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1.
根据连续定位测定数据,应用空气动力学和生态动力学原理探讨了杉木人工林林冠层的动力效应及动能的传输规律.结果表明:密度2000株/(104m2)、林分平均高度16 m、平均胸径15.5 cm、叶面积指数8、冠层厚度9 m、郁闭度0.9的杉木林,其零平面位移长度11.15~11.98 m,冠层粗糙度2.32~2.53 m,林冠上表面乱流切应力0.135 N·cm-2,枝叶阻力系数0.367,摩擦速度0.339m·s-1,冠内混合长度0.12 m,相对湍流强度0.7;由于林冠的存在,枝叶对气流的阻滞作用使风速廓线发生形变,在杉木林内离地面11.15 m高度上,风速随高度的变化呈对数规律,在此以下高度符合指数法则,林冠内风速削减因子1.98;乱流切应力和动能从林冠上表面传输到林冠下表面时,乱流切应力削弱70%,动能削弱90%.乱流切应力和动能在林冠内传递变化规律与林分结构特征有关,尤其与林冠内湍流性质和温度层结影响关系极大. 相似文献
2.
台风是影响我国沿海及内陆地区重要的天气系统,为了探索、了解沿海防护林对登陆台风强风过程的湍流特性的影响及其防风效应,本研究利用设置在南沙沿海防护林临海边和相距70 m的林内自动气象站实时观测了2012年的1208号"韦森特"台风过程中气象因子的时程变化,重点分析了"韦森特"台风过程强风时段的平均风速和风向特征。研究发现"韦森特"台风过程的风速时程曲线出现两次极值风速,呈M型变化,强风风向角出现大幅度的转换;南沙沿海防护林对"韦森特"台风最大风速减弱系数为0.58,对整个台风过程的风速减弱系数为0.7,林内和海边的平均湍流强度比值为1∶2.25,南沙沿海防护林对"韦森特"台风的防风效应明显。 相似文献
3.
树木风荷载与流场特性的风洞试验 总被引：1，自引：0，他引：1
【目的】研究不同树木布置方式下风荷载与风速的关系,同时分析树后流场特性,以期初步探明树木间存在相互干扰时的风荷载与流场特性,进而为树木防护和树木抗风提供依据。【方法】以豆瓣黄杨为试验树木,通过风洞试验,探讨单株、一排和一列3种布置方式下树木风荷载与风速的关系,同时对单株和一排布置下树后特定平面的流场特性进行研究。【结果】3种布置方式下树木所受到的阻力与倾覆力矩均随风速的增大呈幂函数增大;一排布置下树木的受力略小于单株布置情况,但两者差值随着风速的增大呈减小趋势,一列布置下树木的受力显著减小,其阻力值仅为单株布置时的1/3;单株和一排布置下树木的阻力系数与倾覆力矩系数均随风速的增大呈幂函数减小,一列布置下树木的阻力系数基本不受风速变化影响,倾覆力矩系数则随风速增大近似线性增加;在10 m·s~(-1)的来流风速下,单株布置下树后横风向平面内相对风速最小值为0.47,相对湍流度最大值为2.1,相对风速与相对湍流度的等值线均以树冠为中心呈辐射状分布,一排布置下树后横风向平面内相对风速最小值为0.42,相对湍流度最大值为2.2,相对风速与相对湍流度的等值线均以树冠为中心呈平行带状分布,2种布置下树后顺风向平面内相对风速与相对湍流度的等值线均以树冠为中心呈椭圆线分布【结论】树木风荷载随风速的增大近似呈幂函数增加,但树木间的相互干扰会对树木风荷载产生影响。风速相同时,单株、一排和一列三种布置方式下树木所受到的阻力和倾覆力矩均依次减小。树木的背风面存在风影响区,此区域的流场特性会发生显著改变,体现为风速降低和湍流度增大。单株布置时树后风影响区为以树冠为中心的辐射状区域,一排布置时树后风影响区为相对连续的区域。 相似文献
4.
