Mount Yukikura-dake (2611 m ASL, in the center of the photo), with austere, elegant landscapes, is situated in the northernmost part of the Japanese Alps. The torrential Shirakochi-sawa Valley originates from the north face of Yukikura-dake; its drainage basin was glaciated during the late Pleistocene. Holocene landslides continue to occur throughout the basin, affecting the topographies and vegetation and thus the landscape development in this area. Gentle slopes are seen in the foreground area of part where landslides originate. The marginal ridge where snow melts early in summer and soil moisture is low is covered by subalpine conifers, while the central depression where snow melts later and soil moisture is high is covered by dwarf trees and grass. (Photograph & Explanation: Yoshihiko KARIYA; Photographed on October 4, 2009)
The Japanese Alps collectively refer the Hida Mountains, Kiso Mountains, and Akaishi Mountains, ranging approximately 200 km north to south and 100 km east to west. In terms of span, the Japanese Alps region includes the Ryohaku Mountains to the west and Mt. Fuji, Mt. Yatsugatake, and Mikuni Mountains to the east, making the geographical extent of the region more than 200 km in the east-west direction. The maximum altitude of the Japanese Alps is around 3000 m; however, climatic conditions vary widely because the region lies at the center of Honshu, between the Japan Sea coast and the Pacific coast, and the northern area is known to experience one of the heaviest snowfalls in the world. It is thought that mountainous areas are particularly sensitive to global-scale environmental changes, such as warming. When attempting to evaluate the effect of a global-scale warming event on regional environmental change in the high-altitude Japanese Alps, we note a lack of high-altitude meteorological observation data. This presents difficulties when evaluating the effects of warming on ecological systems and water resources in mountainous regions. In this study, we discuss long-term variations of winter temperature, as well as the amount of snowfall and depth of snow cover at twelve observational stations in the Japan Alps region. At eleven sites other than Mt. Fuji, a trend of increasing annual minimum temperature is recognized, which is statistically significant at the 1% significance level. At locations such as Mt. Fuji, which are located at extremely high altitudes, the annual minimum temperature over the last several decades has not been seen to increase or decrease. The trend of decreasing annual cumulative snowfall is statistically significant at the 10% level at Takada, Toyama and Kanazawa stations. At the other eight sites, it is shown that the recent annual cumulative snowfall does not show either an increasing or decreasing trend. The increasing trend of the annual maximum snow depth is statistically significant at the 5% level at Mt. Fuji, whereas a decreasing trend of the annual maximum snow depth is statistically significant at the 10% level at Takada and Kanazawa. At the other nine sites, annual maximum snow depth has not shown a statistically significant change in recent decades. Recent studies report that the amount of snowfall in Japan will decrease as a result of global warming; however, these studies use data collected at low altitudes. It is, therefore, important to question whether the same theory can be applied to high-altitude mountainous areas. In high-altitude areas of the Japanese Alps region, it is reasonable to expect that a cold atmosphere will be maintained even with global warming, and an increase in evaporated moisture vapor in the air caused by warming on a global scale will increase the amount of snowfall in the region.
This paper reviews paleoclimate data from around the Japanese Alps in the late Quaternary period. The major data sources are total organic carbon content (TOC) of lake deposits and pollen composition from various sediments covering more than several thousand years. TOC reflects air temperature through the biological productivity of lake water. Pollen composition can show paleovegetation, and can be transformed into climate parameters using a modern analog method. The paleoclimate was reconstructed as follows under assumed conditions of altitude of 600–700m and latitude of around 36°N. Subarctic conifer forests were predominant and TOC was constantly low in the late MIS 6 (160–130 ka). It was cold as in MIS 2, the last glacial maximum. Vegetation changed significantly around 130 ka, and deciduous broadleaf trees of the cool-temperate zone became dominant in MIS 5e. TOC content in MIS 5e was also high, and temperature was as high as, or slightly cooler than, in MIS 1. Vegetation in MIS 5d to 5a comprised mixed forests of conifer trees and deciduous broadleaf trees, and their ratio changed substage by substage. TOC also fluctuated in periodicities of several thousand years, suggesting frequent temperature change. Climate in MIS 5d to 5a was a little colder than in MIS 5e and warmer than in MIS 3. The subarctic conifer forest was predominant and deciduous broadleaf trees were almost absent in MIS 4. TOC was also constantly low and temperature was much lower, as in MIS 2. Deciduous broadleaf trees flourished in MIS 3, and the ratio changed frequently in short periods of several hundreds of years to thousands of years, which corresponded to the D-O cycle. Although the annual mean temperature in MIS 3 was 5.0°C on average, that of a warm interstadial was 7.2°C and that of a cold stadial was 4.4°C. The vegetation in MIS 2 was characterized by the predominance of subarctic conifer forests and by the lowest TOC content. The reconstructed annual mean temperature was constantly around 3°C. Deciduous broadleaf trees increased abruptly from 14 to 12 ka and simultaneously TOC also increased sharply. Deciduous broadleaf trees became predominant in the Holocene (MIS 1), occupying more than 90% of arboreal pollen. TOC contents were also high, and reconstructed annual temperature was as high as 12°C in the early Holocene, a little higher than recent temperatures.
