Edge effects: impact of anthropogenic activities on vegetation structure and diversity in western Umfurudzi Park,Zimbabwe

Understanding the patterns and intensity of anthropogenic impacts on habitats is important in the conservation of tropical ecosystems. The aim of the study was to establish the associated edge effects of anthropogenic disturbances on vegetation in western Umfurudzi Park, Zimbabwe. Three study strata were established using distance from the boundary into the park. Vegetation attributes and anthropogenic disturbance levels data were collected in 2012. Significant differences (P < 0.05) were noted on tree and shrub density, woody plant height, woody plant diversity, grass height and grass sward width across the three strata. Land clearing, livestock grazing and firewood collection were the most frequent and pronounced disturbances occurring along the park boundary. These disturbances decreased in intensity as distance from the boundary increased. We recommend the following: (i) the need to revisit the buffer zone concept and policy measures associated with ecosystem services and goods provision for communities surrounding protected areas, (ii) engaging neighbouring communities on sustainable ways of deriving ecosystem goods and services from buffer zones and protected areas and (iii) further studies on the regeneration and recovery of cleared patches along the boundary and their use by wildlife species in the park.     

The effects of bankside management on chalk stream invertebrate communities

SUMMARY 1. Communities of aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects were investigated from short stretches of English chalk streams with two different bankside vegetation types: simply structured grazed grass (grazed) and structurally complex herbaceous vegetation with scattered trees (ungrazed). Macroinvertebrates were sampled in spring, summer, autumn and winter 1996–97 from three aquatic habitats: mid-channel gravel, patches of the aquatic macrophyte Ranunculus and marginal emergent macrophytes. The terrestrial adult phases of aquatic insects were sampled in spring, summer and autumn from bankside vegetation.
2. Total macroinvertebrate abundance did not differ between stretches with different bankside vegetation. Taxon richness of mid-channel gravel was, however, significantly higher in ungrazed compared with grazed stretches and Shannon diversity ( H ') of mid-channel gravel and marginal vegetation was significantly higher in ungrazed compared with grazed stretches. Total abundance, taxon richness and Shannon diversity ( H ') of the terrestrial adult phases of aquatic insect were significantly higher from the bankside vegetation of ungrazed compared with grazed stretches.
3. Ordination of communities of aquatic macroinvertebrates and terrestrial adults demonstrated that individual families of both groups were generally more abundant in ungrazed stretches. Many more families were significantly associated with ungrazed stretches than with grazed stretches.
4. This investigation has shown that high structural diversity of bankside vegetation along lowland chalk streams is accompanied at the reach scale by increased diversity of both aquatic macroinvertebrates and the terrestrial adult phases of aquatic insects. The conservation potential of such streams may thus be lowered by management practices that result in the removal or simplification of bankside vegetation along extensive stream stretches.     

Impact of three aquatic invasive species on native plants and macroinvertebrates in temperate ponds

Biological plant invasions pose a serious threat to native biodiversity and have received much attention, especially in terrestrial habitats. In freshwater ecosystems impacts of invasive plant species are less studied. We hypothesized an impact on organisms from the water column and from the sediment. We then assessed the impact of three aquatic invasive species on the plants and macroinvertebrates: Hydrocotyle ranunculoides, Ludwigia grandiflora and Myriophyllum aquaticum. Our research on 32 ponds in Belgium indicated that the reduction in the native plant species richness was a common pattern to invasion. However, the magnitude of impacts were species specific. A strong negative relationship to invasive species cover was found, with submerged vegetation the most vulnerable to the invasion. Invertebrate richness, diversity and abundance were measured in sediments of invaded and uninvaded ponds along a gradient of H. ranunculoides, L. grandiflora, and M. aquaticum species cover. We found a strong negative relationship between invasive species cover and invertebrate abundance, probably due to unsuitable conditions of the detritus for invertebrate colonization. Taxonomic compositions of aquatic invertebrate assemblages in invaded ponds differed from uninvaded ponds. Sensitive benthos, such as mayflies were completely absent in invaded ponds. The introduction of H. ranunculoides, L. grandiflora, and M. aquaticum in Belgian ponds has caused significant ecological alterations in the aquatic vegetation and the detritus community of ponds.     

