Importance of low-flow and high-flow characteristics to restoration of riparian vegetation along rivers in arid south-western United States

1. Riparian vegetation in dry regions is influenced by low‐flow and high‐flow components of the surface and groundwater flow regimes. The duration of no‐flow periods in the surface stream controls vegetation structure along the low‐flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow‐regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low‐flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought‐tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient‐holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood‐dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood‐suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south‐western United States, some focus on re‐establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment.     

Relationships Between Plant Assemblages and Water Flow Across a Boreal Forest Landscape: A Comparison of Liverworts,Mosses, and Vascular Plants

The distribution of water across landscapes affects the diversity and composition of ecological communities, as demonstrated by studies on variation in vascular plant communities along river networks and in relation to groundwater. However, non-vascular plants have been neglected in this regard. Bryophytes are dominant components of boreal flora, performing many ecosystem functions and affecting ecosystem processes, but how their diversity and species composition vary across catchments is poorly known. We asked how terrestrial assemblages of mosses and liverworts respond to variation in (i) catchment size, going from upland-forest to riparian settings along increasingly large streams and (ii) groundwater discharge conditions. We compared the patterns found for liverworts and mosses to vascular plants in the same set of study plots. Species richness of vascular plants and mosses increased with catchment size, whereas liverworts peaked along streams of intermediate size. All three taxonomic groups responded to groundwater discharge in riparian zones by maintaining high species richness further from the stream channel. Groundwater discharge thus provided riparian-like habitat further away from the streams and also in upland-forest sites compared to the non-discharge counterparts. In addition, soil chemistry (C:N ratio, pH) and light availability were important predictors of vascular plant species richness. Mosses and liverworts responded to the availability of specific substrates (stones and topographic hollows), but were also affected by soil C:N. Overall, assemblages of mosses and vascular plants exhibited many similarities in how they responded to hydrological gradients, whereas the patterns of liverworts differed from the other two groups.     

陆地植物群落物种多样性的梯度变化特征

研究陆地植物落物种多样性随环境因子及群落演替梯度的变化特征是揭示生物多样性与生态因子相互关系的重要方面,根据近期国内外的文献,综述了这方面的研究进展。随纬度的降低,通常物咱多样性随中,随不分梯度的变化,物种多样性的变化有６种趋势;随海拔高的变化,物处多样性有５种模式;随土壤养分梯度的变化,表现出不同的规律;演替过程中物种多样生的变化趋势相似。关于植物群落物种多样性梯度格局的机制有多种假说,但仍需进     

Effects of stream restorations on riparian mesohabitats,vegetation and carabid beetles

We investigated the effects of hydromorphological restoration measures (mainly the removal of bank fixations) on riparian mesohabitats, vegetation and carabid beetles by comparing 24 restored to nearby non-restored floodplain sections in Germany. Mesohabitats were recorded along ten equally-spaced transects, plant communities and riparian plant and carabid beetle species along three transects per section. Based on 18 indices including habitat and species diversity, taxonomic diversity and functional indices we compared the frequency and magnitude of changes following restoration, both for the overall dataset and for each site individually. Riparian habitat diversity doubled in restored sections compared to non-restored sections. The numbers of vegetation units and plant and carabid beetle species richness also doubled in restored sections, whereas changes in Shannon diversity were most pronounced for mesohabitats and riparian plants. Taxonomic diversity of carabid beetles decreased in restored sections reflecting post restoration dominance of riparian Bembidion species. Stress-tolerant pioneers of plant and especially carabid species benefit strongly from the re-establishment of open sand and gravel bars, while hygrophilous species, which also include non-riparian species, did not respond to restoration. We conclude that restoring river hydromorphology has almost generally positive effects on riparian habitats and riparian biodiversity. Riparian biota are thus well-suited indicators for the effects of hydromorphological restoration.     

