Mount Norikura Research Articles

Foraging efficiency of two alpine bird species in central Japan

ABSTRACT Capsule The foraging efficiency of Alpine Accentors Prunella collaris and Japanese Accentors P. rubida is highest on the snow surface in the alpine zone, where they forage for fallen arthropods. Aims To compare the foraging efficiency of two bird species across alpine habitats, including the snow surface, and discuss the impact of changes in snow cover on their foraging behaviour. Methods The foraging efficiency of two alpine bird species, recorded as the number of pecks per unit time, was compared in the alpine zone of Mount Norikura in central Japan, among four habitat types: snow surface, Japanese Stone Pine scrub, alpine tundra and scree. Results In total, respective 45 and 32 foraging sequences of Alpine Accentors and Japanese Accentors were recorded. For both species, foraging efficiency was markedly higher on the snow surface than in other habitats. Conclusion Alpine bird species exhibit high foraging efficiency on the snow surface in the alpine zone, assuming that prey sizes are similar across habitats. With the decreasing amount of remaining snowpack in the alpine zone, due to the general trend of climate change, bird species will likely have a shorter period to efficiently utilize these foraging habitats in the future.

Drivers of functional and phylogenetic structures of mountain bird assemblages along an altitudinal gradient from the montane to alpine zones

Understanding the process underlying the spatial gradients in biodiversity is a fundamental issue in ecology. Altitudinal gradients are ideal systems for examining the community assembly process because they represent rapid changes in environmental conditions over relatively short distances. The functional and phylogenetic approaches allow a deeper mechanistic understanding of the underlying assembly process. However, whether community assembly from montane to alpine zones is driven more by ecological constraints or human settlement patterns is not fully resolved and may vary by system. Here, we examined the phylogenetic and trait-based functional structures from the montane to alpine zones and clarified the effects of natural environmental factors and human-induced landscape transformation on the breeding bird assemblage on Mount Norikura, central Japan. Breeding birds from 700 to 3026 m a.s.l. were surveyed in 2016–2017. Bird community structures were examined based on species richness, functional and phylogenetic structures. A null modelling approach was performed to examine functional and phylogenetic cluster/overdispersion structures; clustering and overdispersion imply species elimination by environmental filters and limiting similarity as a corollary of competitive exclusion of species, respectively. Furthermore, we examined the relative effect of natural environments and human disturbance. Bird species richness was high in the mountain base to mid-elevation, then decreased with elevation. We found a contrasting pattern in the phylogenetic and functional structures in the alpine zone: phylogenetic overdispersion and functional clustering. In contrast, the functional and phylogenetic structures were clustered in the upper parts of the subalpine zone. The functional and phylogenetic clusterings in the lower parts of the subalpine and montane zones were negligible with the weak effects of the environmental filtering. Single-trait analysis showed that the high abiotic tolerance and foraging or nesting capabilities in treeless environments were clustered in the alpine zone, and mobility was clustered in the subalpine zones. Natural environments strongly affected bird community structures, but human disturbance added species to assemblages in the mountain base to mid-elevation and changed the functional and phylogenetic structures. Our findings highlight that filtering by severe natural environments is a fundamental community assembly process in high mountain regions, whereas filtering effects can be weaker at lower elevations. Furthermore, the filtering effect should differ between the alpine and the upper parts of the subalpine zones because of different combinations of clustered traits. Climate change and landscape transformation pressures may strongly impact biodiversity in the alpine and subalpine zones, respectively.

