Head Hollow Research Articles

Population structure and regeneration strategy of relict deciduous broadleaved trees on Mount Tianmu, Zhejiang Province, China.

The population structure, regeneration ways and spatial relationships of six relict deci-duous broadleaved trees were examined based on community investigation on Mount Tianmu, East China. The results showed that relict deciduous broadleaved trees had a strong ability of vegetative reproduction and their population structure was generally belonged to intermittent type. Some relict species such as Cyclocarya paliurus and Liquidamb aracalycina regenerated discontinuously at appropriate sites via long-distance diffusion. Some species such as Emmenoptery henryi and Euptelea pleiospermum regenerated discontinuously around mature trees due to habitat limitation and frequent disturbance. After occupying forest gaps by seedling regeneration, C. paliurus, L. acalycina, Nyssasinensis and Liquidambar formosana could recruit and form multi-stemmed individuals by their inherent sprouting ability at relatively stable sites such as crest slope and side slope. At riverbed, valley slope and head hollow, recognized as unstable habitats, Emmenopterys henryi, E. pleiospermum, and L. formosana could also recruit by strong sprouting ability due to sparse seedlings and individual loss incurred by disturbance. Therefore, the relict deciduous broadleaved trees could be classified into two ecological species groups (repairment species for forest gap and supplement species for special habitat) based on spatial distribution and strategy of regeneration and competition. We suggested that the protection of special habitats of their communities should be strengthened.

Разработка научных основ и оптимизация технологических режимов нового способа протяжки литых слитков

The paper considers an idea of realization of alternating deformation in forging cast ingots and determines a rational shape of forging tools. The results of the analysis of the strained state of metal during compression in heads with a profiled surface and in smooth heads (at the second stage of deformation) are presented. The use of new tools provides the formation the metal structure in first passes by means of additional alternating deformation without a significant change of the cross-section shape of the billet. Alternating deformation increases the accumulated strain without changing the cross-section shape of the billet, stimulates the formation of the polygonized subgranular structure and refines the grain structure. Results of the strained state analysis of metal during forging in profiled and flat heads are presented. The degree of the accumulated strain in particles in the deformation zone is calculated for six points along the height of the section of the head hollow in order to estimate strain inhomogeneity in the ingot height. The accumulated strain for a specific particle is determined from the problem solution for a flat deformed state under isothermal conditions by means of Deform software. In layers adjacent to the contact zone the strain is minimal since there are areas of hindered deformation (sticking areas), the size of these areas decreases towards the depth of the metal; at the beginning of plastic deformation a free surface appears which is not under the working tool. Ways to control the technological process of forging are found for increasing homogeneity of strained state in the ingot section and stimulating the formation of the polygonized substructure during compression and the ultradisperse structure after metadynamic recrystallization during a pause.

Effects of micro-topographies on stand structure and tree species diversity in an old-growth evergreen broad-leaved forest, southwestern Japan

Stand structure and species diversity were studied in correspondence with micro-topographies in an old-growth forest in southwestern Japan. The study was conducted in a 200×200m2 permanent plot, which were divided into 400 subplots using grids of 10m×10m. Subplots were categorized to four micro-topographies as crest slope (CS), head hollow (HH), upper slope (US) and lower slope (LS), basing on slope of forest floor and plot position, and to two elevational zones as below 450 m and above 450 m. Tree censuses for all individuals with diameter at breast height (DBH) ⩾ 5 cm were conducted in 2009 and 2013. The results indicated that CS had subplot means of living stems, dead stems, DBH, basal area (G), and basal area increment (▵G) significantly higher than that in LS. While, means of recruited stems and Shannon diversity index were significantly lower. Comparing between below and above 450 m elevational zones indicated the significantly higher parameters of stand structure and species diversity in above 450 m elevational zone. The differences of edaphic conditions led to difference of density of living stems, species density, DBH, G, and ▵G among micro-topographies. Therefore, crest slope, upper slope, and higher elevational zones should be encouraged for the purposes of carbon accumulation and storage. While, the lower elevational zones should be used for the purposes of species diversity conservation.

