Riparian vegetation‐environment relationships: complimentarity of gradients versus patch hierarchy approaches

Abstract. Two prominent conceptual frameworks, environmental gradients and patch hierarchies, are used in combination to describe vegetation patterns along a riparian corridor in a semi‐arid South African system. We adopt both approaches, since riparian corridors are characterized by both strong environmental gradients above, away from and along the river, as well as a mosaic of patches in the geomorphology at multiple hierarchical scales. Constrained and unconstrained ordinations were used to determine the variability in vegetation pattern accounted for by the gradient and the geomorphic patch hierarchy data sets. The gradient data set consisted of vertical, lateral and longitudinal dimensions of the macro‐channel, while the patch hierarchy data set consisted of substratum type, morphological unit and channel type. Elevation up the macro‐channel bank, of the gradient data set, explained the main variation in vegetation pattern, and alluded to overriding processes of flooding frequency and water availability as determinants of vegetation pattern. Along the fluvially dynamic macro‐channel floor (lower elevation range), patchiness at the scale of the morphological unit best explained vegetation pattern. This relationship with morphological units suggests that the formation of well developed alluvial bars, and the degree of bedrock influence are important processes. The nested hierarchical framework used provided a good basis for identifying scale specific pattern in a relational manner. In systems characterized by strong environmental gradients as well as a patch mosaic at different spatial and temporal scales, the combined use of both perspectives to develop a fuller understanding of vegetation pattern is imperative and is encouraged.     

Associations of Phlebotomus orientalis and other sandflies with vegetation types in the eastern Sudan focus of kala-azar

Abundances of Phlebotomus orientalis, P. papatasi (Diptera: Psychodidae) and other sandflies were investigated in relation to different types of vegetation associated with endemic foci of visceral leishmaniasis (kala-azar) in eastern Sudan. Sandfly collection sites were in Umsalala Village (Galabat Province) and Dinder National Park (Dinder Province). Sandfly species found in the area were P. orientalis, P. papatasi, Sergentomyia africana, S. antennata, S. clydei, S. schwetzi and S. squamipleuris. Among the types of trees in the Dinder area, P. orientalis was more abundant in forests dominated by Acacia seyal than where Combretum kordofanum, Balanites aegyptiaca, Hyphaena thaibaica or Ziziphus spinachristi were the dominant trees. At Umsalala, P. papatasi was more abundant in the village than at any site with dense vegetation, but P. orientalis was uncommon. Sergentomyia spp. were distributed fairly evenly amongst most types of vegetation investigated at both localities. The ecological distribution of sandflies and epidemiology of kala-azar in Sudan are discussed with emphasis on the association of P. orientalis with A. seyal woodlands.     

Spatial relationships in a dendritic network: the herpetofaunal metacommunity of the Mattole River catchment of northwest California

We investigated the aquatic and riparian herpetofauna in a 789 km² river catchment in northwest California to examine competing theories of biotic community structuring in catchment stream networks. Research in fluvial geomorphology has resulted in multi‐scale models of dynamic processes that cyclically create, maintain, and destroy environments in stream networks of mountain catchments. These models have been applied to understanding distributions of invertebrates, algae, fishes and their habitats across entire basin networks, but similar approaches with herpetofauna are rare. We examined multi‐scale spatial patterns of multiple species as they related to variation in channel types, channel settings, and within‐channel attributes that result from these processes. From 83 reaches distributed randomly throughout the watershed, we distinguished four channel types: 1) high gradient with cascade structure; 2) 2–4% gradient with step‐pool structure controlled by moderately steep valleys; 3) slightly entrenched, lower gradient, plane‐bed structure; and 4) low gradient, shallow, unconfined, multiple or migrating pool/riffle channels in broad alluvial valleys. The composition of herpetofauna differed in five of six pair‐wise comparisons among these channel types, indicating a minimum of three distinct mesoscale assemblages. We used non‐parametric multiple regression (NPMR) to examine relationships at multiple spatial scales. NPMR revealed species‐specific associations with channel settings and within‐channel environments among species sharing the same sets of channel types. Morphological adaptations, biophysical limits and natural histories of each species best explained their associations with distinct sets of attributes surrounding and within channel types. While each set of species has similarly adapted to fluvial and geomorphic disturbance processes structuring channels at the mesoscale, species within each set have adapted to a unique set of attributes that are best discerned when their spatial relationships are examined across multiple spatial scales. We evaluated the various spatial patterns against hypotheses of stream community organization and metacommunity perspectives.     

