霍林河防护林体系建设对生态环境的影响分析

利用霍林郭勒市1973-2005年气象资料，对该地区生态环境的变化进行了对比分析。分析表明，防护林体系建设后，生态环境明显改善。     

霍林河防护林体系建设对生态环境的影响分析

利用霍林郭勒市1973-2005年气象资料,对该地区生态环境的变化进行了对比分析.分析表明,防护林体系建设后,生态环境明显改善.     

深圳市海洋灾害防御体系建设的现状及对策

初步分析深圳市的海洋灾害防御体系建设的现状,就如何完善海洋灾害的监测体系、加强预警系统建设、推进政府应急救援体系建设、启动海洋灾害机理研究、加强防护林建设和促进人才培养等方面提出了一些具体的对策。     

沿海防护林气象效应研究综述

本文结合笔者自身的研究工作,介绍国内外关于防护林体系的生态效益研究,侧重介绍沿海防护林体系气象（气候）效应的研究动态及其取得的成果,为全社会重视保护森林环境,加强沿海防护林的营造提供科学依据。     

秦安春季造林与秋季造林的气候分析

秦安县地处陇中黄土高原梁峁沟壑区,是“三北”防护林建设重点县,也是全省十一个重点造林县之一。该县历来习惯于春季一次造林,虽成活率低,仍年复一年,“年年造林不见林”,这主要是造林季节不适宜,违背了降水“秋多春少”的气候规律,以及重造轻管造成的。1977年以来五窑公社在黄委会天水水保站的指导下,打破常规,变春季一次造林为“春     

新疆气候变化与生态环境关系的近期研究

1987年以来，新疆气候向“暖、湿”方向变化，引起社会上的关注。本文综合分析了气候变化的基本特征，根据考察和分析，认为气候的这种变化主要是通过水资源的配置对生态环境修复和建设产生积极影响。新疆正处在干旱气候背景下极为难得的“相对湿润期”和生态环境建设的“政策优惠期”，生态环境已显露出有所恢复和改善的迹象，但总体上还处于一个严峻的形势，需要加快修复和建设。     

河北省生态环境监测系统建设初探

根据国内外有关生态环境监测研究的现状，提出了河北省生态环境监测系统建设的基本框架。系统主要包括：生态环境监测的基本思路和步骤；监测方法和监测内容；生态环境监测体系，如监测标准规范、站网布局、信息传输和信息服务等。对生态环境监测的未来前景进行了展望。     

新疆生态环境近期变化与应对措施的初步分析

新疆的生态安全已引起全社会的极大关注。作者依据近年几次考察和资料信息分析，分析了新疆生态环境近期变化的主要特点和引起变化的主要原因，强调指出新疆气候“暖湿”变化不可能从根本上改变新疆干旱地区生态环境的基本状态，对此不能盲目乐观，只能因势利导，抓住有利时机加大修复生态环境的力度。文中提出了五项加强新疆生态环境修复、保护和建设的应对措施。     

互助县气候变化特征及对农业生态的影响分析

本利用30a的气象资料对影响互助县生态环境主要气候因子的基本特征及其变化进行分析，并探讨自然灾害及人类经济活动对生态环境的影响，为生态环境的保护和建设提供参考依据。     

农田防护林的小气候效应

我县地处辽河下游,渤海之滨,春季和夏季多西南大风。为了减轻大风对农业生产的危害,多年来我县营造了大面积农田防护林。农田防护林对改善农田小气候确实起到了显著作用。近年来我们和营口市盐碱地改良利用研究所、荣兴农场农科站气象哨、高家农场农科站,共同对荣兴农场中央屯大队、良种场大     

“天气-风障-产量”系统中林带结构的马氏决策

“天气-风障-产量”是一个复杂巨系统, 若想通过该系统取得最佳效益, 必须对林带结构做出优化决策。该文论述了马尔可夫决策过程 (MDP) 在该决策中的应用问题。利用在沈阳市康平县对农田防护林带考察中所取得的资料, 依据概率论的基本原理, 计算出不同结构林带对玉米气象产量影响这一生态控制系统中有关状态的转移概率; 用MDP折扣模型计算出折扣率β=0.9条件下的最优策略并加以改进。结果表明:在当地天气、作物状况下所形成的复杂系统中, 采用透风系数为0.35的疏透结构农田防护林带具有最优决策结果。     

On three-dimensionality of shelterbelt structure and its influences on shelter effects