环境因子对上海城市园林春季鸟类群落结构特征的影响

2004年3—5月,对上海8个园林绿地的春季鸟类做了研究。在调查中共观察到55种鸟类,其中留鸟31种,候鸟24种。运用回归与相关统计分析方法分析了鸟类群落结构和分布特征与8个园林绿地的公园面积、水体比例、植被种数、乔木层盖度、灌木层盖度、草本层盖度、地形坡度异质性、临主干道状况、人流量、行道宽度10项环境指标的关系。结果表明：(1)公园面积、植被种数、灌木层盖度、草本层盖度、地形坡度异质性、临主干道状况、行道宽度等7个因子在影响园林鸟类群落结构和分布中起关键性作用;(2)上海城市鸟类数量、多样性呈单一化趋势,而且公园绿地内大面积水体等建设方案并不利于鸟类的栖息。     

Relationships of water temperature and aquatic macroinvertebrate community structure with non-native riparian plant densities in the southern Cape,South Africa

Non-native vegetation in the riparian zone impacts on water temperatures, flow patterns, degree of shading, channel modification, and changes to natural sediment loads. Freshwater ecosystems in the Garden Route Initiative planning domain are of particular conservation value, because of the rich Gondwanaland relict aquatic macroinvertebrate fauna found in the rivers there, which are vulnerable to thermal changes. Data were collected during 2013 and 2014 at 19 sites on seven river systems between George and Knysna in the southern Cape, South Africa. These included 12 months of hourly water temperatures at all sites, and quantitative sampling of aquatic macroinvertebrates at ten sites. Each site was characterised in terms of water quality (pH, conductivity and turbidity) and general characteristics, including impacts such as density of non-native riparian trees. At the family level, aquatic macroinvertebrate communities showed variation between sites and seasons. Differences were more pronounced on the basis of natural land cover type (fynbos versus indigenous forest) than densities of non-native invasive riparian vegetation. Conservation of these river systems will depend on maintaining a mosaic of natural vegetation types.     

Abundance and diversity of macroinvertebrates and fish in the Tamiraparani river, South India

Occurrence of macroinvertebrates and fish was studied at 11 stations along the course of a tropical river, Tamiraparani, South India. Monthly variations in macroinvertebrate density were studied during 1991. Among macroinvertebrates, hemipterans were the dominant group at all sites, except site 2. Using an ordination technique, density and occurrence of macroinvertebrates were correlated with dissolved oxygen, biological oxygen demand and chemical oxygen demand. A total of 36 species of fish was recorded and their diversity in undisturbed and disturbed regions of the river was compared on a spatial scale. Different diversity indices were calculated to assess fish response to pollution and to determine species richness and composition.     

祁连山国家公园植被时空变化及其对人类活动的响应

祁连山国家公园地处青藏、蒙新、黄土三大高原交汇地带的祁连山北麓,作为国家公园体制试点之一,是我国重要的生态功能区、水源涵养地和生物多样性保护优先区域,其生态功能不可忽视。以祁连山国家公园2000—2019年归一化植被指数(NDVI)和净初级生产力(NPP)数据为基础,结合气温、降水、土地利用、矿产开采和旅游发展数据,利用泰尔-森趋势分析(Theil-Sen趋势分析)、曼-肯德尔检验(Mann-Kendall显著性检验)、土地转移概率矩阵和多元残差分析方法,分析该区域的植被时空分布特征、变化趋势特征及其对气候变化和人类活动的响应。结果表明：(1)2000—2019年祁连山国家公园内NDVI和NPP在空间上呈现出东南高西北低,由东南向西北递减的格局。时间上呈现上升趋势,上升速率分别为0.0053/a和0.0014/a;(2)祁连山国家公园内NPP提高、降低和稳定区域分别占总面积的87.29%、0.40%和12.30%。降低区域零星分布于整个国家公园,其中在走廊南山和冷龙岭交汇处,靠近甘青两省交界边缘分布最为集中。提高区域分布广泛,尤其以国家公园东部最为明显;(3)祁连山国家公园NDVI与气...     