This review paper synthesizes geomorphic dynamics, sediment transport and resulting natural hazards in mountains of the southern Japanese Alps and their drainage basins, where climatic and geological situations produce highly active landform dynamics. In alpine areas above the timber line, shallow diurnal freeze-thaw action operating in the thin topsoil produces small-scale periglacial forms, and gravitational spreading leads to numerous sackung features where snow-melt and heavy rain in places promote rockslides. In subalpine and montane areas, deep-seated landslides originate from fractured sedimentary rocks, deep V-shaped valleys, and heavy rain, while shallow landslides continue with historical forest clearance. Continuous slope failures prevent vegetation recovery and maintain debris input to valleys. Steep valleys contribute to high-density debris flows. Frequent or repetitive occurrences of these mass movements promote continuous denudation of slopes, rockfall accidents along hiking trails, and sedimentation at artificial dams. They occasionally cause significant hazards to villages further downstream. Predicting and mitigating slope hazards require distinguishing among annual, low-magnitude processes, episodic high-magnitude processes and geomorphic changes associated with long-term climate change.
Integrated studies based on the flux tower network during the past two decades reveal the spatial variability of the annual values of net ecosystem production (NEP) in different terrestrial ecosystems. These ecosystems act as a huge carbon sink for human-induced CO2 emissions as a whole. Now, we need to understand the factors controlling carbon fluxes over timescales to comprehend how terrestrial ecosystems will respond to upcoming decades of climate change. This paper reviews studies of year-to-year changes of NEP of terrestrial ecosystems and shows how NEP responds to present climate fluctuations. It also reports long-term and intensive studies of carbon cycling in temperate regions, not only eddy covariance but also biometric measurements, conducted at Harvard and Takayama Forests. These temperate forests are not climax forests at non-equilibrium stages due to human disturbances in the mid-20th century. Successional changes of ecosystem structures that respond to disturbances greatly affect ecosystem functions such as NEP. Therefore, we need to understand not only ecosystem responses to climatic factors, but also age and structural effects on NEP. Long-term monitoring of ecosystems is necessary to determine how successional dynamics affect carbon cycling in mountainous forest regions of Japan.
Artificial warming experiments on alpine, subalpine, boreal, and subboreal ecosystems are reviewed to understand the impacts of global warming on the ecosystems of these regions. Among various warming methods, passive warming methods, especially open top chambers (OTC), have mainly been used in these outland regions due to limited electricity supplies and need for regular maintenance. Many researchers have studied the effects of experimental warming on variable ecological variables. The authors classify those variables into: (1) phenology, (2) plant growth, (3) plant reproduction, (4) plant community and diversity, (5) net primary production, and (6) biogeochemical cycle. After reviewing the effects on these variables observed with warming experiments, the following are discussed: i) differences in response speed between ecological variables, ii) local environment-dependence of warming effects, and iii) possible solutions to undesirable side-effects of OTC, such as snow deposition change, followed by future challenges for warming experiments in the ecosystems of these regions.
