Forest In Japan Research Articles

Vertical profile measurements for ammonia in a Japanese deciduous forest using denuder sampling technique: ammonia emissions near the forest floor

Ammonia (NH3) has received considerable attention as a major reduced nitrogen. However, accurate estimates of the deposition amount are difficult due to its complex behavior characterized by bidirectional exchange between the atmosphere and the surface. We observed the vertical profile of NH3 concentration in a deciduous forest in Japan for 1 year to further advance the studies on NH3 bidirectional exchange in Asia, especially focusing on the process near the forest floor. The observation period lasted from September 29, 2020, to September 28, 2021, including leafy and leafless periods. Using the denuder sampling technique, we measured NH3 concentration in the forest at three heights (above the forest canopy, 30 m, and near the forest floor, 2 m and 0.2 m). NH3 concentrations tended to be highest at the top of the canopy (30 m). Focusing on the concentration near the forest floor, the concentrations at 0.2 m were frequently higher than those at 2 m regardless of the leafy and leafless period, thus suggesting NH3 emissions from the forest floor. NH3 concentration near the forest floor showed strong positive correlations with air temperature during the leafy period. The NH3 emissions from the forest floor during the leafy period were possibly due to the decomposition of leaf litter with increased air temperature. The decrease in leaf area index might induced the increase in NH3 concentration and emission. NH3 emission during the leafless period was also possibly dependent on the state of the deposition surface, apart from air temperature, relative humidity, and leaf area index.Graphical

Seasonal and interspecific variations in the water uptake depth of trees in a moist cool-temperate mixed forest in Japan

ABSTRACT The water uptake depth of trees affects their overall water use and the water cycle of forest ecosystems. However, empirical data on the depth from which water is drawn are lacking for many moist forests. In this study, we estimated the water uptake depths of 24 coexisting tree species in a moist cool-temperate mixed forest in Japan using stable oxygen isotopes. Our goal was to clarify the factors influencing water uptake depth including season, species, slope position, and tree height under moist conditions. Water uptake depth was determined during three periods in which temperatures differed but soil moisture levels remained similar. Season was shown as one of the factors affecting water uptake depth, which was shallowest in August, when temperatures reached maximum values, and deepest during May, when temperatures were lowest. This seasonal variation is likely to be related to physiological processes such as increasing transpiration which leads to water uptake shifting to the water-rich shallow soil layer and/or activation of fine root production at the soil surface, where temperatures are high. Water uptake depth also varied with tree species, suggesting the occurrence of belowground resource segregation among moist forest tree species. Slope position and tree height did not affect water uptake depth. This study highlights the importance of considering temperature-driven physiological processes when examining water uptake depth in moist forests, which could have implications for predicting the responses of these ecosystems to climate change.

Habitat fragmentation strongly restricts gene flow in endangered ectomycorrhizal fungal populations: Evidence from Rhizopogon togasawarius, specific to Pseudotsuga japonica, across the entire distribution range.

Habitat fragmentation reduces gene flow, causing genetic differentiation and diversity loss in endangered species through genetic drift and inbreeding. However, the impact of habitat fragmentation on ectomycorrhizal (ECM) fungi remains unexplored, despite their critical roles in forest ecosystems. Here, we investigated the population genetic structure and the demographic history of Rhizopogon togasawarius, the ECM fungus specifically colonizing the host tree Pseudotsuga japonica, across its entire distribution range (>200 km). These two species are designated as endangered species on the IUCN Red List since they are found only in small, fragmented forests in Japan. We analysed 236 R. togasawarius individuals from five remaining populations across the Kii Peninsula and the Shikoku Island, separated by a sea channel. Simple sequence repeat analyses using 20 loci revealed strong genetic differentiation among populations (FST = 0.255), even significant in the nearest population pair separated by a distance of only 8 km (FST = 0.075), indicating extremely limited gene flow between populations. DIYABC-RF analyses implied that population divergence occurred approximately 6000 generations ago between the two regions, and nearly 1500 generations ago between the nearest populations within Shikoku Island, related to past climate events. Because of prolonged genetic isolation, significant inbreeding was confirmed in four of five populations, where effective population sizes became very small (Ne = 9.0-58.0). Although evaluation of extinction risks for microorganisms is challenging, our conservation genetic results indicated that habitat fragmentation increases extinction risk through population genetic mechanisms, and therefore should not be overlooked in biodiversity conservation efforts.

