影响农田防护林防风效益的主导因子探讨

通过对半干旱风沙区单林带、林网、林农间作、片林等不同类型农田防护林结构和防风效益的调查研究,提出了疏透度、林带间距、树高与林带宽度的比值、单位面积树冠体积分别是影响各类防护林防风效益的主导因子,确定了单林带最佳结构时的疏透度为０．３,有效防风距离为树高的１３．８倍。     

盐池县旱作农田防护林结构及防风阻沙效能研究

针对宁夏盐池沙地风蚀严重的现状,对当地的农田防护林(片状灌木林、带状灌木林、带状乔木林)的防风阻沙效能进行了实地观测.结果表明:不同下垫面的起沙风速差异显著,植被覆盖度相对较高的稀疏沙质草场起沙风速明显大于旱作农田及流动沙地的起沙风速;不同林带结构的防风阻沙效能不同,就研究对象而言,防风阻沙效能的顺序为:小叶锦鸡儿片林＞白榆林带＞沙柳林带.     

乌兰布和沙漠绿洲农田防护林防风阻沙效益研究

对乌兰布和沙漠绿洲几种典型结构和配置的农田防护林带进行风速观测表明,其防风效益与林带高度、结构、疏透度等因子有关,稀疏型林带防风效果最佳,疏透型次之,通风型防风效果最差;在林带结构相同的情况下,林带降低风速的作用随着林带高度的增加而增加;防护林可降低地表输沙量,且林后输沙量下降比例大于林前。     

农田防护林树木根系调查

通过对农田防护林树林根系的调查，了解树木与农作物及树种之间的根系分布状况和相互关系，可为林带树种的选择和配置提供依据。     

农牧防护林网区域性防风效应及评价模型

提出了农牧防护林网区域防风效应的新概念，同时，根据风洞实验资料和野外系留气球观测资料提出了新的防风效应评价方法和评价模型，并给出了应用实例。农牧防护林体系区域性防风效应Ｅ的模式为：Ｅ＝１－Ｕ＊／Ｕ＊０｛１－１ｎＡ／ １ｎ（ｚ／ｚ０）｝； Ａ＝ｚ０／ｚ０＝３．３４１（ｕ＊／ｕ＊０）＾４－２．３４１     

试议农田防护林的作用及其规划设计

根据多年生产实践经验,提出农田防护林的防风原理、结构、影响因子、防护作用,并对营造农田防护林的技术措施等进行了阐述,对于山东农田防护林建设具有指导意义。     

乌兰布和沙漠绿洲农田防护林防风阻沙规律及防护效益

在绿洲边缘及内部营造农田防护林最重要的作用是降低风速、控制农田土壤风蚀、防止或减轻地表起沙和风沙入侵,为农业生产营造一个良好的生产环境。绿洲农田防护林是绿洲防风阻沙、控制风蚀必不可少的技术措施之一,对农业生产具有重要意义。本文通过定位观测实验与定量分析相结合的研究方法,对不同结构类型的防护林防风阻沙的基本规律及防护效益进行了研究。     

农田防护林体系结构优化配置研究

农田防护林体系结构优化配置研究范志平，姜凤歧，林鹤鸣，朱教君（中国科学院沈阳应用生态研究所沈阳１１００１５）为达到农田防护林防护效益和经济效益最大并永续利用，防护林体系必须具有在空间上布局的合理性及树种、群落和林分的多样性和稳定性特征。因此，构筑大面...     

兴久生态村防护林体系防风效应研究

通过对兴久村防护林体系防风效应研究,得出通风结构林带背风面,迎风面和平行风面平均降低风速分别为22.1％、8.4％和8.08%;林网内平均降低风速16.1％;片林周围平均降低风速13.2%,片林内平均降低风速50.O3％。     

影响农田防护林防护效益的几项主要因子的探讨

目前国内对农田防护林的研究多数集中在对风的作用以及由此而引起的小气候变化，对于农田防护林带的结构、宽宽、全叶期、无叶期、林带背风面，不同距离以及林带与主风交角等项因子专门报道甚少。本文对农田防护林结构与带宽的选择进行了探讨，结构不合理或者林带过宽，不仅费工费时且占地多，防护效益并不明显，太窄又起不到保护农田的作用，探讨合适的结构与带宽，最大限度的发挥农田防护林的防护效能，确保农田在风沙危害严重地区持续不断连年稳产高产丰收提供了有益经验。     

External economic benefits and social goods from prairie shelterbelts

Shelterbelts are a valuable resource to those who plant them and to other members of society. The external benefits to society can be worth as much as the private benefits to producers. However, the external benefits have not been quantified or monetized in a well-documented way. In this study, external benefits were estimated for tree seedlings distributed by the Agriculture and Agri-Food Canada Shelterbelt Centre in the Canadian Prairie Provinces for the period 1981–2001. Estimation of these benefits required information on the biophysical changes caused by shelterbelts and their valuation. Using literature, we estimated that the value of these external benefits amounted to over $140 million (2001 CDN$; CDN$1 = US$0.63). The majority of this value was derived from carbon sequestration ($73 million) and reduced soil erosion ($15 million) services with the remainder being contributed by biodiversity and water and air quality services. Other external benefits, such as health values, transportation safety, aesthetics and property values were identified but could not be estimated due to a lack of data. The estimated value for external benefits conferred by shelterbelts in this study indicates that they are large and suggests that both private and external benefits need to be considered in formulating policies or programs so that benefits to the society can be maximized.     

