Mangrove Habitat Formation and Response to Holocene Sea-level Changes on Kosrae Island,Micronesia     

Fujimoto  Kiyoshi  Miyagi  Toyohiko  Kikuchi  Takao  Kawana  Toshio 《Mangroves and Salt Marshes》1996,1(1):47-57

Mangrove habitats on Kosrae are divided into three types, i.e., an estuary or delta type, a backmarsh or lagoon type and a coral reef or tidal-flat type. Most of the mangrove forests of Kosrae have been developed during the last 2000 years by accumulating mangrove peat with the gradual sea-level rise of 1 to 2 mm/yr except the landward part of the estuary or delta type. On the other hand, during the period of rapid sea-level rise of about 10 mm/yr between 4100 and 3700 yr B.P., the mangrove forests ceased peat accumulation and retreated landward. Until 3500 yr B.P., mangrove forests were distributed only in narrow bands in the inlets. Therefore, the critical rate of mangrove peat accretion with sea-level rise is estimated at more than 2 mm/yr and less than 10 mm/yr. If the anticipated sea-level rise exceeds this critical rate, all of the mangrove forests of Kosrae will retreat landward and reduce rapidly.  相似文献   

Response of gas exchange rates in <Emphasis Type="Italic">Abies firma</Emphasis> seedlings to various additional stresses under chronic acid fog stress     

Koji?YoshidaEmail author  Ryota?Shibasaki  Chika?Takami  Chisato?Takenaka  Kazukiyo?Yamamoto  Takafumi?Tezuka 《Journal of Forest Research》2004,9(3):195-203

In order to clarify the chronic influence of acid fog on the gas exchange rates of momi fir (Abies firma Sieb. et Zucc.) trees, we exposed them to simulated acid fog (pH 3) for 3 years. The composition of the acid fog was similar to that observed in a region where momi fir trees have been declining, and it contained organic acids. We then treated the firs with various additional stresses, such as drought, low temperature, fine root cutting, ozone exposure, soil acidification, nitrogen load, and rhizosphere aluminum stress. Under chronic exposure to acid fog, the momi fir seedlings exhibited a pattern of stomatal behavior whereby they excessively opened in summer and closed in winter. Furthermore, the stomata of these seedlings tended to open during drought stress, and their needles were visibly injured after ozone exposure. The net photosynthesis rates of the seedlings exposed to acid fog were regulated by their stomatal aperture, rather than directly by acid fog. These results suggest that acid fog exposure disturbs the control of stomatal function in the momi fir seedlings. In addition, we found that chronic acid fog exposure suppressed the decrease in net photosynthesis rate, due to its nitrogen load.  相似文献   

Stand structure and the regeneration ofChamaecyparis pisifera (Sieb. et Zucc.) Endl. on sites with different soil development in an old-growth coniferous forest, central Japan     

Shin-Ichi Yamamoto  Yasuko Moriyama 《Journal of Forest Research》1997,2(3):133-140

Stand structure and the regeneration ofChamaecyparis pisifera on sites with and without well-developed soil in an old-growth coniferous forest, Akasawa Forest Reserve, central Japan, were investigated, along with their relationships to other important coniferous species. Of stems ofC. pisifera≥5 cm diameter at breast height, stems with intermediate size were absent in stands on the developed-soil site, while those with smaller size increased in stands on the undeveloped-soil site, which supported a higher density ofC. pisifera. In the stands without recent tree-fall of canopy stems on the developed-soil site, canopy stems ofC. pisifera were distributed uniformly and the understory stems, patchily. On the other hand, both canopy and understory stems ofC. pisifera in stands on the undeveloped-soil site were distributed patchily. In the understory,C. pisifera occurred as clonal patches formed by vegetative reproduction on various types of microsites including bare rocks. However, the clonal patches did not occur in a stand on the developed-soil site with dense saplings of an evergreen conifer,Thujopsis dolabrata, which can expand vegetatively with a well developed soil layer. Gap formation may induceC. pisifera to develop tree-form stems from shrubby clonal patches. On developed-soil sites,C. pisifera stands that survive a long disturbance-free period on this site need catastrophic disturbance for their regeneration, which will eliminateT. dolabrata in the understory and create bare soil for colonization ofC. pisifera from seeds. On undeveloped-soil sites,C. pisifera replaces itself continuously by effective vegetative reproduction. Ground instability and the wet condition of this site may promote the replacement.  相似文献   

