土地覆被变化与管理对土壤动物群落演变的耦合效应

以黑河中游人工绿洲边缘天然草地及其转变的人工梭梭灌木林（21 a）、人工杨树林（28 a）、人工樟子松林（33 a）和农田（开垦27 a和100 a）为研究对象,基于6种研究样地中小型土壤动物群落的调查数据,采用多变量排序和通径分析等方法,研究了土地利用/覆被变化与管理措施对中小型土壤动物群落及其主要类群演变的耦合效应。主要结果是:①将天然草地转变为未实施管理措施的人工梭梭灌木林后并未引起土壤动物群落组成、数量和物种多样性的显著变化,而转变为实施管理措施的杨树和樟子松人工林及农田后,导致了土壤动物群落组成、数量和物种多样性的变异,证实了土地覆被变化对中小型土壤动物群落的作用及其效应受管理措施的强烈调控。②土壤动物群落的演变过程受土地覆被变化与灌溉和施肥管理的共同影响,其中灌溉的贡献率最大,是关键驱动因子。③不同土壤动物类群对土地覆被变化和管理耦合作用的响应不同。灌溉对跳虫、甲螨和革螨的个体数量和物种丰富度的直接影响和总效应最大;施肥对辐螨的个体数量和物种丰富度的直接影响和总效应最大;灌溉和施肥对稀有类群的个体数量和物种丰富度的直接影响和总效应均较大,具同等重要的作用。结论是,土地覆被变化与管理耦合作用通过改变土壤水文和生态环境条件驱动了中小型土壤动物群落的演变过程。     

Effect of environmental factors on the flora of alluvial fans in southern Sinai

The purpose of this study was to elucidate the floristic and structural characteristics of simple alluvial fan vegetation of southern Sinai and to relate them to environmental variation. The main question addressed was: how does the floristic composition of fan habitats, species richness and life-form vary in relation to environmental change? Thirty-seven alluvial fans, randomly selected in two mainwadis(WadiFeiran andWadiDahab) were analysed quantitively. Two-way Indicator Species Analysis (TWINSPAN) classification and Canonical Correspondence Analysis (CCA) were applied in successive stages of the data analysis to describe vegetational variation in relation to physical gradients. Seven main clusters of fans were defined on the basis of environmental variation. These clusters are divided into three main groups of species richness. Species richness varied along a moisture gradient. The richest fans were the driest habitats, indicating that maximum species richness did not occur at high moisture availability. The moisture gradient is a complex gradient correlated with elevation, slope, climatic aridity, soil texture and the nature of the soil surface. Fine sand, silt plus clay and calcium carbonate showed significant differences between the internal groups and subgroups of the first and second level of the TWINSPAN classification.     

Disentangling Fabiana imbricata (Solanaceae) regeneration: The importance of disturbance and rainfall

In Mediterranean ecosystems, fire influences plant population dynamics and changes plant community structure by affecting germination and establishment of seeder shrubs. Fabiana imbricata is a long-lived seeder shrub with a broad distribution in South America. In Northwestern Patagonia grasslands there are many records of F. imbricata recruitment after fires. We hypothesized that recruitment is promoted by: 1) soil erosion that exposes deeply buried seeds; 2) direct fire effects such as heat that could break seed dormancy; 3) indirect fire effects (i.e. increase of light availability and elimination of allelopathic substances) and 4) water availability in spring. In field conditions, we tested the effects of shading and soil disturbance on F. imbricata recruitment and seed availability and distribution in the soil profile. Under controlled conditions, we investigated the influence of leaf leachate, light, heat and water on seed germination and seedling emergence. Seed germination was inhibited by leachate, and seedling emergence was inhibited by seed heated to 80 °C and 120° for 5 min. F. imbricata seedlings only emerged in germination treatments that simulated wet and very wet spring conditions. Fire and postfire wind that favor seed exposure, combined with high precipitation early in the growing season, would be necessary for successful shrub recruitment. When F. imbricata shrubland colonizes the grassland, it strongly modifies local vegetation structure, reduces species richness and increases fuel loads. F. imbricata is a key species in the ecosystem specially related to fire regime. Information on the postfire regeneration of this species would provide valuable knowledge of the changes in biomass accumulation in a fire-prone Mediterranean ecosystem.     