Factors Affecting Activeness and Sustainability on Forestry in the Family Forests in Japan—From the Comparison between Aso in Japan and Styria in Austria

Forestry in Japan and Austria share many similarities in their natural and social conditions. However, the Family Forest Owners (FFOs) in Japan seem not to be active and sustainable. To understand the factors affecting activeness and sustainability in family-owned forests in Japan, in 2021 and 2022, questionnaire surveys were done with members of Forest Owners’ Cooperatives (FOCs) in Aso, Japan, and Styria, Austria. Survey responses were comparatively analyzed via correlation analysis and binary logistic regression. Timber production was found to be more active in FOC Styria than in FOC Aso. One reason for this was the high-income dependence on forestry in Styria. Higher income was realized by self-harvest and the larger size of forest holdings and forest stands. The younger age of the members in FOC Styria, strongly affected by the pension system, leads to a higher self-harvest ratio. The culture of a sole child inheriting the family forest maintains the general size and scale of owned forests and stands in Styria. High distribution costs in FOC Aso reduced forestry income. As a result, sustainability was reduced in Aso because the availability of successors was low, and elderly forest owners who were once motivated by forestry tended to quit forestry.

The space occupation and use by tree crowns explain variations of individual growth rates in an old-growth temperate forest in Japan

Relative growth rates (RGR), i.e., growth rates per unit biomass (ΔM/M, where M is plant mass and ΔM is the change in M over a period of time), reflect growth strategies of plant species. Partitioning of RGR to net assimilation rate (ΔM/leaf area) and leaf area ratio (leaf area/M) provides further insights into allocation strategies. To apply this analytical approach to large canopy tree species, we used crown area (Ac) as a proxy for leaf area to understand variations of RGR partitioned to space use efficiency (SUE, ΔM/Ac) and space occupation efficiency (SOE, Ac/M). With UAV imagery, we measured Ac of 226 co-occurring individuals of 14 canopy tree species in a 1-ha stand in a temperate old-growth mixed-forest in Japan, and analyzed how RGR was related to SUE and SOE. The results show that deciduous species exhibited higher SOE and lower SUE compared to evergreen species, even though their RGR values largely overlapped. Late successional species tended to have higher RGR through higher SUE than early-to-middle successional species. We also analyzed the relationship of absolute growth rates (AGR) with several functional traits including DBH (diameter at breast height), Ac, leaf- and stem traits. Both Ac and DBH were strong determinants of AGR across species. Low specific leaf area (SLA, leaf area per unit leaf mass) and high wood density positively contributed to AGR across species, offering long-term growth advantages for old-growth natural forest. The analytical framework introduced in this study may be useful to elucidate the variation of tree growth strategies of canopy trees in natural forest stands.

Effects of stochastic intraspecific seed dispersal variation on dispersal distance predictions in a temperate forest in Japan

The incorporation of seed dispersal models into conservation practices plays a pivotal role in predicting future ecosystems. Seed dispersal significantly influences plant population dynamics; however, our understanding of its implications at a landscape scale remains limited. We investigated how different seed dispersal processes impact the distributions of individual species within a 20 km × 20 km plot centered around a temperate old-growth forest reserve in Japan. We hypothesized that random variation in seed dispersal (i.e., stochastic processes) and variation mediated by distance (i.e., deterministic processes) would explain landscape-scale species distributions more effectively than deterministic seed dispersal processes alone. We evaluated 16 tree species with different seed dispersal modes by simulating seed dispersal processes. Stochastic simulations predicted higher dispersal distances for the majority of species. The findings of this study suggest that stochastic simulations are a more reliable tool for identifying dispersal restrictions in the context of climate change and biodiversity loss, highlighting the significance of using stochastic simulations for analyzing seed dispersal patterns in temperate forests, rather than more conventional deterministic methods.

