Aiming for the production of logs for mushroom cultivation, the radiocesium (¹³⁷Cs) distribution in the tree trunk and the factors of decreasing the external contamination of Konara oak (Quercus serrata) after the Fukushima Dai-ichi Nuclear Power Plant (FDNP) accident were investigated. 16 tree trunks were collected from 8 tree stands by height of the trees at one site in Fukushima Prefecture in 2016, and ¹³⁷Cs concentration and ¹³⁷Cs distribution of several parts were investigated. As a results, ¹³⁷Cs were still attached on the bark surface 5 years after the accident, and ¹³⁷Cs concentration of the outer bark was higher than that of the inner bark, sapwood and heartwood, and 60 to 70％ of total ¹³⁷Cs in the trunk were distributed in the outer bark. This suggested that even five years after the accident, external contamination could still be a problem for the utilization of mushroom logs. An inversely proportional correlations was found between the growth rate of trunk diameter and ¹³⁷Cs concentration of the outer bark. From the above results, the dilution of bark surface contamination caused by the growth of trunk may contribute to the decrease in ¹³⁷Cs concentration of the outer bark. In addition, ¹³⁷Cs concentration of the outer bark decreased more than the effect of dilution, suggesting the existence of other effects.

Determining the flowering stage accurately is crucial for successful artificial fertilization. However, visually identifying the stage requires skill and is subjective. To address this, we developed a simple method for determining the developmental stage of female strobili of Pinus thunbergii using deep learning. A classification model was created, and an associated web application was developed, eliminating the dependency on human observation. The process involved several skilled investigators classifying various images of P. thunbergii female strobili into stages I, II, and III. From a total of 3,074 images with unanimous evaluations, we used MobileNetV2's transition learning to construct and evaluate the model. Although the model had a high accuracy rate of 0.974 and an F-score of 0.949, i.e., a balanced evaluation of precision and recall, it failed to predict some images correctly. Specifically, it struggled with images containing small female strobili in relation to the entire screen, as well as images that included unrelated objects. Additionally, it had difficulty with female strobili that were yellowish-green in color. However, despite these limitations, we propose that this tool can be useful for evaluating traits in the field.

In Mt. Kamagamine, a forest stand dominated by large-diameter Q. variabilis trees has been established. We attempted to reveal the stand structure and establishment process of the forest stand by using data-obtained in forest inventory, literature survey, and tree-ring analysis. The survey results indicated that the forest stand is more than 30 m hight and has the same amount of above-ground biomass (294.2 t/ha) as that of natural beech forests. The origin of the forest stand was estimated to be the regeneration by sprouting after logging around 1880. In the Q. variabilis trees occupying the forest canopy, growth release of the middle-layer and under-layer trees were detected in three periods of the 1940s, 1970s, and after the 1990s. The growth release of these individuals was assumed to be due to occurrence of canopy gaps by thinning of unnecessary trees, and by pine dieback. The forest stand is a valuable example that deciduous broad-leaved secondary forests dominated by Quercus spp. reached an above-ground biomass comparable to that of natural beech forests in a short period of approximately 140 years. This forest stand would be a good reference in developing abandoned charcoal forests to well-developed mature forests by thinning.