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1.
Recently, riparian forests have attracted attention as they are effective for ecological preservation and landscape enhancement.
Uses of such forests in flood prevention, sediment control, and erosion control works have been actively promoted. This study
aims to clarify the effect of density of riparian trees on drag exerted on trees along river channels under the regime of
bed load transport. Hydraulic model experiments were performed using a straight channel, and the methods to calculate the
drag coefficient necessary for deriving drag exerted on trees were studied. Previous studies have stated that the drag coefficient
of a cylinder is fairly constant when Reynolds number,R
e, is between 103 and 105 (e.g., Schlichting, 1979). This study clarified, however, that in cases of relatively dense arrangements of model trees (cylinders),
the drag coefficient varies greatly with the density of the trees. As such, correlation between the drag coefficient and Reynolds
number was found to be slight. Test results indicated that the drag coefficient of trees,C
d, correlates strongly with the coefficient of velocity,U′/U
*
′, friction factor of the channel bed,f′, and roughness concentration of trees × flow depth,aH′ or ratio of the area occupied by trees,λ. Furthermore, the drag coefficient,C
d, was also found to be slightly correlated with the gradient of the channel bed,I. Equations using either of the following parameters were obtained for deriving the drag coefficient,C
d, based on the experiment results:aH′; λ; U′/U
*
′; and Froude numberF
r. These equations allow fairly accurate calculation of drag exerted on trees. 相似文献
2.
Acoustics provide opportunities for non-destructive evaluation of the mechanical properties of wood, especially stiffness.
In this work, Fakopp 2D a time of flight (TOF) tool and WoodSpec a resonance-based system were used. In a scoping study on
young Pinus radiata trees (aged 8–11) no systematic differences were found between the Fakopp acoustic velocity on opposite sides of young trees.
These Fakopp values were then averaged and correlated with that from the equivalent log using WoodSpec. Finally stem and log
values were correlated with acoustic velocity in outerwood and in corewood lumber. External measurements on the log (standing
tree) correlated well with those for lumber cut adjacent to the bark and modestly for the corewood (R
2 of 0.89 and 0.74, respectively). In a separate study, the acoustic velocities were measured on standing trees in three adjacent
stands aged 8, 16 and 26 and the data were used to construct a “Russian Doll” model to demonstrate the enormous range in wood
stiffness within and between trees. The stiffest 20% of the population was estimated to be 146, 87 and 76% stiffer than the
poorest 20% in the corewood (age 8), intermediate (age 16) and outerwood zone (age 26) respectively.
相似文献
M. GrabianowskiEmail: |
3.
We developed a new microelectrode technique for measuring CO2 concentration ([CO2]) in xylem sap of trees. This technique enabled us to make rapid and continuous measurements of xylem sap [CO2] in situ. In this report, we discuss the methodology and establish the feasibility of the technique. We also describe calibration procedures, temperature sensitivity, field use and other characteristics of the microelectrodes. An example of data collected in the field is provided. Microelectrode calibration was accomplished at constant temperature in air of known [CO2]. When sampling temperature differed from calibration temperature, correction was necessary. We developed an equation to correct for temperatures between 15 and 35 degrees C when calibration was conducted at 25 degrees C. Equations based on Henry's Law were used to convert measured gas phase [CO2] (%) to concentration of all products of CO2 dissolved in sap (mmol l(-1)). We inserted microelectrodes into stems of three tree species to measure diurnal changes in [CO2] in the xylem sap. A diurnal pattern with depression during the day and elevation at night was observed. Mean daily [CO2] ranged from 1.6 to 10.3 mmol l(-1). Microelectrodes were suitable for making diurnal measurements for up to 7 days without recalibration. We also used the microelectrodes to measure [CO2] of soil in situ. Soil [CO2] ranged from 1 to 4% (gas phase), with little diurnal variation. 相似文献
4.
Eileen S. Scott 《Forest Pathology》1984,14(6):334-339
Wetwood was detected in living trees by determining the electrical resistance patterns across the stem with a Shigometer. The resistance of wetwood to a pulsed electric current was low compared with that of healthy sapwood. Bacteria were isolated from wood with low resistance, but rarely from wood with high resistance. Provided that drilling and measurements were performed in a stepwise fashion, the extent of wetwood could be assessed with little damage to the trees tested. This procedure may be useful in identifying trees containing wetwood, particularly in the early stages before crown symptoms become apparent. 相似文献
5.