Mating Disruption of a Flighted Spongy Moth, Lymantria Dispar Japonica (Motchulsky) in Japan.

Mating disruption of a flighted spongy moth, Lymantria dispar japonica (Motchulsky)(Lepidoptera: Lymantridae), with a synthetic version of its sex pheromone, (+)-disparlure ([7R,8S] -cis-7,8-epoxy-2- methyloctadecane), was tested in the forests in Japan. Pheromone trap catches and the percentage mating of tethered females were measured in the pheromone-treated and untreated control forests. The attraction of male moths to pheromone traps placed at a height of 1.5m was significantly disrupted when the pheromone dispensers were placed at 1.5m height, but many moths were captured in control plots. Mating of tethered females placed at 1.5m was inhibited entirely, while 44% of females were mated in an untreated control forest. We report the first trial of mating disruption against a flighted spongy moth, and these results suggest that mating disruption with the synthetic sex pheromone appears promising for reducing damage caused by L. dispar japonica.

Effects of the Co-Application of Glucose, Nitrogen, and Elevated Temperature on Buried Black Soil Carbon in a Cool Temperate Deciduous Broad-Leaved Forest

Accurately predicting the feedback mechanisms between forest ecosystem carbon cycling and climate change is crucial for effective climate mitigation. Understanding soil organic carbon (SOC) responses to the combined impacts of plant biomass, litter, and nitrogen deposition, especially regarding temperature sensitivity, is essential but remains poorly understood. We conducted incubation experiments using buried black soil from a cool temperate deciduous broad-leaved forest in Japan, which has high C content and a highly stable molecular structure. The stepwise addition of glucose and a temperature increase from 15 to 35 °C accelerated SOC mineralization by 74.0 mg C kg−1 with a positive priming effect (PE) during the 49-day incubation period, while the simultaneous addition of nitrogen had no significant effect on this phenomenon, with SOC mineralization measured at 75.5 mg C kg−1. Conversely, glucose mineralization was significantly accelerated by 10%, from 241.0 to 261.3 mg C kg−1, by stepwise nitrogen addition and temperature increase. Under the combined impacts, the Q10 value of the soil increased significantly from 1.6 to 2.0 compared to that in the unmodified conditions, primarily due to the stepwise addition of glucose. We also found a strong positive correlation between activation energy (Ea) and Q10. This result strongly supports the carbon quality–temperature (CQT) hypothesis. These results likely stem from interactions between SOC quality and carbon availability, suggesting that, in the future, climate change is likely to have a positive feedback effect, especially on buried black soils.

Accuracy assessment of GEDI terrain elevation, canopy height, and aboveground biomass density estimates in Japanese artificial forests

Global forests face severe challenges owing to climate change, making dynamic and accurate monitoring of forest conditions critically important. Forests in Japan, covering approximately 70% of the country's land area, play a vital role yet often overlooked in global forestry. Japanese forests are unique, with approximately 50% comprising artificial forests, predominantly coniferous forests. Despite the Japanese government's extensive use of airborne Light Detecting and Ranging (LiDAR) to assess forest conditions, these data need more availability and frequency. The Global Ecosystem Dynamics Investigation (GEDI), the first Spaceborne LiDAR data explicitly designed for vegetation monitoring, is expected to provide significant value for high-frequency and high-accuracy forest monitoring. To assess the accuracy of GEDI data in Japanese artificial coniferous forests, the reference data were gathered from 53,967,770 artificial coniferous trees via airborne LiDAR data in Aichi Prefecture, Japan. This data was then compared to the corresponding GEDI-derived terrain elevations, canopy heights (GEDI RH98), and aboveground biomass density (AGBD) estimates to assess the accuracy of GEDI data. This research also explored how different factors influence the accuracy of GEDI terrain elevation estimates, including the type of beam, time of acquisition (day or night), beam sensitivity, and terrain slope. Additionally, the effects of various forest structural parameters, such as the height-to-diameter ratio, crown length ratio, and the number of trees on the accuracy of the GEDI canopy height and AGBD, were investigated. The results showed that GEDI terrain elevation demonstrated high accuracy across various slope conditions, with rRMSE ranging from 2.28% to 3.25% and RMSE ranging from 11.68 m to 16.54 m. After geolocation adjustment, the comparison of canopy height estimates derived from GEDI to airborne LiDAR-derived canopy height also showed high accuracy, exhibiting a rRMSE of 22.04%. In contrast, the GEDI AGBD product showed moderate accuracy, with a rRMSE of 52.79%. The findings also indicated that the accuracy of GEDI RH98 was influenced by terrain slope and crown length ratio, whereas the accuracy of GEDI AGBD was mainly impacted by the number of trees and crown length ratio. This study provided the first baseline accuracy assessment of GEDI terrain elevation, RH98, and AGBD estimates in Japanese artificial forests. Furthermore, this study provided valuable insights into the accuracy of GEDI metrics by examining potential factors.

