一种高效的关联规则挖掘算法及应用

针对传统Apriori算法在生成频繁项目集时出现的瓶颈问题以及难以对非精确的或者模糊的概念进行挖掘的不足,给出了一种高效的关联规则挖掘算法。算法首先利用模糊集知识对数据库中的数值属性进行了合理的非精确语义转换,然后通过高效剪枝的挖掘方法对频繁项集进行挖掘,并将其应用到农业气象数据库的灾害分析中。试验结果表明,该算法在时间性能上有很大的提高。     

宁夏半干旱偏旱区旱地引进苜蓿品种适应性及生态耗水状况

2003-2005年对引进的15个苜蓿品种在旱地进行比较试验.结果表明,在干旱少雨的条件下,不同品种生长速度和地上生物产量不同,水分生产效率和耗水强度各有差异.第二年生长期耗水强度17.4～22.95 m3/(hm2·d),其中当年第一茬占全年65%～71%.第二年以后土壤水分出现亏缺状态,0～2 m土壤水分亏缺60.9～123.5 mm,平均87.8 mm,生产年度(包括非生长季节)同层土壤水分亏缺值高达121.9～165.5 mm,平均143.1 mm,生产年度土壤缺水系数为0.454～0.607.根据品种各综合性状指标生态适应性分析,对引进品种进行了种植区域界定,并按土壤水分逐年亏缺量下限频率(P=70%)推算,半干旱偏旱区旱地苜蓿适应当地多年降水资源的效益型生长年限不超过5年就需进行粮草轮作.     

基于饲养标准的家畜单位折算方法

为解决载畜量核定工作中存在的家畜单位折算体系不健全、与畜牧业统计口径脱节等问题,根据肉牛单位、绵羊单位的定义和肉牛、肉羊、奶牛饲养标准中的代谢能或净能需求以及标准干草的代谢能或净能含量,研究确定肉牛单位、绵羊单位和不同生理阶段奶牛的标准干草需求及其家畜单位折算关系.结果表明:标准干草代谢能或净能含量分别为肉牛综合净能4.89 MJ/kg,奶牛产奶净能5.57 MJ/kg,绵羊代谢能8.68 MJ/kg;1个肉牛单位、绵羊单位的能量需求分别是肉牛单位72.10 MJ/d综合净能、绵羊单位18.46 MJ/d代谢能,其家畜单位折算关系是6.93∶1;不同生理阶段奶牛的平均产奶净能需求分别是断奶犊牛27.19 MJ/d、育成母牛52.07 MJ/d、初孕母牛70.11 MJ/d和中产泌乳母牛123.95 MJ/d,折合标准干草需要量分别为4.88 kg/d、9.35 kg/d、12.59 kg/d和22.25 kg/d,分别折合2.29、4.39、5.91和10.45个绵羊单位;生产上一般按照奶料比3.5∶1补充精饲料,则中产泌乳母牛对标准干草的平均需要量调整为15.06 kg/d;从天然草地的放牧压力和区域粗饲料的供需状况评价的角度,建议中产泌乳母牛与绵羊单位的折算系数由10.45调整为7.07.     

Owner-specific factors associated with conversion activity in secondary pine plantations

The conversion of secondary pine plantations into mixed broadleaf stands is considered to be an important mechanism in the process of sustainable forest management. The silvicultural process of forest conversion in ageing pine plantations is associated with active management aimed at inducing, steering or accelerating stand development. The aim of the present study was to investigate owner-specific factors – socio-demographic and forest-related characteristics, and motivation of ownership – influencing NIPF owners' active engagement in silvicultural conversion (henceforth referred to as ‘conversion activity’). The study relies on a survey of non-industrial private owners (n = 276) of pine plantations on poor sandy soils in Flanders (northern Belgium). The study revealed that NIPF owners, in general, make only minor contributions to forest conversion. Conversion activity (including thinning, making space for broadleaves, removing invasive species, clear-cut, planting) was rather low, but positively influenced by a number of factors. Private forest owners with clear motivations of ownership were more likely to engage in conversion activity. However, the nature of motivation was not very decisive as most of the items listed (with exception of land investment goals) had a positive influence. Furthermore, the conversion activity of owners called ‘economists’ did not significantly differ from those of ‘recreationists’, but ‘passive owners’ (those with unclear motivations of ownership) were less active. We thus suggest that it is the absence of clear motivations of ownership, rather than a particular ownership goal that would explain low conversion activity. Socio-demographics like age, gender and education, and also forest size had only marginal influence. But frequency of forest visits and proximity to the forest had a significant influence. As an overall conclusion from this study, we emphasize the importance for active forest management, and silvicultural conversion in particular, of forest owners being connected to their forest. In this sense, mental connectedness (motivation of ownership), as well as physical connectedness (living close to the forest and visiting it frequently) do matter.     