The relationship between macroscopic strain and crystal lattice strain in wood under uniaxial stress in the fiber direction     

Takahisa Nakai  Hiroyuki Yamamoto  Tetsuya Nakao 《Journal of Wood Science》2005,51(2):193-194

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Initial shapes of stress-strain curve of wood specimen subjected to repeated combined compression and vibration stresses and the piezoelectric behavior     

Takahisa Nakai  Hiroyuki Yamamoto  Masatoshi Hamatake  Tetsuya Nakao 《Journal of Wood Science》2006,52(6):539-543

This study investigated the relationship between the initial shape of the stress (σ)-strain (ε) curve of a Chamaecyparis obtusa wood specimen subjected to repeated combined compression and vibration stresses at various angles between the fiber direction and load direction and the piezoelectric behavior. The main findings of the study are: (1) the σ-ε curve became convex initially, and then the stress was proportional to the strain. The σ-ε curve had almost the same shape during both loading and unloading. (2) The σ-piezoelectric voltage (P) curve was nonlinear, with a maximal point or cusp on the curve, which had almost the same shape during both loading and unloading, as was also observed for the σ-ε curve. (3) The plot of the first derivative of the stress [dσ/dε (= σ′)] against ε was nonlinear. The σ′-ε and P-ε curves at various angles were fairly similar. (4) The stress at the maximal point (or cusp) of the σ-P curve decreased with an increase in the angle between the fiber direction and load direction. The tendency of the stresses was very similar to that of Young’s modulus and compression strength calculated from Hook’s law and Hankinson’s law, respectively.  相似文献   

The influences of boiling and drying treatments on the behaviors of tension wood with gelatinous layers in <Emphasis Type="Italic">Zelkova serrata</Emphasis>     

Kentaro Abe  Hiroyuki Yamamoto 《Journal of Wood Science》2007,53(1):5-10

This study examined how boiling and drying treatments influenced various physical properties of the tension wood with gelatinous fibers (G-fibers) of a 29-yearold Zelkova branch. By boiling treatment, tension wood with numerous G-fibers contracted considerably in the longitudinal direction and the longitudinal Young’s modulus decreased in spite of the water-saturated condition. The drying treatment caused green tension wood and boiled tension wood with numerous G-fibers to shrink longitudinally and increased their longitudinal Young’s moduli. These specific behaviors in tension wood were highly correlated with the proportion of G-fibers in a specimen and were probably caused by the microscopic behavior of cellulose microfibril (CMF) in the gelatinous layers (G-layers). The longitudinal shrinkage of tension wood due to drying suggests the existence of a hygro-sensible, noncrystalline region in the CMF, which is abundant in the G-layer. Furthermore, the noncrystalline region in the CMF softens during boiling treatment, resulting in the reduction of the longitudinal Young’s modulus in tension wood. The longitudinal contraction of tension wood with G-fibers by boiling might be caused by the tensile growth stress remaining in green G-layers. However, no changes were detected in the 004 d-spacing of cellulose crystal in tension wood from the boiling and drying treatments, regardless of the proportion of G-fibers.  相似文献   

The effect of compression and incision on wood veneer and plywood physical and mechanical properties     

Maija Kymäläinen  Akio Yamamoto  Kasperi Sokka  Lauri Rautkari 《Wood material science & engineering》2020,15(2):97-103

ABSTRACT

Drying takes the largest share of energy in plywood production, and varying moisture content of veneers necessitates re-drying that often leads to over-dry veneers with deactivated surfaces, which may promote imperfect bonding. In order to decrease the drying time, reduce the need for re-drying of veneers, and improve the quality of plywood, birch and spruce veneers were subjected to pre-treatment by cold compression, incision, or a combination of the two. The effects of pre-treatment on the veneer and plywood quality were assessed by standard tests. Compression had a beneficial effect on water removal of the wettest veneers (spruce sapwood (SW) and birch), but some thickness reduction was observed in the veneers as well as the finished birch plywood. Compression led to thickness reduction of spruce veneers, but had no effect on SW plywood thickness likely due to higher viscoelasticity. Both compression and the combination of incising and compression levelled the moisture variation within the compressed stacks. Incision improved the modulus of elasticity of birch plywood, shear strength of SW plywood, and both bending and shear strengths of heartwood plywood. Higher surface pressure decreased the drying time of spruce SW in both plain compression and combined incision and compression pre-treatment.  相似文献   