Xiping Wang 《Wood Science and Technology》2013,47(5):965-975
Acoustic technologies have been well established as material evaluation tools in the past several decades, and their use has become widely accepted in the forest products industry for online quality control and products grading. Recent research developments on acoustic sensing technology offer further opportunities to evaluate standing trees and logs for general wood quality and intrinsic wood properties. Although the concept of using acoustic velocity as an effective measure of stiffness applies to both standing trees and felled logs, the method typically used to measure acoustic velocity in trees is different from that used in logs. Consequently, there is a significant difference in measured velocity values between trees and logs. Other factors affecting tree–log velocity relationships include tree diameter, stand age, operating temperature, and wood moisture content. This paper presents the fundamentals of acoustic wave propagation in trees and logs and discusses two different mechanisms of acoustic velocity measurement, time-of-flight for standing trees and resonance for logs. Experimental data from previous studies are reviewed and analyzed to examine the strength of the tree–log velocity relationships and discuss the factors that influence tree velocity deviation. 相似文献
6.
The spatial heterogeneity of water uptake by fine roots under field conditions was analyzed in situ with miniature sap flow gauges in a mature beech-oak-spruce mixed stand. Sap flow rate (J), sap flow density (Jd), and root surface-area-specific flow rate (uptake rate, Js) were measured for eight to 10 small-diameter roots (3-4 mm) per species in the organic layer (superficial roots) and in the mineral soil (30-80 cm, deep roots) during four months in summer 1999. We calculated Js by relating J to the surface area of the section of the fine root system distal to the position of the gauge on the root. When measured synchronously, roots of the three species did not differ significantly in mean Js, although oak roots tended to have lower rates. However, Jd decreased in the sequence spruce > beech > oak in most measurement periods. Microscopic investigation revealed differences in fine root anatomy that may partly explain the species differences in Jd and Js. Oak fine roots had a thicker periderm than beech and spruce roots of similar diameter and spruce roots had fewer fine branch rootlets than the other species. Synchronously recorded Jd and Js of nearby roots of the same tree species showed large differences in flow with coefficients of variation from 25 to 150% that could not be explained by patchy distribution of soil water. We hypothesize that the main cause of the large spatial heterogeneity in root water uptake is associated with differences between individual roots in morphology and ultrastructure of the root cortex that affect root radial and root-soil interface conductivities. The high intraspecific variation in Js may mask species differences in root water uptake. Superficial roots of all species typically had about five times higher Jd than deep roots of the same species. However, Js values were similar for superficial and deep roots in beech and spruce because small diameter roots of both species were more branched in the organic layer than in mineral soil. In oak, deep roots had lower Js (maximum of 100 g m(-2) day(-1)) than superficial roots (about 1000 g m(-2) day(-1)). We conclude that temperate tree species in mixed stands have different water uptake capacities. Water flow in the rhizosphere of forests appears to be a highly heterogeneous process that is influenced by both tree species and differences in uptake rates of individual roots within a species. 相似文献
7.
The atmospheric hydrocarbon budget is important for predicting ozone episodes and the effects of pollution mitigation strategies. Isoprene emission from plants is an important part of the atmospheric hydrocarbon budget. We measured isoprene emission capacity at the bottom, middle, and top of the canopies of a white oak (Quercus alba L.) tree and a red oak (Quercus rubra L.) tree growing adjacent to a tower in the Duke University Forest. Leaves at the top of the white oak tree canopy had a three- to fivefold greater capacity for emitting isoprene than leaves at the bottom of the tree canopy. Isoprene emission rate increased with increasing temperature up to about 42 degrees C. We conclude that leaves at the top of the white oak tree canopy had higher isoprene emission rates because they were exposed to more sunlight, reduced water availability, and higher temperature than leaves at the bottom of the canopy. Between 35 and 40 degrees C, white oak photosynthesis and stomatal conductance declined, whereas red oak (Quercus rubra) photosynthesis and stomatal conductance increased over this range. Red oak had lower rates of isoprene emission than white oak, perhaps reflecting the higher stomatal conductance that would keep leaves cool. The concentration of isoprene inside the leaf was estimated with a simplified form of the equation used to estimate CO(2) inside leaves. 相似文献
8.