Natural shelterbelts, unlike planar barriers, have a certain width, within which interactions among wind speed, drag force and pressure perturbations create a net sheltering effect. The variations of flow, drag force, permeability, and pressure perturbation for shelterbelts of different widths and different horizontal structures are numerically studied, and their influences on shelter efficiency are discussed. Comparisons are made of fourteen medium-dense shelterbelts, with the same overall leaf-area, that differ only in width or horizontal distribution of leaf-area density. The simulated results are consistent with both field observations and wind-tunnel measurements.The simulations demonstrate that the total drag force of the entire shelterbelt varies little with changes in width and structure. The results also show that shelter distance and the overall average wind speed reduction decrease only by 15–18% as width increases by a factor of 100, and changes even less for different internal structure. However, width greatly affects the location of minimum wind speed, pressure perturbation, and the permeability of shelterbelts. Horizontal changes of wind speed inside the uniform shelterbelts have four different patterns, which depend on shelterbelt width and height. The absolute pressure perturbation significantly decreases with increasing width. A possible cause of the insensitivity of shelter efficiency to width and internal inhomogeneous structure is the compensation between the effects of permeability and pressure perturbation on shelter efficiency.     

MOMENTUM BUDGET AND SHELTER MECHANISM OF BOUNDARY-LAYER FLOW NEAR A SHELTERBELT

We use a nonhydrostatic shelterbelt boundary-layer turbulence model with Mellor–Yamada second-order closure to evaluate quantitatively the dynamic processes of surface boundary-layer flow perturbed by shelterbelts of different densities and to understand the shelter mechanism. We first analyze the drag exerted on air by shelterbelts of different densities, a root cause of any shelter function, and the resulting wind reduction. The results show that the effectiveness of a shelter is determined not only by its total drag but also by the distribution of the drag-generated momentum deficit in the sheltered area, and that medium-dense shelterbelts have the maximum shelter effect. We also analyze the horizontal momentum budget and find that the shelter mechanism is the product of several processes. The results reveal that strong vertical mean transport and the pressure gradient also play important roles in shelter efficiency. The pressure perturbation caused by the shelter extends far downstream of the shelter, and combines with advective transport to provide the larger shelter efficiency of medium-dense shelterbelts. We finally analyze the changes of perturbed pressure, turbulence, and vertical velocity with shelterbelt density to further clarify the shelter mechanism.     

Air movement and its consequences around a multiple shelterbelt system under advective conditions in semi-arid Northern Nigeria

Summary Horizontal wind speed patterns above a scarce millet row crop on inhomogeneous sandy soil revealed insufficient protection from hot winds by multiple shelterbelts in semi-arid Northern Nigeria. This appeared mainly due to too high distances between the belts. Marked yield drops occurred with distance between the belts, in what McNaughton defined (under mechanical damage and microclimate disturbance from strong winds) as the unprotected wake zone. These may, in the case of hot winds, mainly be attributed to combined negative effects on soil moisture and crop physiology of the combination of turbulence, worsened by the shelterbelts, and advected heat. Other parameters confirm the picture of the wake zone and the quiet zone, the latter also being present windward of the belts in a reduced form. The results have serious consequences for the design rules of multiple shelterbelts and alternatives under African semi-arid conditions.     

Shelter effects of vegetation belts — Results of field measurements

The results of full-scale measurements of the wind reduction behind four different types of shelterbelts are reported. Two of the shelterbelts in question were of the single-row type. The remaining two consisted of at least two rows of deciduous trees and in both cases some conifers.Wind measurements were made under various weather conditions, both in winter and in summer. The minimum relative wind speed on the lee side varied from ca 0.1 behind the most dense shelterbelt to 0.4 behind the most porous one when the wind was blowing at right angles in summer. In the winter, the shelter effect was much less than in the summer but the two most dense shelterbelts did reduce the wind speed considerably also then.When the wind was blowing at an angle to the shelterbelt, the lee maximum occurred closer to the belt and the wind speed recovered faster than when it blew at right angles. The wind reduction just behind a shelterbelt always tended to be greater in oblique than in perpendicular wind. The wind reduction behind a leafy vegetation belt decreased as the reference wind speed increased. The approach wind speed affected wind reduction much more at a porous shelterbelt than at a dense one.The difference between reference and local wind directions could be great just behind a shelterbelt but this difference disappeared within a few h downstream of the belt. With further increasing distance (up to 4–11h), the wind continued to veer so that the direction became more parallel with the shelterbelt than in the case of the undisturbed wind. Then the wind slowly veered back to the direction of the approaching wind again.The present data give a good idea of the amount of wind reduction which can be expected in the lee of some common types of shelterbelts.     

