To clarify the population maintenance mechanism of Berberis sieboldii, which grows in the overly humid stressful environment of a spring-fed marsh, we investigated the distribution, emergence and survival of stem at Kippataike Mrash, a typical spring-fed marsh in Toki City, Gifu Prefecture from 2017 to 2020. The advanced stems (stems that were growing in 2016) were distributed discontinuously and grew densely in areas with a higher coverage rate of woody plants. The total number of stems, including advanced stems, sprouts, and seedlings, had decreased by 114 (15.2％) over the four years from 748 in 2017, and the number of advanced stems in particular had decreased by 241 (39.6％) over the four years from 608 in 2017. On the other hand, the total number of stems, including seedlings and sprouts, increased by 127 (90.7％) from 140 in 2017. The proportion of sprouts to the total number of stems, including advanced stems, seedlings, and sprouts was higher than that of seedlings in each year, and this tendency became more pronounced year by year. The survival rate of sprouts was significantly higher than that of seedlings and also the growth rate of the sprouts was also higher than that of the seedlings. These results suggest that the population of B. sieboldii may persist in the spring-fed marsh by compensating for the decline in stem number through sprouting from the base of the trunks and rhizomes.

Herein, we attempted to verify the possibility of a relic forest of sugi (Cryptomeria japonica) individuals distributed on the Oninome Mountain in Nobeoka City, Miyazaki Prefecture, Japan, based on DNA analysis. Measurements of breast height diameter (DBH) and tree height of individuals in the study area showed that DBH had grown more than in the previous survey conducted 40 years ago, but there was no clear increase in tree height. As a result of obtaining the geographical coordinates of each individual in the survey area, it was not possible to strictly match the individuals with the results of the survey conducted about 40 years ago, but no significant decrease in population was observed. It is deemed necessary to ensure appropriate conservation for these individuals based on periodic surveys. DNA analysis of individuals in study area revealed that the level of heterozygosity was comparable to that observed in other tested sugi populations, and no distinct genetic structure was identified within the population. Furthermore, these individuals showed a different genetic structure compared to the other sugi populations, and there was no evidence of planting by cuttings or active use of sugi local cultivars. The findings from the DNA in this study corroborate the conclusions drawn in the previous report.

UAV-based laser scanning (UAV Laser Scanning: ULS) has been attempted in forest surveys, and high-density point cloud data can be used to obtain detailed DTM and DSM. However, within the forest, point cloud data is scarce, and measurements such as tree trunk diameter have not been sufficiently verified. Therefore, it is necessary to clarify measurable parameters and measurement accuracy. In this study, we conducted measurements using ULS on a cedar plantation and compared the measurement accuracy of tree data (number, tree height, tree trunk diameter) using 20 point-cloud data sets with different UAV flight course intervals and point cloud densities. The detection rate and tree height obtained from DCHM were hardly affected by the flight course interval and point cloud density. The estimated tree height was 3％ higher but was within the practical allowable range. By filtering based on the geometric characteristics of the point cloud data, “tree trunk clusters,” which correspond to the tree trunks, were detected, and the diameter was calculated by approximating the clusters as cylindrical. However, most tree trunk clusters were detected at positions higher than breast height, making it difficult to estimate breast height diameter. Additionally, considering the results of this study, such as the fact that high-density point cloud data does not necessarily lead to improved measurement accuracy, we examined the grid size of flight course intervals and point cloud densities necessary to ensure the measurement accuracy required in forest surveys.