Stream-head migration in a head hollow of the hills

Stream-head migration in a head hollow of the hills

A BRIEF REVIEW OF STUDIES ON DIFFERENTIATION OF VEGETATION PATTERN ALONG A TOPOGRAPHIC GRADIENT IN HILLY REGIONS

The relationship between plants and environmental conditions is one of the most basic characteristics of plant communities. The humid hilly regions are a complex habitat that has various degrees of disturbance related to water erosion. At an intermediate_scale level, the region can be divided into an upper and lower hillslope area divided by an erosion front. At a more detailed_scale, the sections can be divided further into micro_scale geomorphological units. The upper hillslope area contains a crest slope, upper sideslope and head hollow etc. and the lower hillslope contains a lower sideslope, foot slope, flood terrace and river bed etc. The upper and lower hillslopes are two basic functional land area types for assessing species composition and forest structure. On the upper hillslope area, the vegetation changes gradually and continuously from the crest slope, to upper sideslope and head hollow. On the lower hillslope, however, the micro_landform units have little effect on vegetation structure as disturbance plays the most important role in regulating vegetation patterns. The lower hillslope area is characterized by active soil erosion, landslides and slope failures. Thus, the plant communities that develop on it are early successional communities, and their regeneration depends on active surface disturbance. However, the plant communities that develop on the upper hillslope areas are climate climax communities as it has been stable for a long time, and their regeneration can be explained based on the gap dynamic theories. Topography is the most basic and important habitat factor affecting vegetation patterns. Habitat niche differentiation related to topographic variation supports the coexistences of species and results in high species diversity at small spatial scales.

Management and micro-scale landform determine the ground flora of secondary woodlands and their verges in the Tama Hills of Tokyo, Japan

We investigated the influence of management and micro-scale landform on the species composition and richness of ground flora in secondary woodlands and their verges next to paddy fields in the Tama Hills, Tokyo, Japan. Sites representing various micro-scale landforms and different management regimes were sampled. The results of Detrended Correspondence Analysis and Indicator Species Analysis showed that there was no significant difference between management regimes on species composition in head hollow sites. However, species composition was unique in other landform types having the same management regimes. Micro-scale landform units had less effect on species composition than management regime on crest slopes and side slopes of secondary woodlands. A large variation in species composition of verges, all on the lowermost side slopes, was found within sites, but the composition was different when compared with other sites. We recognized five habitat types associated with species composition that resulted from the combined effects of landform and management regimes. Among habitat types, the verges and the well-managed woodlands had high species richness. Management practices within woodlands have enhanced the species richness on crest slopes and side slopes. High beta diversity of ground flora could be due to the variation in micro-scale landform along soil moisture regimes. Intensive management involving clear-cutting on the lower side slopes (an ecotone of mesic and wet environments) accompanied by paddy cultivation on valley bottoms enhanced the diversity of herbaceous vegetation in the verges.

多摩丘陵の里山における植生管理の違いが土壌の化学性と湧水の水質に及ぼす影響

The study aims to understand chemical characteristics of soil solution and spring water on different vegetation management regimes in secondary woodlands of Tama Hills, central Japan. Soil samples were collected at different vegetation management regimes and EC, pH and ion concentration in dissolved water were measured. In results, management types determined the soil chemical characteristics. Ion concentration of Ca2+, Mg2+, and NO3- was significantly lowest at the surface of moved and fallen-leaf-rid sites and highest at those of abandoned. Soil solutions were collected at different micro-scale landforms in a neglected watershed and a managed one. At crest slopes and head hollow, accumulation of EC, Ca2+, and NO3- was significantly higher in the neglected watershed than in the managed watershed. The similar trend was also found in subsurface soil solutions. At valley bottom, however, NO3- concentration declined remarkably, and then it was few in spring water of both watersheds. On the contrary, Na+ and Ca2+, concentrations were increased. Therefore, there was no management effect on chemical characteristics of spring water. This implied denitrification and mineral elution from geological formation could characterize ion components of spring water at an ordinary water-stage.