Spatial variation in leaf nutrient traits of dominant desert riparian plant species in an arid inland river basin of China

Understanding how patterns of leaf nutrient traits respond to groundwater depth is crucial for modeling the nutrient cycling of desert riparian ecosystems and forecasting the responses of ecosystems to global changes. In this study, we measured leaf nutrients along a transect across a groundwater depth gradient in the downstream Heihe River to explore the response of leaf nutrient traits to groundwater depth and soil properties. We found that leaf nutrient traits of dominant species showed different responses to groundwater depth gradient. Leaf C, leaf N, leaf P, and leaf K decreased significantly with groundwater depth, whereas patterns of leaf C/N and leaf N/P followed quadratic relationships with groundwater depth. Meanwhile, leaf C/P did not vary significantly along the groundwater depth gradient. Variations in leaf nutrient traits were associated with soil properties (e.g., soil bulk density, soil pH). Groundwater depth and soil pH jointly regulated the variation of leaf nutrient traits; however, groundwater depth explained the variation of leaf nutrient traits better than did soil pH. At the local scale in the typical desert riparian ecosystem, the dominant species was characterized by low leaf C, leaf N, and leaf P, but high leaf N/P and leaf C/P, indicating that desert riparian plants might be more limited by P than N in the growing season. Our observations will help to reveal specific adaptation patterns in relation to the groundwater depth gradient for dominant desert riparian species, provide insights into adaptive trends of leaf nutrient traits, and add information relevant to understanding the adaptive strategies of desert riparian forest vegetation to moisture gradients.     

河岸无脊椎动物多样性维持机制研究进展

河岸是河流与陆地之间重要的生态界面,生物多样性丰富,但受到人为活动的严重威胁。无脊椎动物在河岸生物多样性中占有重要地位,发挥着非常重要的生态功能,也是水生生态系统和陆地生态系统之间物质和能量联系的重要纽带。尽管已有很多学者对河岸无脊椎动物群落进行了研究,但缺乏对河岸无脊椎动物多样性维持机制的总结。本文结合洪水和干旱、营养物质、微生境多样性、河岸植被、微气候梯度、食物资源以及河流空间梯度等影响因素,初步讨论和归纳了河岸无脊椎动物多样性的维持机制。周期性洪水和干旱引发了无脊椎动物的繁殖和迁移等行为,增加了河岸无脊椎动物群落周转率,为无脊椎动物创造了理想的条件。充足的营养物质使河岸具有较高的初级生产力,支撑了较高的无脊椎动物多样性。较高的微生境多样性为无脊椎动物提供了多样的生态位空间,孕育了特殊的河岸无脊椎动物种类。复杂的河岸植物群落不但是河岸无脊椎动物的食物来源之一,也为河岸无脊椎动物提供了多样的生态位空间和重要的避难场所。微气候环境的空间分异提供了复杂多样的生境条件,为水生无脊椎动物和陆生无脊椎动物种类在河岸共存创造了条件。跨越界面的资源补给增加了河岸无脊椎动物的食物可利用率,为河岸无脊椎动物提供了特殊的食物来源。这些因素在空间上呈现出明显的纵向梯度和侧向梯度,从更大尺度上为河岸无脊椎动物的多样化提供了条件。因此,探讨河岸无脊椎动物多样性的维持机制对于河岸生物多样性保护以及河流生态系统综合管理具有重要的指导意义。     

Unnatural flooding alters the functional diversity of riparian vegetation of the Three Gorges Reservoir

