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1.
影响防风带近距离防风效果的结构因子的研究 总被引：2，自引：0，他引：2
以山西北部半干旱风沙区为研究区,调查现有防风林带的距离防风效果,用回归分析法分析了冠层疏通度、冠下疏通度、林带宽度、栽植密度、林带与风向夹角、林带高和平均枝下高占林带高的百分比与距离带缘5倍树高处的风速降低百分数之间的关系。结果表明：影响防风林带近距离防风效果的主导因子为冠下疏透度、林带与风向的夹角和枝下高占林带高的百分比。 相似文献
2.
林带防风效应的实验 总被引：6，自引：0，他引：6
本实验采用野外模式林带的观测与风洞模拟实验相结合的方法,探讨了三种结构林带的防风性能和机制:林带垂直和水平影响范围分别达到4H和50H左右(测试仪器NLF2型四道电子风速仪,精度±0.5m/sec),透风系数为0.35的疏透结构林带减低风速20％的有效防护距离(L_(20))为18.5H;林带影响下的风速与湍流度的大小呈密切的负相关(r=-0.94)。同时提出了一个评价林带防风效应的新指标——隙高比(X_i),并阐明了如何应用隙高比值与林带的行距、行数的关系,来规划设计防风林带以及判断现有林带的防风性能。文中按有效防护距离(L_(20))给出了1—8行通风结构林带各行的最佳隙高比值。 相似文献
3.
4.
福建省沙地木麻黄基干防护林带是沿海地区抵御风沙的生态屏障，在改善沿海地区的生态环境中发挥了重要作用。通过建立的生态定位监测站，利用长期观测的年序列数据针对沿海风口木麻黄基干林带不同季节、风向的防风效能进行统计分析，结果表明：春季、秋季和冬季主风向以NNE、NE和ENE为主，夏季以SSW、SW为主，主风向上风速等级高频率也大。主风向在不同季节垂直方向上，随着高度增加，风速增加，防风效能降低；林带内垂直于林带的风向，防风效能最小，而随着角度的减少，防风效能逐渐增大；水平方向上，林带后1 H防风效能最大，垂直于林带的风向防风效能最大，随着角度的减少，防风效能逐渐减小，林带后5～20 H随着距离的增加防风效能下降，但趋势变缓。 相似文献
5.
防风障和防风林从两方面影响风蚀。第一是减低背风面风速;第二是缩短了田间长度,因而减轻了风蚀。目前已用来作为防风障的有如下方法:营造1—10行乔木和灌木的防风林,种植窄条状农作物,建立雪墙、木篱笆、石墙和土堤等。每一种防风障的效果取决于风速、风向和风障的形状、宽度、孔隙度。当风向与防风林成直角时,林带附近风速可减低70—80%,距离二十倍带高处风速减低20%;但 相似文献
6.
林带的防风效能及数字模拟 总被引：3，自引：0，他引：3
林带的防风效能既与林带本身的结构因子如:林带结构类型、疏透度或透风系数、截面形状、高度、宽度等有关,也受天气和地面状况等因子的影响。因此,通过野外观测研究,弄清单因子对不同透风系数、幅宽对林带的防风效能的影响很困难,采用风洞模型模拟试验,可以取得满意的结果。本试验于1989年6月在日本北海道大学环境研究科风洞试验室进行。风洞风速与实 相似文献
7.
本文以生态经济型防护林为例 ,对“京九”铁路大兴段绿化模式的动力效应进行了研究。结果表明 :对比旷野农田 (对照点 ) ,防护农田的风速平均约降低 18.9% ,距林带树高 0 .5倍距离处 (0 .5H)风速的降低率可达 30 .0 %左右 ,距林带 4H处至农田中心的风速降低率为 1.8% 7.1% ,林带的有效防风距离至少可达 4H ;防护农田内理查逊数 (Ri)总体平均值比对照点约高 4 .6 % ,动力速度总体平均值比对照点约低 14 .7%。 相似文献
8.
9.