Influence of micro‐landforms on forest structure, tree death and recruitment in a Japanese temperate mixed forest

The micro‐landform unit system offers an effective way of analyzing vegetation–geomorphology relationships at a 10‐m scale in areas such as the hilly regions of Japan. We analyzed relationships between micro‐landforms and tree population parameters over a 9‐year interval to elucidate the influence of geomorphic processes on vegetation dynamics. A 2.16‐ha permanent plot was established in a temperate mixed forest. Each 5 m × 5 m quadrat within this plot was classified according to six types of micro‐landform units: (i) crest slope (CS); (ii) upper sideslope (US); (iii) head hollow (HH); (iv) lower sideslope (LS); (v) foot slope (FS); and (vi) river bed (RB). All living trees larger than 10 cm in diameter at breast height (d.b.h.) were identified, mapped and marked in 1989 and resurveyed in 1998. Almost all of the 23 common tree species persisted in their own core habitats (i.e. the micro‐landforms) between the two surveys. The species distribution in both surveys showed that the six micro‐landforms could be combined into two larger groups: upper and lower hillslope areas. The upper hillslope area had higher tree densities and larger basal areas than the lower hillslope area. It is possible that these differences result from the longer lifespans of trees on the upper hillslope area rather than from differences in mortality and recruitment rates. In addition, the different ways in which trees die in the different micro‐landform units may affect the regeneration process in hilly regions through different gap formation. The effects of different geomorphic processes are reflected in the lifespans of the trees and may result in different forest structure and dynamics among micro‐landform units.

Soil creep process and its role in debris slide generation — field measurements on the north side of Tsukuba Mountain in Japan

We measured the ground inclination movement, moisture content, and amount of rainfall on a valley-head slope and a side slope along the valley on the northern side of Tsukuba Mountain, and elucidated the process and role of soil creep in debris slide generation. Soil creep usually occurs during and after rain. The amount of creep caused by one rainfall has a positive correlation with the amount of rain and increase in soil moisture. For the valley-head slope, soil creeps down and accumulates at the bottom bottleneck part of the head hollow, in which soil is compressed and forms a wavy landform. The lower end of the head hollow gradually becomes steeper and unstable. Side slopes along a valley-head slope show differences in topsoil thickness and creep speed between sections near and below a knick line. The amount of soil creep per year is larger in a section near a knick point than that below it. Soil gradually concentrates directly below the knick point, and the slope becomes steeper and unstable. The total amount of soil movement in 1year was several millimeters for both the valley-head and side slopes. This means several liters/year of soil squeeze out for every slope section of 1m in width. This value is similar to the general speed of erosion caused by debris slide (mainly topsoil failure, or shallow landslide) in Japan. Furthermore, neither surface erosion nor internal erosion has been observed in this site. Soil creep seems to carry most of the debris to places where debris slides will occur in this site. Soil creep prepares future debris slides and dominates the cycle of debris slide as well.

A zero-order basin?its contribution to catchment hydrology and internal hydrological processes