1. The response of riparian vegetation to flow regulation has been a research focus for decades. Several studies have shed light on the effects of flow stabilisation on riparian woody species, but other life forms exposed to intensified inundation have been overlooked. Furthermore, studies from a functional perspective are scarce.
2. We evaluated the functional response of riparian vegetation along the shores of the Three Gorges Reservoir on the Yangtze River in China to unnaturally long annual flooding (>7 months) after the first year of filling. We aimed to answer the following: (1) can we derive well-defined flow-response guilds from the riparian zones of the Yangtze River? and (2) which plant traits and guilds are favoured or disfavoured by the unnaturally long flooding environment?
3. Woody and herbaceous species were inventoried in 12 reaches along the shorelines of the Three Gorges Reservoir and another 12 reaches along the free-flowing Yangtze River. We performed a cluster analysis to derive riparian guilds using abundance data (projective coverage) from 40 riparian plant species and 13 responsive traits. Structural composition and functional diversity of the unnaturally and naturally flooded riparian vegetation were compared.
4. Unnaturally long flooding substantially reduced species richness, but it did not change the riparian vegetation cover. This novel flooding reduced functional diversity, mostly owing to the loss of stress-tolerant woody species and competitive perennial herbs. However, competitive annual herbs and flood-tolerant riparian herbs, as the most abundant functional guilds, were favoured even under such long-term hypoxic conditions.
5. These guilds under regulation revealed a high functional resilience to prolonged flooding along the upstream reaches of the Yangtze River. Flooding tolerance and the capacity to synchronise germination and growth with short-exposure periods underlie the plant species changes. Our findings are useful for anticipating the effects of long-lasting inundation on riparian areas triggered by flow regulation or warmer climates. The functional perspective lends confidence that our conclusions can be generalised to other geographical regions despite not sharing the same species pool. Finally, the plant species that showed a high flooding tolerance should be considered for the restoration of riparian areas affected by the Three Gorges Reservoir.

     

Importance of scale,land‐use,and stream network properties for riparian plant communities along an urban gradient

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Effects of climate‐induced increases in summer drought on riparian plant species: a meta‐analysis

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The boundaries of river systems: the metazoan perspective

1. This overview of metazoans associated with the riparian/groundwater interface focuses on the fauna inhabiting substratum interstices within the stream bed and in alluvial aquifers beneath the floodplain. The objective is to integrate knowledge of habitat conditions and ecology of the interstitial fauna into a broad spatiotemporal perspective of lotic ecosystems. 2. Most aquatic metazoans of terrestrial ancestry, secondarily aquatic forms including insects and water mites (Hydracarina), are largely confined to surface waters (epigean), most of the time penetrating only the superficial interstices of the stream bed. 3. Primary aquatic metazoans include crustaceans and other groups whose entire evolutionary histories took place in water. Some species are epigean, whereas other members of the primary aquatic fauna are true subterranean forms (hypogean ) , residing deep within the stream bed and in alluvial aquifers some distance laterally from the channel. 4. The hypogean/epigean affinities of interstitial animals are reflected in repetitive gradients of species distribution patterns along vertical (depth within the stream bed), longitudinal (riffle/pool), and lateral (across the floodplain) spatial dimensions, as well as along recovery trajectories following floods (temporal dimension). 5. Fluvial dynamics and sediment characteristics interact to determine hydraulic conductivity, oxygen levels, pore space, particle size heterogeneity, organic content and other habitat conditions within the interstitial milieu. 6. Multidimensional environmental gradients occur at various scales across riparian/groundwater boundary zones. The spatiotemporal variability of hydrogeomorphological processes plays an important role in determining habitat heterogeneity, habitat stability, and connectivity between habitat patches, thereby structuring biodiversity patterns across the riverine landscape. 7. The erosive action of flooding maintains a diversity of hydrarch and riparian successional stages in alluvial floodplains. The patchy distribution patterns of interstitial communities at the floodplain scale reflect, in part, the spatial heterogeneity engendered by successional processes. 8. Interstitial metazoans engage in passive and active movements between surface waters and ground waters, between aquatic and riparian habitats, and between different habitat types within the lotic system. Some of these are extensive migrations that involve significant exchange of organic matter and energy between ecosystem compartments. 9. The generally high resilience of lotic ecosystems to disturbance is attributable, in part, to high spatiotemporal heterogeneity. Habitat patches less affected by a particular perturbation may serve as ’refugia ‘; from which survivors recolonize more severely affected areas. Mechanisms of refugium use may also occur within habitats, as, for example, through ontogenetic shifts in microhabitat use. Rigorous investigations of interstitial habitats as refugia should lead to a clearer understanding of the roles of disturbance and stochasticity in lotic ecosystems. 10. Development of realistic ’whole river ‘; food webs have been constrained by the exclusion of interstitial metazoans, which may in fact contribute the majority of energy flow in lotic ecosystems. A related problem is failure to include groundwater/riparian habitats as integral components of alluvial rivers. A conceptual model is presented that integrates groundwater and riparian systems into riverine food webs and that reflects the spatiotemporal complexity of the physical system and connectivity between different components. 11. Interstitial metazoans also serve as ’ecosystem engineers, ‘; by influencing the availability of resouces to other species and by modifying habitat conditions within the sediment. For example, by grazing on biofilm, interstitial animals may markedly stimulate bacterial growth rates and nutrient dynamics. 12. Although there has been a recent surge of interest in the role of interstitial animals in running waters, the knowledge gaps are vast. For example, basic environmental requirements of the majority of groundwater metazoans remain uninvestigated. Virtually nothing is known regarding the role of biotic interactions in structuring faunal distribution patterns across groundwater/riparian boundary zones. Interstitial metazoans may contribute significantly to the total productivity and energy flow of the biosphere, but such data are not available. Nor are sufficient data available to determine the contribution of groundwater animals to estimates of global biodiversity. 13. Effective ecosystem management must include groundwater/riparian ecotones and interstitial metazoans in monitoring and restoration efforts. Evidence suggests that a ’connected ‘; groundwater/riparian system provides natural pollution control, prevents clogging of sediment interstices and maintains high levels of habitat heterogeneity and successional stage diversity. River protection and restoration should maintain or re-establish at least a portion of the natural fluvial dynamics that sustains the ecological integrity of the entire riverine–floodplain–aquifer ecosystem. Keywords: groundwater/riparian ecotones, hyporheic habitat, epigean, hypogean, interstitial fauna, biodiversity, food webs     

