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根据“2001—2015年林业生态建设规划和建设宜居生态、和谐富裕巴彦淖尔”的奋斗目标，巴彦淖尔市提出了今后林业建设的“三五”发展（用五年时间，抓好五大工程建设，以五项措施做保障）思路，在五项保障措施中科技支撑是其中一项重要内容；明确了每年完成林业建设面积不低于100万亩，林业产值每年增加1亿元的奋斗目标。完成上述建设目标和任务，需要进一步加快造林绿化进程，不断增加森林资源总量。 相似文献
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林冠的结构和光的分布——光的吸收理论的探讨 总被引：1，自引：0，他引：1
本文提出了短波辐射通过林冠层时的吸收理论。讨论中将叶层结构分为水平叶层、垂直向光叶层、特殊交角叶层和随机分布叶层等四种情况来考虑,分别推导出被林冠吸收的直射和散射光强的数学模式。 相似文献
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神秘的地下的原始森林老诚在黑龙江省乐南部的张广才岭中，有一个闻名遐尔的旅游胜地——地下原始森林。大约在１万年以前，张广岭中发生火山爆发，堵塞了河道，不但为人类留下了美丽的镜泊湖，同时，在这里形成了内壁深壑陡峭的大小不等、形状奇异的１０个火山口。它们呈... 相似文献
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根据中苏两国政府的协定,中苏科学家对黑龙江流域生产力的共同考察工作已是第二年了。由各种专业的科学家们亲手来完成的伟大事业,有利于苏联远东和中国东北地区社会主义经济的发展。在考察计划中,森林学问题佔有很重要的地位。按照森林植物条件及树种组成来说,苏联远东的森林和中国东北的森林似乎是一个林区,这就便于我们选择研究这块森林资源的方法及其开发技术。 相似文献
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区域的持续发展和林业的相关研究的评述杨学军（南京林业大学２１００３７）关键词：持续发展，系统研究，区域经济，林业景观，生态系统１区域的持续发展与林业的作用１．１区域及其持续发展的战略目标区域是一定地域范畴中各种自然生态要素、社会要素、经济要素综合作用... 相似文献
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邹幸福 《中南林业科技大学学报(自然科学版)》1990,(2)
本文对两个具有时滞的生物数学模型进行了研究。结果表明:当时滞大到一定程度时,模型的任何非常数解,都绕其平衡状态振荡。从而揭示了具时滞的模型的解与不具时滞的模型的解之间的本质差别。也较好地解释了传统生态学观点不能解释的有关实验结果。将时滞看作为生物种群数量振荡的内在原因,这是对有关传统观点的更新和补充。 相似文献
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正黄柏山,一座连接鄂豫皖三省的大山。群山巍峨,烟波浩渺,垒垒岩石,纤纤翠草。这条大别山腰间的绿色丝带就像千里大平原惊艳而凝重的舞台,内敛而壮阔的山川画卷,吸引着一批又一批崇尚绿色的人群。造访黄柏山,它的博大震撼了我。高山不朽,水润万物,作为长江和淮河的分水岭,淮河的发源地,黄柏山用一颗清澈如水的心滋养着四季不凋的广袤森林,那些古树遮天蔽日透着古朴清新的气息。沿着略加整饬的林中小路走入密林深处,踏着厚实的苔藓,感觉泥土的潮气和植物 相似文献
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本文通过对9条分布均匀、相对较窄的不同疏透度(透光疏透度,下同)(0.13～0.33)的树木林带和不同疏透度(0.00～0.80)风障组合的野外风速观测,确定了树木林带和风障的最适疏透度分别为0.25和0.13。基于林带结构(疏透度)与风速降低的关系,确定了林带主带间距离的主要参数,即,林带结构系数(δ)和以主害风为代表的小气候参数(Lrp)。另外,通过对林带树木的野外调查,应用树木解析技术确定林带成林高(H0)。因此,树木林带的主带间距可以通过林带结构系数、希望降低风速的比例和树木生长模型来确定。本文以杨树林带为例,具体确定了杨树林带的主带间距。该研究结果不仅适于树木林带的设计,同时适于其它生物材料或人工风障的设计。图4表5参40。 相似文献
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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 (Lrp), 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 (H0). 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. 相似文献
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Optical porosity and windspeed reduction by coniferous windbreaks in Southern Ontario 总被引：6，自引：1，他引：5
Relative windspeed reduction was measured behind nine relatively narrow, homogeneous windbreaks in southern Ontario, Canada
to assess whether any characteristics of the windspeed reduction curve could be predicted from optical porosity. The latter
was determined for each windbreak using high contrast black and white photographic silhouettes on a computer digitizing system.
