Considerable uncertainty exists with regard to the effects of thinning and harvesting on N₂O emissions as a result of changes caused in the belowground environment by tree cutting. To evaluate on the effects of changes in the belowground environment on N₂O emissions from soils, we conducted a tree manipulation experiment in a Japanese cedar (Cryptomeria japonica) stand without soil compaction or slash falling near measurement chambers and measured N₂O emission at distances of 50 and 150 cm from the tree stem (stump) before and after cutting. In addition, we inferred the effects of logging on the emission using a hierarchical Bayesian (HB) model. Our results showed that tree cutting stimulated N₂O emission from soil and that the increase in N₂O emission depended on the distance from the stem (stump); increase in N₂O emission was greater at 50 than at 150 cm from the stem. Tree cutting caused the estimated N₂O emission at 0–40 cm from the stem to double (the % increase in N₂O emission by tree cutting was 54%–213%, 95% predictive credible interval) when soil temperature was 25 °C and WFPS was 60%. Posterior simulation of the HB model predicted that 30% logging would cause a 57% (47%–67%) increase in N₂O emission at our study site (2000 trees ha⁻¹) considering only the effects of belowground changes by tree cutting during the measurement period.

The central mountainous area of Japan is affected by air pollutant emissions from nearby countries such as China and Korea. Sharp increases in the consumption of fossil fuels in the early 21st century, associated with rapid industrialization in China, resulted in long-range transport of pollutants from East Asia and increases in the harmful effects of pollution. However, the air pollutants emissions have decreased since 2006, when air pollution countermeasures were implemented in China. Furthermore, climatic patterns during 2008–2013 reduced tropospheric ozone concentrations around Japan. Such major changes in the social and climatic environment may have had a significant impact on forests. To investigate this, long-term forest monitoring data obtained at Buna-daira (1190 m a.s.l.), Buna-zaka (1090 m a.s.l.) and Arimine (1350 m a.s.l.) were analyzed. Buna-daira and Buna-zaka forests face the continental side of Mt. Tateyama in Toyama Prefecture. In both stands, the girth growth rate of Fagus crenata was found to have increased after 2008; however, such a tendency was not detected at Arimine, which is surrounded by mountains. The growth rates of Cryptomeria japonica, a conifer resistant to air pollution, were found to remain unchanged or decrease. Here, regional long-range transport of air pollution (including ozone and sulfur oxide) has been demonstrated to influence mountain forests in Japan. In particular, recent decreases in regional air pollution may be an important factor controlling increases in F. crenata, likely through changes in interspecific relationships between species sensitive to and tolerant of air pollution.

With the continued growth of cities in many areas of the world, it is important to understand variations in atmospheric deposition in relation to site-specific geographic factors. Accordingly, this research investigated wet or bulk deposition (WD/BD) and dry deposition (DD) of SO₄²⁻, NO₃⁻, and NH₄⁺ onto Japanese cedar within the Tokyo metropolis and surrounding areas with the primary aim of evaluating which geographical factors most influence the deposition of pollutants. Two new sites were established and, along with five existing sites, comprised an array of sites with varied geographic settings (distance from the center of Tokyo, elevation, and azimuthal difference between slope aspect and dominant wind direction). Annual WD/BD and DD values of SO₄²⁻, NO₃⁻, and NH₄⁺ ranged from 9–35, 16–83, and 12–96 mmol m⁻² year⁻¹, respectively, and 1–25, − 5–104, and − 7–142 mmol m⁻² year⁻¹, respectively. Annual WD/BD values only showed a statistically significant difference with azimuthal difference for SO₄²⁻ and NH₄⁺. In contrast, annual DD values of SO₄²⁻, NO₃⁻, and NH₄⁺ were found to significantly decrease with distance from the center of Tokyo. In addition, site elevation was a significant factor influencing the DD of SO₄²⁻, NO₃⁻, and NH₄⁺ in linear regression models. Azimuthal difference was not significantly related to DD variability. Given these results, it is necessary to consider both the distance from emission source as well as the geographic factors of particular locations when evaluating the deposition of atmospheric pollutants from megacities to forested areas within and beyond the city.

