Dispersal success on fractal landscapes: a consequence of lacunarity thresholds

Habitat fragmentation is expected to disrupt dispersal, and thus we explored how patch metrics of landscape structure, such as percolation thresholds used to define landscape connectivity, corresponded with dispersal success on neutral landscapes. We simulated dispersal as either a purely random process (random direction and random step lengths) or as an area-limited random walk (random direction, but movement limited to an adjacent cell at each dispersal step) and quantified dispersal success for 1000 individuals on random and fractal landscape maps across a range of habitat abundance and fragmentation. Dispersal success increased with the number of cells a disperser could search (m), but poor dispersers (m<5) searching via area-limited dispersal on fractal landscapes were more successful at locating suitable habitat than random dispersers on either random or fractal landscapes. Dispersal success was enhanced on fractal landscapes relative to random ones because of the greater spatial contagion of habitat. Dispersal success decreased proportionate to habitat loss for poor dispersers (m=1) on random landscapes, but exhibited an abrupt threshold at low levels of habitat abundance (p<0.1) for area-limited dispersers (m<10) on fractal landscapes. Conventional metrics of patch structure, including percolation, did not exhibit threshold behavior in the region of the dispersal threshold. A lacunarity analysis of the gap structure of landscape patterns, however, revealed a strong threshold in the variability of gap sizes at low levels of habitat abundance (p<0.1) in fractal landscapes, the same region in which abrupt declines in dispersal success were observed. The interpatch distances or gaps across which dispersers must move in search of suitable habitat should influence dispersal success, and our results suggest that there is a critical gap-size structure to fractal landscapes that interferes with the ability of dispersers to locate suitable habitat when habitat is rare. We suggest that the gap structure of landscapes is a more important determinant of dispersal than patch structure, although both are ultimately required to predict the ecological consequences of habitat fragmentation.     

灌溉模式与施氮水平对土壤渗滤液氮浓度动态变化的影响

以Ⅱ优838为水稻供试品种,湖北潮土为供试土壤,通过2年稻麦轮作柱栽试验研究2种灌溉模式(FW:土表淹水3cm;CW:保持土壤湿润但土表不积水)和4个施氮水平(N0:0kg·hm-2,N1:126.0kg·hm-2,N2:157.5kg·hm-2,N3:210.0kg·hm-2)对水稻土渗滤液不同形态氮浓度变化动态的影响。结果表明:土壤渗滤液的总氮浓度随水稻生育期推移呈由高到低的变化趋势,氮素淋失风险主要存在于水稻移栽后的前40d左右;在稻麦轮作制中,前作小麦明显提高后作水稻土壤渗滤液氮浓度;硝态氮(NO3--N)和可溶性有机氮(SON)是土壤渗滤液氮素的主要形态,铵态氮(NH4+-N)所占比例较低;水稻移栽后20～30d左右出现土壤渗滤液NO3--N高峰,在高峰期土壤渗滤液的NO3--N浓度随施氮量增加而提高;减氮25%处理(N2)相对于常规施氮量处理(N3)显著提高氮肥利用率,并降低氮素淋失风险。     

MAKING AN APPROACH TO THE SOIL CAVITY PROBLEM

This paper presents that the soil cavity is a kind of the environmental-geological problem.The formation and development of the soil cavity arein close relationship with the construction of buildings.Some problemsof the soil cavity still need to be further studied.This paper proposes someviews on its concept,forming conditions,classification,mechanism,infl-uencing formation factors and development of different types.The investiga-tion of their appearance development and distribution is of significance inengineering geology and hydrogeology.     

西北黄土窑洞减渗防塌措施的研究

黄土窑洞在我国北方分布极广,目前仍有四千万人居住在各种形式的黄土窑洞中。长期以来连阴雨是造成窑洞坍塌的主要原因。本文根据近代土壤水能量原理,结合室内外的实验研究,证明在黄土窑洞洞顶土层设置砂层,可以防止和减少土壤水分的下渗。     

安徽大别山库区不同林分类型的土壤特性及其水源涵养功能

对安徽大别山库区7种不同林分土壤理化性质、凋落物持水量以及林地土壤贮水性能等进行了研究。结果表明,不同林分的土壤理化性质及其水源涵养功能差异明显。在相同的立地条件下,天然次生林和混交林具有更好的维持地力作用和更高的水源涵养功能。依据林地总贮水量的大小,7种林分的水源涵养功能依次为:天然次生林(2360.3t/hm2)>杉木黄山松混交林(2318.3t/hm2)>马尾松枫香混交林(2193.2t/hm2)>杉木林(2121.3t/hm2)>黄山松林(2055.1t/hm2)、马尾松林(2053.0t/hm2)>板栗林(2002.0t/hm2)。     