Improved management of farm dams increases vegetation cover,water quality,and macroinvertebrate biodiversity

In many farming landscapes, aquatic features, such as wetlands, creeks, and dams, provide water for stock and irrigation, while also acting as habitat for a range of plants and animals. Indeed, some species threatened by land‐use change may otherwise be considerably rarer—or even suffer extinction—in the absence of these habitats. Therefore, a critical issue for the maintenance of biodiversity in agricultural landscapes is the extent to which the management of aquatic systems can promote the integration of agricultural production and biodiversity conservation. We completed a cross‐sectional study in southern New South Wales (southeastern Australia) to quantify the efficacy of two concurrently implemented management practices—partial revegetation and control of livestock grazing—aimed at enhancing the vegetation structure, biodiversity value, and water quality of farm dams. We found that excluding livestock for even short periods resulted in increased vegetation cover. Relative to unenhanced dams (such as those that remained unfenced), those that had been enhanced for several years were characterized by reduced levels of turbidity, nutrients, and fecal contamination. Enhanced dams also supported increased richness and abundance of macroinvertebrates. In contrast, unenhanced control dams tended to have high abundance of a few macroinvertebrate taxa. Notably, differences remained between the macroinvertebrate assemblages of enhanced dams and nearby “natural” waterbodies that we monitored as reference sites. While the biodiversity value of semilotic, natural waterbodies in the region cannot be replicated by artificial lentic systems, we consider the extensive system of farm dams in the region to represent a novel ecosystem that may nonetheless support some native macroinvertebrates. Our results show that management interventions such as fencing and grazing control can improve water quality in farm dams, improve vegetation structure around farm dams, and support greater abundance and diversity of aquatic macroinvertebrates.     

Rainbow Trout diets and macroinvertebrates assemblages responses from watersheds dominated by native and exotic plantations

Over the past few decades, land-use changes through conversion of global forest cover to exotic plantations is contributing to both habitat and biodiversity loss and species extinctions. To better understand human influences on ecosystem, we use diet composition from introduced Rainbow Trout Oncorhynchus mykiss as indicator of potential changes in the composition of stream-macroinvertebrates due to land use changes from native to exotic vegetation (eucalyptus plantations) in southern Chile. Water quality variables, aquatic macroinvertebrates and Rainbow Trout diet were studied in 12 sites from mountain streams located in two watersheds including one dominated by native riparian vegetation and the other dominated by exotic vegetation. As expected, richness and abundance of macroinvertebrates were clearly higher at sites in native forest than in those with exotic vegetation. Collector-gatherer was the most abundant functional feeding group, but there was no statistical difference in the functional composition between the two watersheds. Differences in in-stream macroinvertebrate availability was more higher correlated with changes in Rainbow Trout diets. Specifically, taxa consumed from the watershed dominated by native forests was higher than from the watershed with exotic vegetation. Additional environmental variables showed statistical differences between watersheds. The exotic vegetation sites had the highest concentrations of dissolved solids, suspended solids, nitrates, chlorides and sulphates. Our findings show that macroinvertebrate assemblage structure and trout diets can be altered by changes in riparian vegetation. The absence of specific macroinvertebrate taxa in streams with exotic vegetation was captured by the composition of trout diets. This suggest that Rainbow Trout diets can be a good biological indicator of land use practices and thus, diet can be used as a rapid and effective tool for evaluate environmental quality. Our findings provide insights about the design of aquatic monitoring programmes to improve detection of anthropogenic impacts in streams in South America and elsewhere.     