Effect of pollinator size on seed set in Lamium album var. barbatum

Background and aims – Previous researchers have demonstrated that geographic variation in pollinator community composition can generate diversity in the floral traits of animal-pollinated plants. Our study focused on the bumblebee-pollinated white dead-nettle Lamium album var. barbatum. Geographic variation in corolla length of this species is known to be correlated with regional pollinator size. The aim of this study is to clarify whether size-matching between flower and pollinator affects seed set in L. album.Material and methods – In the present study, we investigated two L. album populations on Mount Norikura, central Japan. We determined the pollinator community composition and corolla length during the flowering period of L. album and recorded seed set after a single visit by different pollinator categories.Key results – We observed that the main pollinators of L. album were bumblebee queens and workers. Bumblebee queens visited flowers more frequently than workers during peak flowering. Furthermore, size-matching between flowers and bumblebee queens, but not workers, strongly promoted seed set. These results suggest that L. album flower size is adapted to bumblebee queens, the main pollinator during peak flowering season in our study sites.

Bird Community Heterogeneity Along Four Gradients of Different Orientations on a Temperate Mountain

Mountains harbour high biodiversity that is facing a crisis due to recent climate change. Bird communities shift along mountain gradients. Some previous studies have suggested that the effect of vegetation is prevalent on temperate mountains. In this study, we investigated the limiting effects of vegetation on the altitudinal distribution of birds on Mount Norikura in central Japan, by comparing bird communities along four gradients of different orientations. We recorded birds using the line-transect method and classified vegetation into six types: montane deciduous broadleaved forest, subalpine coniferous forest, subalpine birch forest, Japanese Stone Pine scrub forest, alpine tundra and bare ground below the alpine area.We identified the treelines and ecotones between the predominant vegetation types along each gradient. We found that bird species composition changed drastically at the treeline along three gradients. A non-metric multidimensional scaling (NMDS) ordination revealed: 1) the similarity between bird community structures in the subalpine coniferous forest and the Japanese Stone Pine scrub forest differed among the gradients, 2) despite birch being broadleaved, the bird community in the subalpine birch forest was a subset of that in the subalpine coniferous forest and was more similar to that in the subalpine coniferous forest than that in the montane deciduous broadleaved forest, and 3) in upper parts of the subalpine zone, the bird community structures in the subalpine coniferous and birch forests were similar to each other.Our findings suggest that although the treeline limits the distribution of forest-dwelling bird species, this effect differs among gradients with different orientations, probably depending on the scrub height of the Japanese Stone Pine scrub forests. Furthermore, the heterogeneity of coniferous and birch forests in the upper parts of the subalpine zone may have little effect on the altitudinal distribution of birds.

Altitudinal changes in vegetation of tree, herb and fern species on Mount Norikura, central Japan

Altitudinal changes in vegetation of tree, herb and fern species on Mount Norikura, central Japan

Effects of topographic and edaphic conditions on alpine plant species distribution along a slope gradient on Mount Norikura, central Japan

AbstractThis study examined the effects of topographic and edaphic conditions on alpine plant species distribution along a slope gradient on Mt. Norikura (3026 m a.s.l.), central Japan. Topographic and edaphic factors investigated at 40 plots were: slope inclination, ground surface texture, soil water content and soil inorganic nitrogen concentration (NO3‐N, NH4‐N). The topographic and edaphic factors changed with slope positions: slope inclination was steeper, soil texture was coarser, and soil water and inorganic nitrogen concentration decreased with increasing slope position. Five vegetation types were located along the slope gradient and related to two factor‐groups: (1) changes in soil water, NH4‐N, slope inclination along the slope gradient, and (2) ground surface texture. A tall herbaceous plant community developed at the low slope position, near tarns, with fine soil surface texture, high soil water and NH4‐N, while Dicentra peregrina dominated on an unstable rubble slope near the ridge top. The distribution of each species was predictable from the two factor‐groups. Although the five vegetation types were related to the two factor‐groups, responses to the two factor‐groups differed among species, even within the same vegetation type. Therefore, this study showed that the topography of the terrain largely regulated alpine plant distribution by affecting edaphic conditions, and that global warming may alter species composition by changing edaphic conditions.