Meteorological data collected at mountain sites during the period 2006–2010 were archived under the Japanese Alps Inter-university Cooperative Project (JALPS). The site managers developed the data policy, and in situ data with metadata sets from 28 observation sites were prepared using a uniform format on a home page. Surface temperature lapse rates, including 3000-m level station data, agreed with previous results, in which the diurnal temperature range varied depending on location and season. A preliminary analysis comparing in situ and reanalysis data for temperature and wind speed showed a better agreement in terms of day-to-day variability but discrepancies in the diurnal mode. An evident weakening (warming) of daytime surface wind speed (temperature) was found at stations above the 3000-m level, indicating the development of convective layers. A new concept of data archiving using a super-site network within the framework of inter-university cooperation was proposed, and the importance of environmental monitoring by means of atmosphere-land interaction in mountainous areas was verified.
The Japanese Alps region is one of the heaviest snowy regions in Japan. The aim of this study is to clarify the spatial distribution of chemical components in fresh snow, as well as the relationship between weather conditions and chemical characteristics of fresh snow in the Japanese Alps region. We conducted a snow pit study immediately after a snowfall on the route inland from Itoigawa city (N1) and Joetsu city (N2). We collected only fresh snow samples during the 2011/2012 winter season. The samples were melted and pH, electric conductivity, and major ions (Na+, K+, Mg2+, Ca2+, Cl-, NO3-, and SO42-) were analyzed in a clean room. The pH of all samples was below 5.62. Na+ concentration correlates well with Cl- concentration. These ions are considered to be sea-salt components. These ions indicate the absence of chlorine loss. On the other hand, SO42- concentrations included non-sea-salt components. Na+ and SO42- concentrations decreased rapidly inland from the coastal area. The Na+ concentration of the N2 route was higher than that of the N1 route. It is considered that geomorphological features such as valley width and altitude differences influenced the transportation of chemical components. The chemical characteristics of the fresh snow layer changed with differences in weather conditions. Concentrations of sea-salt components were high in fresh snow when the vicinity of Japan was under the strong winter monsoon pattern. On the other hand, concentrations of sea-salt components were very low with snowfalls of plain snow. As a result of extracting the characteristic layer of Na+ concentration, changes in the vertical profiles of Na+ concentration became similar from the coast to the inland study sites. At the inland study sites, most SO42- was of non-sea salt origin. We compared the depositions of Na+ and SO42- in the fresh snow layer. Whereas there were large depositions of Na+ at the sampling sites near the sea, depositions of SO42- increased inland. This is because non-sea salt components were carried inland more than sea salt components. At the inland sites, there was a layer of high NO3-/nssSO42- component in the fresh snow. It is thought that the generation of NO3- by human activities near the site had an influence.
Deuterium excess (d-excess), as well as δ18O and δD, can offer an opportunity to understand hydrological cycles. However, there have been few investigations on d-excess of precipitation within a broad area observation network, including high-latitude areas. This study presents spatiotemporal variations in d-excess of precipitation observed in the Japanese Alps region. Precipitation samples, collected monthly at 14 locations across the Japanese Alps region from July 2010 to June 2011, were sampled for isotopic analyses. Annual precipitation amount weighted mean values of d-excess ranged from 11.0 to 14.7‰, and a correlation with altitude was found. No correlation with longitude and latitude was observed. Monthly variations in d-excess indicated a tendency toward higher d-excess values during the winter months at all sampling points. Spatial distribution of d-excess in each month showed significant correlations of d-excess with altitude in summer months. In winter months, relatively high values of d-excess were observed in precipitation caused under winter-type synoptic pressure patterns. Thus, spatiotemporal variations in d-excess of precipitation over the Japanese Alps region can be characterized by the correlation with altitude in summer months and the influence of synoptic conditions on its spatial distribution in winter months.