Composition of Woody Species in a Dynamicforest–woodland–savannah Mosaic in Uganda: Implications for Conservation and Management

Forest–woodland–savannah mosaics are a common feature in the East African landscape. For the conservation of the woody species that occur in such landscapes, the species patterns and the factors that maintain it need to be understood. We studied the woody species distribution in a forest–woodland–savannah mosaic in Budongo Forest Reserve, Uganda. The existing vegetation gradients were analyzed using data from a total of 591 plots of 400 or 500 m² each. Remotely sensed data was used to explore current vegetation cover and the gradients there in for the whole area. A clear species gradient exists in the study area ranging from forest, where there is least disturbance, to wooded grassland, where frequent fire disturbance occurs. Most species are not limited to a specific part of the gradient although many show a maximum abundance at some point along the gradient. Fire and accessibility to the protected area were closely related to variation in species composition along the ordination axis with species like Cynometra alexandri and Uvariopsis congensis occurring at one end of the gradient and Combretum guenzi and Lonchocarpus laxiflorus at the other. The vegetation cover classes identified in the area differed in diversity, density and, especially, basal area. All vegetation cover classes, except open woodland, had indicator species. Diospyros abyssinica, Uvariopsis congensis, Holoptelea grandis and all Celtis species were the indicator species for the forest class, Terminalia velutina and Albizia grandbracteata for closed woodland, Grewia mollis and Combretum mole for very open woodland and Lonchocarpus laxiflorus, Grewia bicolor and Combretum guenzi for the wooded grassland class. Eleven of the species occurred in all cover classes and most of the species that occurred in more than one vegetation cover class showed peak abundance in a specific cover class. Species composition in the study area changes gradually from forest to savannah. Along the gradient, the cover classes are distinguishable in terms of species composition and vegetation structure. These classes are, however, interrelated in species composition. For conservation of the full range of the species within this East African landscape, the mosaic has to be managed as an integrated whole. Burning should be varied over the area with the forest not being burnt at all and the wooded grassland burnt regularly. The different vegetation types that occur between these two extremes should be maintained using a varied fire regime.     

黄河三角洲湿地蒸散量与典型植被的生态需水量

蒸散量（ET）是黄河三角洲湿地水资源的主要消耗项,包括植被蒸腾、水面蒸发以及裸土蒸发等。植被生态需水是为了保证植被生态系统能够健康维持并确保其生态服务功能得到正常发挥而必须消耗的一部分水量。准确地估算湿地蒸散量、研究植被生态需水量对于保护湿地生态环境是十分必要的。应用MODIS的地表反射率、地表温度数据与常规气象数据以及土地利用/覆盖图,利用蒸散量的遥感估算模型SEBS模型估算了晴天条件下的黄河三角洲湿地日蒸散量,采用HANTS算法插补了非晴天条件下的日蒸散量,从而得到2001～2005年的该湿地年蒸散量的时间序列,并对蒸散量进行验证和分析。结合该地区典型植被生态需水量与植被蒸散耗水量,估算了2001～2005年的生态补水量。结果表明：与实测值相比,遥感估算月蒸散量的均方差RMSD为16.4mm,平均绝对百分比误差MAPD是11.9%,两者基本一致。黄河三角洲湿地的蒸散量在空间分布上以水体及周围地区、滨海滩涂、黄河故道以及黄河两岸沼泽湿地等的蒸散量较高,居民地蒸散量较低。蒸散量的年际变化不大,季节变化呈单峰型,以5、6、7月份蒸散量最大,月蒸散量在110～120mm之间。2001～2005年期间,每年至少有40%面积的芦苇沼泽和60%面积的芦苇草甸水分供应不足,植被的正常生长受到影响,尤其2002年较为严重,2004年以后情况有所改善。2002年芦苇的生态补水量最大,在9.9×10^7～3.19×108m^3之间,而2004年的生态补水量最小,在3.0×10^7～2.39×108m^3之间。     