Financial feasibility of using shelterbelts for swine odor mitigation

A farm-level financial feasibility was performed to examine the use of shelterbelts as a swine odor mitigation technology. Shelterbelts are purposefully planted rows of trees and shrubs around the main sources of swine odor—swine buildings, manure storage systems, and crop fields that receive land applied manure. By using a series of model pork finishing farms and a number of differing shelterbelt design scenarios, the shelterbelt establishment and long-term (20 years) maintenance costs were calculated using a discounted cash flow analysis. Total costs for examined pork finishing farms, depending upon the shelterbelt design scenario, and whether or not government cost-share programming was used, ranged from $0.01 to $0.65 per pig produced. Study results emphasized the importance of cost-share programs, particularly Environmental Quality Incentive Program (EQIP). In most cases, both with and without cost-share programming, the total costs were well below reported pork producer expenditures for odor management.

山西省怀仁县生态功能区划及生态保护对策

生态功能区划是研究生态系统服务功能、判断生态系统分异和变化规律、提出生态退化恢复对策的基础。在综合分析怀仁县生态环境现状的基础上,以卫星影像图和森林资源二类清查数据库为基础,利用ArcG is软件的多层叠加功能,采用图形叠置法将怀仁划分为3个生态区,6个生态功能区,并根据各区主要生态问题提出了生态建设与保护对策。     

乐都县农田防护林体系建设现状及发展对策

通过对乐都县 2 0年来农田防护林网体系建设的综合分析和评价 ,提出了今后发展对策     

乐都地区坡耕地防护林体系建设规划设计

通过坡耕地防护林体系建设必要性的分析 ,提出了坡耕地防护林体系建设规划设计的指导思想 ,应遵循的原则 ,阐述了工程建设布局及营造模式 ,营造技术等     

冀北山地落叶松人工林直径生长与空间结构的关系

在河北省围场县桃山林场落叶松人工林中选取65组林木,进行大小比数与直径生长关系的分析。基于落叶松(Larix olgensis Henry)人工林固定标准地的每木检尺表数据,针对人工林普遍具有混交度低,分布均匀的特点,主要从林分竞争机制和树冠营养空间利用情况等方面提出了利用Hegyi竞争指数、生长空间指数、生长空间竞争指数分析优化林分空间结构,进一步比较不同择伐程度下林分空间结构变化的大小。结果表明:中心树生长出现两种情况,有明显被压过程和无明显被压过程。林分竞争主要集中在8～15a,是进行抚育间伐的最佳时期,可以为林木提供更大的营养空间,保证林木正常健康生长。     

Spacing interval between principal tree windbreaks--Based on the relationship between windbreak structure and wind reduction

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.     

Nutrient distribution and accumulation patterns of natural secondary forests in the Loess Plateau of Shanxi Province, northern China

We studied the biomass and its allocation in natural secondary forests, as well as the amounts, accumulation and distribution of nutrient elements (N, P, K, Ca and Mg) in sample plots established in the Loess Plateau in Shanxi Province, northern China. The results show that biomass in natural secondary forests amounted to 36.09 t/hm², of which the tree layer accounted for 46%, the shrub layer for 29%, the herb layer for 13% and the litter layer for 12%. The total storage of the five nutrient elements is 1089.82 kg/hm². Nutrient storage in the tree layer is the largest, at 41%. The sequence of storage of the elements varied among different layers and is given as follows: shrub layer 31.27%, herb layer 12.55% and litter layer 15.36%. The accumulation of nutrient elements in the tree layer, ordered from high to low, is: branches > roots > stems >bark > leaves. The total storage of the five nutrient elements in the soil is 634.97 t/hm², where the accumulation of the nutrients accounts for 95.32% (N), 99.64% (P), 99.91% (K), 99.84% (Ca) and 99.95% (Mg) of the total amounts. The accumulation coefficients of different organs in the tree layer are, from high to low: leaves > branches > roots > bark > stems. The accumulation coefficients in the different layers are listed as follows: shrub layer > tree layer > herb layer and for the elements as: N > P > Ca > K > Mg. __________ Translated from Journal of Beijing Forestry University, 2008, 30(3): 57–62 [译自: 北京林业大学学报]