Observed discharge data covering the last three decades (1980–2009) at 16 rivers (i.e., rivers of Ida, Jinzu, Kurobe, Hime, Seki, Sai, Chikuma, Shinano, Uono, Kiso, Tenryu, Keta, Oi, Kamanashi, Fuefuki, and Fuji) in the Japanese Alps region are analyzed to clarify the elevation dependence of runoff characteristics during the snowmelt season. In the Hokuriku area, where large quantities of snow fall, the center time (CT) of snowmelt runoff tends to be delayed more at rivers with higher catchment-mean-elevations. In addition, the long-term (1980–2009) trend of a forward shift of snowmelt runoff timing becomes more remarkable at rivers in this area, with the exception of Hime River, as catchment-mean-elevation increases. However, the correlation between flowering dates of cherry trees and snowmelt runoff timing is stronger at rivers in the area with a lower catchment-mean-elevation. Consequently, snowmelt runoff at lower elevations in the Hokuriku area is sensitive to year-to-year fluctuations of spring onset, while progressive warming has greater impacts on snowmelt runoff timing at higher elevations, not only in winter to early spring but also in winter to late spring or summer. On the other hand, elevation dependence of snowmelt runoff timing is not detected at rivers in other areas; the runoff characteristics described above are neither clear nor statistically significant at both lower and higher elevations. Our results prove that the hydrological response to global warming is elevation dependent in a snow-dominated region, providing important knowledge for better water-resource management and flood control.
A snowpatch hollow is a landform that may reflect the timing of snow disappearance associated with Holocene climate fluctuations. Thus, the development of a snowpatch hollow provides information on geomorphic processes and landscape evolution on alpine slopes in the Holocene. In this study, first, we investigate micro-landforms and slope forming materials of snowpatch hollows located at the valley head of Okunishikochi-sawa, where the slopes were glaciated during MIS 4, around Daishojidaira (2699 m a.s.l.; 35°28.64′N, 138°09.40′E), near Mount Akaishi-dake, in the Southern Japanese Alps. Second, we monitor ground temperature at 1 cm depth and 20 cm depth in the snowpatch bare ground, and measure slow mass movements with a paint line drawn on the bare ground. The snowpatch hollows are divided into three landscape units based on slope profile, vegetation, and soil stratigraphy. Surface I unit is comparable to the margin of the snowpatch hollow. Pinus pumila communities occupy large parts of these slopes. The humic loam layer is generally thick, and directly covers the solifluction deposit, which is the surface material of the snowpatch hollow. The humic loam layer intercalates Kikai Akahoya tephra (K-Ah; 7300 cal BP) in the lower part. Surface II unit is located within surface I. The humic loam layer is less than 20 cm thick, and contains many clasts transported from nearby snowpatch bare ground. This layer does not intercalate K-Ah. Snowpatch plant communities are established on surface II. Surface III unit is comparable to the present-day snowpatch bare ground. Periglacial processes such as frost creep, needle ice creep, and gelifluction act on the slope surface. The presence of K-Ah below surface I indicates that the nivational process became less active by the early Holocene. These geomorphic changes would have been promoted by atmospheric warming after the Late Glacial age. Subsequently, surface II was formed mainly by solifluction and slope-wash erosion. A layer composed of granules and fine pebbles, which were transported from snow-free ground by niveo-fluvial processes, overlay most of surface II. Deposition of this layer started around 5600 cal BP, and continued until at least 1200 cal BP. Therefore, surface II is estimated to have formed from 5600 cal BP to 1200 cal BP. Frost creep, needle ice creep, and gelifluction have been partially active on the snowpatch bare ground of surface III, although the slope processes weakened in the Holocene.
The upper reaches of the Azusa River in the Kamikochi Valley, a gravel-bed river with braided channels, are characterized by Salix arbutifolia occurring in patches and as isolated trees in the active riverbed. This study aims to clarify the relationships between geomorphological dynamics of the riverbed and environmental diversity of the active riverbed in the Kamikochi Valley in the establishment and growth of pioneer plants. The discussion on geomorphological processes is based on five geomorphological maps of the observation site in the Kamikochi Valley, which were made every summer from 2007 to 2011, and which record annual landform changes of the riverbed. In addition, images taken with an interval shooting camera were used to observe flood conditions of the riverbed from 3 July 2011 to 4 October 2011. Landform changes and/or sediment transport in the riverbed occurred almost every year from 2007 to 2011 during severe flood events. Channel migrations are generally caused not by lateral shifting with lateral erosion but by channels being buried with sediments and new channels being excavated. There are some stable spots at bars and/or islands in the active riverbed where only slight landform changes occur over a period of four or more years. At those locations, pioneer plants, especially Salix arbutifolia, germinate and grow to form young pioneer patches. When lateral erosion occurs, it causes the destruction and/or size reduction of patches. If a small seedling willow patch survives for several years, it becomes a grown patch and finally old isolated trees. Because each patch was established in a different year, patches in various age and size classes are found in the active riverbed. The fluvial geomorphic processes provide dynamic environmental diversity for pioneer species in the active riverbed and cause the destruction and re-establishment of vegetation. As a result, vegetation diversity is created in the active riverbed of the Kamikochi Valley.
