Yield regulation, including cutting volume restriction, is indispensable for sustainable forest management. Under the Collective Forest Management Plan (CFMP) in Japan, the allowable cutting volume restriction of forest stands is defined by a formula similar to the Austrian formula. We examined two scenarios for the development of a CFMP-for each forest compartment or for each municipality-for 220,521 ha of all non-national forests in Tochigi Prefecture, eastern Japan. The allowable cutting volume and the proportion within it of clearcutting volume were calculated for two five-year periods. Analysis of the single-compartment-CFMP scenario indicates that the clearcutting of all available volumes was allowed in compartments with a low ratio of potential harvestable forests to total forest. However, clearcutting based on the currently permissible lot size was sometimes not allowed owing to severe cutting restriction in compartments with a high ratio of potential harvestable forests to total forest. In contrast, in the entire-municipality CFMP scenario, the clearcutting volume was mostly congruent with the allowable cutting volume; intensive large-scale clearcutting in a compartment was mostly allowed in the entirety of Tochigi Prefecture. The allowable cutting volume restriction of CFMP thus has disadvantages in both single-compartment and entire-municipality CFMP and is not an appropriate rule for regulating clearcutting under various regional forest conditions.

To establish guidelines for the reliable production of straight Melia azedarach timber up to 4 m long without knots or discoloration, the relationship between planting density and pruning time was examined. Artificial M. azedarach stands (3,000 trees ha⁻¹) were pruned 3 years after planting and the branch stubs were removed completely. This resulted in no discoloration around stubs that were below 2 cm in diameter within 1 year after pruning. However, discoloration occurred in 78–100％ of branch stubs greater than 2 cm in diameter, which also required more than 2 years for occlusion. There was an average of approximately ten branches (live and dead) per tree and they were distributed around the top, which was 0.2–5.2 m in height for three planting densities (3,000, 5,000, and 7,000 trees ha^－1) without pruning for 3 years. The number of branches above 2 cm in diameter and the proportion of live branches were highest in the low-planting-density stand. These results suggest that the optimal timing for pruning of M. azedarach is within 2 years after planting before the diameter of branches and the tree height exceed 2 cm and 4.5 m, respectively. In addition, the optimal planting density of the species is 5,000 trees ha^－1 due to the high probability of crooked trunks at lower planting densities.

To investigate the effects of feeding damage caused by the folivorous insects Fagineura crenativora and Quadricalcarifera punctatella on the xylem of current-year shoots of Japanese beech, we clipped leaves from beech trees at different intensities and seasons. At clipping treatment in May simulating F. crenativora feeding, the xylem vessel mean inner diameter and theoretical specific water conductivity (K_st) decreased, while vessel density increased as clipping intensity increased. This tendency increased in beeches growing under water stress. On the other hand, although intense clipping in June simulating Q. punctatella feeding also affected xylem structure of trees under water stress, there was no effect under suitable water conditions. Based on these results, defoliation by F. crenativora larvae might more affect the xylem structure of Japanese beech, especially in trees under water stress than defoliation by Q. punctatella.

A provenance test stand of Abies sachalinensis, a major plantation woody species in Hokkaido, was severely damaged by a typhoon in 2016. Because this was a valuable opportunity to evaluate the inter-provenance variation in the susceptibility of trees to wind damage, we conducted a field study to assess the tree damage caused by the typhoon. The 37-year-old provenance test stand was located in the southern part of Hokkaido. Of the 1,594 trees in the test stand, 892 (52.6％) were damaged by the typhoon. Uprooting of trees was the most prominent damage, accounting for 47.7％ of the damaged trees. According to the model analysis, provenance was a significant factor associated with the occurrence of damage, indicating the clear inter-provenance variation in wind damage. Trees in South and West provenances, proximal to the test stand, and Eastern Edge provenance, distant to the stand, were resistant to wind damage. The difference in the ratio of intact trees to total trees among provenances was more than 50％ (72.6％ in the South provenance and 20.4％ in North provenance). It was suggested that inter-provenance variation in wind damage might be derived from local adaptation and/or genetic variation in the wind tolerance.

The genetic diversity and genetic structure of B. xylophilus in 8 populations of the Kyushu region were elucidated using the nucleotide polymorphism of 10 EST loci. Considerable genetic differences among regional populations were observed with the gene differentiation (G_ST) of 0.53, which showed that more than half of the total gene diversity (H_T＝0.63) was possessed among regional populations. The H_T values of 8 regional populations were between 0.12 and 0.59. Sendai, Shintomi, Matsuura, and Karatsu populations were rich in gene diversity (0.59, 0.57, 0.56, and 0.55), and their high G_ST (0.43, 0.35, 0.25, and 0.25) indicated that the genetic compositions were notably different among the populations within damaged trees (subpopulations). On the other hand, in Amakusa and Miyazaki populations, extremely low gene diversity (0.12 and 0.18) and small G_ST (0.01 and 0.02) were confirmed, which showed that little genetic difference existed among subpopulations. It seemed that a bottleneck effect or founder effect had a great impact on the formation of these regional populations. The genetic diversity of the regional populations was polarized in Kyushu.

To explore adaptive sapling types, with the goal of low-cost silviculture, we examined survival rates and growth in height of Japanese cedar and hinoki cypress saplings for five years (partly four years) at 13 sites in Japan. We tested normal bare-rooted saplings, large bare-rooted saplings (height ＞60 cm), and saplings grown in multi-cavity containers, vinyl pods and ceramic pipes. All the saplings originated from seedling or cutting. As for Japanese cedar, the large bare-rooted saplings originating from seedling showed the greatest growth in height among all sapling types, and the saplings from seedling showed significantly greater growth in height than the saplings from cutting. The hinoki ceramic-pipe sapling showed a significantly lower survival rate than all sapling types and less growth in height than the normal bare-rooted hinoki cypress saplings. The GLMM analyses for Japanese cedar showed that the height growth rate of the saplings was affected by the frequency of weeding, the sapling type (bare-rooted, multi-cavity container or pod), and their origin (seedling or cutting). Our results suggest that large bare-rooted saplings of Japanese cedar may contribute to reducing the cost of reforestation; however, it has specific requirements, such the vicinity of roads for their installation.