In this study, the bending strength properties of finger-jointed (FJ) sugi (Cryptomeria japonica), hinoki (Chamaecyparis obtusa), and ezomatsu (Picea jezoensis) lumber having finger lengths of 17, 6.3, and 3.7 mm were investigated. Additionally, the bending strength properties of the hinoki FJ lumber with finger lengths of 6.5 and 6.7 mm were investigated. The following results are obtained. (1) There was no difference in the bending strength of the sugi FJ lumber with finger lengths of 17 and 6.3 mm. (2) No difference was observed in the bending strength of 17- and 6.3-mm hinoki FJ lumber composed of sawn lumbers with a bending Young's modulus of less than 14 kN/mm². For FJ lumbers composed of sawn lumber with a bending Young's modulus of 14 kN/mm² or more, the bending strength of FJ lumber with finger length of 6.3 mm was slightly lower than that of FJ lumber with finger length of 17 mm; however, the bending strength of FJ lumber with finger lengths 6.5 and 6.7 mm was equivalent to that of FJ lumber with finger lengths of 17 mm. If finger pitch is the same, the longer the finger length is, the larger the adhesive area; thus, it is considered that the bending strength of 6.5- and 6.7-mm FJ lumber is higher than that of 6.3-mm FJ lumber for larger adhesive area. Additionally, by setting the feed per knife during cutting to 0.50 mm, the bending strength of FJ lumber with finger lengths of 6.5 and 6.7 mm was significantly improved. (3) The bending strength for both sugi and hinoki FJ lumber with the finger length of 3.7 mm was low. (4) For ezomatsu, the bending strength of 17-, 6.3-, and 3.7-mm-length FJ lumber was the same.

View full abstract

Long-term monitoring of radiocesium (¹³⁷Cs) contaminations in the bark and wood caused by the Fukushima Dai-ichi Nuclear Power Plant accident in 2011 requires partial sampling from a standing tree without felling it. Because ¹³⁷Cs distributions within the bark and wood are assumed not to be uniform, it is necessary to understand the observational errors in ¹³⁷Cs concentration caused by partial sampling and to check the validity of this method. The objectives of this study are to examine 1) the circumferential distributions of ¹³⁷Cs concentration in the bark and wood and 2) the observational errors in ¹³⁷Cs concentration determined via partial sampling compared with bulk (felling) sampling. The circumferential distributions were investigated by dividing the tree stems collected in 2015 into eight directional segments (four segments for small trees). The relative standard deviations of the ¹³⁷Cs concentration among the directions (the mean of all trees) were 34% and 13% for the bark and wood, respectively. The patterns of the circumferential distributions were not biased toward a specific direction and were not speciesdependent. Partial sampling was achieved by collecting bark pieces (3 cm × 3 cm) from four directions and wood cores (12 mm in diameter) from 1–2 directions during the period of 2016–2020. The observational errors caused by the partial sampling were estimated to be approximately 38% and 8%–18% for the bark and wood, respectively, and were considered random (unsystematic). These results indicate that, for example, to estimate the mean value of the ¹³⁷Cs concentration in the bark in a forest stand with the same accuracy as the bulk sampling with n = 3, n for the partial sampling should be increased to 6–8.