This study aims to evaluate the relative contribution of a zero-order basin to runoff generation in a headwater catchment as well as to elucidate internal factors affecting hydrological response. Runoff, piezometric heads, and soil temperatures were measured for a 0.25 ha zero-order basin (ZB) together with discharges from an adjacent 0.84 ha 1st-order basin (FA) and a larger 2.48 ha 1st-order basin (FB) which includes both ZB and FA. Data collected over a year showed ZB contributed to runoff generation in FB at three different levels. While continuous runoff was recorded from both FB and FA, no substantial runoff was measured for ZB during dry conditions when discharge from FB 5 mm d-1, all three basins generated runoff of the same order per unit area (level 2: linear contribution). Piezometers installed above the soil-bedrock interface (0.5 to 1.2 m depth) along the longitudinal axis of ZB responded only in the lower locations when runoff from ZB 5 mm d-1, all three basins generated runoff of the same order per unit area (level 2: linear contribution). Piezometers installed above the soil-bedrock interface (0.5 to 1.2 m depth) along the longitudinal axis of ZB responded only in the lower locations when runoff from ZB≪discharge from FB. Conversely, the major runoff contribution from ZB to the discharge from FB generally coincided with a large piezometric rise near the head hollow. Soil temperatures in the head hollow fluctuated even during some rainstorms, indicating that such a large piezometric rise was caused by a convergent subsurface flow from the further upslope. Thus, shallow groundwater, which developed above the trough of ZB, would not always extend from the base to the upslope but may appear simultaneously in the head hollow. This additional contribution due to upslope topography may create additional variability and non-linearity in runoff response from ZB relative to planar hillslopes.

Suspended sediment discharge in subsurface flow from the head hollow of a small forested watershed, northern Japan

Surface flow and suspended sediment discharge from the head hollow of the Jozankei Experimental Watershed in Hokkaido, northern Japan, were measured to clarify the implications of subsurface hydrology for soil movement. Subsurface discharges during the extremely large storms of 1993 to 1994 were measured in a V-notch weir installed at a natural spring near the bottom of the head hollow, and shallow groundwater levels were observed in the wells excavated in the hollow. Sediment samples whose particle size range from 0·001 to 0·1 mm were manually and automatically collected at 15 to 60 min intervals, by use of 1 or 21 polyethylene bottles. Maximum concentration and flux of suspended sediment during the storms preceded the peak discharge of subsurface flow by several hours. Neither the changes in concentration (mg l−1) nor flux (mg s−1) of suspended sediment coincided with those in subsurface discharge (l s−1). Furthermore, sediment concentration was poorly correlated with the rate of change in subsurface discharge (l s−2) during the rising limb of the hydrograph. Suspended sediment flux during the acceleratory limb, however, was closely correlated with the rate of change in subsurface discharge. The relationship between suspended sediment flux and rate of change in subsurface discharge were in inverse proportion to initial subsurface discharge before the storm runoff and they represented rare seasonal variation. Subsurface hydraulic erosion and transport of suspended sediment resulting from changes in rate of change in subsurface discharge actively occur during the acceleratory rising limb of the hydrograph. Accordingly, subsurface hydraulic erosion during the acceleratory rising limb of the hydrograph can be physically understood by analysing suspended sediment flux associated with rate of change in subsurface discharge and initial subsurface discharge. © 1997 John Wiley & Sons, Ltd.

Suspended sediment discharge in subsurface flow from the head hollow of a small forested watershed, northern Japan

Suspended sediment discharge in subsurface flow from the head hollow of a small forested watershed, northern Japan

Distribution of colluvia and saprolites and their physical properties in a zero-order basin in Okinawa, southwestern Japan

The thickness and physical properties of colluvium and saprolite were investigated to clarify their role in the hydrological processes in a forested basin. We measured their thickness using a handy dynamic cone penetrometer, and surveyed soil profiles to obtain undisturbed cylindrical samples for measuring physical properties, i.e., effective porosity. Saprolite is divided into strongly weathered saprolite and weakly weathered saprolite with their hardness. In the study area, colluvia are mostly over 0.5 m thick, especially in a head hollow, where it is over 3 m thick. On the other hand, they are less than 0.5 m thick in crest flats. Strongly weathered saprolite is thickest on crest flats, and it is also thick along the axis of a hollow. The physical properties that contribute to water storage show different values for each microtopographic unit. The effective porosity of the colluvia in head hollows and terraced bottomland is large, whereas in crest flats and crest slopes it is small. Strongly weathered saprolites show effective porosity mostly as much as in the lower colluvium layer. As the Nc value is strongly related to bulk density and total porosity, we could evaluate water storage capacity in deep sites where soil sampling is difficult. We also found that similar-shaped geomorphic surfaces often have different colluvium-saprolite systems and ages.