Minimum windspeeds behind the windbreaks ranged from 29 to 71% of open windspeed; these minima were located 2 to 6 multiples
of windbreak height away from the windbreak. Optical porosities of the bottom half of the windbreak ranged from 0 to 31%.
Multiple regression of the shelter parameters (location and value of minimum relative windspeed) on the independent variables
(optical porosity, open windspeed, surface roughness, approaching wind direction relative to the windbreak, average tree diameter
and average tree spacing) showed that the minimum relative windspeed could be predicted from the optical porosity of the bottom
half of the windbreak. The results suggest that optical porosity can be used to predict minimum relative windspeeds and may
therefore be useful as a guide in the field evaluation of windbreaks. 相似文献
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Windspeed reduction in shelter is generally expressed relatively and is usually assumed to be independent of open windspeed. The purpose of this study was to re-examine the relationship between open windspeed and windspeed reduction in shelter using windspeeds and wind directions measured for two windbreak systems at various distances from the windbreaks and with three windbreak porosities. Optical windbreak porosities were estimated from digitized color photographs using an intelligent (trainable) image processing program. Relative windspeed reduction in shelter was found to be related to the open windspeed. There existed a threshold windspeed at approximately 5 m s–1, below which relative windspeed reduction varied but generally decreased as the open windspeed increased. Above the threshold windspeed, open windspeed did not have an effect on relative windspeed reduction in the sheltered zone. Using the threshold windspeed reduction, the authors propose an index to evaluate the effectiveness of a windbreak for the overal windspeed protection.Published as Journal Series No. 10815 of the Agricultural Research Division, University of Nebraska. 相似文献
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In Patagonia, where strong winds are a constraint to agricultural production, live windbreaks are often planted in agricultural fields to protect crops, livestock, and soils from wind hazards. The major factors that determine the efficacy of windbreaks are height, porosity, orientation, length, and location in the landscape. A review of the research on the effect of live windbreaks during 1993 through 2000 is presented in the paper. Porosity and distance from windbreak were found to have major effects on relative windspeed reduction. The greatest degree of protection was for dense windbreaks (windspeed reduction of 85%) at 1H (1H = a distance of one tree height, leeward of the windbreak). Different crops showed a differential yield response to wind stress. The production of garlic (Allium sativum) was not significantly affected by wind. Tulip (Tulipa sp.) bulb yield decreased on average by 25% between 2H and 17H. The production of lucerne (Medicago sativa) at 1H was 40% higher than lucerne grown in open conditions. In contrast, strawberry (Fragaria sp.)and cherry (Prunus avium) were more sensitive to the effect of the wind. Dendrometric models (diameter, site index, volume and crown dynamics) were developed to define the wood potential productivity that could be expected from different site qualities. The prediction of height growth as a function of age, allows the estimation of the area protected by the windbreak. An economic assessment based on realistic estimates of shelter benefits is required to encourage the development of windbreak systems that could also offer other benefits, including erosion control and timber production.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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Florida citrus and vegetable crops generate billions of dollars in revenue every year. However, wind, freezing temperatures,
hurricanes, and diseases negatively impact production. Windbreaks located perpendicular to the prevailing wind can increase
farm production simply by reducing wind and modifying microclimate. Windbreaks can also help in managing pathogens such as
citrus canker (Xanthomonas campestris pv. citri). To study the modification of wind speed, temperature, and relative humidity on the leeside of single-row tree windbreaks
in southern Florida, automated weather stations were installed in 2007/2008 at 2 m above the ground along transects perpendicular
to a eastern redcedar (Juniperus virginiana) and three cadaghi (Corymbia torelliana) (WB1–WB3) windbreaks. All windbreaks reduced wind speed, with minimum wind speed (~5% of the open wind speed) at two times
the distance of windbreak height (2H, where H = windbreak height in m) on the leeside of a E. redcedar (~17% porosity) and
at 4H (~3–30% of the open wind speed) and 6H (<50% of the open wind speed) on the leeside of cadaghi windbreaks WB1 (~22%
porosity) and WB2 (~36% porosity), respectively, when the wind direction was nearly perpendicular to the windbreaks. Wind
speed reduction was observed up to 31 times the windbreak height (31H). Cadaghi windbreaks reduced wind speed on the leeside
even during a tropical storm event. Temperatures on the leeside of the windbreaks were warmer during the day and cooler near
the windbreaks at night compared to temperature in the open fields. This study demonstrates that single-row tree windbreaks
can reduce wind and modify the microclimate to enhance crop production for Florida growers. 相似文献