Evaluation of cold resistance of ornamental species for planting as urban rooftop greening 总被引:2,自引:0,他引:2
Rooftop gardening or green roof establishment, one of the methods of afforestation for urban greening, has many benefits for the environment, the economy and urban landscapes. Various environmental stresses including heat, strong wind, sunshine and cold prevent most plants from growing well in extensive green roof systems. For the establishment of urban rooftop gardening in Beijing, we evaluated 13 ornamental plant species [Berberis thunbergii ‘Atropurea Nana’, Euonymus fortune (Turcz.) Hand., Viburnum dilatatum Thunb., Cotinus coggygria Scop., Swida alba Opiz., Weigela florida (Bunge.) A. DC., Jasminum nudiflorum Lindl., Euonymus japonicus Thunb., Euonymus japonicus ‘Cuzhi’, Buddleja davidii Franch., Pyracantha fortuneana (Maxim.) Li., Ligustrum lucidum Ait. and Spiraea salicifolia L.] for greening of flat rooftops. We obtained three indices concerning cold resistance, i.e., electrical conductivity of leaves, amounts of soluble sugars and amounts of free proline, providing a theoretical basis for selection of plants fit for roof and balcony greening. The results show that the six species P. fortuneana (Maxim.) Li., B. thunbergii ‘Atropurea Nana’, J. nudiflorum Lindl., E. fortune (Turcz.) Hand., E. japonicus Thunb. and E. japonicus ‘Cuzhi’ are excellent plants for rooftop gardening, judging from their strong ability in cold resistance. Plants such as L. lucidum Ait., C. coggygria Scop. and W. florida (Bunge) A. DC. showed a medium ability in cold resistance. However, these species can be used in roof and balcony greening after intensive management or acclimatization of variety. The ability to resist cold of plants such as W. florida (Bunge) A. DC., S. salicifolia L., V. rhytidophyllum and S. alba Opiz. (Cornus alba L.) was found to be rather weak. Therefore, cold-proof measures are recommended when using these species. 相似文献
9.
10.
Microcracks produced in an Acacia hybrid (Acacia mangium × Acacia auriculiformis) and Melia azedarach during drying were visualized in situ using confocal laser scanning microscopy (CLSM); the morphological differences were
compared. In the Acacia hybrid, numerous microcracks were found between the wood fiber and ray parenchyma, which propagated
toward both the pith and bark. The microcracks closed with further drying, but persisted until the last stage of drying. In
Melia azedarach, however, few microcracks formed between the wood fiber and ray parenchyma in the latewood region; they also propagated toward
both the pith and bark. Because the microcracks subsequently closed, some could not be detected by CLSM. These morphological
characteristics resulted from differences in the wood structure and we conclude that the interface zone between the wood fiber
and ray parenchyma is one type of weak point on the transverse surface that is susceptible to checking. 相似文献
11.
黑龙江省主要木本固氮植物资源及开发利用 总被引:1,自引:0,他引:1
木本固氮植物不仅具有固氮能力,而且大多数木本固氮植物具有很多的用途。随着大面积人工速生丰产林的发展,森林土壤肥力逐步下降,充分认识木本固氮植物资源的生物学特性,利用生物固氮技术,既有利于提高森林生产力,又不会对自然造成环境污染。黑龙江主要木本固氮植物资源的生物学特性,及其开发利用价值进行了初步的探索。 相似文献
12.
Changes in moisture content of sugi (Cryptomeria japonica D. Don) wood during high-temperature saturated and superheated steam treatments were investigated. A system for in situ weighing of specimens was used, and the reduction of wood substance by heating was taken into consideration. At 160°C the loss of wood substance due to heating was significant and influenced the moisture content values, but it was almost negligible at 120°C. Treatment time and temperature affected the moisture content in saturated steam but not in superheated steam. Excess water in a saturated closed system appears to promote the decomposition of wood and condensation in or on specimens.Parts of this work was presented at the 49th, 50th, and 52nd Annual Meetings of the Japan Wood Research Society in Tokyo, April 1999; Kyoto, April 2000; and Gifu, April 2002 相似文献
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We used long-term in situ (15)N labeling of the soil to investigate the contribution of the two main nitrogen (N) sources (N uptake versus N reserves) to sun shoot growth from bud burst to full leaf expansion in 50-year-old sessile oaks. Recovery of (15)N by growing compartments (leaves, twigs and buds) and presence of (15)N in phloem sap were checked weekly. During the first 2 weeks following bud burst, remobilized N contributed ~90% of total N in growing leaves and twigs. Nitrogen uptake from the soil started concomitantly with N remobilization but contributed only slightly to bud burst. However, the fraction of total N due to N uptake increased markedly once bud burst had occurred, reaching 27% in fully expanded leaves and 18% in developed twigs. In phloem sap, the (15)N label appeared a few days after the beginning of labeling and increased until the end of bud burst, and then decreased at full leaf expansion in June. Of all the shoot compartments, leaves attracted most of the absorbed N, which accounted for 68% of new N in shoots, whereas twigs and new buds accounted for only 28 and 3%, respectively. New N allocated to leaves increased from unfolding to full expansion as total N concentration in the leaves decreased. Our results underline the crucial role played by stored N in rapid leaf growth and in the sustained growth of oak trees. Any factors that reduce N storage in autumn may therefore impair spring shoot growth. 相似文献
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18.
