At present in Japan, there is a scarcity of large, high-quality timber that is required to construct and repair traditional wooden buildings. This study revealed the history of the policies regulating the production of large timber in Japanese national forests, detected characteristics of the history, and detected future issues of the policy. The basic need of large timber for industrial modernization and armaments in Japan was recognized between the 1870 s and 1890 s. Consequently, a basic guideline for large timber production was established in 1899, and specific measures for sustainable production were established in 1919, but these collapsed in 1940 under the wartime regime. In 1955, a new policy was proposed which changed the purpose of large timber production to the supply of “high-quality timber”, and limited the forest area for production to a “minimum” of approximately 36,000 ha. However, in 1967, the area decreased to < 5,000 ha because of the political pressure on national forests to harvest more timber. A new system was proposed in 1974, but it was abolished in 1991 with the revision of the National Forest Management Regulation, and large timber production was conducted under the general management scheme. Since the fundamental reform of the national forest management system in 1998, large timber production is currently conducted according to each National Forest Regional Office. The government has designated national forests as producers of large timber throughout the modern age, but the nature of large timber production policy has been changing frequently due to the change in the management policy of the national forest. It has also become obvious that some National Forest Regional Offices have not preserved policy documents regarding large timber production. It is important to examine the policy for large timber production that includes non-national forests.

The effects of deer grazing and seed supply from adjacent deciduous broadleaved forests on natural regeneration after clearcutting of a conifer plantation in a warm temperate region were assessed at two sites. A few frugivore-dispersed seeds were dispersed into the clearcut area, irrespective of the adjacent deciduous broadleaved forest. A pioneer species Mallotus japonicus, the seeds of which are dispersed by birds, germinated from buried seeds and became dominant inside the deer fence. Although M. japonicus is not a species that will make up the forest canopy at late stages of succession, it plays an important role in early stages of vegetation recovery. Wind-dispersed seeds, such as those of Zelkova serrata and Carpinus spp., showed large annual variation in seed production; the tree height of regenerated individuals germinated from dispersed seeds exceeded the criteria of tree height 4 to 5 years after construction of the deer fence. Thus, in warm temperate regions, adjacent deciduous broadleaved forests play a certain role in natural regeneration after the clearcutting of conifer plantations. There were few tall tree species, larger than 1.5 m in height, outside the deer fence irrespective of adjacent deciduous broadleaved forests. Thus, to ensure successful natural regeneration in areas with a high population of sika deer, the construction of a deer fence is needed when plantations are clearcut.

Population expansion of sika deer (Cervus nippon) and the resulting increase of debarking have been reported throughout Japan. For effective management of such debarking, the factors that determine the intensity of debarking should be clarified by each management unit. In this study, we analyzed the relationship between the sight per unit effort (SPUE) of sika deer, which is one of the density indicators of sika deer, slope, snow depth, tree diameter at breast height, tree species, and the occurrence probability of debarking by sika deer at a stand unit and an individual tree unit. The analyses were conducted in Gifu Prefecture, Yamanashi Prefecture, Tochigi Prefecture, and nine prefectures around the Kanto region. The occurrence probability of debarking at a stand unit initially increased with the increase of snow depth but decreased in deeper snow depth. The effects of SPUE and slope on the occurrence of debarking at a stand unit differed among prefectures. The occurrence probability of debarking at an individual tree unit increased with the increase of SPUE and deer preference of debarking by tree species was generally similar among prefectures. In conclusion, factors that determine the intensity of debarking were mainly common among prefectures in the Kanto region.

This study aimed to estimate the tree height and volume based on image data, which are obtained by conversion of the sound generated from hammering a stem using deep learning. We hammered 20 trees 100 times, recorded the hammering sound, and generated the spectrogram, which presented the sound pressure at each frequency for 0.6 s. Data comprising 10,000 images were loaded into a deep learning model. We used the Neural Network Console (NNC) as the deep learning system and the LeNet, which forms a programmed regression layer to an output layer, as the deep learning algorithm. We divided 10,000 images into 5 equal sets, and performed three learning patterns (LP-I, LP-II, and LP-III). LP-I used the four sets as training data and the remainder as test data, LP-II used three trees and LP-III used six trees, which select for each tree from three divisions (large, medium, small), as test data. A performance evaluation of the proposed model was performed using three indicators: mean absolute error (MAE), mean absolute percentage error (MAPE), and coefficient of determination (R²). Each learning pattern provided very good estimates (R² values for each learning pattern for the test data ranged from 0.9192 to 0.9996), except for the height estimate by LP-III (R²＝0.3672). LP-III generated very poor height estimates with a bias and tended to underestimate by > 30 m and overestimate by < 30 m. However, each learning pattern provided a good estimate of the tree volume, generally without any bias. Thus, we found this method to be more effective for estimation of tree volume than tree height.

I evaluated the effects of horticultural soil application, depth of sand deposition, and codling moth attack on survival and growth performance of containerized seedlings of Japanese black pine, Pinus thunbergii (Pinaceae), during the first year after planting, in order to examine the reforestation planting techniques for sand-gravel deposition areas generated by a typhoon storm surge. Electronic conductivity and ion concentration indicated that sand-gravel sedimentation had no harmful salinity for the seedling growth even five months after the occurrence of typhoon. Generalized linear model analysis revealed that more seedlings failed to survive with no horticultural soil application. The height and diameter growth of black pine seedlings were negatively affected by codling moth attack on winter buds. The diameter growth was negatively affected by sand deposition depth whereas a positive effect was observed due to application of horticultural soil. Significant increase was observed in the diameter growth of these seedlings upon the application of 3 L of horticultural soil per seedling as compared to that of 1 L application per seedling. Thus, I conclude that increased horticultural soil and enhanced protection against codling moth are required for better growth performance of black pine seedlings at deeper sand-gravel deposition sites.

In this study, we aimed to evaluate the risk of pine wilt disease (PWD) caused by the pinewood nematode (PWN) due to the trimming of pine twigs. For this, we determined if the pine twig trimming attracts the adults of the Japanese pine sawyer (Monochamus alternatus), a potential vector of this disease. Twelve healthy pine (Pinus densiflora) trees (six each in the treatment and control group) were selected as test trees. Twigs of the six individuals in the treatment group were intensively trimmed in mid-July 2020. Feeding wounds and oviposition scars created by M. alternatus following trimming were compared between the treatment and control groups. The number of feeding wounds did not significantly differ between the two groups (mean, 4.7 and 4.0 per tree). However, oviposition scars were observed only in the treatment group (mean, 1.8 per tree), indicating a significant treatment effect. Conclusively, the pine twig trimming attracts the mature females of M. alternatus for oviposition, thereby increasing the possibility of PWN transmission into the pine trees. Accordingly, to reduce the risk of PWDPWN, twig trimming should be avoided during the season when females carry many nematodes.

An object detection model for detecting the cones of Abies sachalinensis on the tree crown using images shot by unmanned aerial vehicles (UAV) was developed. We used the image recognition algorithm "You Only Look Once (YOLO) v4" based on a convolutional neural network and examined its accuracy. Training was performed using 356 pictures with 6,138 cones, and the constructed model was adapted to 92 validation pictures with 1,692 cones. As a result, an average precision (AP) of 88.5％ was obtained. However, small white round objects were often detected as cones (false positives) and densely situated cones were not detected (false negative). Improvement of those misdetections will be future subject. We conclude that cone detection of A. sachalinensis using YOLOv4 is possible, and the model will be useful to confirm cone producing individuals in seed orchards.