Acacia communities and species responses to soil and climate gradients in the Sudano-Sahelian zone of West Africa

Abiotic environmental factors have a major impact on the distribution and performance of plant species. In order to assess two major species–environmental relations in Sudano-Sahelian Acacia woodlands, we tested the relationship of soil and climate variables on plant diversity as well as on species responses.The indicator species values clustered in five vegetation units characterized by three to ten diagnostic species with woody species richness means varying from three to seven species per 0.09 ha. The NMS ordination explained 65% of the variation in species composition and revealed that soil properties, annual precipitations and temperature range structured the diversity of Acacia communities. Along the annual precipitations gradient, the response of Acacia polyacantha and Acacia hockii showed maxima in the wettest zone of our study area (more than 850 mm/year) whilst Acacia laeta showed a maximum response in the driest zone (below 500 mm/year). The unimodal response of A. hockii, Acacia gourmaensis and Acacia seyal to the soil available water gradient spanned their central borders, respectively from 13 to 18% (optimum 16%), 11–20% (optimum 15%) and 4–12% (optimum 7.5%).The response of Acacia communities and species to soil and climate gradients, makes them performant afforestation species in specific habitats of the Sudano-Sahelian zone.     

Modeling the optimal grazing regime of Acacia victoriae silvopasture in the Northern Negev,Israel

Silvopasture, the planting of suitable tree species in pastures, can improve the sustainability and productivity especially in dry rangelands. While recent studies provide information on the effects of different tree compositions on biological productivity, water and soil protection, additional parameters such as fodder production by the trees or the impact of silvopasture on the grazing potential themselves have rarely been addressed. We determined fodder production in Acacia victoriae woodland and savanna by measuring annual vegetation and tree biomass growth. We developed mathematical models for calculating the vegetative biomass available for grazing. In order to get accurate estimation for the grazing capacity, we differentiated between the grazing and the browsing fodder availability, and adapted the model to the most abundant grazers in the Negev, goats and sheep. Grazing capacity for sheep and goats was twice bigger in A. victoriae woodland than in the adjacent sustainably managed shrubland and four times higher than in degraded shrubland. The mathematical model presented in this paper can be applied in order to plan and realize high yielding and sustainable silvopasture in arid environments resistant to degradation and desertification while providing adequate fodder reserves during drought years.     

Floristic uniformity across abrupt boundaries between Triodia hummock grassland and Acacia shrubland on an Australian desert sandplain

The tension between pyrophytic hummock grasslands and fire-sensitive mulga shrubland is a major ecological theme in central Australia. On a sandplain on the edge of the Tanami Desert, grassland and shrubland are juxtaposed with abrupt boundaries that cut across a subtle environmental gradient. We compare woody plant diversity among vegetation types and explore correlates of the distribution of woody plant species. Alpha diversity in grassland and shrubland was almost identical, but plot-level species richness was greater in grassland. Gamma (landscape) diversity was scarcely greater than alpha diversity. Few long-lived plants, and not even the dominant hummock grass and shrub, were exclusively associated with one vegetation type, but most common species were aligned with elements - soil texture, fire frequency and the extent of physical soil crusting - that characterise the environmental gradient between vegetation types. Most species were resprouters and there was no tendency for obligate seeders or facultative resprouters to be associated with the less fire-prone shrubland. Our data are consistent with the suggestion that hummock grasslands and mulga shrubland are alternative stable states maintained by fire-soil feedback loops and possibly also by competitive exclusion of pyrophytic species by Acacia aneura.     

A comparison of classification systems for the conservation of sparsely wooded plains on Melville Island,Northern Australia

A floristic quadrat study of sparsely wooded plains on western Melville Island was conducted and used to define and describe floristic and structural vegetation types and identify their associated environmental correlates. The results were compared with an existing land‐unit survey of the area in order to identify the relative merits of these schemes for conservation planning. All schemes identify a range of broad structural types including Acacia shrubland, Grevillea pteridifolia low woodland, Lophostemon lactifluus low woodland, and Banksia dentata low woodland. However, some of the structural and land‐unit types are composed of two plant communities with distinctive environmental relations. Despite being structurally distinctive, some community types are floristically indistinguishable from surrounding forest dominated by Eucalyptus miniata and E. tetrodonta. The number of species captured by randomly selecting sites from each classificatory type revealed little difference between schemes. All the classificatory approaches were less effective at species capture than a simple iterative procedure. Some of the plant communities seem to be unique and require preservation initiatives in the face of current forestry operations and planned horticultural development.     