喀斯特峰丛洼地生态系统服务空间权衡度及其分异特征

我国西南喀斯特峰丛洼地区脆弱的生态环境与剧烈的人类活动导致石漠化现象以及生态功能退化,制约了区域生态-福祉耦合效益的提升。首先从数值变化与空间变异综合的角度,构建了融合均方根偏差法与地理探测器的生态系统服务空间权衡度指标,进而围绕喀斯特水源涵养-土壤侵蚀关系以及植被固碳-土壤侵蚀关系,在不同环境因子梯度下和地貌形态类型区内开展生态系统服务空间权衡度计算及其分异特征研究。环境因子梯度分析表明,由于植被显著的保持水土能力,水源涵养与土壤侵蚀之间的空间权衡度随植被覆盖度的增大而逐渐减小;地形因子对地表水土过程与植被功能影响深刻,植被固碳和土壤侵蚀之间的空间权衡度随海拔和坡度的升高而逐渐增大,1000 m以上中海拔以及陡坡地区的空间权衡度是低海拔与缓坡地区的4-6倍。地貌形态类型区的统计结果显示,地貌特征对生态系统服务之间的空间权衡关系具有宏观控制作用,植被固碳-土壤侵蚀之间的空间权衡度随地形起伏度的升高而逐渐增大,具体为：中海拔平原 < 中海拔台地 < 中海拔丘陵 < 小起伏中山 < 中起伏中山,水源涵养与土壤侵蚀之间则成相反趋势。因此,今后在以生态系统服务协同提升为目标的喀斯特石漠化治理工作中,应强调环境因子作用程度的空间差异以及地貌形态特征的宏观控制作用。     

The relation between geomorphology and forest community types of the Haut-Saint-Laurent,Quebec

The highly disturbed community types of the Haut-Saint-Laurent in southern Quebec were classified using an hierarchic approach with three levels: geomorphology, pedology and vegetation. Considered as distinct entities were, on the one hand, the herbaceous and shrub species that made up ecological groups as defined by Meilleur et al. (1992), and, on the other hand, individual tree species. Great importance was given to geomorphological variables because they are one of the most stable ecological factors of the region. We identified 47 community types from 452 sites sampled, based on a TWINSPAN analysis of the vegetation data. Binary Discriminant Analysis (BDA) showed the importance of disturbance on community composition, especially for sites included in the forest mosaic. Other important abiotic parameters included morphogenic features, topography and drainage. The BDA showed that 24 community types were found to be significantly associated with at least one morphogenic feature. The results indicate that the Beech-Hemlock association is a more stable state for mesic sites than the often cited Sugar Maple with Hickory. On glacial deposits, the presence of Thuja occidentalis is significantly associated with grazing practices. The other 23 community types are not significantly associated with any morphogenic features. On one hand, these types tend to be ubiquitous on different deposits with the same drainage class and reveal that their composition was altered through disturbances. On the other hand, some community types are more associated with microclimates as is the case of Sugar Maple with Striped Maple, or with their ecological amplitude limits as is the case of Sugar Maple with Ironwood and Aspen or Sugar Maple with Red Maple and Black Ash. A classification of the stands, given the high number of disturbed communities within the territory, appears difficult to use as a basis for ecological units.     

