The regeneration characteristics of Picea jezoensis and Abies sachalinensis on cut stumps in the sub-boreal forests of Hokkaido Tokyo University Forest

The regeneration characteristics of Picea jezoensis Carr. and Abies sachalinensis Masters on cut stumps in natural forest under selection cutting and natural regeneration were studied in a sub-boreal forest of the Hokkaido Tokyo University Forest. The following points were investigated: (1) what decay class of cut stumps are suitable for regeneration of the two conifer species; (2) what part, either a root collar or a cut surface, of a cut stump is suitable for regeneration; and (3) what percentages of cut stumps support conifer seedlings. The percentages of cut stumps that supported conifer seedlings increased as the decay class advanced, but slightly decreased in the latest stage of decay class, V. Both P. jezoensis and A. sachalinensis seedling densities per cut stump and per square meter of cut stumps increased as the decay class advanced. Some root collars in decay class IV supported A. sachalinensis seedlings, but few supported P. jezoensis. Densities of P. jezoensis per cut surface and per square meter of cut surface in decay class IV were higher than those of A. sachalinensis. On the other hand, densities of A. sachalinensis per root collar and per square meter of root collar in decay class IV were higher than those of P. jezoensis. Cut stumps in advanced decay classes are more suitable for regeneration of P. jezoensis and A. sachalinensis than those in early decay classes. Whereas a cut surface is more suitable for regeneration of P. jezoensis, a root collar is more suitable for regeneration of A. sachalinensis. Cut stumps are not sufficient to ensure enough conifer regeneration because not all conifer cut stumps in advanced decay classes support conifer seedlings.     

Characterization of genes for novel thaumatin-like proteins in Cryptomeria japonica

Thaumatin-like proteins (TLPs) are induced by a variety of phytopathogens in many plants and several TLPs are allergenic. Previously, we isolated three TLP-encoding cDNAs (Cry j 3.1, Cry j 3.2 and Cry j 3.3) from a cDNA library derived from the pollen of Cryptomeria japonica D. Don. Here, we describe three new TLP cDNAs (Cry j 3.4, Cry j 3.5 and Cry j 3.6). We compared the sequences, the genetic map location and the expression patterns of the Cry j 3 genes. The amino acid sequence predicted from Cry j 3.5 exhibits only limited similarity to those predicted from the other Cry j 3 genes. Linkage analysis showed that the Cry j 3.1 to Cry j 3.4 genes are located in the same linkage group, but Cry j 3.5 is located in a different group. Organ-specificity and induction by stresses and plant hormones differed among the Cry j 3 mRNAs. In pollen grains, the Cry j 3.5 mRNA expression level was higher than that of the other Cry j 3 genes. Exposure to UV-B and salt stress induced expression of Cry j 3.1. The ethylene-releasing compound ethephon strongly induced expression of Cry j 3.4. Salt stress and salicylic acid also induced expression of Cry j 3.4. Abscisic acid weakly induced expression of Cry j 3.5. Arachidonic acid strongly induced expression of Cry j 3.4 and Cry j 3.6, and weakly induced that of Cry j 3.3, whereas expression of Cry j 3.1 and Cry j 3.5 was unaffected. These results suggest that the roles of TLPs and the cascades that regulate their expression differ among the members of the TLP family in C. japonica.     

Hardness distribution on wood surface

For better understanding wood hardness, we developed a new hand-operated hardness tester that works with Brinell's method. With this tester we investigated the hardness distribution of wood minutely using a 2mm diameter ball tip. The following results were obtained: (1) On preliminary examination with medium-density fiberboard, we found that the value of Brinell's hardness decreased with the increase in the tip ball's diameter but that it was almost constant with the indenting velocity. (2) By using a small diameter tip, the difference of the hardness became clearer between earlywood and latewood. (3) With radial and tangential sections, we obtained hardness distribution patterns similar to those of wood grain. It seems that the hardness distribution reflects the distribution of density on wood surfaces.     

Effect of moisture content of members on mechanical properties of timber joints

To investigate the effect of moisture content (MC) of members on the mechanical properties of timber joints, bending tests of precut joints and shear tests of dowel-type joints were carried out using timbers of Japanese cedar (Cryptomeria japonica D. Don) with three moisture conditions: green, kiln-dried with a MC target of 15%, and over-kiln-dried with a MC target of 5%. For the bending test, timbers were processed with a precut processing machine into “koshikake-ari” (a kind of dovetail joint) and “koshikake-kama” (a kind of mortise and tenon joint). A pair of members was jointed together without mechanical fasteners. Bolts (diameter = 12 mm) and nails (diameter = 2.45 mm) were used as dowels in the shear test. Bolted joints were constructed with one bolt and two metal side plates. Two nails and two metal side plates were used for the nailed joint. For precut joints, no clear effect of MC was recognized on maximum moment and initial stiffness. The maximum strength of mechanical joints assembled with kiln-dried wood was changed by the degree of drying. Stiffness of the joints assembled with kiln-dried specimens was larger than that of the joints assembled with green specimens.Part of this study was presented at the 7th International IUFRO Wood Drying Conference, Tsukuba, July 2001     

Dynamic excitation and static loading tests of glulam lattice floor

A wooden lattice floor with high stiffness and damping capacity has been developed to solve noise problems in wooden apartment houses. The lattice floor consisted of Douglas fir glulam beams with inserted steel plate joints and drift pins. To examine the structural performance of the floor, dynamic excitation and static loading tests were conducted on the full size floor. The first and second order resonance frequencies of the floor were 13.5Hz and 27.0Hz, respectively. These frequencies are similar to the peak frequency of a conventional wooden floor and the combined floor fabricated from glued laminated timber and iron. The maximum static load of the floor was 127kN. The apparent flexural rigidity was less than half the value of several floors studied in the past. However, it is considered that the stiffness is improved by constructing panels and this floor has almost equivalent performance. Relative deflection was not affected by the loading history.Part of this study was presented at the International Wood Engineering Conference, New Orleans, October 1996.     