塔里木河中游天然植被的数量分类与排序研究

通过塔里木河中下游天然植被带的调查研究，应用数量分类(TWINSPAN)和排序(CCA)方法，对塔里木河中下游地区天然植被类型进行了划分，并探讨了决定该地区天然植物群落类型的主要环境因子。该地区天然植被可分为4个植被型组，4个植被型，6种植被亚型，9个群系，15个群丛。通过对8个环境因子的CCA排序分析，结果表明制约塔里木河中下游天然植被组成和结构的主导环境因子为地下水位、地下水矿化度、地下水酸碱度。通过CCA二维排序图将16种植物对干旱、盐碱的适应性划分5类型。21个样地在CCA二维排序图上可聚集成9个植物群落类群，即胡杨(Populus euphratica)群落、铃铛刺(Halimodendron halodendron)群落、库尔勒沙拐枣(Calligonum Kuerlese)群落、多枝柽柳(Tamarix ramosissima)群落、黑果枸杞(Lycium ruthenicum)群落、盐穗木(Halostashys caspica)群落、花花柴(Karelinia caspica)群落、疏叶骆驼剂(Alhagi sparsifolia)群落、罗布麻(Apocynum venetum)群落，与TWINSPAN结果中的群系分类单位一致。CCA连续排序与TWINSPAN分类结果吻合较好。9种植物群落类型中，能耐受最大盐胁迫的为盐穗木群落，能耐受最大干旱胁迫的为铃铛刺群落，能耐受最大地下水碱胁迫的为黑果枸杞群落。     

Piospheres in the dry Chaco. Contrasting effects of livestock puestos on forest vegetation and bird communities

In arid and semiarid ecosystems, the congregation of livestock around water sources gives rise to a utilization gradient termed the “piosphere pattern”. We evaluated piospheres surrounding the puestos livestock management system in the Chaco dry forests of Argentina. We sampled vegetation and bird communities around eighteen puestos and we fitted curves to describe the responses of vegetation and bird community variables to the distance from the puestos. We used Partial Canonical Correspondence Analysis to evaluate the organization of bird guilds constrained by vegetation variables and the distance from the puestos. Vegetation structure increased with the distance from the puestos. In contrast, the abundance of most bird's guilds decreased with distance from the puestos, likely in response to the gradient in resources associated to the water source, food and changes in vegetation. Rare or low abundance bird species peaked at intermediate or long distances from the puestos. Our results concur with studies characterizing the puestos as a focus of vegetation degradation, but the analysis of the avian community shows that the nature of this piosphere is more complex, as is a favorable habitat for some ecological groups.     

The impact of African elephants on Acacia tortilis woodland in northern Gonarezhou National Park, Zimbabwe

We investigated the impact of African elephants (Loxodonta africana) on the structure and composition of Acacia tortilis woodland in northern Gonarezhou National Park, southeast Zimbabwe. A. tortilis woodland was stratified into high, medium and low elephant utilisation categories based on evidence of elephant habitat use as determined through dung-count surveys in relation to distance of woodland patches from perennial and natural surface water sources. The following variables were recorded in each study plot: tree height, species name, number of species, plant damage, basal circumference and number of stems per plant. A total of 824 woody plants and 26 woody species were recorded from the sampled A. tortilis woodland patches. Mean tree densities, basal areas, tree heights and species diversity were lower in areas with medium and high elephant utilisation as compared to low elephant utilisation areas. Plants damaged by elephants increased with increasing elephant utilisation. The study findings suggest that A. tortilis woodland is gradually being transformed into an open woodland. We recommended that protected area management in arid and semi-arid areas should consider (i) formulating clear thresholds of potential concern to allow for the conservation of sensitive woodlands such as A. tortilis woodlands and (ii) establishing long-term vegetation monitoring programmes.     