自然界中的强风常常对树木造成不可逆破坏,分析强风穿过时树林内部的气流情况有利于评估树木的抗风性,更好地理解如何减轻风的影响。以阔叶树和针叶树为原型,提取了二者叶团簇和枝干构造的特点,建立两种结构不同的树木模型,组合成树林模型,在3个不同叶面积密度下进行风力作用下的仿真模拟实验。分别使用改进的k-ε双方程模型和k-ω双方程模型以设置风环境,并且用龙格-库塔法分析求解湍流模型。k-ε双方程模型下,当叶面积密度分别为1,5和10 m2/m3时,阔叶林背风侧20 m处的最低风速与入口风速相比下降了49.60%,67.23%和80.40%,针叶林分别为55.13%,68.90%和78.29%。k-ω双方程模型展示了阔叶树林内部风场的复杂性。结果表明,叶面积密度与树林挡风能力之间是非线性关系,树林的挡风能力随叶面积密度的上升而增强,增强到一定程度后上升幅度减缓。不同的树木结构会导致风场的变化,影响同等强度风荷载下的受损概率和挡风能力。叶面积密度高、树冠体积大的树木更容易在强风中受到损害。 相似文献
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6.
广西猫儿山典型植被林冠结构比较研究 总被引：1，自引：0，他引：1
运用LAI-2000冠层分析仪对广西猫儿山3种典型森林植被进行叶面积指数测定,对比3种典型森林植被叶面积空间分布以及其水平空间分布的均匀性。结果表明,(1)杉木林、木荷林和毛竹林叶面积指数水平分布由内向外逐渐减小,叶面积指数与距林冠投影中心距离呈二次函数关系;(2)杉木林叶分布的最大值在树冠顶部,从上到下叶面积指数逐渐下降;而木荷林从上层到下层叶面积指数呈增加的趋势;(3)杉木林的冠层在水平空间分布的均匀性要好于其他2种林型,毛竹林分布均匀性最差。本研究对揭示不同林型叶面积在森林植被中的空间格局,探究林冠结构和水文过程的关系,具有重要的理论和实践意义。 相似文献
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8.
以广东省东莞市大岭山森林公园33个乡土树种为研究对象,使用半球面影像技术和Li-6400光合仪分别获取林木冠层结构、光分布和光合作用指标,用方差分析和粗糙集理论进行评价。结果表明,林冠开度、叶面积指数、林下直射光、林下散射光、透光率和净光合速率均在各树种间存在极显著差异(p<0.0001),各指标在树种间的变化幅度也各不相同,其中林冠开度、林下直射光、林下散射光和透光率的变化幅度均超过了20%,分别为29.95%、20.40%、23.77%和22.56%,而叶面积指数和净光合速率的变化幅度分别为3.24和7.80。林冠结构和光分布均对林木净光合速率有重要贡献,但其影响程度不同。其中林冠开度最大,重要值为1/11,其余几项指标对光合作用的重要性相同,为2/33,略小于林冠开度的重要性。在评价林木冠层结构和光分布对净光合速率的综合影响力中,林冠开度贡献的权重最大,为0.27,林下直射光、林下散射光和透光率贡献的权重均为0.18。冠层结构和光分布对林木净光合速率的综合影响力在一定程度可指示冠层结构和光分布的合理性,与林木净光合速率大小不存在线性正相关关系,它只表明冠层结构和光分布对林木净光合速率的影响程度。 相似文献
9.
为阐明不同栽植密度下欧美杨无性系树冠叶片耐荫性与生物累积量的关系,选择高密度(2 m×3 m)和低密度(2 m×5 m)栽植的不同亲本的5个欧美杨无性系为研究对象,测量了生物量、树冠结构、叶面积指数及光合参数。结果表明:(1)不同无性系对栽植密度有不同的反应;(2)具有较高生物量的欧美杨无性系树冠叶片在高、低栽植密度下均表现出较强的耐荫性特征;(3)树冠耐荫性在不同密度中表现出差异性,在低密度栽植中,树冠上层耐荫性与生物量和叶面积指数关系密切;在高密度栽植中,树冠上、下层叶片耐荫性与生物量和叶面积指数关系密切;(4)树冠耐荫性特征受亲本和环境的共同影响,由低密度到高密度,具有较高生物量的03-04-97、03-04-111、03-04-171树冠中下层叶片光补偿点和暗呼吸速率大幅度降低。该研究结果可为选择适合高密度栽植的欧美杨无性系提供数据和理论支持。 相似文献
10.