Soil disturbance regime in relation to micro-scale landforms and its effects on vegetation structure in a hilly area in Japan

To clarify vegetation-landform relationships, we examined the soil disturbance regime in relation to micro-scale landforms and its effects on vegetation structure in a mixed temperate forest in a hilly area in northeastern Japan. Soil profiles in each micro-landform unit were surveyed to elucidate the effects of soil disturbances on the vegetation structure. The hilly area studied consisted of an upper and a lower hillslope area divided by an erosion front, which differed considerably with respect to vegetation structure. In the upper hillslope area, canopy was closed and dominated by Pinus densiflora and Quercus serrata. In the lower hillslope area, on the other hand, canopy was less closed and shrubs, ferns, and herbaceous species were abundant. The species composition changed gradually from the crest slope to the upper sideslope to the head hollow in the upper hillslope area. However, micro-landforms in the lower hillslope area seemed to have less effect on the vegetation structure. This may be because the lower hillslope area, in contrast to the upper hillslope area, has suffered from soil disturbances, and hence shrubs, ferns, and herbs have developed irrespective of micro-landforms. Thus, vegetation can be quite different depending on whether or not sites have suffered from soil disturbance. In disturbed stands, it is suggested that the frequency and intensity of disturbance are more important for species composition than the type of soil disturbance.

Geomorphological Analysis on the Occurrence Factors of Slope Failure around Shimoda City

In order to estimate the influence of geomorphological factors to the occurence of slope failure, geomorphological classification of head hollow slopes and comparison between geomorphological factors of collapsed slope and that of non-collapsed slope is done in the Ochiai river basin (Shimoda City, Shizuoka Prefecture) where many slope failures occurred in September, 1991.Firstly, by gradient change lines of slopes, head hollow slopes of the area are classified into three categories: gentle slope on the ridge top, valley side steep slope, head hollow bottom surface. In the collapsed slope, collapse generally occured in the lowest part of valley side steep slope just above gradient change line of the slope.Secondly, some geomorphological factors are confirmed to be important to the occurrence of slope failure. These are, 1) valley side steep slope gradient, 2) difference of gradient between valley side slope and head hollow bottom surface, and 3) curvature of contour. In regard to collapsed area, negative correlation on logarithmic scale between WM/WE and AF/AB, is clearly confirmed (WM: maximun width of the catchment basin, WE: width at the end of the catchment of basin, AF: collapsed area, AB: catchment area).

北上山地中部の斜面物質移動期と斜面形成

In this paper mass movement and slope formation in the central Kitakami Mountains are discussed with special reference to their periods. Many tephra layers of the late Quaternary found in the study area enable to study the periods of mass movement and slope formation tephrochronologically (Fig. 2).The slopes are classified as follows (Fig. 3). (1) gentle slopes on the summits, (2) piedmont gentle slopes, (3) fan-like gentle slopes, (4) smooth crest slopes, (5) upper head hollow slopes (continuing smoothly from the surrounding slopes), (6) lower head hollow slopes (smaller than (5), surrounded by clear breaks in slopes), (7) talus and alluvial cone, (8) other slopes. In the study area two periods of mass movement, chiefly by solifluction, are confirmed during the Last Glacial.The first period was in the early Last Glacial Stage, perhaps around 50, 000y.B.P., and the second was in the late Glacial Stage, between 30, 000 and 10, 000y.B.P..These periods of mass movement correspond to those of the involutions under periglacial climate in the Northern Kitakami Lowland area (Endo, 1977) (Fig. 7).In the study area not only were well-jointed bedrocks such as shale, slate, and schist susceptible to frost shatterin, bnt also fallen volcanic ash and soil produced from deep weathered bedrock were also susceptible to solifluction.Gentle slopes on the summits and smooth crest slopes have been formed by bedrock frost shattering and solifluction in these periods of mass movement by surface processes. Gentle piedmont slopes have been formed by solifluction. Upper head hollow slopes were developed as smoothly concave profiles by debris accumulation. Fan-like gentle slopes were developed chiefly by slope wash (partly by solifluction in the Last Glacial Stage) at the same time.Most of the piedmont gentle slopes and fan-like gentle slopes began to form in the early Last Glacial Stage or in the cold period before the Last Interglacial Stage, and the deposits of the late last Glacial Stage, which is generally recognized as the maximum period of the last Glacial Stage in Japan, are only 0.5-2.0m thick.During the warming period from the latest Pleistocene to Holocene, landslides have formed lower head hollow slopes and alluvial cones have been formed at the outlet of valleys with small river basins.