The historical Japanese city of Kyoto boasts a great many old Buddhist temples and Shinto shrines, many of which are surrounded by sizable forests that have long been preserved as sacred forests. However, acidic deposition has been fallen on the forests in Kyoto for many years. For this study, we conducted soil surveys and investigated the extent of decline of the trees in two Shinto shrines as historic monuments of ancient Kyoto. Our study revealed clear decline in two key tree species (Cryptomeria japonica (Japanese cedar) and Chamaecyparis obtusa (Japanese cypress)) in both shrines, with some trees showing signs of mortality. The soil was acidic, with an average pH of 4.35. Nutrient salt content too was only about one tenth the national average, with exchangeable Ca (0.52 cequiv./kg) and Mg (0.23 cequiv./kg) for 0-20 cm surface soil. The (Ca+Mg+K)/Al molar ratios were also very low, with 80% of all soil samples having a ratio of 10 or below. Such soil conditions are thought to hamper the sound growth of both Japanese cedar and Japanese cypress, and soil acidification is one of the most likely causes of the decline of temple and shrine forests in Kyoto.

Nitrogen (N) budget was estimated with dissolved inorganic N (DIN) and dissolved organic N (DON) in a forested mountainous watershed in Tsukui, Kanagawa Prefecture, about 50 km west of Tokyo in Central Japan. The forest vegetation in the watershed was dominant by Konara oak (Quercus serrata) and Korean hornbeam (Carpinus tschonoskii), and Japanese cedar (Cryptomeria japonica). Nitrate (NO₃ -) concentration in the watershed streamwater was averagely high (98.0 ±± 19 (±± SD, n = 36) μmol L-¹) during 2001-2003. There was no seasonal and annual changes in the stream NO- ₃ concentration even though the highest N uptake rate presumably occurred during the spring of plant growing season, a fact indicating that N availability was in excess of biotic demands. The DON deposition rates (DON input rates) in open area and forest area were estimated as one of the main N sources, accounting for about 32% of total dissolved N (TDN). It was estimated that a part of the DON input rate contributed to the excessive stream NO- ₃ output rate under the condition of the rapid mineralization and nitrification rates, which annual DON deposition rates were positively correlated with the stream NO₃ - output rates. The DON retention rate in the DON budget had a potential capacity, which contributed to the excessive stream NO- ₃ output rate without other N contributions (e.g. forest floor N or soil N).

The bioavailability of cadmium (Cd) in agricultural soils is a significant health concern due to the potential risk of human exposure via foods grown in Cd-contaminated fields. Biochar has been known to have a highly porous structure and high pH, as well as containing various functional groups; as such, it can immobilize heavy metals. Although it has found that biochar amendment in Cd-contaminated agricultural soils could be effective in reducing Cd bioavailability in previous studies, differences in plant Cd accumulation from Cd-contaminated soils amended with biochars produced from various types of biomass have not been fully discussed yet; we aimed to address this shortcoming in the present work. The soil investigated was an acid soil (pH 5.1) and had an elevated concentration of Cd (total Cd: 3.3 mg kg-DW⁻¹). Six kinds of biochar were produced, i.e., from woodchips (Japanese cedar [CE] and Japanese cypress [CY]), moso bamboo (MB), rice husk (RH), poultry manure (PM), and wastewater sludge (WS), at a pyrolysis temperature of 600 °C. Biochars were incorporated into the Cd-contaminated soil at 3% (w/w) and pot experiments using Brassica rapa var. perviridis were conducted for 28 days in a growth chamber. The Cd concentrations in the above-ground portion of the plants were significantly decreased as a result of the incorporation of all biochars compared to the unamended soil, with reduction ratios following the order PM (78%) > > WS (31%) ≈ RH (29%) ≈ MB (28%) ≈ CY (26%) > CE (19%). Among all biochar-amended soils, soil pH and shoot biomass were highest for those amended with PM-derived biochar. These results suggest that in Cd-contaminated soils, PM-derived biochar may offer significant potential in reducing plant Cd accumulation due to the immobilization of soil Cd and an effect of dilution resulting from enhanced plant shoot biomass.