应用LAI-2000冠层分析仪,研究了苏南丘陵区主要林型的叶面积指数(LAI)季节动态。结果表明:4种林型的LAI随季节变化具有明显的规律性,充分反映了4种林型叶片的生长状态,LAI值由大到小依次为毛竹(3.45)>杉木(2.87)>麻栎(2.62)>马尾松(2.00);冠层空隙度总体变化趋势与LAI的总体变化趋势恰好相反,在8月份出现最小值,分别为杉木6.7%、毛竹2.8%、麻栎5.6%、马尾松15.1%;叶倾角的季节变化不大,均在一定范围内波动。对4种林型的冠层均匀性进行比较分析,结果发现,杉木林冠层均匀性最好,麻栎林冠层均匀性最差。对4种林型的叶面积指数与冠层空隙度进行回归分析,发现两者之间呈指数回归关系(R2>0.95),通式为:y=ae-bx。 相似文献
11.
Simultaneous measurements of windspeed were made outside and inside a pine (Pinus thunbergii Parl.) coastal forest with different thinning intensities. Synchronously, 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 estimated using hemispherical silhouettes in each treatment area. Based on the observations, the frequency distribution
of velocity, turbulence intensity, wind profile, and the corresponding relationships of these respective parameters with the
vertical forest structure (OSP) were examined and compared among the treatment areas. A normal distribution of wind velocity
was observed at the lower zone of the forest stand in all treatment areas. The turbulence intensity, the highest value of
which was found near the canopy, changed greatly with height, wind velocity, and treatment, and decreased with windspeed and
increased with the thinning intensity. It was found that the exponential relationship between windspeed and height could be
used to describe the wind profiles within the canopy of the coastal forest. The results demonstrate that the attenuation coefficient
of the wind profile corresponds to the grade of thinning intensities. The wind patterns in a coastal forest with different
thinning intensities are related to the vertical forest structure, particularly, wind profiles within the canopy are closely
correlated with the distribution of OSP. The results indicate that wind profiles can be estimated simply based on the measurement
of OSP with a very high coefficient of determination. Reciprocally, the estimation of OSP can also be obtained from the measurement
of wind profile.
Portions of this paper were presented at the 111st Annual Meeting of the Japanese Forestry Society.
Appreciation is due to Professor Masashi Yamamoto, Mr. Kenji Sakioka, Mr. Takahiro Yoshida, Mr. Hirotaka Yamazaki, Mr. Yasunori
Hasegawa and the members of the Sabo Division of the Faculty of Agriculture of Niigata University for their help in collecting
the field data and in constructing the observation towers. 相似文献
12.
ZHUJiao-jun LIXiu-fen GondaYutaka MatsuzakiTakeshi 《林业研究》2004,15(4):305-312
One of the most important and frequently studied variable in forests and the most basic element in governing transport processes of airflow is wind speed. The study of wind profile, defined as the change of wind velocity with height, and wind velocity are important because of tree physiological and developmental responses. Generally, wind profiles above the ground or at a canopy surface follow classical logarithm law, but wind profiles in a single tree and in a forest stand are not logarithmic. This paper summarizes the results of wind profile studies within a single tree, in a forest stand, above the forest canopy and in a forest area from recent research in a coastal pine forest. The results demonstrate that: 1) wind profiles with in a single conifer tree crown showed an exponential function with height, 2) wind profiles in forest stands were able to be expressed by attenuation coefficient of wind, 3) wind profiles over a forest canopy could be determined using profile parameters (friction velocity, roughness length and displacement), and 4) for a forest area, the extreme wind speed could be predicted reasonably using the methods developed for the design of buildings. More research will be required to demonstrate: 1) relationships between wind profiles and tree or stand characteristics, 2) the simple methods for predicting wind profile parameters, and 3) the applications of wind profile in studies of tree physiology, forest ecology and management, and the detail ecological effects of wind on tree growth. 相似文献
13.