Rice yield and water use as affected by soil management practices

A field experiment was conducted at the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences,to study the effects of soil management practices on water use and rice (Oryza sativa L.) yield in an axtuic brown soil during 2001 and 2002. A completely random experimental design with three replications was employed, having four soil management practices as treatments, namely: an undisturbed plow layer (CK), a thin plastic film (TN), a thick plastic film (TI) and subsoil compacting (CP). Results indicated no significant differences among all treatments for rice biomass and grain yields. Also, water consumption was about the same for treatments TN and CK, however the treatments TI and CP were much lower with more than 45% and 40% of the irrigation water in the treatments TI and CP, respectively,saved each year compared to CK. Therefore, water use efficiency was higher in the treatments TI and CP. These results will provide a scientific basis for the water-saving rice cultivation.     

BMBF-research-focus ‘percolation water prognosis’ concept and current activities

The 41 participants of the BMBF-research-focus ‘percolation water prognosis’ are working out the scientific basis of the methods, which are needed to carry out this ‘percolation water prognosis’. They are either focussing on the further development of methods for determining the source strength of materials or on improving existing models for predicting the contaminant transport through soils. Validity and transferability of these developed methods/models are evaluated by including the core projects ‘reference materials’ and ‘lysimeter experiments’ . Scientific co-ordination is carried out at the HSL, where — among other activities — a central database will be created to compare and interpret the results of the different projects. A routine procedure for carrying out the ‘percolation water prognosis’ in most cases must be easily applicable and generally accepted. Nevertheless, the research projects are examining the arising questions from different perspectives and apply highly sophisticated methods in order to provide a sound scientific basis [8]. Most of the projects have started in the course of the year 2001, so first results may be expected during 2002.     

公路旁土壤中水分和重金属的迁移

Roads with very high traffic loads in regions where soils are low in both pH and sorption capacity might be a source of percolation water loaded with heavy metals. Looking at some ＂worst case＂ scenarios, this study focused on the input of traffic related pollutants and on Pb, Cd, Cu, Zn, Ni and Cr concentrations in the soil matrix and soil solution, respectively. The analysis also included pH and electrical conductivity and at some sites DOC. The investigations were carried out on sandy soils with more or less low pH values at four motorway sites in Germany. The average of daily traffic was about 50 000 up to 90 000 vehicles. Soil pore water was collected in two soil depths and at four distances from the road. The pH in general decreased with increasing distance from the roadside. The elevated pH near the roadside was presumably caused by deposition of dust and weathering residues of the road asphalt, as well as by infiltration of salt that was used during winter time. At these road sites, increased heavy metal concentrations in the soil matrix as well as in the soil solution were found. However, the concentrations seldom exceeded reference values of the German Soil Protection Act. The soil solution concentrations tended to increase from the road edge to 10 m distance, whereas the concentration in the soil matrix decreased. Elevated DOC concentrations corresponded with elevated Cu concentrations but did not substantially change this tendency. High soil water percolation rates were found near the roads. Thus, even low metal concentrations of percolation water could yield high metal loads in a narrow area beside the road.     

Guilan,a successful irrigation project in Iran

This rapid appraisal study compares the actual and projected performance of a large, rice monoculture irrigation project in the humid climate of the Caspian Sea in Iran. The uniqueness of this project is the co-existence of East-Asia rice farming techniques with advanced technologies of automatic water control found generally in the Mediterranean countries. The paper emphasizes the need to do field tests at the design stage in order to make realistic assumptions on water efficiency and deep percolation. The study confirms that the advanced water control technologies are appropriate for small farm irrigation projects in the humid tropics, a conclusion often debated among experts. The Guilan project now provides some evidence to support that conclusion.     

A hierarchical neutral model for landscape analysis

Empirical studies have revealed scaled structure on a variety of landscapes. Understanding processes that produce these structures requires neutral models with hierarchical structure. The present study presents a method for generating random maps possessing a variety of hierarchical structures. The properties of these scaled landscapes are analyzed and compared to patterns on totally random, unstructured landscapes. Hierar-chical structure permits percolation (i.e., continous habitat spanning the landscape) under a greater variety of conditions than found on totally random landscapes. Habitat clusters on structured maps tend to have smaller perimeters. The clusters tend to be less clumped on sparsely occupied landscapes and more clumped in densely occupied conditions. Hierarchical structure changes the expected spatial properties of the landscape, indicating a strong need for this new generation of neutral models. Research supported by the Ecological Research Division, Office to Health and Environmental Research, U.S. Department of Energy under contract No. DE-AC05-840R21400 with Martin Marietta, Energy Systems, Inc. Environmental Sciences Publication No. 3813, ORNL.