Participatory technology development for incorporating non-timber forest products into forest restoration in Yunnan,Southwest China

Indigenous knowledge has become a topic of considerable interest within the research and development environment. Incorporating indigenous knowledge into state-led ‘top-down’ conservation and development programmes, however, is still a great challenge. This paper presents a case from Yunnan, Southwest China, in which indigenous knowledge has been integrated into the development of an agroforestry model with non-timber forest products for the Sloping Land Conservation Programme (SLCP) by using a participatory technology development (PTD) approach. This approach was adopted to increase the likelihood that technologies developed would be suitable for resource-poor households. It is expected that integrating indigenous and scientific knowledge, will lead to positive ecological and economic outcomes. Finally, the paper argues that the integration of indigenous knowledge in both forestry policy formulation and implementation is important in the context of sustainable forest management in mountain areas.     

花江低热河谷区不同退耕还林模式植被恢复效益研究

对贵州花江低热河谷区不同退耕还林还草模式进行调查研究,结果表明,柚木林模式在退耕还林中高生长和茎生长以及植被覆盖率都取得了较大的效益,其次为花椒生态经济林模式,而林草结合模式以及柿树林模式因农户管护力度相对滞后导致效果不如前者,但总体水平上退耕还林后花江地区植被覆盖率增加,恢复了石漠化植被景观。表明退耕还林模式的建立在考虑生态效益的同时,还应考虑农户经济收入,实现可持续的林业生产机制,推动地方经济发展,从真正意义上改善该地区生态环境面貌和贫穷落后的经济面貌。     

美国能源草柳枝稷的研究进展

柳枝稷（Panicum virgatum）是美国本土植物,因为适应性广、耐贫瘠、产量高、多年生和易于管理等特性被美国能源部和农业部作为纤维素乙醇转化模式植物。在过去30余年里,美国在柳枝稷种质收集、遗传育种、栽培、管理、收获等方面进行了大量的研究,取得了不少成果,以提高产量为主要目标培育了数十个柳枝稷的品种,围绕提高产量和抗逆性的品种改良研究正在深入开展。柳枝稷具有较高的能量转化效率和经济效益,在环保效益表现尤为突出。通过继续提高柳枝稷的产量,科学规划组织生产,创新能源转化加工工艺,柳枝稷转化能源可以在不久的将来实现产业化生产。从遗传选育、栽培管理、转化效益和效率等方面综述了美国柳枝稷的研究进展。     

毕节地区新一轮土地利用规划数据转换与指标分解方法探索

掌握＂规划基数＂分类体系与土地现状分类（二调）分类体系对应关系,按分类释义和转换对应关系,对毕节地区土地现状分类（二调）进行转换,运用信息系统管理学原理、采用＂自上而下＂与＂自下而上＂相结合的方法,对规划年各类用地各项指标按比例法、权重法和综合分析法进行分解。     

农村土地流转问题的法律思考——以合肥市为例

在介绍合肥市农村土地流转的特点与形式的基础上,探讨了农村土地流转中应明确的问题,提出了完善农村土地流转机制的建议。     

退耕还林尾叶桉模式生物量及枯落物持水特性研究

根据退耕还林尾叶桉模式3个样地的调查资料,对乔木层采用平均木法,对灌木层、草本层、枯落物层采用收获法获取生物量,同时对样地内的枯落物进行持水量计算。结果表明:退耕还林尾叶桉模式的乔木层、灌木层、草本层、枯落物层的生物量分别为59 654.7、1 027.38、02.7和3 393.0 kg/hm2,其中乔木层中尾叶桉各器官生物量大小的排列顺序为:干材>树根>树皮>枝>叶。随着林龄的增加,尾叶桉枯落物的持水能力逐年增加。