Bush cover and range condition assessments in relation to landscape and grazing in southern Ethiopia

Progressive growth of bush cover in dry savannahs is responsible for declines in range conditions. In southern Ethiopia, the Booran pastoralists assisted our understanding of spatial patterns of bush cover and range conditions in 54 landscape patch types grouped into six landscape units within an area of 30000 km². The size of landscape patches sampled was 625 m². We assessed the relationships between bush cover, grass cover and bare soil and grazing pressure and soil erosion and changes in range condition. Externally, political conflicts and internally, break down of land use, and official bans on the use of fire promoted bush cover and the decline in range conditions. Bush cover was negatively correlated with grass cover, and positively correlated with bare soil. Grass cover was negatively correlated with bare soil and grazing pressure in most landscape patch types. Grazing pressure was not significantly correlated with bush cover or bare soil, while soil erosion was directly related to bare soil. Soil erosion was absent in 64% of the landscape patch types, and seemingly not a threat to the rangelands. The relationship between bush cover, grass cover, bare soil and soil erosion is complex and related to climate, landscape geology, and patterns of land use. Main threats to range conditions are bush climax, loss of grass cover and unpalatable forbs. Currently, >70% of the landscape patch types are in poor to fair range conditions. Decline in range conditions, unless reversed, will jeopardise the pastoral production system in southern Ethiopia.     

Lacunarity indices as measures of landscape texture

Lacunarity analysis is a multi-scaled method of determining the texture associated with patterns of spatial dispersion (i.e., habitat types or species locations) for one-, two-, and three-dimensional data. Lacunarity provides a parsimonious analysis of the overall fraction of a map or transect covered by the attribute of interest, the degree of contagion, the presence of self-similarity, the presence and scale of randomness, and the existence of hierarchical structure. For self-similar patterns, it can be used to determine the fractal dimension. The method is easily implemented on the computer and provides readily interpretable graphic results. Differences in pattern can be detected even among very sparsely occupied maps.     

Agricultural soil redistribution and landscape complexity

A number of hypotheses and conceptual models, particularly those emphasizing nonlinear dynamics and self-organization, postulate increases or decreases in complexity in the evolution of drainage basins, topography, soils, ecosystems, and other earth surface systems. Accordingly, it is important to determine under what circumstances and at what scales either trend might occur. This paper is concerned with changes in soil landscape complexity due to redistribution of sediment by fluvial, aeolian, and tillage processes at historical time scales in an agricultural field system near Grifton, North Carolina. Soil mapping and soil stratigraphic investigations were used to identify and map soil changes associated with erosion and deposition by water, wind, and tillage; reconstruct the pre-agricultural soil pattern; and identify transformations between soil types. The Kolmogorov entropy of the pre- and post- agricultural landscapes was then compared. The soil transformations associated with erosion and deposition created four distinct new soils and made possible new transformations among soil series, increasing the number of soil types from seven to 11 and the number of possible transformations from 14 to 22. However, the entropy and complexity of the soil landscape decreased, with associated increases in information and redundancy. The mass redistributions created a lower-entropy landscape by concentrating particular soils and soil transformations in specific landscape settings. This result is contrary to studies showing a trend toward increasing pedological complexity at comparable spatial scales, but over much longer time scales. These results point to the importance of temporal scale, and to the fact that environmental complexity is influenced by factors other than the number of different landscape units present.     

Dynamics of small biotopes in Danish agricultural landscapes

The contemporary pattern of small biotopes - small uncultivated areas in the agricultural landscape, its historical development and recent trends have been studied in Eastern Denmark. The study is based on ordinance maps dating back to 1885, aerial photographs, and field studies (1981 and 1986). The development of these areas is seen in changes in agricultural production. A general decrease in the overall density, and especially in the density of the smallest, wet biotopes, is demonstrated. This change, however, is hiding a more dynamic process of removal, establishment and change within the individual biotopes. The consequences on research, monitoring and management of the agricultural landscape are discussed.     