How the timberline formed: altitudinal changes in stand structure and dynamics around the timberline in central Japan

Altitudinal timberlines are thought to move upward by global warming, a crucial topic in ecology. Tall tree species (the conifer Abies mariesii and the deciduous broad-leaved Betula ermanii) dominate the sub-alpine zone between 1600 and 2500 m a.s.l., the timberline, on Mount Norikura in central Japan. Dwarf pine Pinus pumila dominates above the timberline to near the summit (3026 m a.s.l.). This study evaluated how the timberline formed on Mount Norikura by examining altitudinal changes in stand structure and dynamics around the timberline. One hundred and twenty-five plots of 10 m × 10 m were established around the timberline (2350-2600 m a.s.l.). Trunk diameter growth rate during 6 years was examined for A. mariesii, B. ermanii and P. pumila. Mortality during this period and mechanical damage scars on the trunks and branches due to strong wind and snow were examined for A. mariesii only. The density, maximum trunk height and diameter of A. mariesii in plots decreased with altitude. The maximum trunk height of B. ermanii decreased with altitude, but density and maximum trunk diameter did not decrease. In contrast, the density of P. pumila abruptly increased from around the timberline. A strong negative correlation was found between the densities of P. pumila and tall tree species, indicating their interspecific competition. Trunk diameter growth rates of A. mariesii and B. ermanii did not decrease with altitude, suggesting that these two tall tree species can grow at the timberline. The ratio of trees with mechanical damage scars increased with altitude for A. mariesii, a tendency more conspicuous for larger trees. The mortality of larger A. mariesii was also greater at higher altitude. Tall tree species may not increase their trunk height and survive around the timberline because of mechanical damage. This study suggests that the altitudinal location of the timberline is mainly affected by mechanical damage due to strong wind and snow rather than by growth limitation due to low temperature. Therefore, the timberline would not move upward even under global warming if these growth and mortality characteristics do not change for a long time.

Effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura, central Japan

We investigated the effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura (3026ma.s.l.), Japan. We examined the vegetation of herb and tree species shorter than 1.3m along roadsides and adjacent natural vegetation at 200m intervals between 1600 and 3000m a.s.l. The timberline was at 2500ma.s.l. Although the canopy opening was greater at the roadsides than in the natural vegetation, it was similar above the timberline. Soil cover and litter depth of the soil surface were less at roadsides than the natural vegetation, and gravel and rock cover were greater at roadsides. Species composition changed in similar directions from natural vegetation to roadsides along the altitudinal gradient. This direction was related to canopy opening and litter depth. Liliaceae, Ericaceae and Pinaceae were dominant families in the natural vegetation, and Asteraceae and Poaceae were greatest at the roadsides. Roadside plants were mostly herb species, while tree species increased in natural vegetation. Five exotic species were also observed at the roadsides. Sunny plant species gradually increased with altitude in the natural vegetation, indicated by the increase in canopy opening. By contrast, roadside plants were mostly sunny plant species irrespective of altitude. The number of lowland and montane species increased at the roadsides in the subalpine zone. Thus, roads strongly altered species composition of the natural vegetation along the altitudinal gradient probably because of changes in light and soil-surface conditions for growth and seedling establishment.

How the scrub height of dwarf pine Pinus pumila decreases at the treeline

AbstractPlant height decreases much within narrow altitudinal spans near treelines. We compared the stem age, stem inclination and shoot elongation rates of alpine dwarf pine Pinus pumila between the upper distribution limit (treeline, 2,850 m a.s.l.) and the lower distribution limit (2,500 m a.s.l.) on Mount Norikura in central Japan, to examine how the growth traits of P. pumila change with altitude. The mean stem height at the upper distribution limit (49 cm) was about a quarter of that at the lower distribution limit (187 cm). The mean ratio of stem height to length was lower at the upper distribution limit than at the lower distribution limit, indicating that P. pumila stems inclined more at the higher altitude. The mean stem age at the upper distribution limit (48 years) was less than a half of that at the lower distribution limit (109 years). Although the shoot elongation rate positively correlated with stem length at the two altitudes, the shoot elongation rate at a given stem length was lower at the upper distribution limit than at the lower distribution limit. Thus, less developed scrub at the upper distribution limit than at the lower distribution limit was due to shorter stem age, more creeping stems and lower shoot elongation rates. Generally, wind velocity is greater in higher altitudes. Probably, strong wind reduces the growth and mean stem age of P. pumila stems at the upper distribution limit. Therefore, this study concludes that the scrub height of P. pumila is controlled not only by temperature, but also by strong wind.

