We investigated the annual changes in damage caused by Japanese oak wilt in a Lithocarpus edulis forest in Kamogawa, Chiba Prefecture, and in a Quercus serrata forest in Seto, Aichi Prefecture. The number of trees infested by Platypus quercivorus increased over the first 3-4 years in both study sites, but rapidly declined when the percentage of the infested trees exceeded 90％ in L. edulis forest and 80％ in the Q. serrata forest. At the end of the damage period, most trees with diameters less than 10 cm at breast height were not infested, whereas 70-80％ of the trees with diameters of 10-20 cm at breast height and 90-100％ of the trees with diameters of 20 cm and above at breast height were infested. The annual changes in symptoms of the individual trees showed that more than 95％ of Q. serrata trees that survived beetle infestation the previous year were still alive the following year. In contrast, 20-30％ of L. edulis trees that survived beetle infestation the previous year deteriorated or died the following year, indicating that the process leading to mortality differs between the two study sites. This study suggests that forest damage caused by Japanese oak wilt ended when almost all the trees, except for small diameter trees around 10 cm in diameter, were infested in both L. edulis and Q. serrata forests.

To evaluate soil compaction by vehicles on skid roads in a Todo fir (Abies sachalinensis) plantation in Bibai, Hokkaido, we established road and control (forest) sections on a survey road 1 year after construction. Soil penetration resistance (Nc) was measured in both sections for a period of 4 years, and dry bulk density and porosity were measured for 3 years. The soil compaction index (SCI), which reflects the compaction of surface soil, was calculated for each survey year using the Nc values. The median Nc value of the road section was higher than the median value of the control section. The median SCI for soil depths of 0-10 cm decreased over time, whereas the value for depths of 0-0.3 m decreased from the first to third year after construction but remained unchanged thereafter. The dry density in the road section was higher than the density in the control section from the second year onward, and the porosity of the road section remained low. In the control section, dry density and porosity remained nearly constant throughout the study period. The longitudinal change in soil compaction indicated different tendencies depending on the measured soil physical properties. These results demonstrate that the skid road surface remained strong throughout the 4-year period, although the degree of compaction decreased by the third year.

In mid-July 2020, a gray mold outbreak was confirmed in current-year Sugi (Cryptomeria japonica D. Don) seedlings grown in the open field and in the glass room at the containerized seedling production site in western Shimane Prefecture, Japan. The percentage of diseased seedlings in the open field was only 11％, whereas in the humid glass room, it was as high as 38％. BLAST analysis of the nucleotide sequence of the rDNA internal transcribed spacer region revealed that the isolated strain was 100％ homologous to Botrytis cinerea Pers. The strain was inoculated on the branches and leaves of Sugi current-year-old containerized seedlings in late August and late November under 20 ℃, wet, and dark conditions. After 10 days, the outbreak of the disease was investigated. The percentage of diseased seedlings was as high as 94％ in August, but decreased to 0％ in November. The branches and leaves of the seedlings in August (during the growing season) were softer than those in November (during the resting period). It is therefore inferred that the softer nature of the seedlings during the growing season makes them more susceptible to infection by the pathogen.

Ubame oaks (Quercus phillyraeoides) are intensively processed into Binchoh charcoals in Kochi Prefecture. Quantifying the stem volume is necessary to estimate sustainable usage of the oak. The diameters of stems strongly relate to the specifications of the charcoal as well as the processibility of the stems into charcoals. Therefore, a stem volume model that enables us to estimate the volume for a given stem diameter distribution as well as the volume is desired. In this study, we measured the geometries of the oaks by felling in Muroto region, the major production of the Binchoh charcoal in Kochi Prefecture, and modeled the stem volume formula that estimates the volume for a given processible diameter. Stem volumes for a given processible diameter were approximated with linear regression model of D²H. A unified regression model that assumes linearity of the slopes and exponentiality of the x-intercepts with processible diameters slightly increased the root of mean square error but reduced AIC more than five. Estimations of this regression model and the actual stem volume measured were larger than the estimations of the stem volume table appropriate for the region and species and the volumes of Ubame oaks reported in Wakayama Prefecture.

Throughfall near the trunk was measured for three Japanese cedar (Cryptomeria japonica) trees by installing water pools around tree boles in a Japanese cedar plantation forest. These amounts were compared with throughfall index measured using 10 storage-type rain gauges, which generally measure throughfall in the forest. Observations of rainfall, throughfall, and stemflow during rainfall of three targeted trees clarified that processes of rainwater collection at the tree canopy and stemflow generation differed among trees, as did the probability of departure from the trunk. The total annual throughfall near the trunks was approximately equal to the average throughfall index observed using 10 storage-type rain gauges, but less than the throughfall index during a low rainfall event and greater at times of heavy rainfall, which sometimes recorded twice the throughfall index. Results demonstrated the possibility of underestimating throughfall amounts when near-trunk throughfall is ignored during heavy rainfall.

Forest ecosystems have high biodiversity and provide various ecosystem services. However, anthropogenic activities have degraded biodiversity, and impaired ecosystem services. The maintenance and improvement of soil biodiversity in forests are essential because soil organisms contribute to the recycling of matter flows in the soil food web. Among them, nematodes are one of the most abundant animals on earth and play key roles in soil ecological processes. Although nematode community studies are accumulated, a review of its community patterns in forest ecosystems is largely lacking. Nematodes can accelerate nutrient flows by eating microbes and plant roots. Clarifying nematode communities in various ecosystems provide valuable information for understanding soil ecological processes. Thus, to overview trends and foresee future studies of nematodes in forest ecosystems, firstly, I reviewed the diversity, abundance and contributions of soil nematodes in forest ecosystems. Second, I showed determinant factors of nematode communities. Finally, I mentioned the possible application of soil nematodes as bioindicators, and the methodology of nematode communities by using the latest molecular techniques.