Dynamic modulus of elasticity and bending properties of large beams of Taiwan-grown Japanese cedar from different plantation spacing sites

The effect of plantation spacings (types A-E) on the bending strength and dynamic modulus of elasticity of 41-year-old Taiwan-grown cedar (Cryptomeria japonica D. Don) was investigated. The results indicate that the highest values for the static bending modulus of elasticity (MOE), modulus of rupture (MOR), and dynamic modulus of elasticity (E_D, E _Dt) occurred in trees obtained from those most densely planted (type A); there was a significant difference between type A and the other four spacing types (B, C, D, and E), but there were no significant differences among those four types. Interrelations among MOE, MOR, E _D, and E _Dt could be represented by positive linear regression formulas, which revealed highly significant differences. The relations among the square value of stress-wave transmission velocity (V_t ² and V_t ²⁾ and MOE, MOR, E _Dl, and E _Dt, respectively, could be represented by positive linear regression formulas. The differences were highly significant.Part of this report was presented at the International Wood Engineering Conference '96, New Orleans, LA, USA, October 1996     

Genotypic effects on the variation of wood quality and growth traits in plantation forest made by cutting cultivars of Japanese cedar

We studied the effect of genotypes of planting stocks regarding the variation of the modulus of elasticity of tree trunks on standing trees (trunk-MOE), tree height (TH), and diameter at breast height (DBH) in a 19-year-old Japanese cedar plantation made with root cuttings. Trunk-MOE was assessed nondestructively using a tree-bending method. Genotypes of individual trees were detected using the random amplified polymorphic DNA (RAPD) technique. RAPD analysis revealed that the sampled plantation consisted of 14 genotypes. Genotypic effects on DBH and TH were unclear, and there was no significant difference among genotypes. This result indicated that an acquired variation should have more influence than an inherited variation on DBH and TH. For trunk-MOE, there were significant differences among the four largest genotypes at the 5% level. However the coefficient of variation in trunk-MOE of each genotype ranged from 7.5% to 26.8%. It seems reasonable to assume that the wide variation in trunk-MOE in a sampled plantation may depend on the environmental effect within a clone as well as on the genetic origin of clones. We therefore conclude that the use of multiple planting stocks from different cuttings for which the wood quality is unknown contributed strongly to the wide variation in trunk-MOE in the plantation of Japanese cedar.     

Growth and quality response of Bilinga (Nauclea Diderrichii Merril.) to spacing

The effect of spacing on growth and tree bole quality was examined in a seven year old Bilinga (Nauclea diderrichii Merril.) stand. Four spacings ranging from 2.5 m to 5.0 m, were planted in a complete randomozed block design with three replications. Survival rate was significantly affected by spacing only at age 7. Diameter at breast height (DBH), crown ratio and number of knotty trees increased with wider spacing, while basal area and number of dead limbs increased inversely with spacing. Spacing did not seem to have any significant effect on total height growth. Trends in this study confirm some commonly held beliefs about spacing's effect on tree growth and quality. The results are still of limited application due to the juvenile age of the stand.     

Impact of selective logging on genetic diversity of two tropical tree species with contrasting breeding systems using direct comparison and simulation methods

The impact of selective logging on genetic diversity of two tropical tree species with contrasting breeding systems was examined using direct comparison and simulation methods. Shorea leprosula is a diploid and predominantly outcrossed species, whereas Shorea ovalis ssp. sericea is an autotetraploid species with apomictic mode of reproduction. Direct comparison of adjacent natural and logged-over stands showed reduction of genetic diversity of S. leprosula, but not of S. ovalis ssp. sericea. These results clearly demonstrated that a single logging event would cause the genetic erosion of S. leprosula. However, the apomictic mechanisms and the effects of tetrasomic inheritance of S. ovalis ssp. sericea might be a way of maintaining the level of genetic diversity. These results clearly implied that outcrossing species might be more susceptible to the negative impact of logging on genetic diversity than apomictic species. Simulation studies were conducted using three approaches: (1) simulated-removal of individuals based on diameter size classes; (2) simulated-removal of individuals at random; and (3) simulated-removal of individuals in clump. The simulation study based on the first approach showed that the loss of genetic diversity was higher for the Malayan Uniform System (MUS) compared with the Selective Management System (SMS). This might suggest that SMS is more orientated towards the conservation of genetic diversity. In addition, the simulation study showed that to conserve 100% of the total number of alleles, the tolerable cutting limits of S. leprosula in the 50-ha plot of Pasoh FR should be >85 cm diameter at breast height (dbh). Comparison of simulation studies based on the second and third approaches showed that the loss of genetic diversity was more rigorous if logging activities were anticipated through extraction of trees in clump rather than to extract trees at random. Implications of the studies for conserving and managing the tropical forests are discussed.     

Efficiency of extracting microarthropods from the canopy litter in a Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) plantation: a comparison between the washing and Tullgren methods

We compared the efficiency of washing versus the Tullgren method for extracting microarthropods from dead leaves and branches in the canopy of Cryptomeria japonica trees. Oribatida and Collembola were consistently the numerically dominant taxa of microarthropods, but the relative abundance differed between the two extraction methods. Oribatida accounted for more than 70% of all the microarthropods collected by the washing method but less than 30% by the Tullgren method. Collembola accounted for less than 10% collected by the washing method but about 60% by the Tullgren method. The density of Oribatida was higher when collected by the washing method than by the Tullgren method, and vice versa for the density of Collembola. Our results suggest that the washing method is appropriate for collecting Oribatida and other microarthropods, whereas the Tullgren method is better for collecting Collembola from the canopy litter of C. japonica trees.