Influence of typhoon disturbances on the understory light regime and stand dynamics of a subtropical rain forest in northeastern Taiwan 总被引：1，自引：0，他引：1
Teng-Chiu Lin Steven P. Hamburg Yue-Joe Hsia Tzer-Ton Lin Hen-Biau King Lih-Jih. Wang Kuo-Chuan Lin 《Journal of Forest Research》2003,8(3):139-145
In 1996 and 1997 we examined the effects of typhoon disturbance on the understory light environment and sapling dynamics of the Fu-shan Experimental Forest, a subtropical rain forest in northeastern Taiwan. Mean understory light levels were approximately 30% of those in the open immediately following the two 1996 typhoons which affected the forest, yet in 1997, following two more typhoons, mean understory light levels were 10%–20% of those in the open. The decline of understory light levels to those present prior to the typhoons was more rapid in 1996 than in 1997, even though the two typhoons in 1996 were more intense than those in 1997. This difference might be the result of the timing of the typhoons. In 1996 the typhoons occurred earlier in the growing season, before August 1 rather than the middle and end of August in 1997. The regular defoliation caused by the frequent typhoons that impact Fu-shan (average of 1.4 per year) and the low stature of the forest (mean canopy height of 10.6m), results in much higher light levels beneath the canopy (9%–30% of levels in the open) than those found in most tropical and temperate forests. As a result, understory light levels are not limiting the distribution of canopy tree saplings within the forest and there is no evidence that canopy gaps play an important role in canopy tree regeneration within the Fu-shan Experiment Forest. This is in contrast with the pattern reported for some tropical forests. With frequent typhoons impacting northeastern Taiwan, the forests of this region are perpetually recovering from wind disturbances. 相似文献
14.
15.
Wind Measurements in a Pine Forest During a Destructive Gale 总被引：3，自引：0，他引：3
Anemometer readings were recorded during a gale which blew downsome of the trees in an even-aged 16 m stand of Pinus sylvestrison sandy soil at Thetford forest. Gusts at the top of the canopyattained 17•5 m/sec. Wind profiles agreed well with thetheoretical logarithmic profile above the canopy and the exponentialprofile below. During the gale the zero plane displacement androughness length values were similar to those at lower windspeeds. It is therefore possible to estimate wind profiles andthe forces to which a tree in the crop is subjected from measurementsof wind speed at a single point within or above the forest.The wind speeds which blew trees down were much lower than thosepredicted as necessary from ‘tree pulling’ studiesin the same forest. This discrepancy suggests that any considerationof windthrow must take into account the effects of tree vibrationon the deterioration in the strength of the root-soil complex. 相似文献
16.
为揭示油松中龄林的气候效应,笔者运用自动气象站对晋东南油松中龄林林内外的气温、相对湿度、风速和风向、气压进行了为期1年的同步、连续观测,分析不同因子在林内外变化特征的差异性。结果表明,太行山油松中龄林林内外气温、相对湿度、风速、气压、太阳辐射的变化趋势相近,林内的年平均气温、年平均相对湿度、年平均气压、年平均风速、年平均太阳辐射强度分别为6.43℃,69.06%,0.09 m/s,87.94 KPa和39.67 W/m^2;林外分别为8.92℃,62.27%,0.82 m/s,87.81 KPa和137.14 W/m^2.油松林具有降温、防风、增湿、改变风向和减少太阳辐射的作用。此外,油松中龄林不仅具有明显的小气候效应,且改变了上述气象因子的相关性。 相似文献
17.