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The effectiveness of windbreaks in windspeed reduction is often evaluated without regard to the objects to be protected. In fact, many objects may have different sensitivities to wind and often require different degrees of wind protection. Since commonly used indexes do not consider the sensitivity to wind, a concept of specific protection efficiency is developed. A critical windspeed is used to represent the sensitivity of each object. Windspeeds greater than this value are considered damaging. A dimensionless protection index is defined to evaluate windbreak efficiency. The maximum index value is 1 for the highest protection, and the index is negative when sheltered windspeed is greater than the critical windspeed. This index can be compared, summed, and averaged across different windbreaks, objects, and leeward locations. A sample of critical windspeed values was compiled from the literature. The index was evaluated using actual wind data measured under both sheltered and open conditions. The results indicated that the index can be used for evaluating windbreak effectiveness in terms of objects protected under various conditions. This model could be used as a tool for windbreak-related research and policy making. 相似文献
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The beneficial effects of shelterbelts and windbreaks have been convincingly demonstrated in the temperate regions of the world. Investigations conducted on the biological effects of windbreaks are relatively few in arid and semiarid zones. In the semiarid regions of Haryana under Social Forestry programmes large scale plantations along roads, canals, fields, etc. were undertaken. In this region, an area having a windbreak of Dalbergia sissoo (18 years old) was selected and cotton was raised in the agricultural fields. The tree belt is able to reduce the windspeed by 15 to 45% depending upon season and wind speed. Observations on morphological characters and crop yield revealed that the belt height had a significant effect on plant growth. In general growth and cotton productivity increased upto distance of four times the tree height to the leeward of belt. Depending upon the orientation of tree belt, an increase in cotton yield was found to be 4 to 10%. Plant growth (in terms of leaf area, leaf number, plant height) and yield (seed cotton production) were observed to be high in sheltered area as compared to open fields. The results indicate that windbreak establishment should be adopted and integrated to a whole farming system, in semiarid regions. 相似文献
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Soil erosion by wind is a persistent problem in central Wisconsin. The extent and effectiveness of windbreaks in erosion-prone
areas are unknown. We investigated the potential effectiveness of windbreaks established for soil erosion control in Portage
County, Wisconsin. Our objectives included quantification of their extent and condition, development of a routine method for
field assessment, and compilation of a reference database of windbreak information. We used aerial photographs to identify
the windbreak population, and a two-stage, stratified random sampling technique to obtain samples for field evaluation. Variables
and attributes examined included species, number of gaps, height, width, porosity, spacing, live crown ratio, crown condition,
and a condition rating. Methods included simple photo-interpretation techniques, field measurements, optical scanning techniques,
and data manipulation in geographic information systems. We identified over 2600 windbreaks comprising a total extent of 834
km; only a small proportion of this may offer effective protection at critical periods. Collectively, field windbreaks protect
a very small proportion only of the county‘s agricultural land area from wind erosion. These results imply a need for increased
planting rates, explicit maintenance or renovation of existing barriers, and windbreak designs that are both sustainable and
compatible with current agricultural production efforts.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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At sites in the Sahel where windbreaks are used to control wind erosion, management strategies are required to minimise competition for water between trees and crops. Uptake of water by windbreak trees was therefore studied in experiments designed to compare water use among tree species, assess which variables exert most control over transpiration and determine the source of water transpired by windbreak trees. Transpiration and soil-water extraction by Acacia nilotica, Acacia holosericea and Azadirachta indica trees in windbreaks were measured at the ICRISAT Sahelian Centre, Niger. Coupling of windbreaks to the atmosphere was evaluated and a stable isotope technique was used to compare utilisation of groundwater by windbreaks and crops at two sites in Niger with different water table levels. Azadirachta indica used least water, probably as a result of lower stomatal conductances, since windbreaks exhibited good physiological control over transpiration. The potential for competition for water was most severe with Acacia nilotica and Acacia holosericea, as they extracted large quantities of water through lateral roots, and at the location where trees could not access groundwater. At such sites, the effects of competition on crop productivity should be minimised by planting tree species with low water requirements and by using pruning to limit tree transpiration.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献