A novel use of the lacunarity index to discern landscape function

Discerning the function of a landscape involves comparing landscape use with spatial patterns. To do this requires both quantification of landscape use and landscape pattern and a means of comparing the two. An index of lacunarity has been used to quantify spatial pattern (specifically, habitat contagion). We demonstrate a new way of using the lacunarity index to quantify landscape function as well. We calculated lacunarity to describe landscape patchiness of experimental landscapes with respect to patterns of habitat and non-habitat areas (the previous use of lacunarity) as well as to describe patterns of patch use by animals in those landscapes, irrespective of habitat-patch patterns (a novel application of lacunarity). We demonstrate a disparity between landscape pattern and landscape use. This finding suggests that drawing generalizations of, and making predictions about, how animals respond to landscape spatial structure may not be straightforward.     

Effects of sensor spatial resolution on landscape structure parameters

We examined the effects of increasing grain size from 20 m to 1100 m on landscape parameters characterizing spatial structure in the northern Wisconsin lake district. We examined whether structural parameters remain relatively constant over this range and whether aggregation algorithms permit extrapolation within this range. Images from three different satellite sensors were employed in this study: (1) the SPOT multispectral high resolution visible (HRV), (2) the Landsat Thematic Mapper (TM), and (3) the NOAA Advanced Very High Resolution Radiometer (AVHRR). Each scene was classified as patches of water in a matrix of land. Spatial structure was quantified using several landscape parameters: percent water, number of lakes (patches), average lake area and perimeter, fractal dimension, and three measures of texture (homogeneity, contrast, and entropy). Results indicate that most measures were sensitive to changes in grain size. As grain size increased from 20 m using HRV image data to 1100 m (AVHRR), the percent water and the number of lakes decreased while the average lake area, perimeter, the fractal dimension, and contrast increased. The other two texture measures were relatively invariant with grain size. Although examination of texture at various angles of adjacency was performed to investigate features which vary systematically with angle, the angle did not have an important effect on the texture parameter values. An aggregation algorithm was used to simulate additional grain sizes. Grain was increased successively by a factor of two from 20 m (the HRV image) to 1280 m. We then calculated landscape parameter values at each grain size. Extrapolated values closely approximated the actual sensor values. Because the grain size has an important effect on most landscape parameters, the choice of satellite sensor must be appropriate for the research question asked. Interpolation between the grain sizes of different satellite sensors is possible with an approach involving aggregation of pixels.     

滨海碱性土壤的综合改良尝试及效果分析

综合运用工程技术改良、化学改良、生物改良的措施在滨海碱性土壤进行绿化尝试,1a后土壤有机质含量从0.32％上升至0.38％,pH从8.2下降至7.5,取得了较为理想的景观效果,并较大幅度地降低了土壤改良的成本.试验区植物配置尝试了少量喜弱酸性土壤的植物并得以成活,说明前期适当的抗性锻炼对后期栽种的存活具有重要的作用.     

Deciduous forest and resident birds: the problem of fragmentation within a coniferous forest landscape

Six species of resident birds were censused in patches of deciduous forest within a coniferous forest landscape in south central Sweden. Here, the forests have been subjected to active forestry for a long time, but with recently increased intensity. Although the forest cover is more or less continuous in this landscape, mature deciduous forest is now a rare element compared with the untouched forest.All censused patches were similar with regards to size, proportion and amount of deciduous trees, but were either isolated in the coniferous forest (isolated patches) or near to other deciduous patches (aggregated patches). We concentrated on six species of resident birds, with moderate area requirements, that are tied to deciduous forest and whose ecology is well-known. The Nuthatch and the Marsh tit, which both show strict year-round territoriality and have a restricted dispersal phase, were significantly more likely to be found in aggregated than in isolated patches. No effect was found for the Great tit and the Blue tit, which are less territorial outside the breeding season and have a longer dispersal phase. Moreover, the Great tit is less specialized on deciduous forest than the other species. Also, the Long-tailed tit was negatively affected by isolation, which may be due to restricted dispersal and to larger area requirements of this flock-territorial species. The Hazel grouse, finally, was not affected, but this larger bird probably uses the forest in a different way from the smaller species.Our study clearly shows that fragmentation of one type of forest (deciduous) within another can have serious detrimental effects on forest-living species and raises important issues for forest management practices and conservation within a forest landscape.     