Light is the most common limiting factor in forest plant communities,influencing species composition,stand structure,and stand productivity in closed canopy stands.Stand vertical light structure is relatively simple under a closed canopy because most light is captured by overstory trees.However,wind disturbance events create canopy openings from local to landscape scales that increase understory light intensity and vertical light structural complexity.We studied the effects of an EF-1 tornado on horizontal and vertical(i.e.three-dimensional)light structure within a Quercus stand to determine how light structure changed with increasing disturbance severity.We used a two-tiered method to collect photosynthetic photon flux density at 4.67 m and 1.37 m above the forest floor to construct three-dimensional light structure across a canopy disturbance severity gradient to see if light intensity varied with increasing tornado damage.Results indicate that increased canopy disturbance closer to the tornado track increased light penetration and light structure heterogeneity at lower forest strata.Increased light intensity correlated with increased sapling density that was more randomly distributed across the plot and had shifted light capture higher in the stand structure.Light penetration through the overstory was most strongly correlated with decreased stem density in the two most important tree species(based on relative dominance and relative density)in the stand,Quercus alba L.(r=-0.31)and Ostrya virginiana(Mill.)K.Koch(r=-0.27,p<.01),and indicated that understory light penetration was most affected by these two species.As managers are increasingly interested in patterning silvicultural entries on natural disturbances,they must understand residual stand and light structures that occur after natural disturbance events.By providing spatial light data that quantifies light structure post-disturbance,managers can use these results to improve planning required for long-term management.The study also provides comparisons with anthropogenic disturbances to the midstory that may offer useful comparisons to natural analogs for future silvicultural consideration. 相似文献
18.
Kenichi Daikoku Shigeaki Hattori Aiko Deguchi Yuji Fujita Hotaek Park Kazuho Matsumoto 《Journal of Forest Research》2007,12(6):452-466
We explored the relationship between directional variation (changes in direction from a reference point) in vegetation and
wind profiles, and propose an empirical wind profile model that may reproduce the wind profile within the canopy (such as
secondary wind maximum) and reduce calculation loads. Based on the results of our observations in secondary broad-leaved forest,
we clarified the variation in secondary wind maximum and aerodynamic parameters in wind direction, and assessed the influence
of forest structural heterogeneity on the wind profile. Wind blew from specific directions depending on the time of day and
season, and secondary wind maxima were observed in particular wind directions. Outlier estimations of aerodynamic parameters
were determined for wind directions of 45°, 120–210°, and 300°, and these did not show a logarithmic distribution. Our proposed
model reproduced the wind profile within and above the canopy, closely resembling K-theory and closure models, and reduced
the required number of calculations and observations. The influence of forest structural heterogeneity was greatest in the
upper part of the canopy (9.14 m), and reproducibility of the wind profile was improved by 0.05 m/s (3.4% on average) by changing
the forest structural parameters of the model according to the wind direction. It was clear that forest structural heterogeneity
did not cause critical errors in estimation of the wind profile, even at our study site, which had complex forest structure. 相似文献
19.
We report on a wind-tunnel study with 1 : 75 scale model treesdesigned to examine the influence of canopy structure on theformation of turbulent gusts above forests. This was to testthe hypothesis that more irregular canopy structures produceless intense gusts because the change in wind speed with heightat canopy top is less severe. Measurements were made of windspeeds and turbulence within and above the model forests andof the wind loading on model trees in four different silviculturalsystems. The systems tested were even-aged, single-tree selection,shelterwood/group selection and strip felling. The measurementsshowed that the profiles of different mean wind and turbulencecharacteristics above the forests are remarkably similar whenvertical heights are normalized by the height of the tallesttree but differences do exist within the canopy. The wind loadingmeasurements indicated no difference between the systems interms of stability except possibly for the shelterwood/groupselection. In the shelterwood/group selection system the presenceof smaller sub-canopy trees appears to reduce the loading onthe main canopy trees either by providing support and increasingdamping or by absorption of energy from the canopy-penetratinggusts. 相似文献