Nucleation mode particles in upslope valley winds at Mount Norikura, Japan: Implications for the vertical extent of new particle formation events in the lower troposphere

Number‐size distributions of atmospheric aerosol particles of 9–300 nm diameter were observed along with SO2 and NH3 concentrations at Mount Norikura, Japan (36.1°N, 137.5°E, 2770 m asl), during September 2001 and August–September 2002. Particle size distributions between the free troposphere and the mixed layer were measured at the site under local wind system conditions, comprising downslope mountain and upslope valley winds. The local wind system was well developed under clear‐sky conditions and was determined according to temporal variation of the water vapor mixing ratio at the site. Nucleation mode particles were observed on 4 of 23 clear‐sky days during our observation periods. Nucleation mode particles were observed in the mixed layer air, but never in the free tropospheric air, suggesting that new particle formation occurred in the air transported from the mixed layer. Nucleation‐mode‐particle growth rates during new particle formation events were 2.6–3.1 nm h−1. Preexisting particle concentrations on event days were about half those of nonevent sunny days on average, but no positive correlation was found between the events and either SO2 or NH3 concentrations. The events always occurred in a cold air mass advected from the north behind cold fronts. Horizontal advection of the northern cold air mass might bring a clean air mass with low preexisting particle concentration in the mixed layer and trigger a new particle formation event at Mount Norikura.

Changes with altitude of the stand structure of temperate forests on Mount Norikura, central Japan

Changes in stand structure with altitude have been studied at ten sites between 800 and 2,500 m above sea level (a.s.l.) in temperate forests on Mount Norikura (36°06′N, 137°33′E, 3,026 m a.s.l.) in central Japan. Vegetation in this range of altitudes was roughly classified as a montane deciduous broad-leaved forest zone between 800 and 1,600 m a.s.l. and a subalpine coniferous forest zone between 1,600 and 2,500 m a.s.l. at the timberline. The frequency distribution of trunk height was an L-shaped pattern at 800 m a.s.l., changed to a flat pattern with increasing altitude up to 2,000 m a.s.l., but changed to an L-shaped pattern again from 2,000 to 2,500 m a.s.l. This change in frequency distribution of trunk height with altitude was related to the change in maximum trunk height with altitude. The maximum trunk height did not change with altitude between 800 and 2,000 m a.s.l. but it decreased markedly from 2,000 to 2,500 m a.s.l. Although mechanical damage to conifer trunks and branches was not observed between 800 and 2,000 m a.s.l., the proportion of damaged trees increased from 2,000 to 2,500 m a.s.l., suggesting that subalpine conifers cannot grow in height near the timberline because of mechanical damage. The increase in the number of small trees from 2,000 m a.s.l. to the timberline was therefore because of a less developed canopy structure, i.e. small trees can grow without shading by canopy trees. This study suggests that mechanical damage, probably because of strong winds in the winter, affects changes with altitude in regeneration and formation of the timberline.

