基于不同尺度的干旱区城市景观生态研究--以陕西榆林市为例   总被引：6，自引：0，他引：6  

张艳芳  任志远 《干旱区研究》2003,20(3):175-179

从区域与城市两个尺度水平 ,对毛乌素沙漠南缘的榆林市城市景观进行研究认为 :在大尺度水平上 ,区域景观生态特征对城市景观特征具有一定的控制作用 ,而城市景观强大的功能流对区域景观产生干扰作用。城市景观的空间扩展与演化 ,既受区域景观特征的影响 ,也是区域景观演化的一个有机构成部分 ;在小尺度空间上 ,景观功能区、景观斑块与廊道的格局与功能 ,对城市景观格局动态以及维持城市景观多样的生态功能具有重要意义。在不同的利益追求下形成的景观文化 ,将深刻地影响到区域与城市景观演化的方向与过程。  相似文献   

Modelling Plant Disease Epidemics     

A. van Maanen  X.-M. Xu 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(7):669-682

An epidemic is the progress of disease in time and space. Each epidemic has a structure whose temporal dynamics and spatial patterns are jointly determined by the pathosystem characteristics and environmental conditions. One of the important objectives in epidemiology is to understand such spatio-temporal dynamics via mathematical and statistical modelling. In this paper, we outline common methodologies that are used to quantify and model spatio-temporal dynamics of plant diseases, with emphasis on developing temporal forecast models and on quantifying spatial patterns. Several examples of epidemiological models in cereal crops are described, including one for Fusarium head blight.  相似文献   

旅游地空间竞争与弱势旅游地的发展研究   总被引：19，自引：1，他引：19  

马晓龙  杨新军  贾媛媛 《干旱区资源与环境》2003,17(5):113-117

本文在介绍旅游地空间竞争的基础上 ,导入弱势旅游地的概念。并以游客吸引半径为尺度 ,对西安和宝鸡的客源市场竞争进行分析。最后总结了发展弱势旅游地的契机和方法。  相似文献   

毛乌素沙地典型地形断面土壤水分动态     

杨佩国  李保国  吕贻忠 《干旱区研究》2004,21(4):333-337

基于毛乌素沙地的野外观测资料,对毛乌素沙地典型地形断面土壤水分动态进行分析。结果表明,土壤水分季节变化可划分为土壤水积聚期、消耗期和稳定期;根据土壤水分垂直变化可把土壤剖面划分为土壤水分易变层、利用层和调节层;沿着坡度减小的方向,各地形断面对应层次的土壤水分含量逐渐升高,丘间地土壤水分含量明显高于该断面上其余各点。  相似文献   

内蒙古沙尘暴的成因、趋势及其预报   总被引：2，自引：0，他引：2  

高涛  徐永福  于晓 《干旱区资源与环境》2004,(Z1)

本文利用内蒙古1961～2001年的天气气候资料,对内蒙古中西部地区沙尘暴作了统计分析,阐述了沙尘暴的危害并给出了沙尘暴的基本定义。分析了引起沙尘暴的天气和气候因子的变化趋势,研究了他们对沙尘暴的影响,结果表明近40年内蒙古的沙尘暴总体呈减少趋势,但从1998年开始有所增加;沙尘暴的空间分布以阿拉善盟偏北地区为最高发区;降水、气温、大风、寒潮、北半球极涡、西太平洋副热带高压、亚洲西风环流、东亚大槽和南方涛动等天气和气候因素均对该地区沙尘暴的发生有不同程度的影响。  相似文献   

当归茎线虫病田间分布型及抽样技术研究     

柴兆祥  李金花  李应东  丁峰 《植物保护》2004,30(3):59-61

为提高当归茎线虫病(Ditylenchus destructor)田间抽样的准确度,用7种聚集指标判断了当归茎线虫病的田间分布型.结果表明,当归茎线虫病在田间呈聚集分布,其中奈曼分布(核心分布)的适合率为100%,嵌纹分布(负二项分布)的适合率为77.8%.理论抽样数量约820株.4种抽样方法差异均不显著,在保证抽样数量合理的情况下,4种方法均可采用.  相似文献   