Secondary flows in the lee of porous shelterbelts

The results of wind-tunnel experiments indicate that the flow close to the surface behind shelterbelts is quite sensitive to the orientation of the barrier to the mean flow direction, and that orientation is more important for short than long windbreaks. The implications of these findings are discussed in the context of field experiments to validate mathematical models of shelter effects.     

塔克拉玛干沙漠公路人工防护林植被的C, N化学计量特征及其固存能力研究

本研究以塔克拉玛干沙漠公路沿线生物防护林为研究对象,研究防护林三种主要建林植物不同器官的C,N含量及其生物量,进而估算其C, N固存能力及固碳释氧价值。结果显示：沙拐枣每个器官的生物量均显著高于梭梭和柽柳(P<0.05),个体的总生物量是梭梭和柽柳的2-3倍。整个防护林在建林8年后的总生物量达到116786.4 t。C,N含量在不同器官中的含量不尽相同,三种植物均表现为凋落物C含量最低。而植物叶中的N含量均显著高于枝,凋落物和根系(P<0.05)。建林8年后梭梭单株的固碳量为1404.6g,固氮量为201.5g,柽柳单株的固碳量为1449.7g,固氮量为195.4g,沙拐枣单株的固碳量和固氮量显著高于其他两种,分别为3979.8g,为520.9g,(P<0.05)。建林8年后整个防护林的总固碳植为35886.3 t,总固氮值为4917.7 t。整个防护林的固碳总价值为22555.3万元,释氧价值为50320万元,总的固碳释氧价值达72875.3万元。     

A numerical simulation of boundary-layer flows near shelterbelts

We have developed a shelterbelt boundary-layer numerical model to study the patterns and dynamic processes relating to flow interaction with shelterbelts. The model simulates characteristics of all three zones of airflow passing over and through shelterbelts: the windward windspeed-reduction zone, the overspeeding zone above the shelterbelt, and the leeward windspeed-reduction zone. Locations of the maximum windspeed reduction and recirculation zone, as well as the leeward windspeed-recovery rate are well simulated by the model. Where comparisons with field measurements and wind-tunnel experiments were possible, the model demonstrated good performance for flows over and through shelters ranging from almost completely open to almost solid. The dynamic pressure resulting from the convergence and divergence of the flow field alters the perturbation pressure field. The disturbed pressure controls not only the formation of the separated flow but also the location of maximum windspeed reduction, streamline curvature, speed-up over the shelterbelt, and leeward windspeed recovery rate. The interaction of pressure with the flow produces complex flow patterns, the characteristics of which are determined, to a great extent, by shelterbelt structure.     

Climate change and biodiversity conservation in Great Plains agroecosystems

Global change and habitat fragmentation are critical issues in our society. While considerable progress has been made in these issues worldwide, the unique features of the agroecosystems in the Great Plains have not been given enough attention. In this region, croplands occupy the majority of the landscape, forming the mosaics with linear riparian zones and shelterbelts. These three elements play different roles in the maintenance of biodiversity, and their continued effectiveness under a changing climate is critical to maintaining a healthy and productive agricultural ecosystem. This article evaluates current research and discusses future directions. The goal is to provide a scientific base for future conservation biology and wildlife management.     

区域大气质量评价数值模式系统的建立及试用

区域大气质量评价数值模式系统是以CALPUFF的应用开发为核心,根据陕西省的实际情况和大气环境业务服务需求,利用预报实时业务的网络环境,通过VB6.0编程,建立了一个具有自动数据处理、操作简便、比较实用的区域大气质量评价数值模式系统平台。依据2004年1月1日至12月31日的气象资料及源排放清单,对某工程的5个拟建地进行了大气质量数值模拟评价分析。结果表明,5地日均浓度超标的概率分别为27%、11%、5%、3%、8%。年平均浓度5地中3地未出现超负荷浓度值,满足2级标准要求,其他2地出现超负荷浓度值。其中一地污染超标最重,其可能原因是由于山体的影响,山谷中低层水平风速相对较小,不利于污染物的水平扩散,同时易形成地形山谷风次级环流,次级环流的存在把输送出去的污染物带回原地,形成二次污染。