Lesions of variable size, associated with the hymenomycete Inocutis jamaicensis, a white‐rot fungus, have been observed on the stems of Eucalyptus globulus trees in Uruguay. The aim of this study was to evaluate some ecophysiological characteristics of I. jamaicensis and assess its ability to colonize E. globulus trees of two different seed origins (Geeveston and Jeeralang) and the clone, 334‐1‐AR, obtained by micropropagation (ENCE, Spain). The growth of an I. jamaicensis isolate (MVHC11379) was evaluated at 25°C in a medium with a water potential of 0 (Ψ = 0). The growth rate did not vary significantly with a growth medium pH of between 4 and 7. I. jamaicensis showed no growth at either 5 or 37°C at any pH or Ψ tested. Weight loss of heartwood and sapwood of different plant provenances inoculated with I. jamaicensis under laboratory conditions was evaluated, and significant differences observed. Lignin‐modifying enzyme activity was evaluated in culture medium with or without E. globulus sawdust as substrate or inducer. Laccase activity was observed with sawdust and manganese peroxidase activity with and without sawdust. Only slight activity of aryl‐alcohol oxidase and lignin peroxidase was detected without sawdust. Experimental inoculation with I. jamaicensis of 3‐year‐old Geeveston and Jeeralang, and of 4‐year‐old 334‐1‐AR stems, resulted in successful fungal colonization of 56% of the 334‐1‐AR, 50% of Geeveston and 25% of Jeeralang trees. Only the heartwood was decayed. In 334‐1‐AR, the rotted wood was delimited by a reaction zone. Wood characteristics and the ability of I. jamaicensis to overcome the chemical reactions in the tree could partially explain differences in susceptibility to the fungus among provenances observed under natural and laboratory conditions. 相似文献
19.
Marco Leo Walter Oberhuber Roman Schuster Thorsten E. E. Grams Rainer Matyssek Gerhard Wieser 《European Journal of Forest Research》2014,133(4):691-698
Climate simulations anticipate an increase in mean summer temperature with synchronous decrease in summer precipitation during the course of the current century in Central Europe. As a consequence, transpiration of forest trees and stands may be altered along with soil water availability. In this study, the effect of reduced plant water availability to conifers was investigated into an open Pinus sylvestris forest (Erico-Pinetum typicum; P. sylvestris 60 %, Picea abies 20 %; and Larix decidua 20 %) within the inner alpine dry valley of the Inn River in Tyrol, Austria. For reducing plant water availability, we installed a transparent roof construction above the forest floor to prevent precipitation to reach the soil. The roofed area covered 240 m² and included 10 trees. A respective number of 11 trees served as controls in the absence of any manipulation. Roofing significantly reduced plant water availability as indicated in lower predawn needle water potentials. Sap flow density (Q s) was 63, 47, and 24 % lower in roofed P. sylvestris, P. abies, and L. decidua trees, respectively, as compared to control trees. Our findings suggest that P. sylvestris and P. abies behaves “isohydric” as they close their stomata relatively early under conditions of reduced plant water availability and thus stabilize their water relations, whereas L. decidua behaves “anisohydric” and maintains high transpiration rates. 相似文献
20.
Daryl Ashfod Best Pedro Enrique Lara-Lara Edgar Aguilar-Urquizo Fanny Evangelina Cen-Chuc Juan Carlos Ku-Vera José Roberto Sanginés-García 《Agroforestry Systems》2017,91(6):1079-1085
Apparent digestibility and nitrogen (N) balance were evaluated in sheep fed low-quality Cynodon nlemfuensis grass supplemented with different foliages of forage-potential trees. Four male hair sheep were housed in metabolic cages and fed in a Latin Square design with 30 % inclusion of foliage of Erythrina indica (Ei), Moringa oleifera (Mo), or Trichanthera gigantea (Tg) replacing soybean meal. Adaptation and faeces and urine collection periods were 14 and 7 days, respectively. Sheep received 70 g DM/kg/BW0.75 of the diet in order to achieve total consumption of feed. Dry matter, organic matter, and neutral detergent fiber digestibilities were similar (P > 0.05) among the control, Mo, and Ei diets, while the Tg diet resulted in the lowest (P < 0.05) value. The Ei diet showed the highest (P < 0.05) total N intake among the three diets with 30 % of leaf meal, which was similar (P > 0.05) to the control diet. N excreted in faeces was highest (P < 0.05) in the Tg diet when compared to the other leaf meal diets, in which the Mo diet presented the lowest (P < 0.05) value, but was similar (P > 0.05) to that found in the control diet. The Mo and Ei diets had similar (P > 0.05) values for the percent of N absorbed by the animals, which was much higher (P < 0.05) than that of the Tg diet. The forage of M. oleifera and Ei can be used in diets at 30 % incorporation to substitute the use of soybean meal in small ruminant production. 相似文献