Tiger prowling: Distribution modelling for northward-expanding Aedes albopictus (Diptera: Culicidae) in Japan.

The Asian tiger mosquito, Aedes albopictus, is a significant public health concern owing to its expanding habitat and vector competence. Disease outbreaks attributed to this species have been reported in areas under its invasion, and its northward expansion in Japan has caused concern because of the potential for dengue virus infection in newly populated areas. Accurate prediction of Ae. albopictus distribution is crucial to prevent the spread of the disease. However, limited studies have focused on the prediction of Ae. albopictus distribution in Japan. Herein, we used the random forest model, a machine learning approach, to predict the current and potential future habitat ranges of Ae. albopictus in Japan. The model revealed that these mosquitoes prefer urban areas over forests in Japan on the current map. Under predictions for the future, the species will expand its range to the surrounding areas and eventually reach many areas of northeastern Kanto, Tohoku District, and Hokkaido, with a few variations in different scenarios. However, the affected human population is predicted to decrease owing to the declining birth rate. Anthropogenic and climatic factors contribute to range expansion, and urban size and population have profound impacts. This prediction map can guide responses to the introduction of this species in new areas, advance the spatial knowledge of diseases vectored by it, and mitigate the possible disease burden. To our knowledge, this is the first distribution-modelling prediction for Ae. albopictus with a focus on Japan.

Quantifying effects of changes in forest age distribution on the landslide frequency in Japan

Landslides are destructive natural disasters that cause human and economic losses. Although many studies report the effects of forest age on landslide susceptibility, especially for shallow landslides, no studies have examined the effects at a national scale. We assumed that temporal variations in the annual number of rainfall-triggered landslides in Japan were determined by variations in rainfall and forest age distribution. By this assumption, this study aimed to quantify the decrease in the frequency of rainfall-induced landslides owing to the increasing maturity of forests in Japan. Data were collated from 21 studies covering 11 sites in three countries that reported a landslide susceptibility index (i.e., frequency ratio or landslide density) and the relation between forest age and the normalized landslide susceptibility index (NLSI) was modeled. Using this relation and the area for each forest age class, the change in landslide susceptibility at a national scale (NLSIJpn) was quantified during 1966–2017. The authors developed generalized linear models (GLMs) using the annual number of landslides as the response variable and the NLSIJpn and a rainfall index for each year as the explanatory variables. The number of rainfall-induced landslides was simulated in the GLMs in 15 scenarios with different forest age distributions and rainfall amounts. The number of landslides in young-age-dominated and middle-age-dominated forests was estimated to be 2.4 and 1.1 times, respectively, that in mature-age-dominated forests. The change in the number of landslides from young-age-dominated to mature-age-dominated forests was larger than that from an increase in the rainfall amount of 20%. We conclude that increasing the maturity of forests greatly reduces landslide frequency in Japan. In a changing climate with potentially threatening increases in rainfall, preserving mature forests is important to avoid amplifying landslide susceptibility on a national scale.