Riparian Areas and Conservation of Herpetofauna in a Tropical Dry Forest in Western Mexico

Studies that assess the importance of riparian habitats in maintaining diversity of herpetofaunal assemblages in tropical dry forests are limited. We examined changes in abundance, diversity and composition of anuran, lizard and snake assemblages along stream edge–upslope gradients in conserved and disturbed areas of tropical dry forest on the Pacific coast of México. We sampled 659 plots in six watersheds over 2 yr. Two forest conditions (conserved and human disturbed, with three watersheds as replicates) were evaluated in the dry and rainy season. Within each watershed, plots were randomly located at three different distance categories from either stream edge: 0–10 m (near‐stream environment), 30–40 m (mid‐slope environment), and 50–60 m (upslope environment). Herpetofauna was surveyed by time‐constrained searches with a sampling effort of 1980 person‐hours. Eighteen anuran, 18 lizard and 23 snake species were recorded. Overall, abundance and diversity of lizards and snakes decreased from near‐stream to upslope areas in both forest conditions and seasons; while that of anurans followed this trend only for the conserved forest during the rainy season. Regardless of distance, abundance and diversity of anurans markedly decreased during the dry season, while that of snakes and lizards increased. Overall, our study shows that the importance of riparian areas for herpetofaunal conservation in dry tropical forests varies with forest condition and season.     