We performed this study to further understand the effect of canopy gap stands on surface soil carbon dynamics in cool-temperate deciduous broad-leaved old-growth forests. We investigated the annual aboveground litter production, soil organic matter content, and soil humic acids (soil organic matter) quality in several matured(n = 7) and gap (n = 3) areas (each area was 20 m × 20 m) in a Japanese old-growth beech forest. The annual fine litter (foliage) production from 2005 to 2011 in the matured area was totally higher than that in the gap area; however, those of annual coarse litter production were not so different. The gravimetric soil carbon content in the matured area was significantly higher than that in the gap. In addition, the C:N ratios in the matured area were significantly higher than those in the gap. The estimated compositions of carbonyl C and aromatic C and those of O-alkyl C and alkyl C in total C of soil humic acids in the matured area were higher and lower, respectively, dependent on higher A600/C values, than their respective compositions in the gap area. Furthermore, the ratio of alkyl C to O-alkyl C in the matured area was significantly lower than those of the gap. Our data strongly suggests that, compared to the closed canopy stands, canopy gap stands in this study site can be a carbon source, which is particularly dependent on labile carbon dynamics.
The aim of this study is to clarify changes in the ecosystem carbon cycle in response to predicted global warming in various ecosystems including semi-natural grassland. To clarify responses of the whole ecosystem to warming in a semi-natural cool-temperate grassland, we conducted an in situ warming experiment and examined plant growth and CO2 flux responses. Five pairs (control and warmed plots) of Zoysia japonica plots were established. Warmed plots were warmed using infrared heaters from June to November 2009. Once a month, aboveground biomass (AGB) of Z. japonica was estimated using the point frame method. Net ecosystem production (NEP) and ecosystem respiration (Re) were determined from CO2 flux measured using the closed chamber method. Each month, relationships were obtained between photosynthetic photon flux density (PPFD) and NEP (PPFD-NEP curve) and soil temperature (ST) and Re (ST-Re curve). Monthly cumulative NEP, Re, and gross primary production (GPP, sum of NEP and Re) were calculated using these relationships and continuously recorded PPFD and ST data. Although there were some mechanical problems when using infrared heaters, the soil temperature in the warmed plots where infrared heaters worked well was an average of 2.3°C higher than the control plots. This suggests the heating method using infrared heaters is applicable to grassland ecosystems. AGB in the warmed plots tended to be higher (by a maximum of 70%) than in the control plots throughout the experimental period, suggesting that experimental warming affected the phenology and extended the growth period of Z. japonica. Initial slope and light compensation point of PPFD-NEP curve were significantly affected by the warming. Monthly cumulative GPP in the warmed plots tended to be higher (by a maximum of 32%) than in the control plots. This is partly explained by the increased biomass and changed photosynthetic characteristics in the warmed plots. Although not all parameters of the ST-Re curve were affected by warming, monthly cumulative Re in the warmed plots tended to be higher (by a maximum of 35%) than in the control plots. As a result, monthly cumulative NEP in the warmed plots tended to be higher than in the control plots, especially in July (approximately 70% higher) and October (approximately 100% higher). These results suggest that experimental warming affected the carbon cycle in semi-natural cool-temperate grassland by changing the phenology and photosynthetic characteristics of Z. japonica. To promote a better understanding of whole ecosystem responses to predicted warming, a longer term experiment and more detailed descriptions of carbon dynamics including the belowground part of the ecosystem are needed.