Climatic factors affecting the tree‐ring width of Betula ermanii at the timberline on Mount Norikura, central Japan

AbstractTree‐ring‐width chronology of Betula ermanii was developed at the timberline (2,400 m a.s.l.) on Mount Norikura in central Japan, and climatic factors affecting the tree‐ring width of B. ermanii were examined. Three monthly climatic data (mean temperature, insolation duration, and sum of precipitation) were used for the analysis. The tree‐ring width of B. ermanii was negatively correlated with the December and January temperatures and with the January precipitation prior to the growth. However, why high temperatures and heavy snow in winter had negative effects on the growth of B. ermanii is unknown. The tree‐ring width was positively correlated with summer temperatures during June–August of the current year. The tree‐ring width was also positively correlated with the insolation duration in July of the current year. In contrast, the tree‐ring width was negatively correlated with summer precipitation during July–September of the current year. However, these negative correlations of summer precipitation do not seem to be independent of temperature and insolation duration, i.e., substantial precipitation reduces the insolation duration and temperature. Therefore, it is suggested that significant insolation duration and high temperature due to less precipitation in summer of the current year increase the radial growth of B. ermanii at the timberline. The results were also compared with those of our previous study conducted at the lower altitudinal limit of B. ermanii (approximately 1,600 m a.s.l.) on Mount Norikura. This study suggests that the climatic factors that increase the radial growth of B. ermanii differ between its upper and lower altitudinal limits.

Effects of atmospheric electric fields on cosmic rays

Physikalisches Institut, Universitaet Bern, CH-3012, Bern, Switzerland~Received 18 December 2003; published 30 June 2004!The electric fields associated with thunderclouds change the intensity of secondary cosmic rays observed onthe ground. This effect has been investigated using several detectors located at the Mount Norikura CosmicRay Observatory where excesses of 1% and more of the average counting rate may be observed when theObservatory is covered by thunderclouds. A frequency analysis of the time series of days with such excessesfor the period 26 October 1990 to 15 January 2002 shows the expected summer maximum in the rate ofoccurrence and, more surprisingly, a 26-day variation. An electric field mill was installed to help determine therelationship between the intensity variations and the strength and direction of the field near the detector system:the excess is usually observed when a negative electric field~accelerating negative charges downward! greaterthan 10 kV/m is present in the atmosphere above the observatory. Based on Monte Carlo simulations wepredict that excess counting rates measured without charge discrimination will be expected as a consequenceof the excess of positive muons among the secondary cosmic rays.DOI: 10.1103/PhysRevD.69.123010 PACS number~s!: 96.40.Kk, 52.80.Mg, 92.60.Pw, 96.50.PwI. INTRODUCTION

A data taking system with low power consumption for cosmic ray research

We have succeeded in operating the 64m2 solar neutron detector based on 24W power consumption. The detector has been operated at the Mount Norikura Cosmic Ray Observatory (2770m) with the small amount of power delivered by solar cell arrays and windmills, without generator service, throughout severe winter of 2003–2004. The results of our experiences are described.

Effects of climate on the radial growth of tree species in the upper and lower distribution limits of an altitudinal ecotone on Mount Norikura, central Japan

Tree‐ring width chronologies were developed for Abies veitchii, Betula ermanii and Betula platyphylla var. japonica in their altitudinal ecotone (approximately 1600 m a.s.l.) on Mount Norikura, central Japan, to determine what climatic conditions affect the growth of tree species in the upper and lower distribution limits of an altitudinal ecotone. This altitude was the lower distribution limit for A. veitchii and B. ermanii in the subalpine zone, and was the upper distribution limit for B. platyphylla var. japonica in the montane zone on Mount Norikura. Tree‐ring widths of the two Betula species and A. veitchii were positively correlated with the August precipitation of the current and previous years, respectively. Precipitation in August (the hottest month) was reduced compared with other months during summer. Tree‐ring width of B. platyphylla var. japonica showed no correlation with temperatures in any month in its upper distribution limit. In contrast, tree‐ring widths of B. ermanii and A. veitchii were negatively correlated with the August temperatures of the current and previous years, respectively, at the lower distribution limit of these species. Therefore, the two Betula species and A. veitchii responded to climatic conditions of the current and previous years, respectively. The present study also suggests that a water deficit in August reduces growth of these three species in this altitudinal ecotone, irrespective of the upper or lower distribution limits, and that a high August temperature is more detrimental to the growth of A. veitchii and B. ermanii in their lower distribution limits. Thus, the three species with different altitudinal distributions examined in the present study responded differently to climatic conditions in this altitudinal ecotone on Mount Norikura.