The effect of breeding-habitat patch size on bird population density

An individual-based simulation model was used to study the effect of the relative location of food and nest sites in the landscape on the relationship between the breeding habitat patch size and bird population density. The model predicted that when both food and nest sites are located exclusively in the breeding habitat patches, larger patches tend to harbor higher population densities. But when food starts to be added to the `matrix' habitat and taken out of the breeding habitat the advantageous effect of larger patches diminishes and eventually the trend reverses, with small patches having higher population densities. This pattern arises from the combined effect of the existence of an extended foraging area around patches and an intrinsic advantage of large habitat patches associated with the concentration of food resources and potential colonizers. The effects of interspecific interactions and the management implications of the model are discussed.     

浅谈园林树木在城市生态建设中的功能

随着科技的进步,人们对生活的条件和质量有了更高的要求。可持续发展、生态等关键词越来越深入人心。现在的发展已经抛弃了原来的只要经济不要环境的发展观。城市里高楼林立,车行如梭,烟尘弥漫,工作节奏很快,缺乏自然美,易使人产生压抑感、疲劳感,缺乏宁静感。美好的园林景色,不仅能满足人们的观赏需求,其改善环境质量的功能是不容置疑的。种植园林树木是防治污染、保护环境的重要措施,树木在调节气候、净化空气、保护环境方面有着重要的作用。     

Metapopulation theory and habitat fragmentation: a review of holarctic breeding bird studies

Metapopulations are conceived as spatially structured populations consisting of distinct units (subpopulations), separated by space or barriers, and connected by dispersal movements. Metapopulations characteristically demonstrate a turnover of local populations going extinct and becoming re-established, resulting in a distribution pattern that shifts over time. Metapopulation theory is used to analyse the effects of habitat fragmentation on birds in the temperate zone, integrating various explanations for the paucity of species in isolated ecotopes.There is some evidence that turnover of local populations occurs in fragmented systems. A few studies based on time series demonstrate the local extinction rate to be related to the size of the habitat fragment, whereas the recolonization rate depends on the degree of isolation. Most evidence comes from short-term pattern studies in which the probability of occurrence was found to depend on the size of habitat fragments, on their relative position in the landscape and on the density of corridors lowering the landscape resistance. These data are consistent with predictions from metapopulation theory. However, almost all investigations consider wood fragmentation in agricultural landscapes, and there is a great need for studies in naturally fragmented landscapes as well as for studies focussing on other, less predictable, habitat types.     

“森林城市”模式与城市绿地园林景观及功能的弱化

“森林城市”的提法导致城市园林绿化建设模式产生一定的偏差,“森林城市”忽视了城市内绿地与城市外绿地功能的诸多差异,甚至导致城市园林绿地丧失其应该体现的园林艺术特征和休闲、游憩、娱乐、健身等综合功能。除生态效益之外,只有强调城市绿地的园林艺术特征和多功能性才能防止城市绿化中过密、过滥的“森林式”的种植模式。正确定位城市中心和城市外围两种不同地域绿地的功能和结构,并以生态的楔形绿地为桥梁是实现城内外绿地相互联系、功能互补的一个有效途径。     

基于真正自然思想的生态城市景观规划探索

通过系统分析“真正自然”的要素、内涵和特征,总结基于“真正自然”思想的丹东环保园景观规划过程中的关键问题与解决方式,以期为生态城市的建设提供借鉴.     

The importance of patch attributes and context to the management and recovery of an endangered lagomorph

We investigated the role of patch attributes and context on patch occupancy of the Lower Keys marsh rabbit (Sylvilagus palustris hefneri). The Lower Keys marsh rabbit is a federally endangered lagomorph endemic to the Lower Keys of Florida. The marsh rabbit occurs in subpopulations on patches of high marsh that interact to form a metapopulation. Between March 1991 and July 1993, all known patches of high marsh in the Lower Keys were surveyed for presence or absence of marsh rabbit pellets three times per year. Of the 59 habitat patches, 20 had pellets present during all of the surveys (occupied patches), 22 had pellets present during at least one survey (variable patches), and 17 never had any pellets present (empty). Ten variables were measured at each of the 59 patches; seven of these variables concerned attributes of the patch (food, cover, patch size), and three were patch context variables (distance of patch to other patches, distance of patch to other features). Two discriminant function analysis (DFA) were performed. The first DFA compared empty patches to occupied patches (both variably and consistently occupied). Patch isolation explained the most variation in patch occupancy followed by area. The second DFA compared the variably occupied sites with the consistently occupied sites, and patch attributes variables involving the type and height of vegetation were significant. Management efforts for the Lower Keys marsh rabbit should be aimed at both improving habitat quality and decreasing distance between patches.     