关于林带走向与防风效果的关系,国内外有过大量的报道,传统的说法是:当林带与风向成垂直时,防风效果最好,所以主林带应与当地主害风方向相垂直.南京林学院等单位,1960年在对苏北沿海农田防护林防护效果的研究中指出:在林带背风面15倍树高处,当林带与风向垂直时,降低风速17.40%;当林带与风向成67.5度交角时,降低风速14.06%;当林带与风向成45度交角时,仅降低风速9.55%;观测林带宽10米,由5行槐树、4行楝树、4行紫穗槐组成,透风系数为0.41.那么,对于透风系数不相同的林带,在和风向成不同交角时,是否都具有上述的规律呢?我们通过近两年的观测,感到不宜 相似文献
10.
11.
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
12.
Ronald Queck Anne Bienert Hans-Gerd Maas Stefan Harmansa Valeri Goldberg Christian Bernhofer 《European Journal of Forest Research》2012,131(1):165-176
Applications of flow models to tall plant canopies are limited, amongst other factors, by the lack of detailed information
on vegetation structure. A method is presented to record 3D vegetation structure and make this information applicable to the
derivation of turbulence parameters suitable for flow models. The relationship between wind speed, drag coefficient (C
D
) and plant area density (PAD) was experimentally investigated in a mixed conifer forest in the lower part of the Eastern
Ore Mountains. Essential information was gathered by collecting multi-level high-frequency wind velocity measurements and
a dense 3D representation of the forest was obtained from terrestrial laser scanner data. Wind speed dependence or streamlining
was observed for most of the wind directions. Edge effects, i.e. the influence of the here not regarded pressure gradient
and the advective terms of the momentum equation, are assumed to cause this heterogeneity. Contrary to the hypothetic shelter
effect, which would reduce the drag on sheltered plant parts, the calculated profiles of drag coefficients revealed an increasing
C
D
with PAD (i.e. a dependence on canopy and plant structure). 相似文献
13.
农田防护林主要间距离的确定——基于林带结构与风速降低的关系 总被引：3，自引：0，他引：3
Relative windspeed reduction was measured behind nine relatively narrow, homogenous tree windbreaks with porosities between
0.13–0.33, and behind 28 combinations of model stubble barriers representing 25 different optical porosities (0.00–0.80).
The optimum porosities observed were 0.25 and 0.13 for tree windbreaks and stubble barriers respectively. Based on the relationship
between windbreak structure (optical porosity) and wind reduction, the chief indices for determining spacing interval, i.e.,
the windbreak structure index (δ) and the parameter of microclimate, represented by the problem wind (L
rp
), were determined. Additionally, investigations on shelterbelt trees were carried out, and stem-analysis techniques were
used, to develop a method for determining the mature height of tree windbreaks (H
0). Optimal spacing intervals between windbreaks could be predicted from the indices of a given windbreak structure, percentage
of reduction of windspeed desired and tree growth model. A hypothetical example for determining the spacing interval of principal
poplar windbreaks is given at the end of this paper. The results can be applied not only to tree windbreak design but also
to other plant materials and artificial barriers for wind protection.
Foundation item: This study was supported by Innovation Research Project of Chinese Academy of Sciences
Biography: ZHU Jiao-jun (1965-), male, Ph. Doctor, PhD advisor. Professor of Institute of Applied Ecology, the Chinese Academy of Sciences,
China, Scholar researcher of Faculty of Agriculture, Niigata University, Japan.
Responsible editor: Song Funan 相似文献
14.
Lei Wang Zhi Wang Lianyou Liu Eerdon Hasi Bingyan Sun Yan Tang 《Frontiers of Forestry in China》2006,1(2):136-141
The field investigation was undertaken to determin the characteristics of Salix psammophila plant morphdogy and airflow structure of single-line S. psammophila on the southern edge of the Mu Su sandland. The results showed that artificially cultivated single-line S. psammophila could accumulate sand because the plant decreased the windward and leeward wind velocity. There was a significant correlation
(R = 0.696) between accumulated sand volume (V
2) and plant volume (V
1). The wind velocity was 6 m/s at a 4 m height of single-line S. psammophilahedge row. The wind velocity decreased at 3 H windward and increased at 2 H to windward. The wind velocity then steeply decreased to leeward and reached its lowest value at 1 H to leeward and gradually recovered to the open field velocity. The protection distance of the single-line S. psammophila was about 17 H′ and the effective protection distance was about 13 H′. Single-line S. psammophila had few effects on the wind velocity when the wind was above the plant height.