View full abstract

The distribution of naturally occurring cesium-133 (¹³³Cs) in soil can be used to predict soil-to-plant transfer of cesium-137 (¹³⁷Cs was released during the 2011 Fukushima accident). However, when the distributions of ¹³⁷Cs and ¹³³Cs differ with soil depth, the relative amounts transferred to plants may vary with fine-root depth, since these roots are involved in nutrient absorption. Therefore, we investigated the influence of fine-root depth on soil-to-young-plant-tissue ¹³⁷Cs aggregated transfer factors (T_ags) and exchangeable ¹³³Cs T_ags (Young-shoot ¹³³Cs concentration/Soil exchangeable ¹³³Cs inventory) in 10 edible wild-plant species collected in Fukushima Prefecture between 2013 and 2017. The ¹³⁷Cs T_ag values were strongly positively correlated with those of exchangeable ¹³³Cs T_ag, implying that the distribution of ¹³³Cs can be used to predict the distribution of ¹³⁷Cs in plant bodies. However, in species with deep fine roots, ¹³⁷Cs T_ag values tended to be smaller than those estimated from exchangeable ¹³³Cs T_ag. Since ¹³³Cs is derived from minerals and is abundant in deep soil, such species likely absorbed large amounts of ¹³³Cs from deep soil layers. Relative to a simple regression model where variation in ¹³⁷Cs T_ag was explained only by exchangeable ¹³³Cs T_ag (adjusted R² = 0.59), a multiple regression model that included fine-root depth increased the explanatory power (adjusted R² = 0.82). Thus, when predicting plant ¹³⁷Cs concentrations using exchangeable ¹³³Cs T_ag, it is important to consider the effect of fine-root depth.

View full abstract

We reported the condition after 20 years installing treeshelters on Chamaecyparis obtusa seedlings in Tsushima Island. Of the 198 seedlings that installed treeshelters in 1999, 150 (75.8%) were alive in late 2018. Since 24 seedlings had fallen due to the movement of surface soils, which is considered as accident during the initial period, the survival rate of the seedlings was 82.2% when the denominator was 174 seedlings after deducting this. Regarding the durability of the treeshelter, 37 of the surviving individuals were dropped, 53 were break, and 53 remained in a normal state. However, since the most of the 53 C. obtusa with the normal state treeshelter did not reach the diameter of treeshelter, they would likely to fall off when the seedlings grow. The treeshelter used in this study is unlikely to occur problems such as deformation of planted trees and early break of treeshelter even if it is left until thinning.

View full abstract

Genetic resources from two willow species (Salix udensis and S. schwerinii) were collected in Hokkaido, and their clones were preserved at the Hokkaido Regional Breeding Office, Forest Tree Breeding Center, Forestry and Forest Products Research Institute. Clonal test sites were established to evaluate clonal characteristics by direct plantation of stem cuttings to the test sites. A large variation was observed in the dry mass of the clone stems after three growing seasons. Predicted values of the clonal stem dry mass were calculated via the best linear unbiased prediction (BLUP) method. There was a 3.89-fold difference among the clones at a site. Here, we report the results of clonal evaluations of the stem dry mass production and clonal selection based on their evaluations, with the goal of improving woody biomass production using short rotation forestry for the willow species.

View full abstract

Teak (Tectona grandis L. f.) seedlings planted in sandy soil in northeastern Thailand often experience suppressed growth due to nutrient deficiency and drought stress. Based on a preliminary field pot experiment, it was observed that biochar increased the root growth of the seedlings. To verify the effects of biochar under field conditions, teak seedlings were planted in a sandy soil treated with 1 kg of biochar in July 2014 (2.5 Mg ha⁻¹), and were cultivated until November 2015. Biomass, photosynthetic rate, and the concentrations of elements in soil and plant materials were compared between biochar and control (no application) treatments. The biochar used in this study contained nitrogen, calcium, and potassium, and thus acted as a fertilizer. Its application accelerated the growth of teak seedlings, increased their photosynthetic rates, and chlorophyll and calcium concentrations in plant tissues. It was concluded that biochar is a useful material to improve the quality of sandy soils and accelerate the growth of teak seedlings.

View full abstract

The Nachi Falls in the southern Kii Mountain Range in Japan has been experiencing high water turbidity during heavy rainfall, primarily because of debris from landslides triggered by torrential rain during the severe typhoon Talas in 2011. In recent years, however, the impact of debris on turbidity appears to have sharply declined. At the same time, filamentous algae communities bloomed extensively in the submerged stream channels of the headwater in early 2019 but were undetectable by mid-2019 in the regional climate of humid subtropical type and annual rainfall exceeds 3500 mm.

View full abstract