Effects of distance from the sea and bedrock on foliar mineral contents in Japanese forests: Implications for mineral acquisition by folivores

AbstractMinerals are among the important nutritional components that are indispensable for animals. In particular, the acquisition of sodium is important for plant‐feeding animals because sodium may be deficient for these animals as plants do not need sodium. This study compiled data on the mineral contents of leaves in 28 forests in Japan, with special emphasis on the effect of distance from the sea and bedrock type. The aim of this study was to provide basic data on mineral availability for forest‐dwelling folivores, which provide important baseline data for understanding the mineral acquisition strategy of plant‐feeding animals. Sodium and phosphorus contents of live leaves were lower than the levels required for folivores (captive non‐human primates and ungulates). The effect of the distance from the sea was evident only for magnesium and sodium. The sodium content of live leaves was high enough to satisfy folivores' requirements at only a few hundred meters from the sea. The live leaves in forests growing on sedimentary bedrocks contained more minerals than those on granite/rhyolite. Seasonality was also evident based on repeated sampling at three study sites. The mineral contents of dead leaves at the three study sites showed similar inter‐site and inter‐season variations to those of live leaves. Phosphorus and potassium contents in dead leaves were consistently lower and iron content was consistently higher than in live leaves.

Responses of a bird community to sporadic outbreaks of woody herbivorous insects in a temperate beech forest in Japan

Sporadic large outbreaks of herbivorous insects alter forest ecosystems via a top-down effect, and a high frequency of outbreaks led to the death of the trees on which the insects fed. The top-down effect of predators, such as other insects and birds, often regulates the outbreaks. Predator insects exert effective top-down control on outbreaks of herbivorous insects, but the effect of bird predation varies because birds have a broader diet range and higher mobility than insects. It was hypothesized that when large insect outbreaks occur during the breeding season of birds, most bird species would not respond owing to a fixed home range during this season and would, therefore, not exert top-down effects. To test this hypothesis, the relationship between bird and beech sawfly abundance was investigated for over nine years in the Tanzawa Mountains of central Japan, where temperate beech forests and large sporadic outbreaks of woody herbivorous insects occur. In this study, 28 649 female beech sawfly adults were captured, and 2515 individuals were identified from 50 bird species. The abundance of most bird species foraging on beech sawfly larvae, except Sitta europaea, did not increase proportionally with the number of beech sawfly adults. Many bird species did not respond to the unpredictable and temporary abundance of food resources in a way that would enhance their density, supporting the hypothesis. These results can be explained by examining the nesting and foraging guilds of the birds. S. europaea is less restricted in nesting sites and nests earlier in the season than other species; therefore, they could select nests in areas where beech sawfly larvae were abundant. Regarding foraging, S. europaea has a unique foot shape that allows it to move down the tree trunk freely and respond rapidly to fluctuations in beech sawfly abundance. Bird species that exert top-down effects on insects show promise for use in an integrated pest management approach to manage sporadic outbreaks of herbivorous insects in forest ecosystems.

Two‐stage soil core sampler to collect a less‐compressed core from forested areas

AbstractA two‐stage sampler was designed to investigate the vertical distribution of heavy metals and trace elements that contaminate forest soils through atmospheric deposition. The hand‐corer consisted of two L‐shaped aluminum angles that were driven separately into the soil to reduce friction between the corer wall and the soil. This allowed for soil cores to be collected with less compression than with traditional corers. The corer is easily made, inexpensive, lightweight, and easy to carry. The degree of compression of soil cores collected at a depth of 20 cm from various montane forests in Japan was usually less than 10% (collected core length >18 cm); although, more compression occurred in soil with a higher air content. The degree of compression of soil cores collected from urban forests was lower than that in montane forests. When the two‐stage sampler was compared with a tube‐type sampler in a Japanese cedar (Cryptomeria japonica) forest, the compression degree of a soil core collected with the two‐stage sampler was a quarter that of the tube‐type sampler. The collection of less‐compressed soil cores will allow for reconstruction of a more accurate linear depth distribution of contaminants. To demonstrate this, we investigated the vertical distribution of Pb, Sb, and radioactive 137Cs in soil cores collected from conifer plantations on Mount Tsukuba, Japan, in April 2011. The migration centers of anthropogenic Pb, Sb, and 137Cs were positioned at 7.9, 7.5, and 3.3 cm from the ground surface, respectively. These distances probably reflect differences in the history of atmospheric pollution.