__________
Translated from Chinese of Applied Ecology, 2005, 16(11) [译自: 应用生态学报, 2005, 16(11)] 相似文献
15.
Drag force due to vegetation in mangrove swamps 总被引：8，自引：0，他引：8
Mazda Yoshihiro Wolanski Eric King Brian Sase Akira Ohtsuka Daisuke Magi Michimasa 《Mangroves and Salt Marshes》1997,1(3):193-199
Field studies of tidal flows in largely pristine mangrove swamps suggestthat the momentum equation simplifies to a balance between the water surfaceslope and the drag force. The controlling parameter is the vegetation lengthscale LE, which is a function of the projected area ofmangrove vegetation and the volume of the vegetation. The value ofLE varies greatly with mangrove species and water depth. It isfound that the drag coefficient is related to the Reynolds number Re definedusing LE. The drag coefficient decreases with increasingvalues of Re from a maximum value of 10 at low value of Re (<104), and converges towards 0.4 for Re < 5 ×104. 相似文献
16.
Akio Koizumi Jun-ichi Motoyama Kei Sawata Yoshihisa Sasaki Takuro Hirai 《Journal of Wood Science》2010,56(3):189-193
To estimate the wind force that causes windthrow damage to a tree, the drag coefficients of actual-sized trees were evaluated
by a field test method. In this method, wind velocity and stem deflection were monitored simultaneously. The wind force acting
on a tree crown was calculated from stem deflection; stem stiffness was evaluated by conducting tree-bending tests. The results
of tests conducted on three poplar trees showed that drag coefficient decreased with an increase in wind velocity. Although
the variation in the drag coefficient was large at low wind velocity because of the vibrating behavior of the stem subjected
to variable wind force, the variation at wind velocities above 10 m/s was small. The average drag coefficient at a wind velocity
of 30 m/s was estimated by the curve-fitting of a power function to the wind velocity-drag coefficient relationship to be
0.102, which was smaller than that of actual-sized conifers studied in previous wind tunnel experiments. The drag coefficients
of these crown areas in the defoliation season were smaller than those measured in the leafy season. 相似文献
17.
海岸林风害危险率评价的理论推导 总被引：2，自引：0，他引：2
本文在对间伐和风害之间关系的讨论和以往有关研究结果的基础上,确定了一种林木风害危险率的估计方法,用于评价间伐对林木风害的影响。这种对单株黑松及整个黑松林分的风害危险率估计,是根据风速廓线、枝条分布和透光分层疏透度(OSP)系数推导出来的。结果表明:如果枝条分布模型中的参数β等于单株树冠中风速廓线模型的衰减系数αs,参数H/D1.33可用于比较和评价对单株树木的风害危险率。这一原理也同样适用于整个林分,即用林分内风速廓线衰减系数α和透光分层疏透度(OSP)的分布中的衰减系数ν,结合D1.33估计和比较林分风害危险率。文中对间伐与非间伐单株黑松风害危险率进行了估计,得出了间伐两年后可以降低单株黑松风害危险率的结论;同时给出了确定林分风害危险率估计的过程图。图3参45。 相似文献
18.