In order to manage log-based shiitake cultivation which maintains radioactivity within the set acceptable level for food, it is important to know how much radiocesium is transferred from the bed-logs into the fruiting bodies. The amount of ¹³⁷Cs transferred from the bed-logs into the fruiting bodies was investigated by using konara oak (Quercus serrata) as the logs, which had fallen down in Fukushima Prefecture from April 2018 to December 2020. Statistical analysis showed significant relationships between the amount of 137Cs in the fruiting bodies and the amount of ¹³⁷Cs in the inner bark and the sapwood. Therefore, it is suggested that ¹³⁷Cs is transferred into the fruiting bodies from the inner bark and the sapwood. The statistical analysis also showed a significant relationship between the amount of ¹³⁷Cs in the fruiting bodies and the ratio of the amount of ¹³⁷Cs in the outer bark to the amount of ¹³⁷Cs in the whole logs (outer bark contamination rate), such that the amount of ¹³⁷Cs in the fruiting bodies increased as the outer bark contamination rate decreased. It is probable that ¹³⁷Cs, which was deposited on the outer bark during the early stages of the Fukushima Daiichi Nuclear Power Plant accident, was difficult to elute, increased the contamination rate of the outer bark. It is suggested that the initially deposited ¹³⁷Cs may be difficult to transfer to the fruiting bodies.

Tree age estimation using increment cores, particularly for large-diameter trees, is known to be susceptible to substantial errors, when the pith of target tree cannot be identified in the core due to heart rot or other causes. To develop a prototype method for estimation of tree age along with its uncertainty using increment cores without pith, we adopted stochastic approaches for a part of estimation processes, i.e., estimation of hypothetical position of pith and initial height growth rate of the tree. Using a Monte Carlo method, we obtained the means and 95％ coverage intervals of the distribution of estimated ages. Estimated ages of fifteen large and six middle-sized Quercus crispula trees in a hardwood forest in eastern Hokkaido, Japan, were 198-436 and 105-118 years, respectively. The 95％ coverage intervals of estimated ages were 18-96 and 13-21 years for large and middle-sized trees, respectively. Considering the uncertainty ranges of estimated ages, these tree samples likely consisted of four age groups. This study showed that uncertainty evaluation of tree age estimate could allow us to discuss to some extent the past regeneration processes of the stand even from information of tree ages estimated by incomplete cores.

We investigated the seasonal changes in the concentrations of ¹³⁷Cs and potassium in various parts of konara oaks (Quercus serrata) that were regenerated after the Fukushima Daiichi Nuclear Power Plant accident. Samples of leaves, branches, and trunks were collected from six individuals at four times between June 2022 and February 2023. We measured ¹³⁷Cs concentrations in the leaves, branches, and trunks, as well as potassium concentrations in the leaves and trunk xylem. Seasonal changes were observed in the ¹³⁷Cs concentrations of the leaves, bark and outer xylem of the trunks. The ¹³⁷Cs concentrations in the leaves decreased from early summer (June) to autumn (November), while the concentrations in the bark and outer xylem of the trunks increased from early summer (June) to late summer (September), and then decreased from autumn (November) to winter (February). The potassium concentrations in the leaves and trunk xylem showed a similar trend with the ¹³⁷Cs concentrations. This study indicated that ¹³⁷Cs concentrations in branches and the whole trunk had only small variations throughout the year. It is suggested that¹³⁷Cs concentrations in konara oak trunks can be estimated by measuring ¹³⁷Cs concentrations in branches potentially reducing the need for seasonal corrections.

Mass oak mortality due to Japanese oak wilt disease caused by the ambrosia beetle vector Platypus quercivorus has rapidly increased in the Kanto Plain since 2020. However, knowledge regarding the seasonal prevalence of beetles is lacking for countermeasure implementation. This study aimed to determine the seasonal prevalence of beetles in a mass-mortality forest in Ashikaga, Tochigi Prefecture, Japan. We used flight interception traps to capture flying adult beetles set in the forest and emergence traps to capture adult beetles emerging from their holes in the living stems of the two oak species during March and December 2022. We found that adult beetles flew between 13th of May and the end of November, and that the adult beetles started to emerge continually and abundantly from the holes on 24th of June and were almost complete in September. These results indicate that the adult beetles started to fly earlier and emerged later than our estimated date of first occurrence (26 May) based on the measured temperature. These results also show that a moderate number of flying adult beetles continued to be captured after September, whereas the emergence of adult beetles almost ended from the holes, implying their partial bivoltinism.