水分梯度下荒漠植物多样性与稳定性对土壤因子的响应

荒漠生态系统多样性的研究对维持荒漠区群落稳定性有着重要意义。以艾比湖流域荒漠植物群落为研究对象,基于野外样方调查数据及实验分析,探讨不同水分梯度下植物多样性与稳定性的变化规律及土壤因子对二者的影响。结果表明:(1)随土壤水分含量下降,Shannon-Wiener多样性指数(H)、Simpson多样性指数(D)、Pielou均匀度指数(J)、Margalef丰富度指数(R)和种群密度稳定性(ICV)指数均呈下降趋势,且当土壤含水量低于4.65%时,荒漠植物多样性与群落稳定性总体显著降低(P<0.05);(2)不同水分梯度下影响艾比湖流域植物多样性的土壤因子具有差异性,高水梯度为硝态氮与有机质,中水梯度下影响植物多样性的因子为pH,低水梯度为全氮和有机质;(3)仅在环境适宜的情况下,土壤因子(土壤含盐量与有机质)才能对群落稳定性产生显著影响(P<0.01);(4)三种梯度下,物种多样性均对群落稳定性有显著性影响(P<0.001),植物多样性与群落稳定性存在正相关关系。     

塔里木荒漠河岸林物种多样性沿地下水埋深梯度的分布格局

探讨荒漠河岸林土壤水分、物种多样性的空间变异性及其相互关系,可为干旱区天然林保护、可持续经营和生态恢复提供科学依据。以塔里木荒漠河岸林为研究对象,基于野外样带调查和采样测定,系统分析了地下水埋深（GWD）梯度下林地土壤水分与物种多样性的空间变异及其权衡关系。结果表明：随GWD增加和土壤水分减少,荒漠河岸林群落物种数减少、结构简化、群落发生退化,退化顺序为浅根系的中生草本植物和灌木,最后留存的是抗旱性较强的乔灌木或灌木;同时土壤水分和物种丰富度、物种多样性指数均呈显著的线性递减趋势,而物种均匀度指数降幅较小。GWD与土壤水分、物种多样性之间均呈极显著的相关（P<0.01）,土壤水分与物种多样性的相对收益随GWD增加而逐渐降低,表明GWD是控制荒漠河岸林土壤水分和物种多样性空间变异的关键因素。荒漠河岸林土壤水分与物种多样性权衡关系的转折点为GWD 4.5m左右,转折点以下（GWD<4.5m）二者沿GWD以相同速率变化,呈协同关系;转折点以上（GWD>4.5m）土壤水分与物种多样性的权衡明显增大,土壤水分相对收益剧降,即维持当前相应的物种多样性以消耗土壤水分为代价,系统通过反馈调节使物种多样性降低。综上表明,维持塔里木荒漠河岸林物种多样性和生态系统功能的合理GWD在4.5m左右,这为塔里木河流域荒漠河岸林保育与生态输水工程实施提供科学依据。     

刈割和施肥对高寒草甸物种多样性和功能多样性时间动态及其关系的影响

强烈扰动和环境胁迫对植物群落的物种多样性(SD)和功能多样性(FD)有重要影响, 但SD和FD随时间的变化模式及其关系至今少有研究。该研究通过对高寒矮生嵩草(Kobresia humilis)草甸为期7年(2007-2013年)的刈割(3个水平: 不刈割、留茬3 cm和留茬1 cm)和施肥(2个水平: 施肥和不施肥)控制实验探讨了SD和FD随时间的变化模式及其关系。研究结果显示: (1)刈割显著增加了SD和FD, 施肥处理则降低了SD, 对FD增加仅有微弱影响; (2)各处理群落的SD随着时间而下降, FD则随时间增加; (3)随着刈割强度的增加, SD(x)-FD(y)关系由正线性相关变为无相关, 斜率大小为slope_l ≥ slope_m > slope_h (下标l、m和h分别表示轻度、中度和重度扰动强度), 施肥并不会改变此关系形式和斜率; (4)刈割与施肥对SD和FD的互作效应都不显著, 且不施肥群落SD(x)-FD(y)关系的斜率也为slope_l ≥ slope_m > slope_h。上述结果说明, 刈割并不一定导致植物功能性状的趋同构建, 也能引发趋异构建, 而施肥引起的强烈种间竞争也并未显著增强趋异构建过程, 这与植物群落构建理论的预测不完全一致。与施肥相比, 刈割扰动是决定群落中SD-FD时间关系形式的主要因素, 并决定着SD-FD关系斜率的变化。     