Phylogenetic taxonomy of the marine mite genus Rhombognathides (Acari: Halacaridae: Rhombognathinae)

This study examined the impacts of the alien waterweed, water hyacinth, on the abundance and diversity of aquatic macroinvertebrates in the littoral areas of northern Lake Victoria in Uganda. The weed had undergone explosive growth on the lake causing serious disruption to people, the economy and the ecosystem. This study was confined to impact of the weed in the littoral zone, not to the large floating mats of vegetation which float across the lake and clog large areas of shoreline.The littoral area studied comprised of fringing mats of Eichhornia crassipes (Mart) Solms (water hyacinth) to the lakeward of Cyperus papyrus; water hyacinth mats undergoing colonisation by Vossia cuspidata (Roxb.) Griff.; and a typical Cyperus papyrus L shore with no outer floating mat of water hyacinth. Numerical abundance (Nos. m^–2) and diversity (No. of taxa) of macroinvertebrates recovered from pure Eichhornia crassipes and the Eichhornia-Vossia succession increased from the fringe of the Cyperus papyrus towards the open water. In the typical Cyperus papyrus fringe, in the absence of water hyacinth, abundance was highest at the papyrus/open water interface and dropped off sharply towards open water. The Shannon–Weaver diversity index (H) of macroinvertebrates decreased progressively from pure Eichhornia crassipes stands, to Vossia/Eichhornia beds and Cyperus papyrus stands (H=0.56, 0.54 and 0.34, respectively) but were not significantly different. Dissolved oxygen decreased from open water into vegetation where it approached anoxia. Water hyacinth appeared to enhance the abundance and diversity of aquatic macroinvertebrates at the interface with the open water. The impoverished abundance and diversity of the macroinvertebrates deeper into the vegetation mats suggested negative environmental impacts of the water hyacinth when the fringe is too wide. Further research is recommended to establish the optimum width of the fringe of stationery water hyacinth that promotes maximum abundance and diversity of aquatic macroinvertebrates and, possibly, of other aquatic life. Since this study in 1997, there has been a dramatic decrease in Eichhornia infestations and by June 2000 it appeared largely to exist only as fringing vegetation in bays and inlets.     

Biodiversity of constructed wetlands for wastewater treatment

Constructed wetlands are often built for wastewater treatment to mitigate the adverse effects of organic pollution in streams and rivers caused by inputs of municipal wastewater. However, there has been little analysis of biodiversity and related factors influencing the ecosystem functioning of constructed wetlands. The purpose of this study was to evaluate the biodiversity of two free-water-surface integrated constructed wetlands in subtropical Taiwan by analyzing the water quality, habitat characteristics, and biotic communities of algae, macrophytes, birds, fish, and aquatic macroinvertebrates in the treatment cells. Our results indicated that the two integrated constructed wetlands (Hsin-Hai II and Daniaopi Constructed Wetlands) achieved good performance in reducing the concentrations of total nitrogen (TN) and total phosphorus (TP), and loadings of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) from municipal sewage. In total, 58 bird species, 7 fish species, and 34 aquatic macroinvertebrate taxa were recorded in the two wetlands. The results of stepwise multiple regressions showed that the richness, abundance, and diversity of birds increased with wetland area. Fish richness and abundance respectively increased with wetland area and dissolved oxygen, while the diversity decreased with increases in TP concentrations. The richness and density of aquatic macroinvertebrates increased with the cover of aquatic macrophytes, while the diversity increased with wetland area. Ordination analyses indicated that variations in the community structures of birds, fishes, and aquatic macroinvertebrates were respectively best explained by water temperature, wetland area, and species richness of fish. Our results suggest that wetland area, cover of aquatic macrophytes, and water quality were the most important factors governing the diversity in the constructed wetlands, and that the factors influencing community structures varied among different taxonomic groups. In addition to improving water quality, this study implied that the biodiversity of constructed wetlands for wastewater treatment can be enhanced through proper design and management.     