Xuanran Li Qijing Liu Yongrui Chen Lile Hu Fengting Yang 《Frontiers of Forestry in China》2008,3(1):16-23
Regressive models of the aboveground biomass for three conifers in subtropical China—slash pine (Pinus elliottii), Masson pine (P. massoniana) and Chinese fir (Cunninghamia lanceolata)—were established. Regression analysis of leaf biomass and total biomass of each branch against branch diameter (d), branch length (L), d
3 and d
2
L was conducted with functions of linear, power and exponent. A power law equation with a single parameter (d) was proved to be better than the rest for Masson pine and Chinese fir, and a linear equation with parameter (d
3) is better for slash pine. The canopy biomass was derived by adopting the regression equations to all branches of each individual
tree. These kinds of equations were also used to fit the relationship between total tree biomass, branch biomass, foliage
biomass and tree diameter at breast height (D), tree height (H), D
3 and D
2
H, respectively. D
2
H was found to be the best parameter for estimating total biomass. However, for foliage biomass and branch biomass, both parameters
and equation forms showed some differences among species. Correlations were highly significant (P<0.001) for foliage biomass, branch biomass and total biomass, among which the equation of the total biomass was the highest.
With these equations, the aboveground biomass of Masson pine forest, slash pine forest and Chinese fir forest were estimated,
in addition to the allocation of aboveground biomass. The above-ground biomass of Masson pine forest, slash pine forest and
Chinese fir forest was 83.6, 72.1 and 59 t/hm2 respectively, and the stem biomass was more than the foliage biomass and the branch biomass. The underground biomass of these
three forests which estimated with others’ research were 10.44, 9.42 and 11.48 t/hm2, and the amount of carbon-fixed were 47.94, 45.14 and 37.52 t/hm2, respectively.
__________
Translated from Chinese Journal of Applied Ecology, 2006, 17(8): 1382–1388 [译自: 应用生态学报] 相似文献
19.
Andrés Dieste Andreas Krause Carsten Mai Holger Militz 《Wood Science and Technology》2010,44(4):597-606
Beech wood (Fagus sylvatica L.) was modified with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU). The equilibrium moisture content (EMC) of wood modified
with DMDHEU calculated on a dry modified basis is reduced. Previous results have shown that the modification with DMDHEU does
not alter the capillary condensation; therefore, the reduction in EMC seems exaggerated. The equilibrium constants of the
Hailwood–Horrobin model (K
d and K
h) and the molecular weight of a hypothetical polymer of modified wood capable of adsorbing one molecule of water (W
i) were calculated from the EMC on a dry modified wood basis (M) and on a dry wood basis (M
R). The hypothetical polymer was also calculated by stoichiometry (W
c) and compared to W
i to estimate the number of operative OH groups. The number of operative OH groups decreased when M was used, in contradiction with the previously obtained results of differential heat of adsorption (∆H
s). Therefore, the use of M
R is recommended for the analysis of moisture sorption in wood modified with DMDHEU. 相似文献
20.
The competition–density (C–D) effect for non-self-thinning Populus deltoides and Populus × euramericana plantations from 3 to 9 years was analyzed using the reciprocal equation of the C–D effect. The C–D effect was well described
by the reciprocal equation, and with the progress of time the C–D curve, on logarithmic coordinates, of the P. × euramericana plantations shifted upward faster than that of the P. deltoides plantations. With increasing physical time t, the biological time τ, i.e. the integral from zero to t of the coefficient of growth λ(t) in the general logistic curve with respect to t, increased rapidly during early growth stages and the increases in τ gradually became slow during later growth stages. This trend was more evident in the P. deltoides plantations than in the P. × euramericana plantations. The coefficients A and B included in the reciprocal equation were calculated at each growth stage. With increasing τ, the coefficient A, the reciprocal of which means the asymptote of yield (=wρ) at a given growth stage, increased abruptly to a maximum value and then tended to decrease gradually to a constant level.
On the other hand, the coefficient B, the reciprocal of which means the asymptote of mean stem volume at a given growth stage, decreased exponentially and tended
to be close to zero with increasing τ. The λ(t) decreased with increasing stand age, whereas the final yield Y(t) defined as W(t) ρ, where W(t) is the asymptote of w in the general logistic growth curve, increased gradually with increasing stand age. The differences in coefficients A, B, and λ(t) between the two species were reported. 相似文献