Does nationality affect landscape perceptions of urban sacred forests? A Japan–China cross‐cultural comparison

AbstractThis study explores the cultural ecosystem services of sacred forests in urban areas, focusing on the Meiji‐Jingu Shrine's forest in Japan. We assessed the forest's sublimity and landscape perceptions among Japanese and Chinese visitors using a mixed‐method approach. Data were gathered from 359 geotagged photographs and a questionnaire completed by 30 participants, evaluating sublimity and psychological aspects. GIS analysis identified scenic hotspots, and statistical methods compared landscape perceptions between the two visitor groups. Text mining analyzed differences in their forest evaluation. Key findings include (1) Cultural differences in perceiving landscape hotspots, (2) insights into the sublime nature of Meiji‐Jingu Shrine's forest, and (3) varied perceptions of forest sublimity between Japanese and Chinese visitors. This cross‐cultural study provides valuable insights for sacred forest conservation.

Vegetation History Characteristics of Planted Forests in Japan: Analysis of the 1960 World Census of Agriculture and Forestry

This study aimed to clarify the vegetation history of planted forests that are still in use today by comparing the types of land afforested in 1960 with the post-war afforestation period in Japan’s Hokkaido, Kyushu, and Kinki regions. It was during that time that the majority of the planted forest in these regions was established. We calculated the afforestation ratios (afforested area of each type of land/total afforested area) for the smallest survey unit, the 1950 administrative sections, using data from the 1960 World Agriculture and Forestry Census on the afforested areas of various types of land (i.e., deforested areas resulting from natural forests, deforested areas resulting from planted forests, and areas other than forests). The afforestation ratios were then sorted into ten categories for each municipality in the three regions and mapped using GIS. The analysis results showed that the vegetation history in Kyushu, even within the same municipality, was frequently mixed in 1960; in Hokkaido, the afforestation ratio for deforested areas resulting from natural forests was extremely high, while the afforestation ratio for deforested areas resulting from planted forests was low. In contrast, the Kinki region has a low afforestation ratio for non-forest regions. This study provides useful information for ecosystem management.

Decomposability of leaf and wood litter are not correlated across species: effects of litter traits on decomposition in field and laboratory conditions

Changes in tree species composition have important effects on the overall rate of litter decomposition at a community level because litter decomposability varies among species and between leaf and wood litter. To understand how changes in tree species composition affect litter dynamics and carbon sequestration at the ecosystem level, it is important to clarify interspecific variations in leaf and wood litter decomposability, and the traits driving the variation. Using field data, field experiments, and laboratory experiments, we explored rates of leaf and wood litter decomposition and their relationships to traits of ten deciduous hardwood species in a temperate forest in Japan. Rates of leaf and wood litter decomposition at the community level were also estimated by considering species‐specific litter inputs and decomposition rates. Rates of leaf and wood litter decomposition were not correlated under either field or controlled laboratory conditions. This is probably because the traits that affect decomposition rate differ between leaf and wood litter. Interspecific variation in litter decomposability of leaves and wood was generally consistent between field conditions and laboratory experiments using a single fungus, suggesting that the decomposing fungi set the species‐specific decomposition rates. Moreover, the leaf and wood traits that affected decomposition by their specific fungi were different. The aboveground input of wood litter was less than half that of leaf litter, but its half‐life was > 3 times longer, suggesting that wood and leaves make similar contributions to litter accumulation. Focusing on either leaf or wood litter alone may produce misleading estimates of how species composition changes affect litter dynamics at the community level. Our results provide insight into predicting the response of carbon dynamics to future climate change.