Effects of Aufwuchs on Colonization by Simuliids (Simuliidae,Diptera)

While different studies investigated effects of surface properties on the adhesion and population dynamics of marine sessile organisms (Balanidae, Bryozoa etc.), little is known about sedentary freshwater macroinvertebrates. Artificial substrates were used to investigate the effects of Aufwuchs on density and distribution of colonizing blackfly larvae and pupae. Although, settlement of blackfly larvae often is said to be impeded by Aufwuchs or siltation, they colonized both bare substrates and those on which a thick Aufwuchs cover had developed. Often no differences in density appeared on substrates exposed for less than 6-9 d. Thus Aufwuchs apparently does not prevent initial settling of larvae. However, simuliid densities on Aufwuchs covered substrates declined after several more days of exposure, suggesting that surface properties may affect long-term settlement.     

Role of aquatic vegetation coverage on hypoxia and sunfish abundance in bays of a eutrophic reservoir

We studied the relation between aquatic vegetation coverage, summer dissolved oxygen and density of sunfishes (Lepomis spp.) in 10 shallow bays of a eutrophic reservoir. The bays ranged 5.2–15.7 ha in area, 0.6–1.3 m mean depth and 6–91% vegetation area coverage. Over the 10 bays mean dissolved oxygen concentration ranged 5.8–9.0 mg l^-1 in open water at least 20 m away from the vegetation, 0.8–8.1 mg l^-1 at the vegetation-water edge and 0.5–7.7 mg l^-1 in dense vegetation. Dissolved oxygen concentrations were inversely related to vegetation coverage. In open water, dissolved oxygen levels were consistently higher than 8 mg l^-1 when vegetation coverage was <20% of the bay and decreased to about 6 mg l^-1 at coverages near 80%. At the vegetation-water edge and within dense vegetation, dissolved oxygen levels dropped rapidly as vegetation coverage increased to 20% of the bay; when vegetation reached about 50% coverage, dissolved oxygen remained near 1.5 mg l^-1at the vegetation-water edge, but oxygen dropped below 1 mg l^-1in dense vegetation. Scarce vegetation harbored high Lepomis relative abundance (fish per m² of vegetation) whereas extensive vegetation harbored low relative abundance, both contributing little to absolute abundance (total fish in all vegetation); however, intermediate coverage offered a combination of mid-level fish relative abundance that together with mid-level plant coverage translated into high absolute fish abundance. We suggest this response is related to hypoxia, and where aquatic vegetation is extensive, the effect of vegetation on hypoxia and water quality in general may influence fish populations in a way similar to that often attributed to reduced foraging efficiency and increased competitive interactions.     

The effects of city–suburb–exurb landscape context and distance to the edge on plant diversity of forests in Wuhan,China

Abstract

We analysed the relative role of landscape context (city, suburb and exurb) and distance to the edge (from forest edge to 45 m in interior) on plant diversity of natural forests in Wuhan city. The results indicated that landscape context had significant effects on plant diversity, and both landscape context and distance to the edge affect vegetation and disturbance characteristics. Landscape context was the main factor affecting richness of woods, herbs, indigenous species, forest generalists and insect or wind pollination species. These species tended to be higher in exurban forests while non-indigenous species were higher in the urban forests. The number of non-indigenous species, forest specialists, herbs and insect pollination species also depended on distance to the edge or on both interactions. Richness of non-indigenous species decreased with increasing distance to the edge in urban forest. Vegetation characteristics that shrub cover was lower and disturbance characteristics that disturbed cover and human activity were higher in the urban edge than in the suburb and exurb edge, which decreased from the edge to the interior. Therefore, we should prioritize the preservation of less disturbed and frequented forests (suburban and exurban) to buffer the invasion of non-indigenous species, and to reserve more indigenous species.     

