower than the control treatment. And the ratios of different treatments under drought were lower than those were not under drought when they were under the same concentration of ozone.

Optimization of Sanding Parameters for Wood Surface of Plantation-Mytilaria laosensis

In order to analyze the relation between wood surface roughness of plantation-Mytilaria laosensis and sanding parameters, two orthogonal experiment were performed. The results show that the mesh of the sandpaper has remarkable influence on wood surface roughness of plantation-Mytilaria laosensis,but the feeding speed and sanding thickness don’t; when the mesh of the sandpaper is 150, the feeding speed is 7 m/min and sanding thickness is 0.6 mm during the first sanding and the mesh of the sandpaper is 240, the feeding speed is 8m/min and sanding thickness is 0.15mm during the second sanding, the smallest roughness (Ra) was obtained as 2.79μm. Considering production efficiency, changing feeding speed into 9 m/min in the theory optimization scheme, engineering optimization scheme was obtained, and the wood surface roughness (Ra) is 2.80μm.

Research and Evaluation on the Planning and Sanding Properties of Mytilaria laosensis

In this paper, the planning and sanding properties of Mytilaria laosensis, compared with Castanopsis hystrix, were tested. The properties were conducted according to the criteria ASTM D1666-87. The results show as follow: the planning and sanding properties of Mytilaria laosensis and Castanopsis hystrix all show excellent; in the evaluation system for full marks 5 points, the planning marks of Mytilaria laosensis and Castanopsis hystrix was separately 4.8 points and 4.7 points, and the sanding marks was separately 4.47 points and 4.3 points, so the planning and sanding properties of Mytilaria laosensis were slightly better than Castanopsis hystrix; feeding speed had remarkable influence on the planning properties of Mytilaria laosensis and Castanopsis hystrix; The wood quality had important influence on the sanding properties.

The Experimental Research on the Sound Absorption Coefficient of Several Different Mytilaria Laosensis Veneering Boards

The composite acoustics board with pore-tank structure and variable cross section structure are made of Medium Density Fiberboard(MDF) as base material, Mytilaria laosensis sheet as veneer board, and sound absorption mat as the substructure material with the micro-perforation interlayer structure. The test was carried out to compare the absorption coefficient of Mytilaria laosensis sheet and nine samples by standing wave tube The test result shows that Mytilaria laosensis sheet has a low sound-absorbing performance itself, and its sound-absorption coefficient in all frequency ranges less than 0.3 and cannot be used as the sound-absorption board alone; The variable cross section structure sound-absorption board has a better performance than the pore-tank structure; When using the micro-perforation layer structure, the sound absorption board performs better and the sound absorption coefficient improves markedly in middle and low frequency scope.