Propagation of solar neutrons through the atmosphere of the Earth

The propagation of solar neutrons through the atmosphere of the Earth has been calculated by a Monte Carlo method using a nuclear interaction model which can reproduce the existing data obtained by accelerator experiments. With this calculation, it has been found that the elastic scattering process plays an important role in the propagation of solar neutrons in the atmosphere at an incident energy below ∼ 200 MeV. By applying this calculation to the analysis of a solar neutron event observed at Mount Norikura Cosmic Ray Observatory on June 4, 1991, it is possible to interpret the event as γ rays and neutrons having been produced impulsively at the time of the solar flare. The event observed at Jungfraujoch on June 3, 1982 can be explained similarly.

Observation of solar neutrons associated with the large flare on 1991 June 4

Evidence for neutrons coming from the Sun associated with a large flare at 03:37 UT on 1991 June 4 is reported. The event was recorded by a neutron telescope, and also by a muon telescope, located at Mount Norikura Cosmic Ray Laboratory (2770 m). The statistical significance of the signal recorded by the neutron telescope is 4.4 σ for neutron kinetic energies between 50 and 360 MeV in the time interval 03:46-03:49 UT. For the muon telescope the statistical significance of the signal is 4.9 σ in the time interval 03:47-03:56 UT

High transverse momentum of -ray bundles in EAS at collision energies around 1014eV

High-energy γ-ray bundles (Σ Eγ ≥ 2 TeV) were observed together with associated air showers at Mount Norikura (738 g cm-2). Many bundles were found to be located away from the air-shower axis determined by the contours of the particle density distribution in spark chambers. The lateral distribution of γ rays gives an average transverse momentum of at least 2.3-0.7+0.8GeV/c for the most forward jet of secondaries, which is equal to 0.57-0.09+0.13GeV/c for each neutral pion, with respect to the collision axis in the energy region around 1014 eV. EAS size dependences of γ-ray bundles suggest high multiplicity and increasing transverse momentum. However, if a change of primary composition is assumed, an interpretation without changing the interaction drastically may be possible.

The NAP flux at mountain altitude 735 g cm-2

The energy spectrum of nuclear active particles (NAP) with energy Sigma Egamma greater than 3 TeV is obtained from an analysis of thick emulsion chamber (140 cu of Pb) exposed on Mount Norikura at 2770 m above sea level and the vertical flux is estimated to be (1.4+or-0.1)*10-10 cm-2 s-1 sr-1. Assuming that the energy spectrum and the zenith angle distribution of NAP are expressed by power functions proportional to E-( gamma +1) and cosn-2 theta respectively in differential form, the exponents gamma and n are obtained as 2.3+or-0.1 and 7.3+or-0.5 respectively. The collision mean free path and the ratio of constituents of NAP are discussed.

Study of extensive air showers at Mount Norikura. IV. Lateral distribution of muons for types of EAS

Muons accompanied by EAS have been observed by a neon hodoscope array 6 m2 in area placed 36 m from the center of the EAS array. The lateral density distribution function of muons and an average density at fixed distance are studied with respect to the size and age parameter of EAS. The EAS are in a size range of 106 to 107, and the muon density at distances of 15–55 m from the axis of EAS has been observed for muons which penetrate 20 cm of lead.Preliminary results obtained in this experiment are as follows: (1) The lateral density distribution of muons shows clear correlation with that of electrons: assuming the distribution function to be a power function of the distance from the axis, the exponent varies from steeper than −1.5 to flatter than −1.0 for younger and older EAS respectively. (2) The size dependence of muon density can be expressed as [Formula: see text], and is independent of the age parameter of EAS.