Evaluation of sampling methods and assessment of the sample size to estimate the weed seedbank in soil, taking into account spatial variability   总被引：1，自引：0，他引：1  

L Ambrosio  L Iglesias†  C Marín  & J P Del Monte‡ 《Weed Research》2004,44(3):224-236

As field sampling is time consuming, it is necessary to develop efficient sampling techniques to obtain accurate estimates of the weed seedbank in soil. The relative efficiency between sampling schemes depends on the spatial variability in weed seed density across agricultural fields. Spatial variability of the weed seed density was characterized by theoretical correlograms. A systematic sampling (square grill) scheme was considered and it was found that, taking into account spatial variability, this sampling scheme was more efficient than simple random sampling. As a result, the sample size can be reduced in comparison with that given in previous studies, where spatial correlation was ignored. The reduction depends on the correlation structure defined as a function of the ratio, τ, between the nugget effect and the sill of the variogram. The maximum reduction of the sample size, without loss of either precision or confidence level corresponds to the case where there is no nugget effect, τ = 0. The opposite extreme case, where the reduction is nil, corresponds to the case of a pure nugget effect τ = 1. The abaci based on given expressions are provided to determine the sample size in species whose spatial pattern can be fitted either to a Poisson or to a negative binomial distribution.  相似文献   

Spatial distribution of Lolium rigidum seedlings following seed dispersal by combine harvesters     

J M Blanco-Moreno  L Chamorro  R M Masalles  J Recasens†  & F X Sans 《Weed Research》2004,44(5):375-387

This paper considers the relationships between the dispersal of seeds and the distribution pattern of an annual weed. A comparative study of seed dispersal by combine harvesters, with and without a straw chopper attached, was established using Lolium rigidum, a common weed in Mediterranean cereal crops. Seed dispersal distance was quantified and the relationships between dispersal and fine‐scale seedling distribution evaluated. Primary dispersal of L. rigidum seeds occurs in a very limited space around the parent plants, but the density of seed is low because most seeds do not fall from spikes spontaneously. In contrast, many seeds are spread by combine harvesters. In this study the maximum dispersal exceeded 18 m from established stands in cereal fields, although the modal distance was close to the origin. In addition, the action of the combine harvesters tended to accumulate L. rigidum seeds predominantly under the straw swath, with some lateral movement. This action could explain the fine‐scale banded pattern of L. rigidum in cereal fields. Although the treatment of straw by the standard and straw chopper combines differed, the resultant seed distribution showed few differences.  相似文献   

松嫩平原优势种羊草与其主要伴生种芦苇空间分布格局分析   总被引：6，自引：0，他引：6  

巴雷  王德利  高莹 《草业学报》2005,14(5):111-116

芦苇是松嫩草地优势种羊草的主要伴生种,两者常常形成物种组成比较单一的混生群落或者与其他物种组成羊草 杂类草群落.选择羊草 芦苇混生群落,羊草群落和芦苇群落的交错区进行羊草、芦苇单物种格局分析.结果表明,1)混生群落和交错区中,羊草和芦苇均是以集聚分布的形式存在;2)羊草在混生群落中的格局强度小于交错区中的格局强度,芦苇在2种类型群落中的格局强度没有显著差异;3)除了考虑物种的生物学特性以外,混生群落种内、种间竞争也是影响羊草集聚分布和格局强度的主要因素,交错区中,环境异质性和种间竞争是影响集聚分布和格局强度的重要因子;4)芦苇在混生群落和交错区中格局强度没有明显差异,由此可以判定芦苇的空间分布格局形成主要受植物本身生物学特性的影响.  相似文献   

湖北利川马的现状分析及对策研究     

程泽信  牟映平  李助男 《中国草食动物》2005,25(2):36-38

对利川马的品种资源近几十年来的资料和调查的结果进行分析。用地方品种资源受威胁的程度和群体的有效大小等指标分析了利川马资源的受威胁程度。结果表明：利川马存栏数量在上世纪70年代以后呈逐渐下降的趋势；利川马的有效群体大小正在逐渐下降，处于潜在威胁中，也正接近最低威胁；整体上看，体尺、体重近几年不断提高．利川马产驹教有下降的趋势。  相似文献