Since the dead branches and leaves of Japanese cedar, Cryptomeria japonica, are kept attached on trees, these substrata are likely to be decomposed by microorganisms such as bacteria and fungi before they fall onto the forest floor. However, some microorganisms are eaten by nematodes, and thus nematode communities can indirectly be involved in the decomposition process of above substrata. In this study, we aimed to clarify the nematode community inhabiting at the above-ground part of cedar forests. We established five plots within a 1 ha cedar stand in Mie Prefecture. In the plots, three mature trees were arbitrarily selected, and fresh leaves, dead leaves, barks, and forest floor litters were collected. Nematodes were collected from each organ by the Baermann funnel method and observed under a light microscope. We identified nematodes into taxa at the order, family or genus level, and they were also categorized into one of 5 feeding groups based on their oral parts. Moreover, mycelial length was estimated directly observing hyphae in each organ under the microscope. Fungivorous nematodes were predominated accounting for more than 70％ in each organ. Furthermore, the nematode feeding groups of fresh and dead leaves were significantly nested with those derived from barks and forest floor litter. Mycelial lengths were significantly greater at dead leaves and forest floor litters than fresh leaves. These results indicated that nematodes inhabit the aboveground parts of cedar forests, and fungal distribution can affect the maintenance and assemblage pattern of nematodes.

Regional forest management policies such should be evaluated appropriately to avoid unintended effects. The local government of the study area have impelled forestry enterprises to plant after clear-cutting inside the “zone to promote planting (zone)” since 2017. This study analyzed the differences of clear-cutting tendencies between inside and outside the zone with respect to area and locations. We calculated ATT (average treatment effect on the treated) by a statistical causal inference method: an inverse probability of treatment weighting method with propensity score. Forest age, slope degree, and distances from roads were used as covariates. As a result, ATT was －0.22％±0.11％, which means clear-cut had been avoided inside the zone compared to outside. Quantitative analysis of policy impacts, as done in this study, is fundamental for EBPM (evidence-based policy making) and sustainable forest management.

This study aimed to alleviate radiocesium pollution in Lentinula edodes (shiitake mushrooms) by using the bed-log cultivation method. In 2013, we set bed logs on the surface of A-horizon soil where A₀ layer was removed in 2012 in a forest located in Iwate Prefecture, Japan. Radiocesium concentrations or amounts of the treated plots were compared with those of non-treated plots for 5 years. In 2017, mean radiocesium concentration in bed logs collected from treated plots was 68％ of that in bed logs collected from non-treated plots. Radiocesium concentration was also reduced in fruiting bodies from treated plots. Radiocesium amount in A₀ layer decreased after the removal of A₀ layer, and this trend continued for at least 5 years, despite the supply of radiocesium from the canopy layer as litter. Radiocesium concentration in A₀ layer of treated plots was 46％ of that in non-treated plots in 2017. These results indicated the successful alleviation of radiocesium pollution in bed-log-cultivated L. edodes. However, 4 years after treatment, radiocesium amount in A-horizon soil (0-5 cm in depth) exceeded that of A₀ layer. Additionally, direct accumulation of radiocesium in A-horizon soil via L. edodes hyphae or adhesion onto bed logs due to rain splash is a matter of concern. Thus, currently, there is a risk of increased radiocesium pollution when the bed log is set directly on A-horizon soil.

The production of Tosa bincho charcoal in Kochi Prefecture is increasing in recent years. The major material of the charcoal is ubame oak, Quercus phillyraeoides that are often attacked by oak ambrosia beetle, Platypus quercivorus. In order to estimate the resource and to establish sustainable resource management system of the oak, it is necessary to understand the attack pattern of the beetle. Therefore, we surveyed the damage of the oak caused by attacking of the beetle in Muroto City, Kochi Prefecture, where is the main production area of the charcoal. A total of 560 ubame trees inhabited in 11 survey plots, of which 179 trees got damaged, but none of completely dead trees with typical symptoms of Japanese oak wilt was found. Logistic regression analysis showed negative correlation between damage ratio and tree species mixture ratio of survey plots, as well as positive correlation between damaged ratio and diameter of the tree.

Melia azedarach, which is attracting attention as an early-maturing tree species, is a domestic alien species in the Hyogo Prefecture, Japan, and has recently migrated to form dominant communities. Therefore, we investigated the causal factors and ecological characteristics of the M. azedarach community established on sabo dam sedimentation beds and changes in constituent tree species and biomass before and after logging in the M. azedarach community on the riverbed. As a result, the causal factors of the M. azedarach community were nearby seed sources and sunny areas formed by logging cedars. In addition, the establishment and growth of competitors of M. azedarach were hindered by the feeding of sika deer. Furthermore, in this community, the invasion of tall tree species was low due to the feeding of sika deer; therefore, although the shade tolerance of M. azedarach was low, the dominance of M. azedarach will continue for the time being. In the riverbed M. azedarach community, although M. azedarach and Ailanthus altissima competed before and after logging, the recovery of biomass due to the emergence and elongation of sprouting after logging tended to be faster in M. azedarach than in A. altissima.

The stand growth process of an overcrowded old-growth plantation of Japanese Cedar (Cryptomeria japonica D. Don) was investigated for 41 years, beginning when the stand was 134 years old, in the slope and flat site. In the slope site, since very weak cutting of about 10％ in number ratio was carried out several times, overcrowding condition could not be eliminated and mortality continued. However, as the trees were continuously cut down, the degree of crowding gradually improved and DBH growth increased, average height: DBH ratio decreased to less than 70, and net increment in stand volume reached more than 10 m³/ha/year. In the flat site, the low thinning of 22％ in number ratio was carried out, when the stand was 146 years old, and overcrowding condition was eliminated and mortality stopped. As DBH growth increased, average height: DBH ratio decreased to less than 70 and net increment in stand volume increased to around 20 m³/ha/year. It was confirmed that since the tree height growth continues at first site class, the net stand volume increment would be around 20 m³/ha/year for about 20 years, if lower thinning is conducted to exceed 15％ of the relative spacing index.

The mortality rate of forest trees is an important parameter in a forest ecosystem carbon dynamic because it determines the amount of leaves and tree litter that are related to photosynthesis and decomposition, respectively. However, few data are available on the mortality rate in weight. In the present study, the mortality rates were assessed in a deciduous broadleaf forest in northern Japan, where the dominant tree species was transitioning from birch to oak. The mortality rates rose after the disturbance caused by a typhoon in 2004. The mortality rates differed depending on the damage degree for several years after the disturbance. The mortality rate in weight was lower than that in number or to the same degree in most periods. However, the mortality rate in weight was higher than that in number when the mass mortality of large trees was caused by the natural processes of death as well as disturbance.

Exotic conifer tree species that exhibit more rapid growth and greater timber value than native tree species tend to be selectively grown in plantations. These exotic species are also expected better adapted to climate change. However, some exotic planted species invade neighboring stands, affecting hydrological and nutrient uptake processes among natural tree species. Countermeasures to prevent exotic tree invasion can be costly; therefore, methods for assessing the impacts of introducing exotic tree species are needed. Such methods should evaluate the effects of the water and soil use of exotic tree species, as well as their invasiveness, resilience, and resistance to herbivory. Exotic species have also been studied from the perspective of novel ecosystems. The regeneration and yield of the exotic tree Cunninghamia lanceorata, which has been selected for industrial plantations in Japan, have declined in its country of origin (China) due to allelochemical production. Since tree species in plantations vary in terms of both timber production and social benefits, the effects of these species should be carefully assessed prior to their selection for large-scale planting.