Structure and regeneration dynamics of dominant tree species along altitudinal gradient in a dry valley slopes of the Bhutan Himalaya

The aim of our study was to characterize the structure and regeneration dynamics of dominant tree species along altitudinal gradient in dry valley slopes of the Bhutan Himalaya. In the typical dry valley slopes of west-central Bhutan, we analyzed forest stratification, tree crown projection, and population structure from lower dry valley bottom (1520 m a.s.l.) to upper humid ridge top (3370 m a.s.l.) across five major forest types: i.e. (1) dry pine forest with Pinus roxburghii as a dominant species; (2) mixed broad-leaved forest with Quercus lanata (evergreen), Quercus griffithii, (deciduous), and Rhododendron arboreum (evergreen) as major canopy species; (3) evergreen broad-leaved forest dominated by Quercus semecarpifolia, Quercus glauca and Quercus oxyodon; (4) cool conifer forest dominated by Abies densa and Tsuga dumosa; (5) cold conifer forest with A. densa and Juniperus recurva as dominants. In general, regeneration pattern of major dominant species shifted from inverse-J (lower altitudes), to sporadic (mid-altitudes), and to uni-modal type (upper altitudes) corresponding to three regeneration trends: (1) invasive at the lower, warm, dry forest under relatively strong human disturbances; (2) stable/balanced at the mid-altitude, in a relatively stable, mature moist evergreen broad-leaved forest with gap regeneration; and (3) poor/low regeneration at the upper, cool, humid conifer forest with a continuously cattle-grazed understory. Overall, regeneration patterns were balanced in all forest types, however care should be taken to prevent excessive exploitation of dry pine forest of lower valley bottom, and to control cattle grazing at higher altitudes. Our findings can be incorporated into management plans for sustainable management and conservation of mountain forests.     

Persimmon breeding in Japan for pollination-constant non-astringent (PCNA) type with marker-assisted selection

Oriental persimmon (Diospyros kaki) originated in Eastern Asia, and many indigenous cultivars have been developed in China, Japan, and Korea. These cultivars are classified into four groups based on their natural astringency loss on the tree and seed formation: pollination-constant non-astringent (PCNA), pollination-variant non-astringent (PVNA), pollination-constant astringent (PCA), and pollination-variant astringent (PVA). PCNA is the most desirable type because the fruit can be eaten without any postharvest treatment; therefore, one of the goals of our persimmon breeding programs is to release superior PCNA cultivars. The PCNA genotype is recessive to the other three non-PCNA genotypes, and PCNA-type F₁ offspring are obtained exclusively from crosses among PCNA genotypes. Moreover, the number of superior PCNA cross-parents have been limited. In the late 1980s, inbreeding depression became obvious, especially in terms of fruit size, tree vigor, and productivity. To mitigate the inbreeding, a backcross program using PCNA [(non-PCNA × PCNA) × PCNA] was started in 1990. This process, however, was inefficient because only 15% of the offspring were PCNA, and all offspring had to be grown to the fruiting stage. Therefore, molecular markers linked to the PCNA locus were developed for discriminating PCNA offspring. A molecular marker linked to Chinese PCNA has also been developed.     

Effects of management, environment and landscape conditions on establishment of hardwood seedlings and saplings in central Japanese coniferous plantations

There is an increasing need to restore natural hardwood forests in landscapes dominated by monocultural conifer plantations. A convenient restoration approach is to exploit natural regeneration processes. Natural regeneration, however, is affected by diverse interacting factors, for which better understanding is required, in order to optimize restoration programs. To identify optimal management practices for improving natural regeneration of hardwood trees in coniferous plantations, we examined the effects of multiple factors on the abundance of seedlings, small saplings and large saplings (height <0.3, 0.3-1.3 and ?1.3 m, respectively) of hardwood tree and shrub species in both line thinned (LT) and unthinned (UT) plantations of sugi (Cryptomeria japonica) and hardwood forests (HF) in central Japan. The effects of management practices (number of the times of weeding and cleaning, thinning method, years after thinning and forest age), environment (slope position, slope angle and canopy openness), and landscape conditions (distance from nearest hardwood forest, altitude and landuse before planting) on the number of hardwood individuals were examined by using the data obtained from the LT plantations. We also compared hardwood density between LT and UT plantations to examine the effect of line thinning. Finally, we examined species composition of LT plantations and HF to identify hardwood forest components in the thinned plantations. The effects on hardwood regeneration of environmental conditions, landscape factors and management practices applied in the plantations varied, depending on the size class and life form of the regenerating species. The abundance of large saplings of tall tree species was affected by several management factors, especially number of the times of weeding. Landscape conditions (distance from the nearest hardwood forest and altitude) affected the abundance of small saplings and seedlings of tall tree species, but not the other classes. Seedlings and small saplings of many tall tree species that contribute to hardwood forest canopies were less abundant in the LT plantations. The results show that numerous factors affect the establishment and abundance of naturally regenerating hardwood tree species, and suggest that successful establishment during early plantation stages can have long-lasting effects on natural regeneration of tall tree species.