Rabbits,weeds and crops: Can agricultural intensification promote wildlife conflicts in semiarid agro-ecosystems?

Agricultural intensification has led to the extreme simplification of agricultural landscapes. The subsequent impoverishment of farmland plant communities can drive dramatic changes in the associated food webs of agricultural systems, with potential implications for vertebrate pest management. Weeds may provide alternative food sources for damaging species and thus contribute to reducing their damage, which is particularly desirable if the species is a valuable resource in its own right. Wild rabbits (Oryctolagus cuniculus) are a game species of great conservation value in the Iberian Peninsula that cause frequent damage to crops. Here we describe the dynamics of non-crop plant communities over an annual cycle in a semiarid Mediterranean agro-ecosystem, and discuss the potential linkages and implications for rabbit damage management. Overall, the availability of alternative food for rabbits was very low, especially in the most extensive habitat types, i.e. olive groves and vineyards. The seasonal pattern in plant productivity, which coincides with the phenology of rabbits in Mediterranean areas was only detectable in the less intensively managed habitat types. Scarce natural vegetation remnants retained the highest richness, diversity and plant cover, potentially acting as a refuge for both, plants and rabbits. Our results indicate that intensive management practices, through reducing alternative food sources for rabbits, are likely to promote conflict between hunters, farmers and conservationists in semiarid agro-ecosystems of Southern Spain.     

Effects of the abandonment of the burrowing mounds of fat sand rat (Psammomys obesus cretzschamar 1828) on vegetation and soil surface attributes along the coastal dunes of North Sinai,Egypt

Fat sand rats (Psammomys obesus) are strictly herbivorous and live in densely complex burrows in the desert of North Africa and the Middle East. Little is known however about the effect of their foraging and burrowing activities on surface morphology and plant community attributes. This study evaluated such effects by comparing burrow and mound surface morphology, canopy of the main host chenopod shrub Anabasis articulata, vegetation cover, and plant abundance and species richness on and off both active and abandoned colonies in the semi-stabilized sand dunes of the Northern Sinai. In general, active burrow systems were characterized by reduced A. articulata canopy area, and more soil disturbance, with higher and larger burrow mounds dominated by bare ground, dung, and dead and fresh litter. The abandonment of mounds for five years has resulted in significant increases of plant cover, canopy height, abundance and species richness. Vegetation structure and plant species assemblages differed between mound and non-mound patches of both active and abandoned sites. The results suggest that fat sand rats can have significant direct and indirect, short-term and long-term effects on vegetation dynamics and structure through their mound building and foraging.     

Assessment of grazing effect on sheep fescue (Festuca valesiaca) dominated steppe rangelands, in the semi-arid Central Anatolian region of Turkey

In the semi-arid steppe rangelands of Central Turkey, Festuca valesiaca and Thymus sipyleus ssp rosulans have become the dominant species on degraded pastures. We hypothesized that decreases in species richness and abundance are correlated with increasing prevalence of these two species. Therefore, our objectives were to determine whether there are patterns in examined vegetation; how dominant species contribute to these patterns; and how patterns differ between grazed and ungrazed vegetation. We determined that protection from grazing increased species richness. Grazing significantly changed composition through decreasing total plant, forb, grass and F. valesiaca covers, while substantially increasing T. sipyleus cover. Topography, soil and grazing appear to impact the dominance of plant communities where F. valesiaca and T. sipyleus prevail. These two dominant species had a significant effect in shaping vegetation patterns. Based on regression analysis, alterations in species richness with changes in cover of forbs and shrubs were evident, and spatial heterogeneity of F. valesiaca and T. sipyleus indicated unstable vegetative patterns in heavily grazed pastures and successional changes in protected pastures. Our study results identify F. valesiaca and T. sipyleus as indicator species of vegetation suppression in condition assessments of degraded steppe rangelands.     