基于氢氧稳定同位素的黄河兰州段河岸植物水分来源

多枝柽柳和旱柳是北方地区河岸生态修复的良好树种,具有护河防洪、调节区域气候的作用和营造河岸地带植被景观的功能。本研究选取黄河兰州段沿岸2处样点,采集了多枝柽柳和旱柳木质部以及各潜在水源的样品,利用氧同位素直接对比法、贝叶斯混合模型MixSIAR和相似性比例指数(PS指数),分析了多枝柽柳和旱柳对各潜在水源的利用率以及两者之间的水分利用关系。结果表明:在整个生长季,浅层土壤水(0～30 cm)是多枝柽柳和旱柳的主要水分来源,利用率分别为28.3%和24.4%,多枝柽柳对河水的利用率最小(16.6%),旱柳对地下水的利用率最小(17.9%);在土壤含水量较低的月份,植物会增加对河水和地下水的利用比例,样点S₁和S₂的PS指数分别为91.0%和87.7%,两个样点均在5月的PS指数最大,不同月份的水分利用关系存在一定的差异;处于河漫滩这一特殊地理位置,多枝柽柳和旱柳对各潜在水源的利用比较平均,最大程度地获取各潜在水源的水分,是一种最优的吸水模式。本研究可为开展黄河兰州段河岸休闲旅游活动和黄河流域生态环境保护中植物水分管理提供一定的理论基础。     

Fluvially-deposited large wood and riparian plant diversity

Out-of-channel wood jams centred by fluvially-deposited large wood represent an important habitat for riparian plant species along large rivers dominated by exposed riverine sediments. Such wood jams often display distinct physical features associated with the jams, such as areas of scour immediately upstream, plumes of fine sediment downstream and abundant organic material deposited throughout the jam. This paper examines the relationship between physical characteristics of young wood jams (1–3 years since deposition) and riparian plant diversity along the braided River Tagliamento in Northeast Italy. Species richness of riparian plants was significantly positively correlated to the depth of scour features and amount of fine sediment around the wood jams, which facilitate improved access to the water table and increase available water in the sediments, respectively. Species diversity was significantly positively correlated to scour pool depth only. Scour depth was in turn influenced by wood jam size, indicating that larger jams may indirectly increase riparian plant diversity. Management and restoration of riparian zones containing exposed riverine sediments should allow for the formation of wood jams and their associated features where possible, in order to potentially increase localised biodiversity.     

Scaling hierarchy of factors controlling riparian vegetation patterns of the Fynbos Biome at the Western Cape,South Africa

Question: How can vegetation gradients be described in riparian zones located in a species‐rich mountain range and how do these gradients explain the variation found in the vegetation? Location: Hottentots Holland Mountains, Western Cape, South Africa. Methods: Three gradients (geographic, longitudinal, lateral) were defined to describe the complex vegetation patterns found here. The gradients are related as follows: (1) the geographic gradient: related to the climatic and topographical changes across the entire mountain range; (2) the longitudinal gradient related to the changes along the different river reaches; (3) the lateral gradient related to the processes along the profile of the riverbed. These three gradients operated on three different hierarchical levels. Partial Canonical Correspondence Analysis (pCCA) was used to determine the amount of variation that is explained on each of the hierarchical levels. Results: The geographical gradient explained the highest fraction (more than 50%) of the total variation explained. This can be ascribed to the high species turnover across landscapes in the Fynbos Biome; this is most likely an outcome that is specific for this region. The second most important gradient was the lateral gradient, which reflects stream power and inundation frequencies of the river. This gradient is represented by ca. 48% of the explained variation and this gradient explains the major disturbances occurring in a riverine ecosystem. The longitudinal gradient was the least important of the gradients and shows overlap with the geographical gradient. Conclusions: In the species‐rich environment of the Fynbos Biome geographical factors do not only account for variation in zonal vegetation but also for variation within azonal vegetation, like riparian corridors.     