Responses of the fish community to the flood pulse and siltation in a floodplain lake of the Trombetas River,Brazil

The distributions of the fish species were examined in relation to environmental variables, to evaluate the effects of environmental degradation on the fish community of Batata Lake, a typical Amazonian clearwater lake. From 1979 to 1989, tailings composed of water and clay, extracted from bauxite by water jets, were discharged into Batata Lake. The tailings spread into about 30% of the lake’s area, where the level of the lake bottom rose and turbidity increased. In the present study, multivariate analyses were performed on data for environmental parameters and fish density and biomass. Fish were collected with gillnets during the annual hydrological cycle (filling, flood, drawdown and dry periods), in the silted area, the partly silted area (intermediate) and the natural area. Values of the Shannon index, density and biomass were compared among areas and periods to evaluate the effects of the tailings on community structure. Sediment resuspension, which reduces transparency, is accentuated in shallow water, and was the main factor regulating differences in the community structure between the natural and silted areas. The decrease in transparency occurs mainly during the filling period in the silted area and during the low-water period in the silted and intermediate areas, when sediment resuspension increases concentrations of nutrients and chlorophyll-a. The strong influence of migratory and piscivore species in low-transparency waters is likely associated with the greater bacterioplankton productivity and turnover rate observed by other authors in the silted area, increasing the importance of the heterotrophic food chain in Batata Lake. Reduction of transparency in the silted area was a selective factor for fish species. The death of part of the flooded forest vegetation was decisive in lowering densities of the igapó-associated species in the silted area. The unconsolidated substrate, the death of part of the igapó forest and the negative effects of low transparency – inhibiting resident visually oriented species in the affected areas – are the main factors causing the low diversity in the silted area as a whole. The correlations between CPUEs, conductivity and nutrients and chlorophyll-a concentrations do not appear to reflect cause–effect relationships, indicating that these environmental parameters are poor predictors of fish density in Batata Lake.     

Shifts in leaf litter breakdown along a forest–pasture–urban gradient in Andean streams

Tropical montane ecosystems of the Andes are critically threatened by a rapid land‐use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico‐chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico‐chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land‐use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf‐shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land‐use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.     

Tree Species Composition and Diversity at Different Levels of Disturbance in Popa Mountain Park,Myanmar

Tropical forests are highly threatened by human activities, even within the protected areas that have been established to conserve biodiversity. Human activities may have different degrees of impact on vegetation structure, composition and diversity. Some studies have measured direct evidence of human activities in forming disturbance gradients, while others have quantified canopy cover as a proxy for disturbance. When measurement is confined to human activities, disturbance may be underestimated in areas of poor canopy cover where forest degrading activities have ceased. Where measurements are restricted to canopy cover, disturbance may be underestimated in areas of extensive canopy cover that may have been subject to past disturbances, and overestimated for areas where canopy cover is naturally sparse. Combining indicators of past and present disturbances is therefore necessary to examine the full spectrum of human disturbances. Forest vegetation in Popa Mountain Park, Myanmar was surveyed and classified into three levels of disturbance—undisturbed, medium disturbed and highly disturbed—derived from evidence of cutting and canopy cover. The forests are second or third growth after clearing for agriculture in the early 20th century. All trees with ≥10 cm diameter at breast height in 168 sample plots (10 m × 10 m) were identified and measured. Density, basal area and diversity decreased and dominance rose when disturbance increased. Canonical correspondence analysis (CCA) clearly discriminated three forest stands and CCA axes were significantly correlated to soil moisture, soil nitrogen, elevation, slope, aspect, distance from park boundary and distance from villages. Abstract in Myanmar is available at http://www.blackwell‐synergy.com/loi/btp .     

Primary producers in a Pampean stream: temporal variation and structuring role

Low current velocities, high nutrient levels, the lack of riparian forest vegetation, and the development of dense and rich macrophyte communities characterize Pampean streams. The objective of this study was to describe the main physical, chemical, and biological characteristics of a headwater Pampean stream as well as to analyze the role of macrophytes and phytobenthos. The study was conducted in a stream considered to be not much disturbed by human activities. Samples of water and organisms (macrophytes, benthic algae and invertebrates) were taken monthly for 14 months in two sampling stations, in fast flow and slow flow sites. Macrophyte biomass and diversity increased in spring and summer, and they decreased in autumn, when the plant community was greatly affected by an important flood. Phytobenthos biomass was lower in late summer, possibly due to the establishment of a dense cover of the floating macrophyte Lemna gibba L. Density of amphipods and gastropods greatly increases in spring and summer, jointly with the macrophyte development. Analysis of correlation showed that current velocity is the most important factor influencing macrophyte biomass and phytobenthos structure, while depth, nutrients, and herbivores are linked factors. Pampean streams could be considered systems dynamically fragile, because habitat heterogeneity is generated by aquatic vegetation, a substratum that varies along time.     