Patterns of alien plant invasions in northwestern Patagonia, Argentina

Invasive plant species are a growing concern in many regions of the world, yet little information is available on the effects of habitat type and distance to urban settlements on the ability of alien plants to become established. We studied plant communities from the arid steppes to the Andean forest within two national parks and surroundings, in northwestern Patagonia, Argentina. Alien and native vascular plant species were sampled using 90 × 100 m² plots and analyzed in relation to both climatic and environmental variables and distance to urban centres. We also compared life-forms of alien and native species. Precipitation and distance to an urban centre were important determinants of alien species community richness and composition, and shrubland sites had significantly more alien species than forest or steppe sites. Alien flora (15% of the species) was composed of a higher proportion of annuals and biennials than native flora. Our results suggest that precipitation, distance to source population, and anthropogenic disturbance influence the invasion process in this region, together with the availability of open niches. This work stresses the importance of monitoring invasive species in natural reserves, and of considering habitat types as well as idiosyncratic characteristics of the non-natives for developing management strategies.     

Species diversity and its relation with soil factors under different site conditions in a desert-oasis ecotone

Vegetation and soil surveys were conducted under different site conditions in 2007–2011 to study species diversity using richness, evenness and diversity indices, in the middle portion of the Heihe River Basin. The relationship between species distribution and soil environmental factors was also studied by Canonical Correspondence Analysis (CCA). Results show that vegetation coverage and species diversity were the highest in the interdune lowland, and the lowest in the mobile dune. Results of the Hill’s index (diversity ordering) shows that species diversity is reduced along decreasing soil water content, and the order of species diversity was interdune lowland, flat slope, fixed dune, semifixed dune and mobile dune. The influence degree of soil factors on vegetation distribution was soil water content > pH > total K > organic matter > available N > total N > available K > total P > saline content > available P. Soil water content and pH were important factors significantly affecting spatial distribution difference of vegetation, the environmental explanation was 98%.     

Comparing biodiversity between protected savanna and adjacent non-protected farmland in the southern Kalahari

In this study we investigated the effect of different land use options (wildlife versus livestock) on species richness of plants and reptiles in the protected Kgalagadi Transfrontier Park (KTP) versus adjacent non-protected farmland within the same savanna habitat type (Aoub dune veld) in the southern Kalahari, South Africa. Our results show that both plant and reptile species richness as well as plant cover and reptile abundance was significantly higher in the protected KTP than in the non-protected farmland. The higher proportion of shrub but lower proportions of perennial grass cover, herb cover, and herb species richness in the farmland can be explained by higher stocking rates and the differences in feeding behaviour between native wild ungulates (e.g. Antidorcas marsupialis, Oryx gazella) and livestock (mainly sheep). The reptile’s prey availability and microhabitats (perennial grass tussocks and rodent burrows) for thermoregulation and protection against predators were significantly lower in the farmland. To conclude, our results clearly show that long term effects of different land use options (wildlife in protected KTP versus extensive livestock production in the non-protected farmland) even within the same habitat type have led to significant changes in vegetation composition, availability of microhabitat structures and in the reptile community.     

How special are Etendeka mesas? Flora and elevation gradients in an arid landscape in north-west Namibia

Seven mesas (i.e. flat-topped, isolated mountains) and the Grootberg mountain in arid north-west Namibia were investigated with regard to floristic relationships in relation to environmental gradients. Relationships between mesas and their surrounding, species richness and number of mesa specialists were used as measures to explore the influence of elevation on these floristic parameters. Also soil properties were investigated along these elevation gradients. The overall questions were designed to investigate the importance, i.e. ‘special status’, of these mesas in terms of contributing to species diversity and to elucidating ecological processes in this arid landscape.With regard to special floristic status, the tops of mesas supported different plant communities than their surrounding plains, while slopes indicated various levels of intermingling with plain vegetation. Differences between mesas and plains became more pronounced with increasing elevation. There were, however, no clear vegetation belts related to elevation. Plant species richness and number of mesa specialists showed a trend of increasing numbers with elevation, but these trends were statistically poorly supported, largely due to high variability between samples.Do soil gradients and elevation, as two important environmental variables, affect this ‘special’ status? Pronounced soil gradients were evident for many soil properties. These in combination with altitudinal effects of increased moisture and lower temperatures were believed to directly influence plant species composition and richness. The soil gradients may also indicate nutrient flow from the mesas to the surrounding lowlands, a process of ecological importance, particularly should degradation due to over grazing become a problem in the lowland areas.     