Learning from the past: palaeohydrology and palaeoecology

Attempts to increase European biodiversity by restoring rivers and floodplains are based on inadequate data on natural systems. This is particularly the case for NW European rivers because all catchments have been impacted by agriculture and river engineering. If river restoration is to have an ecological, as opposed to `cosmetic' design basis then baseline models are required. However, this poses three questions; (a) what is the natural river‐floodplain state, (b) how can it be defined and modelled and (c) can this state be recreated today? The first two questions can only be addressed by using palaeohydrological and palaeoecological data. A second and equally vital consideration is the stability/instability of any restored system to change in external forcing factors (e.g. climate) and in this context it may not be realistic to expect baseline models to provide equilibrium solutions but instead to define process‐form domains. Over the last two decades evidence has accumulated that the natural state of lowland rivers in much of NW Europe was multi rather than single thread‐braided, anastomosing or anabranching. Until recently our knowledge of floodplain palaeoecology was generally derived from pollen diagrams, which have source‐area of problems and lack of taxonomic specificity. The precision and breadth of palaeoecological reconstruction (including richness and structure) has been greatly increased by the use of multiple palaeo‐indicators including macrofossils, diatoms and beetles. The dynamics of small to medium sized, low‐energy, predeforestation floodplains were dominated by disturbance (windthrow, beavers, etc.) and large woody debris. In order to compare the hydrogeomorphological basis of floodplain ecology, both temporally and spatially, a simple index of fluvial complexity is presented. Palaeoecological and geomorphological investigations have the potential to provide in‐depth models of the natural range of channel conditions and sensitivity to external change that can be used to provide a scientific basis for floodplain restoration. There is also the possibility that floodplain‐channel restoration may be a valuable tool in the mitigation of future geomorphological change forced by climatic instability.     

Dynamic patch mosaics and channel movement in an unconfined river valley of the Olympic Mountains

1. River valleys resemble dynamic mosaics, composed of patches which are natural, transient features of the land surface produced by the joint action of a river and successional processes over years to centuries. They simultaneously regulate and reflect the distribution of stream energy and exchanges of sediment, wood and particulate organic matter between riparian and aquatic environments. 2. We determined the structure, composition, dynamics and origin of seven patch types at the reach scale in the Queets River valley in the temperate coastal forests of the Olympic Mountains, Washington (U.S.A.). Patch types included: (1) primary and (2) secondary channels; (3) pioneer bars; (4) developing and (5) established floodplains; and (6) transitional and (7) mature fluvial terraces. 3. Lateral channel movements strongly shape patch distribution, structure and dynamics. The primary channel moved laterally 13 m year^?1, on average from 1939 to 2002, but was highly variable among locations and over time. Mean lateral movement rates ranged from 1 to 59 m year^?1 and moving averages (2 km) ranged from 3 to 28 m year^?1 throughout the valley. 4. Each patch type exhibited characteristic vegetation, soil and accumulations of large wood. Pioneer bars contained peak stem density (69 778 stems ha^?1) and volume of large wood (289 m³ ha^?1). Mature fluvial terraces contained the highest mean stem (1739 m³ ha^?1) and canopy volume (158 587 m³ ha^?1). These patches also contained the most soil nitrogen (537 kg ha^?1) and carbon (5972 kg ha^?1). 5. Patch half‐life (the time required for half of the existing patches to be eroded) ranged from 21 to 401 years among forested patch types. Erosion rates were highest in pioneer bars (2.3% year^?1) and developing floodplains (3.3% year^?1), compared with only 0.17% year^?1 in mature fluvial terraces. New forests formed continually, as pioneering vegetation colonised 50% of the channel system within 18 years, often unsuccessfully. 6. In the Queets River, the structure, composition, and dynamics of the patchy riparian forest depends on the interplay between channel movements and biophysical feedbacks between large wood, living vegetation and geomorphic processes. The cycle of patch development perpetuates a shifting‐mosaic of habitats within the river valley capable of supporting diverse biotic assemblages.     

An ecoregional classification for the state of Roraima, Brazil: the importance of landscape in malaria biology

Understanding the different background landscapes in which malaria transmission occurs is fundamental to understanding malaria epidemiology and to designing effective local malaria control programs. Geology, geomorphology, vegetation, climate, land use, and anopheline distribution were used as a basis for an ecological classification of the state of Roraima, Brazil, in the northern Amazon Basin, focused on the natural history of malaria and transmission. We used unsupervised maximum likelihood classification, principal components analysis, and weighted overlay with equal contribution analyses to fine-scale thematic maps that resulted in clustered regions. We used ecological niche modeling techniques to develop a fine-scale picture of malaria vector distributions in the state. Eight ecoregions were identified and malaria-related aspects are discussed based on this classification, including 5 types of dense tropical rain forest and 3 types of savannah. Ecoregions formed by dense tropical rain forest were named as montane (ecoregion I), submontane (II), plateau (III), lowland (IV), and alluvial (V). Ecoregions formed by savannah were divided into steppe (VI, campos de Roraima), savannah (VII, cerrado), and wetland (VIII, campinarana). Such ecoregional mappings are important tools in integrated malaria control programs that aim to identify specific characteristics of malaria transmission, classify transmission risk, and define priority areas and appropriate interventions. For some areas, extension of these approaches to still-finer resolutions will provide an improved picture of malaria transmission patterns.     