Grasshopper assemblage response to a restored national park (Mountain Zebra National Park, South Africa)

Twelve grassland sites were sampled inside and outside the Mountain Zebra National Park (MZNP), South Africa to assess changes in grasshopper assemblages to grazing by indigenous mammals inside the park compared to grazing by domestic cattle outside. The MZNP has been restored from cattle-grazed farmland to indigenous mammal parkland for 62 years. The number of grasshopper species and families inside the park was not significantly different from outside the park, but the number of individuals inside the park was significantly higher. Multivariate statistics did not reveal any strong site groupings based on simple inside/outside comparisons, but there were clear groupings of sites based on vegetation characteristics and other environmental variables. The park boundary, therefore, does not significantly determine grasshopper assemblages, although intensity of grazing does. The indigenous mammals inside the park had the same effect on grasshoppers as the domestic cattle outside, and it was the level of defoliation and trampling that was important rather than the type of mammal. Intensive livestock grazing and trampling leads to bush encroachment and reduction in grass cover and/or disappearance of several grass species. In response to this pressure, grasshopper populations dropped, with localized extirpation of some species. Vegetation composition and structure, particularly grass height and percentage cover, had a significant effect on grasshopper assemblages. The MZNP is thus an area of localized, elevated grasshopper abundance in comparison with the surrounding farms, and presumably represents a situation prior to the current, intensive farming activities. Such elevated grasshopper abundances are important for maintaining soil quality and hence ecological integrity of this landscape which is poor in organics and nitrogen. The MZNP could be viewed as a centre where species with high mobility may seek refuge from anthropogenic pressures. The MZNP also serves as a reference illustrating the differences between restored-through-natural-succession and anthropogenically disturbed habitats, and compares desirable with undesirable ecosystem changes for herbivorous invertebrates such as grasshoppers.     

祁连山南坡植被景观格局及其破碎化

以扎麻什营林区的林相图和调查资料为基础,运用GIS手段,选取合适的景观格局指数,分析了祁连山南坡植被景观格局基本特征,并进行了破碎化评价.结果表明:研究区植被以草地和灌丛为主,景观基质已退化为裸地,各植被类型斑块密度远大于裸地,平均分维数较低,景观整体破碎化水平较高;草地和灌丛边界密度和破碎化指数均高于其他植被类型,反映出该区自然植被景观主要受放牧活动的影响;森林多以小面积零散分布,其中青海云杉林景观结构破坏较为严重,异质性较低,斑块形状趋于单一,显示出较高水平的破碎化,其他林种多以小面积集中分布于某些小的生境,受人类活动干扰较少,破碎化程度较低.

Abstract：

Based on the forest form map and investigation data of Zhamashi forest area, and by using GIS, appropriate landscape pattern indices were chosen to study the basic characteristics of vegetation landscape pattern on the southern slope of Qilian Mountain, with the landscape frag-mentation evaluated. In the study area, grass and shrub were the main vegetation types, and the landscape matrix had degraded to bare land. The patch densities of all vegetation types were far larger than that of bare land, and their mean fractal dimension was lower than that of bear land. All of these characters emphasized the highly fragmented condition of the vegetation landscape in this area. The total edge densities and fragment indices of grassland and shrub land were higher than those of other vegetation types, reflecting that the natural vegetation was mainly affected by grazing. The forests were more dispersed in small areas, and the landscape structure of Picea crassifollia forest was heavily destroyed, being induced that the heterogeneity became lower and the patch shape tended to single, suggesting a high fragmentation degree. Other forest types were centralized in a certain habitat and less disturbed by human activities, suggesting a lower frag-mentation degree.