江油不同质地土壤对附子苗期生长的影响

采取盆栽试验,对江油附子主要种植区中6个不同质地土壤类型的养分状况和种植于该6个土壤类型之上的附子苗期状况进行研究.结果表明:砂壤土和壤土土壤肥力高,更适合附子的种植,砂土和粘土上的附子生长状况相对较差,建议通过科学的土壤改良,合理施肥,精耕细作来改变砂土和粘土的质地,提高其土壤肥力,以更好地满足附子的生长需要.     

海南高速公路九所互通立交绿化设计探析

分析海南高速公路九所互通立交绿地的现状条件,探讨该区域的绿化设计原则、功能分区及绿化设计方案,为今后海南的互通立交绿化建设提供参考。     

Response of generalist and specialist insect herbivores to landscape spatial structure

The purpose of this study was to investigate the effect ofchanges in landscape pattern on generalist and specialistinsects. We did this by comparing the species richness andabundance of generalist and specialist herbivorous insects inalfalfa (Medicago sativa, L.) fields on 26 agriculturallandscapes that differed in spatial structure. The insects werefrom the families Curculionidae (Coleoptera), weevils, andCicadellidae (Auchennorhyncha), leafhoppers.We hypothesized that: (1) generalist richness and abundancewould be highest in landscapes with high diversity(Shannon-Wiener); (2) specialist richness and abundance would behighest in landscapes with (i) high percent cover alfalfa and(ii) low mean inter-patch distance. We tested for these effectsafter controlling for the patch-level effects of field size,field age, frequency of disturbance and vegetation texture.The important findings of the study are: (1) generalist richness andabundance increased with increasing landscape diversity and (2)isolation (percent cover alfalfa in the landscape and/or meaninter-patch distance) does not affect specialist insects. Theseresults are significant because they indicate that bothgeneralist and specialist insects may move over much largerdistances than previously thought. This is one of the firststudies to demonstrate a large scale effect of spatial structureon insects across a broad range of landscapes.     

Responses of mammals to habitat edges: an overview

Life generates discontinuites (boundaries) in the distribution of matter and energy. One class of these constitutes the edges between habitat-types; these are fundamental structures in landscape functioning, and hence are of central importance in conservation biology. The symposium on which this series of papers is based focused on the responses of mammals to habitat edges. A diversity of views are represented, and a variety of edge related behaviors illustrated. A survey of general ecology texts dating back to 1933 demonstrates a decline of interest in ecotones and edge effects extending into the 1980's but showing a resurgence of interest in the 1990's. Habitat edges are defined operationally with respect to particular focal species leading to a number of important corollary features. The variety of phenomena subsumed under edge effects is emphasized, and an initial attempt at classification is proposed based primarily on the presence or absence of emergent properties in edge response behaviors (matrix vs. ecotonal effects). This scheme provides for clear null hypotheses needed to distinguish the two types, enlightens mechanistic explanations of edge effects, and encourages predictions about the results of untested management schemes or other novel situations. The use and design of landscape corridors are tied to edge related behaviors. A functional and general definition of corridors is urged, so that their effectiveness can be judged with respect to specified attributes rather than to a general collection of things that might be termed corridors. Linear habitat patches are specifically excluded from the definition. Studies on small mammals have contributed to our understanding of the potential role of corridors in metapopulation dynamics. Fine versus coarse grained perceptions of environment by different species will generate ecotonal edge effects such as spillover predation. In general, the effects on landscape processes of various species operating on different spatial scales seems a fruitful direction for future research.