Spatial variability of the soil seed bank in a heterogeneous ephemeral wetland system in semi-arid Australia

Soil seed banks are an important component of plant community diversity in ephemeral wetlands, allowing many species to persist through unpredictable periods of flood and drought. Spatial variation of extant vegetation in such habitats commonly reflects patterns of flood history and often varies predictably between broadly differing hydro-geomorphic habitat types. Here we investigate whether spatial variation of soil seed banks is similarly controlled by fluvial processes at this scale. Results are presented from a seedling emergence trial using samples collected from a range of habitat types, and at different scales within these, in the ephemeral Narran Lakes system in semi-arid Australia. Composition and structure of soil seed banks varied significantly between habitat types reflecting broad differences in flood frequency. As predicted, germinable seed abundance was found to be highest in intermediately flooded habitats. Variability in soil seed bank composition at a local scale was also found to be influenced by hydrology with greater spatial heterogeneity evident in the river channel as well as amongst the least frequently inundated riparian and floodplain habitats.     

Late Glacial and early Holocene environment in the middle Lahn river valley (Hessen,central-west Germany) and the local impact of early Mesolithic people—pollen and macrofossil evidence

The Late Glacial to early Holocene river valley landscape of the middle Lahntal in Hessen, central-west Germany, is reconstructed by means of pollen and macrofossil analyses. AMS ¹⁴C dating combined with pollen, macrofossil and geomorphological mapping provide a detailed chronology of the floodplain sediments of the river Lahn. Archaeological evidence for early Mesolithic settlements in the middle Lahntal is backed up by pollen and macrofossil evidence, which indicates an increase in light demanding plants, together with ones indicating nutrient-rich and disturbed environments and more macroscopic charcoal and charred pieces of pine. Different phases of human impact were dated; a first phase was dated at ca. 9,270 uncal b.p. and a second phase at ca. 9,120 uncal b.p. Comparison of the palynological data from different fluvial channel fills demonstrates that during this second phase, between ca. 9,120–8,700 uncal b.p., there were several cycles of woodland clearance. The outcome of combined archaeological, palynological and macrofossil data is discussed in terms of the impact of early Mesolithic people using fire on the vegetation during the early Holocene in the middle Lahntal.     

The impact on the Senjogahara ecosystem of extreme run-off events from the river Sakasagawa,Nikko National Park

Vegetational data from Senjogahara moor, Nikko National Park, Japan have been analysed using two contrasting but parallel multivariate approaches as a basis for future studies. The plant communities objectively defined using a divisive polythetic classificatory approach (TWINSPAN) have been successfully overlayed on an ordination of the same data using detrended correspondence analysis (DCA). The results reveal a vegetational mosaic reflecting differential levels of flood damage to the vegetation and its subsequent rates of recovery, in a space-time continuum. The results from the TWINSPAN classification show that 13 plant communities are present in the sample area and these correlate closely with complete absence, slight, or extremely heavy disturbance. The form of the disturbance as either channel erosion or alluvial depositional features is shown to also correspond quite closely with the vegetational types and is reflected in the ordination axes derived from DCA.     

Seasonal variations in the distribution and abundance of the tsetse fly,Glossina morsitans morsitans in eastern Zambia