新疆塔里木河下游荒漠河岸(林)植被合理生态水位

 该文依据塔里木河下游地下水位多年监测资料, 将地下水位按不同埋深划分为0~2、2~4、4~6、6~8、8~10和>10 m 6个梯度, 并设置植 被调查样方进行连续监测, 以分析地下水位变化对植物物种多样性与种群生态位的影响。研究结果表明: 在地下水位2~4 m时, 物种多样性最高 , 其次为4~6 m, 再次为0~2 m; 当地下水位在6 m以下时, 物种多样性锐减, Hill多样性指数曲线变化趋势趋于平直化。荒漠河岸(林)植被主要 植物种群生态位随着地下水位的逐步下降而扩展, 并在地下水位4~6 m处达到最宽; 尔后, 生态位又显著变窄; 地下水位4~6 m时, 种群间生态 位重叠最不显著, 物种数较为丰富。因此, 该文分析得出结论: 塔里木河下游植被恢复的地下水位应确保达到6 m以上, 大部分地区地下水位应 维持在4~6 m, 而部分河道附近地区地下水位争取达到2~4 m。     

基于盐分梯度的黑河中游湿地植物多样性及其与土壤因子的关系

湿地植物多样性的研究对维持湿地生态系统完整性和稳定性有着重要意义。以黑河中游湿地为研究对象,基于野外采样数据和不同盐分梯度植物群落多样性指数,重点分析不同盐分梯度植物多样性变化及其与土壤因子关系。结果表明:黑河中游湿地植物组成比较丰富,共出现植物30科71属102种;随土壤盐分梯度增加,植物群落组成发生显著变化,Margalef丰富度指数(R)和Shannon-Weiner多样性指数(H)均减小,说明研究区植物多样性随盐分增加而减少;不同盐分梯度影响植物多样性的土壤因子存在差异,低盐梯度是pH、速效钾和全氮,中盐梯度是pH、速效磷和速效钾,高盐梯度是有机质、全磷、速效钾和速效氮。该研究结果对于认识不同盐分梯度下影响植物多样性的主要土壤因子具有重要意义,同时对黑河中游湿地植物多样性的有效管理和维持具有一定的参考价值。     

南四湖沉水植物物种多样性和功能多样性对水深梯度的响应

从物种多样性和功能多样性探讨沉水植物群落对水深的响应可深刻揭示水深对群落构建的影响机制。以南四湖不同水深沉水植物群落为研究对象,对比分析了群落的9个加权功能性状（株高、茎分支数、茎节数、茎直径、根长、根围直径、生物量分配比、比叶面积、植物体磷含量）、5个物种多样性指数（Berger-Parker生态优势度指数、Margalef丰富度指数、Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数）和5个功能多样性指数（功能丰富度FRic指数、功能均匀度FEve指数、功能离散度FDiv指数、功能分散度FDis指数和二次熵Rao指数）以及物种多样性和功能多样性关系对水深的响应规律。研究结果表明：（1）水深可显著改变群落株高、根长、根围直径、比叶面积、生物量分配比和植物体磷含量6个加权功能性状;群落茎分支数、茎节数和茎直径3个加权功能性状对水深变化无显著响应;（2）水深可显著影响群落物种多样性和功能多样性,中等水深处沉水植物群落具有较高的Margalef丰富度指数、Shannon-Wiener多样性指数、Berger-Parker生态优势度指数、Pielou均匀度指数以及功能丰富度FRic指数、功能均匀度FEve指数、功能离散度FDis指数、二次熵Rao指数;（3）水深可改变5个物种多样性指数与功能丰富度FRic指数、功能均匀度FEve指数、功能离散度FDiv指数3个功能多样性指数间的相关关系,但对5个物种多样性指数与功能离散度FDis指数、二次熵Rao指数2个功能多样性指数间的相关关系无显著影响。研究结论为：群落不同测度的物种多样性和功能多样性指数及其相关关系对水深变化的响应迥异,在探讨水深对沉水植物群落构建的影响机制时应从多个方面综合考量。