Land degradation and vegetation distribution in Chott El Beida wetland,Algeria

The aim of this study is to explore the environmental factors that determine plant community distribution in northeast Algeria. This paper provides a quantitative analysis of the vegetation–environment relationships for a study site in the Chott El Beida wetland, a RAMSAR site in Setif, Algeria. Sixty vegetation plots were sampled and analysed using TWINSPAN and Detrended Correspondence Analysis (DCA) in order to identify the principal vegetation communities and determine the environmental gradients associated with these. 127 species belonging to 41 families and 114 genera were recorded. Six of the recorded species were endemic representing 4.7% of the total species. The richest families were Compositae, Gramineae, Cruciferae and Chenopodiaceae. Therophytes and hemicryptophytes were the most frequent life forms. The Mediterranean floristic element is dominant and is represented by 39 species. The samples were classified into four main community types. The principal DCA axes represent gradients of soil salinity, moisture and anthropogenic pressure. The use of classification in combination with ordination techniques resulted in a good discrimination between plant communities and a greater understanding of controlling environmental factors. The methodology adopted can be employed for improving baseline information on plant community ecology and distribution in often critically endangered Mediterranean wetland areas.     

Soil water deficit and vegetation restoration in the refuse dumps of the Heidaigou open-pit coal mine, Inner Mongolia, China

The sustainability of ecosystem restoration of refuse dumps in open-pit coal mines depends on plant species selection, their configuration, and the optimal usage of water resources. This study is based on field experiments in the northern refuse dump of the Heidaigou open-pit coal mine in Inner Mongolia of China established in 1995. Eight plant configurations, including trees, shrubs, grasses, and their combinations, as well as the adjacent community of natural vegetation, were selected. The succession of the revegetated plants, soil water storage, the spatiotemporal distribution of plant water deficits degree and its compensation degree were also studied. Results indicated that the vegetation cover (shrubs and herbaceous cover), richness, abundance, soil nutrients (soil organic matter, N and P), and biological soil crust coverage on the soil surface are significantly influenced by the vegetation configurations. The average soil water storage values in the shrub+grass and grass communities throughout the growing season are 208.69 mm and 206.55 mm, which are the closest to that of in the natural vegetation community (215.87 mm). Plant water deficits degree in the grass and shrub+grass communities were the lowest, but the degrees of water deficit compensation in these configuration were larger than those of the other vegetation configurations. Differences in plant water deficit degree and water compensation among the different configurations were significant (P<0.05). Plant water deficit degrees were predominantly minimal on the surface, increased with increasing soil depth, and remained stable at 80 cm soil depth. The soil moisture compensation in the natural vegetation, shrub+grass, and grass communities changed at 10%, while that in other vegetation communities changed between 20% and 40%. Overall, we conclude that the shrub+grass and grass configuration modes are the optimal vegetation restoration models in terms of ecohydrology for future ecological engineering projects.     

Bird assemblages of arid Australia: Vegetation patterns have a greater effect than disturbance and resource pulses

Arid birds are known to be highly responsive to spatio-temporal changes in food and water availability, and it is thought that this ‘resource tracking’ will obscure predictable patterns of community structure. Here we examine this resource hypothesis by assessing assemblage structure of birds in relation to landscape-scale environmental variation in the Finke bioregion of arid inland Australia, during an exceptionally high and extended rainfall period. We surveyed 197 sites stratified according to land system, run-off/run-on elements and distance to water, and recorded 106 resident and nomadic species. Cluster analysis produced five assemblages, four of which could be readily linked to a specific habitat type. Constrained ordination (CCA) was carried out using 38 variables that measured environmental gradients, vegetation attributes, food and water availability, and disturbance level. Species patterns correlated most strongly with vegetation variables (woodland, chenopod, grassland, and % mulga cover), and % weed cover. By contrast resource variables (flowering, fruiting, and water proximity), introduced herbivores, and most structural variables were poor predictors of species presence. Thus, we showed that resource availability and grazing disturbance are not major drivers of Australian arid bird assemblage patterns. Instead, patterning relates more to the interaction between bird foraging behaviour and breeding requirements and vegetation assemblages.