Salt distribution in response to optical stratification porosity and relative windspeed in a coastal forest in Niigata, Japan   总被引：3，自引：0，他引：3  

J.J. Zhu  Y. Gonda  T. Matsuzaki  M. Yamamoto 《Agroforestry Systems》2002,56(1):73-85

Wind velocity, vertical stand structure and seasalt distribution were measured at various heights inside a plantation of coastal pine forest, with thinning and unthinning, to assess whether any relationships exist between the wind profile, stand structure and seasalt distribution in the coastal pine forest. The vertical stand structure, i.e., optical stratification porosity (OSP), which is defined as vertical distribution of the proportion of sky hemisphere not obscured by tree elements inside a forest stand, was determined for each height by computer analysis of digital images taken with a hemispherical lens. The distribution of OSP in the coastal forest follows the Lambert-Beer's law with absorbency coefficient (). The relative windspeed within canopy can be described using the exponential form with the attenuation coefficient (). The sea-salt was collected using salt gauze (a surgical dressing of loosely woven cotton) both inside and outside the coastal forest, and the distribution of sea-salt within canopy was also in accordance with an exponential function. The relationships among windspeed, OSP and sea-salt indicate that the distributions of both sea-salt and windspeed within canopy were very closely correlated with the distribution of OSP. A linear relationship between OSP and sea-salt has been found. Additionally, linear regression between coefficients and has been obtained as well. Based on these relationships between OSP, wind and sea-salt in the coastal forest, the sea-salt distribution and wind profile within the canopy of the coastal forest can be predicted according to OSP. These results may therefore be useful in analyzing the effects of sea-salt on vegetation and evaluating the filter functions of coastal forests.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

Surface deterioration of wood-flour polypropylene composites by weathering trials   总被引：1，自引：0，他引：1  

Makoto Kiguchi  Yutaka Kataoka  Hiroshi Matsunaga  Koichi Yamamoto  Philip D. Evans 《Journal of Wood Science》2007,53(3):234-238

The market for wood-fiber plastic composites (WPCs) is expanding rapidly in many countries including Japan, where WPCs are mainly used for exterior products. In such applications, WPCs undergo undesirable color change, chalking, and shrinkage and swelling, and accordingly there is a need to better understand the mechanisms responsible for the weathering of WPC and develop methods of improving their weathering resistance. In this study, weatherability of WPC was assessed by natural and accelerated weathering trials. Discoloration (whitening) of WPC during exposure was caused by degradation of both wood and plastic. Darker color pigments as additives improved the color stability of WPC; however, chalking on the surfaces still occurred. The color stability of WPC was improved by application of exterior coatings. Preweathering of WPC (before coatings were applied) increased the absorption of coatings by the WPC and had a positive effect on the color stability and prevented chalking of the composites. Parts of this study were presented at the IUFRO XXII World Congress Meeting, Brisbane, August 2005 and the IAWPS 2005, Yokohama, November 2005  相似文献   

Mechanical behavior of the crystal lattice of natural cellulose in wood under repeated uniaxial tension stress in the fiber direction     

Takahisa Nakai  Hiroyuki Yamamoto  Tetsuya Nakao  Masatoshi Hamatake 《Wood Science and Technology》2006,40(8):683-695

This study investigated the relationship between the cellulose crystal lattice strain (crystalline region) and the macroscopic surface strain in specimens of Chamaecyparis obtusa wood under repeated uniaxial tension stress in the fiber direction. Changes in the strain of the crystal lattice were measured from the peak of (004) reflection using the transit X-ray method. The macroscopic surface strain of each specimen was measured with a strain gauge. In both loading and unloading, the surface strain changed linearly with changes in stress. However, crystal lattice strain was not linear but exhibited changes along a curve with changing stress. Under stressed conditions, the crystal lattice strain was always less than the surface strain, regardless of the frequency of repetition in the loading and unloading cycle. The ratio of the crystal lattice strain to the surface strain showed a negative correlation for stress in both loading and unloading. That is, the ratio decreased with increasing stress, and finally tend to converge to a specific value. The ratio (I/I ₀) between the diffracted intensity (I ₀) in the (004) plane in the unloaded condition and the diffracted intensity (I) in the (004) plane in the loaded condition tend to converge on a specific value with increasing frequency of repetition. When the substantial tension Young’s modulus of the wood in the longitudinal direction decreased, the ratio of the strain of the crystal lattice to the surface strain also decreased. Moreover, the ratio decreased with increasing microfibril angle of the specimen.  相似文献