The seasonal changes in the distribution of Glossina morsitans morsitans Westwood (Diptera: Glossinidae) and its main host, cattle, were examined in a cultivated area of the plateau of eastern Zambia. During four consecutive years, the tsetse and cattle populations were monitored along a fly-round transect traversing the two main vegetation types in the study area. These were miombo, a one-storied open woodland with the genera Brachystegia and Julbernardia dominant, and munga, a one- or two-storied woodland where the principal tree genera were Acacia, Combretum and Terminalia. Concurrently, a capture/mark/release/recapture (CMRR) exercise was conducted along two other transects also traversing both vegetation types. The index of apparent abundance of tsetse (IAA) in miombo increased at the beginning of the rainy season (November), reached its peak at the end of the rainy season (April) and was low during the cold season (May to late August), but especially the hot dry season (September to late October). The IAA of tsetse in munga showed a pattern that was the reverse of that in miombo. The seasonal changes in the IAA of tsetse in both vegetation types were in accordance with changes in the movement patterns of tsetse between the two vegetation type as observed using CMRR. The distribution and abundance of cattle along the transect also showed a seasonal trend. This was especially so in munga, during the first three years of observations, where cattle abundance increased gradually from June onwards, reached a maximum at the end of the hot dry season (October-November) and declined steeply at the start of the rainy season (November-December). In both vegetation types, the monthly mean IAA of tsetse was positively correlated with the abundance of cattle in the previous month. It is concluded that the distribution of tsetse in cultivated area of the eastern plateau of Zambia undergoes substantial seasonal changes, which can partly be attributed to changes in the distribution of cattle. The implications of these observations for the control of tsetse are discussed.     

The hydrogeomorphic approach to functional assessment of riparian wetlands: evaluating impacts and mitigation on river floodplains in the U.S.A.

1. The ’hydrogeomorphic‘ approach to functional assessment of wetlands (HGM) was developed as a synthetic mechanism for compensatory mitigation of wetlands lost or damaged by human activities. The HGM approach is based on: (a) classification of wetlands by geomorphic origin and hydrographic regime (b) assessment models that associate variables as indicators of function, and (c) comparison to reference wetlands that represent the range of conditions that may be expected in a particular region. In this paper, we apply HGM to riparian wetlands of alluvial rivers. 2. In the HGM classification, riverine wetlands are characterized by formative fluvial processes that occur mainly on flood plains. The dominant water sources are overbank flooding from the channel or subsurface hyporheic flows. Examples of riverine wetlands in the U.S.A. are: bottomland hardwood forests that typify the low gradient, fine texture substratum of the south-eastern coastal plain and the alluvial flood plains that typify the high gradient, coarse texture substratum of western montane rivers. 3. Assessment (logic) models for each of fourteen alluvial wetland functions are described. Each model is a composite of two to seven wetland variables that are independently scored in relation to a reference data set developed for alluvial rivers in the western U.S.A. Scores are summarized by a ’functional capacity index‘ (FCI), which is multiplied by the area of the project site to produce a dimensionless ’functional capacity unit‘ (FCU). When HGM is properly used, compensatory mitigation is based on the FCUs lost that must be returned to the riverine landscape under statutory authority. 4. The HGM approach also provides a framework for long-term monitoring of mitigation success or failure and, if failing, a focus on topical remediation. 5. We conclude that HGM is a robust and easy method for protecting riparian wetlands, which are critically important components of alluvial river landscapes.     

The relation between geomorphological features and species richness in the low flow channel of the Warche,downstream from the Bütgenbach dam (Ardennes,Belgium)

The Butgenbach dam, built on the Warche River (Ardennes, Belgium) in 1931 brought about two major changes: a significant reduction in the frequency and magnitude of the minimum discharges during the growing season (April–September) and the formation of numerous new geomorphological features (islets, pebble bars and rock outcrops) in the low flow channel. These changes have lead to an increase in the number of vascular plants downstream from the dam. Between 1994 and 1997, 74 species (bryophytes and phanerogams) were found downstream from the dam and 12 species were identified upstream. Downstream, most of the species are typical of damp semi-natural grasslands and of the banks of the Haute Ardennes—environments both characterised by oligotrophy. Euryoecious species (with a wide ecological range) and nitrophile species (that indicate pollution of the Warche from urban effluents and agricultural fertilisers) are also present. However, the distribution of plant species in the low flow channel is very heterogeneous. The number of species varies from one geomorphological unit to another. Species are more numerous on islets (54 species) than on rock outcrops (35 species) and gravel bars (28 species). On the islets, the number of species present varies in accordance with the degree of erosion. The islets that are most eroded and those that are least eroded display a poor range of flora. The degree of erosion influences the depth of silt, pebbles and litter on the islets. With regard to rock outcrops, the wealth of flora present depends on the form they take. Stratified outcrops are richer in flora than protruding outcrops. The number of plant species present on gravel bars depends on the frequency and the scale of remobilisation of pebbly material by floods. Following large floods, the vegetation cover and the number of different species decreases. But, if the sites remain stable, the number of species first of all increases, only then to decrease due to the proliferation of competitive species such as Phalaris arundinacea L. The ranges of species found on the different geomorphological features do not display a high degree of similarity. Canonical correlation analysis reveals that the density and the total number of species on geomorphological features are most strongly influenced by the proportion of fine particulates (<2 mm).     