Slope Morphology Controlled by Hydro-Geological Conditions in the Western Part of the Tama Hills, West of Tokyo

The Tama Hills, located in the western edge of the Kanto Plain, are mainly composed of semi- or unconsolidated shallow marine sediments of Plio-Pleistocene age, which, named the Kazusa Group, consist of several clay-silt, sand and gravel beds. On the hilltop gentle slopes in the western part of the Tama Hills, the mid Pleistocene Gotentoge Gravel Bed rests unconformably upon the Kazusa Group. And the Hills are covered with airborne tephras named the Kanto Loam. The lower part of the Kanto Loam is full-weathered and rich in clay.The purpose of the present study is to clarify the distribution and formation of detailed- to micro-scale landforms composing small tributary basins, in connection with the hydro-geologic conditions in the western part of the Tama Hills.In valley-head areas, head hollow and head floor defined by Tamura (1974) are distributed and their location seems to be controlled by the hydro-geologic conditions. The maximum height of each head hollow and the position of springlet correspond well to the height of bedding plane of clay-silt bed in the Kazusa Group or the lower part of the Kanto Loam, both of which have less permeability. Head floor develops on the surface of less-permeable beds. Because of the less permeability, surface and sub-surface flow often occurs and marsh is sometimes formed on this slope unit.Locations of valley-head slopes on the hillsides are also affected by the distribution of less permeable beds. Here the development of the slopes seems to have been initiated by the landslides. Present head hollows were formed by slide type failure. Each mass movement occurs along the bedding plane upon the less-permeable beds.Valley-head slopes are considered to have been formed by surface failures occurred during heavy storms. In addition to the occurrence of pipeflow and returnflow which are also related to hydro-geologic conditions, groundwater itself seems to play an important role in landforming process accompanied by surface failure.It is concluded that the distribution and formation of slope units in the Tama Hills are strongly controlled by the hydro-geologic conditions.

Micro-landform Units Composing a Valley-head Area and their Geomorphic Significance

A valley-head area, where a stream is elongating towards watershed, is composed of the following five micro-landform units: Crest slope, Side slope, Head hollow, Head floor, and Channelway; which is followed with Bottomland (Fig. 1). The conclusion is drawn from the study on landscapes of some hill-lands in eastern Japan (Fig. 2) and may be applicable to the whole hilislopes with adequate soil and vegetation cover in humid temperate zone.Hydrological conditions and present geomorphic processes prevailing in each micro-landform unit are listed in Tab. 2. The conditions and processes are inducible from characteristic surface features and soil morphology of each unit. The induction is supported with knowledge in slope hydrology, especially with facts and theories concerning throughflow (Fig. 3).These processes are considered to be not generative but modificatory agent to a valley-head. Somewhat catastrophic processes such as large landslide (with about 103m3 of debris), which is also provoked with throughflow, may be concerned with outbreak of a new valley-head. It is suggested with morphological and stratigraphic evidences in some micro-landform units.The extent and proportion of each unit in a valley-head area may reflect the total morphogenetic condition of the area. Especially interzonal comparison of the distance between the headmost divide and the point of Channelway initiation (modified 10 of Horton) must be significant from a climato-geomorphological viewpoint.