To clarify seasonal and inter-annual variations in the contribution of heterotrophic respiration to soil respiration and influences of such changes on the carbon balance in a forest ecosystem, relationships between respiration rates, soil temperature and soil water content, and the contribution ratio of heterotrophic respiration, were estimated over almost 3 years. Heterotrophic respiration was separated from soil respiration by the trenching method; CO2 emissions from the soil surface were measured along with soil temperature and volumetric soil water content in a cool-temperate deciduous forest from November 2009 to September 2012. Also, the root bag method and two decay models were used to accurately measure CO2 emissions from decomposing dead roots. The soil and heterotrophic respiration responded differently to changes in soil temperature and soil water content. An increase in soil temperature caused increases in respiration, and the response of heterotrophic respiration was lower than that of soil respiration. Also, an increase in the soil water content caused a slight increase in soil respiration and a decrease in heterotrophic respiration. These responses of the respirations to environmental factors caused a decrease in the contribution ratio of heterotrophic respiration with an increase in soil temperature and soil water content. These results suggest that the contribution ratio could experience complex changes when both factors change simultaneously in field conditions. Annual contribution ratios of heterotrophic respiration were estimated at 62% in 2010 and 2011, and the contribution ratio showed seasonal variation ranging from 60% to 100%. The estimated annual heterotrophic respiration rate in 2010 without such seasonal variation ranged from 1.50 to 2.51 kg CO2 m-2 yr-1, and these rates were 96% to 161% of that with seasonal variation (1.56 kg CO2 m-2 yr-1). Also, the annual contribution ratio in 2010 estimated without the effect of soil water content (using respiration and soil temperature curve) was 80%. The resulting annual heterotrophic respiration rate was 2.01 kg CO2 m-2 yr-1, and this rate was 128% of that with the effects of soil water content (using respiration, soil temperature and soil water content curve). In contrast, the effect of inter-annual variation in the contribution ratio on annual heterotrophic respiration rate was small. Therefore, it is important to take into account the seasonal variation in the contribution ratio and the effects of the soil water content on the contribution ratio for more accurate estimation of heterotrophic respiration and net ecosystem production.
Sackung features (scarps) have developed extensively in the Japanese Alps as a result of gravitational deformation. Electrical resistivity tomography was applied to evaluate the internal structure below eight scarps located above 2600 m a.s.l. The range of resistivity values differed significantly between the scarps and is mainly controlled by the moisture content of the ground. High- and low-resistivity areas were distinctly separated below some scarps. Areas of relatively low resistivity are considered as slightly fractured bedrock. In contrast, areas of high resistivity are likely to indicate highly fractured bedrock and/or talus without matrix. Such boundaries between high- and low-resistivity areas seem to correspond to fracture planes estimated from topography.
We studied the geomorphological and geological characteristics of four medium- to large-scale landslides that occurred in the alpine and subalpine zones of the northern Japanese Alps and assessed the relationship between landslide features and vegetation diversity in the landslide areas. To achieve this, we conducted field investigation and laboratory work including airphoto interpretation and radiometric dating of soils and fossil logs. Our field investigations indicate that, even in alpine and subalpine zones, landslide blocks (i.e., landslide deposition areas) display specific landforms such as scarplets, shallow depressions, and low mounds with linear or curved forms. Vegetation cover and aquatic areas such as peat bogs and moors also display linear or curved patterns that are superimposed on these small topographic features. We found that the highly diverse landscapes in landslide blocks were substantially different from those in present-day or fossil periglacial slopes near the main ridges, both of which displayed monotonous facies. The specific patterns of vegetation cover seen on landslide blocks probably formed under the influence of different slope environments, with variations of parameters such as inclination, soil properties, thermal-water regimes, and microclimate occurring as a result of landslide activities. Similarly, geomorphic changes such as channel migration and waterfall formation in and around areas of landsliding probably affected biological evolution and differentiation, and resulted in multiple modulations of the gene expression of aquatic organisms. Medium- to large-scale landslides are often reactivated by secondary movement. We suggest that subsequent variations of the landforms in the landslide blocks caused sudden or gradual changes in the surrounding natural environments, which had been forming since the initial mass movement. The biota present in a landslide block is the result of evolution and differentiation during geomorphic changes such as those described here; therefore, it is possible that secondary landsliding resulted in increased biological diversity and complexity.