海南昌江石碌铁矿尾矿库区植被调查

实验开展了3个不同年代的海南石碌铁尾矿库区植被调查研究,根据记录数据计算了各样地物种的重要值、物种多样性指数和均匀度等。结果表明,铁尾矿库区内植物种类总体上来看较为稀少,不同尾矿库区内植物群落组成成分差异比较大。已经停止使用20a的尾矿区（样地1）内,自然定居的植物仅有44种,其中禾本科植物种类较多,其次为豆科植物和莎草科植物,表明这3个科的植物种类较其它科植物更容易适应这种环境,特别是禾本科的水竹（Phragmites karka）、雀稗（Paspalum commersonii）和豆科的田菁（Sesbaniacannabina）表现出较强的适应能力;刚停止使用2a的尾矿库区（样地2）内,自然定居的植物有21种,其中硬骨草（Panicum repens）、斑茅（Saccharum arundinaceum）和芒（Miscanthussinensis）等禾本科植物为该样地的优势种群;正在使用的尾矿库区（样地3）内物种单一,只有水竹（Pyllosacys karka）、芒（Miscanthus sinensis）和田菁（Sesbaniacannabina）三种植物能在该恶劣的生境中顽强地生长和发育,表现出极强的适应能力。结果还表明了3个不同年代库区的植物群落的组成与结构存在明显的演替顺序差异,样地3单种优势明显,从样地3到样地1,这种优势依次减弱,物种多样性指数也依次增加,这表现出由较少先锋物种种类组成的简单群落向稳定复杂群落方向演替的趋势,反映了植物群落结构随演替时间的延长越来越趋向复杂化。在同一个尾矿库区内土壤的不同水分含量和理化性质会对植物的定居与群落的组成关系密切。     

Permanent swamp vegetation of the Upper Nile

This paper describes vegetation in the nothern Sudd area of the Sudan. A visit by boat was made in April 1978 along the White Nile from Malakal to Lake No; to the inflow regions of the Bahr el Jebel, the Bahr el Zeraf and to the Bahr el Ghazal. Only the vegetation along the fringe of the rivers was observed as plants were tall and dense and it was not possible to penetrate into the inner swamps.The outer edge of the vegetation was fringed by extensive mats of free-floating Eichhornia crassipes which was easily dislodged and formed floating islands to be carried downstream. The main rivers, excluding the Bahr el Ghazal, were too deep and turbid to support beds of submerged species but plants such as Ceratophyllum demersum could be found amongst floating plants. Vossia cuspidata usually produced a broad zone to the landward of Eichhornia. It dominated the shallow water with a floating raft of stems growing out from the shore over the water surface. Massive stands of Cyperus papyrus and/or Phragmites karka, over 5 metres tall, dominated the vegetation behind and sometimes excluded the Vossia zone. The papyrus could form dense, floating rafts of rhizomes at the water's edge, but Phragmites always remained firmly rooted to the bottom. Floating papyrus and Vossia would become detached from the main beds and drifted downstream with Eichhornia.Creepers were common amongst papyrus but less common amongst Phragmites where the vegetation was generally more dense. Large stands of Typa domingensis were observed behind the fringe vegetation.The vegetation of the Bahr el Ghazal, in marked contrast to the rest, was stunted, and reasons for this are suggested. Species diversity was greater and the less turbid waters allowed considerable development of floating-leaved and submerged species.Estimates of fresh weights and heights of dominant vegetation types were attained but methods were very laborious and alternative ways have been suggested. The fresh weight of Eichhornia from a one metre square quadrat in the White Nile was around 70 kg. The shoots of Phragmites weighed 18.5 kg and Cyperus papyrus, 11.0 kg m^–2.