Visualization and Quantification of the Activities of Animal Vocalizations in Forest Species Using Robot Audition Techniques

Ecoacoustics is a recent ecological discipline focusing on the ecological role of sounds. This study applies robot audition techniques and ecoacoustic methods in the visualization and quantification of forest animal vocalization, focusing mainly on inter-specific interactions between birds and cicadas. We adopt HARK, an open-source robot audition software, which enables us to estimate the direction of arrival of sound sources and their separated sounds using a microphone array unit. We focus on recordings in an experimental forest in Japan, where birds and cicadas dominate the soundscape. Cicada songs were further replayed at a regular interval repeatedly. We create a false-colour spectrogram based on the directions of arrival of sounds to grasp the individual-level dynamics of the soundscape of birds and cicadas in the recording. We further describe a method to classify their vocalizations using three ecoacoustic indices, then illustrate their temporal vocalization dynamics, measured as the total song duration in each time segment. We also conducted a quantitative analysis of their vocal activities to determine if there exist interactions among birds and cicadas, and the effects of replayed vocalizations of cicadas on them. The preliminary analysis implied that there might exist temporal overlap avoidance behaviours between birds and cicadas, and replayed songs of cicadas may reduce the activity of birds. We believe that this proof-of-concept observation and analysis can contribute to the further development of the fine-scale measurement of the biodiversity or habitat quality of environments based on the vocal activities of multiple species, while further detailed analysis is necessary.

Phytosociological characteristics of Betula davurica–Quercus crispula forests in Japan based on a comparison with summergreen broad-leaved forests in Northeast Asia

Betula davurica and deciduous Quercus forests are among the principal forest types in Northeast Asia. They are found throughout continental Northeast Asia and in some mountainous regions of Central Honshu and eastern Hokkaido in the Japanese Archipelago. B. davurica–Quercus crispula forests in Japan are significant for understanding the phytogeography of Japan and Northeast Asia. However, their relationships with B. davurica–Quercus mongolica forests in continental Northeast Asia remain poorly understood. We compared the species composition of B. davurica–Q. crispula forests of Japan, with those of Q. crispula dominant forests and B. davurica–Q. mongolica forests using phytosociological methods. The results suggested that B. davurica–Q. crispula forests of Japan had a significant number of species common to the order Lespedezo bicoloris–Quercetalia mongolicae and the class Querco mongolicae–Betuletea davuricae in continental Northeast Asia than in other associations in Japan. Furthermore, our results showed that associations between B. davurica and Q. crispula forests in Central Honshu and Hokkaido are related to different orders in continental Northeast Asia. The relations of the associations between Japan and the continent are considered to have been caused by the environmental similarities, the histories of taxa, and the changes in vegetation distribution.

Vertical profile and flux measurements of ammonia in a deciduous forest in Japan towards improvement of bi-directional exchange model

Ammonia (NH3) is a major component of reduced nitrogen. A bi-directional exchange of NH3 takes place between the atmosphere and surface. Although the study of reduced nitrogen is gaining prominence in recent years, quantification of NH3 deposition is technically challenging due to its complex properties; consequently, this generates significant uncertainty regarding the estimation of total nitrogen deposition. Based on past studies, it has been reported that Asia has numerous high-risk nitrogen deposition sites; however, only a few studies have investigated the NH3 exchange in this region. To clarify the exchange process and achieve improved accuracy regarding the estimation of nitrogen deposition in Asia, we conducted measurements of vertical profile and flux of NH3 in a forest in Japan during summer (July 21–August 1, 2015), winter (February 23–February 29, 2016), and autumn (September 27–October 11, 2016). We measured daytime and nighttime NH3 concentrations at four or five heights of an observation tower in the forest by using filter-pack holders, and determined NH3 fluxes by using the aerodynamic gradient method. During daytime, NH3 showed emission above the canopy in summer, and near the forest floor in winter. There was no clear emission trend in autumn. During nighttime, NH3 showed deposition from the top of the canopy to the forest floor for all observed periods. NH3 exchange in the forest possibly had seasonal and diurnal variations. The flux measurements showed large NH3 emissions at daytime in summer and small depositions at nighttime in summer and autumn. Mean flux during the observation periods was 0.026 μg m−2 s−1. The daytime flux during leafy periods was found to have a strong correlation with solar radiation. At daytime in summer, flux also had strong correlations with relative humidity and horizontal wind speed. We also estimated NH3 fluxes in summer by employing a bi-directional exchange model to verify the applicability of the model at the study site. Inferred fluxes obtained via the model showed large emissions during daytime and agreed with the observation results; however, the model could not reproduce the nighttime deposition. This discrepancy was improved by applying more suitable cuticular resistances.