Aquatic plant diversity in riverine wetlands: the role of connectivity

1. The hypothesis was tested that intermediate connectivity to a river results in propagule inputs to wetlands, whereas excessive connectivity impedes recruitment, and insufficient connectivity causes less competitive species to be eliminated, with no recruitment of new species. As a consequence, very low or very high nutrient levels should decrease species richness by selecting specialized species, whereas intermediate nutrient levels should favour the co-occurrence of species with contrasting nutrient requirements. 2. Among cut-off channels with high sinuosity and which are infrequently flooded by the river (low flood scouring), one example possesses high species richness because most species are saved from extinction by long-term isolation of the channel and cold groundwater supplies. Other channels are poorly supplied with groundwater and show a lower richness of species, because of low propagule inputs and low recruitment potential. 3. Cut-off channels with low sinuosity and which are flooded at intermediate frequencies were divided into three groups. The first group was species-poor, being closely connected to the river through downstream backflows which maintain nutrient-rich and turbid waters, in keeping with the hypothesis. The second group presents intermediate richness caused by: (i) lower river backflows; and (ii) floods that partly scour substrate and plants, and afford regeneration niches for transported propagules. The third group was species-poor because of excessive groundwater supplies, which probably acted as a limiting factor for species growth and recruitment. 4. The most frequently flooded channel shows the highest species richness, and occurrence of rare and fugitive species, because of floods which compensate competition by scouring sediments and plants, and afford regeneration niches for propagules. In this case, conservation of biodiversity necessitates propagule sources at the level of the river landscape.     

Flow variability maintains the structure and composition of in‐channel riparian vegetation

1. Naturally variable river flows are considered to be important for structuring riparian vegetation. However, while the importance of floods for the ecology of riparian vegetation is well recognised, much less is known about the importance of small fluctuations in river flows. 2. We investigated the effect of water supply diversion weirs on the riparian vegetation of upland streams. These weirs remove within‐channel fluctuations in flow but do not prevent large floods downstream. We surveyed the in‐channel and banktop vegetation of five streams, three of which were regulated by weirs and two of which acted as controls. 3. Unexpectedly, we observed greater species richness within the channel downstream of the weirs. This was because of increased numbers of exotic and terrestrial (‘dry’) plant species. Grass cover was also greater downstream of the weirs. There were no significant differences in the banktop vegetation between the upstream and downstream sites of the regulated streams. 4. Our results highlight the role of within‐channel flow variability in maintaining the composition of vegetation within the stream channel. We suggest that greater species richness does not necessarily indicate a less‐disturbed environment. Rather, a greater number of ‘dry’ species is indicative of the impacts of flow regulation. 5. Small fluctuations in river flows are probably necessary to protect the ecosystem structure and function of regulated streams. It is recommended that variable within‐channel flows be provided in regulated streams.     

Flood regime,dam regulation and fish in the Upper Paraná River: effects on assemblage attributes,reproduction and recruitment

The flood regime is the most important force determining seasonality in neotropical rivers. In the Upper Paran River floodplain, it is the primary factor influencing biological processes. The aim of this paper is to summarize information on the influence of dam-controlled floods on some fish assemblage attributes, reproduction and recruitment in the Upper Paran River floodplain, providing preliminary guidelines for dam operation upstream. Fish were collected in different habitats of the Upper Paran River floodplain (river, channels and lagoons) in the period from 1986 to 2001. The high water period in the Paran River usually occurs from November/December to April/May. Annual variation in the hydrograph affects species with distinct life history strategies differently, and influences the composition and structure of fish assemblages. Large floods were associated with higher species richness. Frequencies of individuals with ripe and partially spent gonads, which indicate spawning, were higher during the period of increasing water level. Dependence on floods seems to be lowest in sedentary species that develop parental care, and highest in large migratory species that spawn in the upper stretches of the basin and use flooded areas as nurseries. Migratory fishes were favored by annual floods that lasted more than 75 days, with longer floods yielding larger populations. The occurrence of high water levels at the beginning of summer is fundamental to the spawning success of migratory species. However, the flood may be less important for recruitment of juveniles if it is of short duration. Dam operation upstream (releasing more water during the raining season) has potential to promote greater floods with appropriate duration improving recruitment, particularly for migratory species.     

Dynamics of Nutrient Contents (Phosphorus,Nitrogen) in Water,Sediment and Plants After Restoration of Connectivity in Side‐Channels of the River Rhine

During the last century, canalization of the Rhine river led to disconnection of side‐arms, over‐sedimentation of these channels, loss of the fluvial dynamics, and aquatic vegetation change or disappearance. Recent restoration projects aim to reconnect disconnected arms to the main channel. The objective of this study was to assess the nutrient dynamics in restored channels during the vegetation colonization process. In spring, summer, and autumn 2009, the phosphorus and nitrogen contents were measured in water, sediment, and plants, sampled in six channels, two reference sites and four restored ones at different dates. Aquatic vegetation was monitored during the same period. Sites were mesotrophic related to the water nutrient concentrations. However, vegetation communities indicated a eutrophic level, as they were dominated by species like Elodea nuttallii, Myriophyllum spicatum, and Potamogeton perfoliatus. Sites were discriminated by P content and mineral nitrogen in the sediment. We showed an effect of species and season on the plant nutrient content, but there was no relationship between plant nutrient content and nutrients in water and sediment. A negative correlation between mean N plant content and the cover of each species was found. Vegetation characteristics (species richness and cover) and bioavailable phosphorus in the sediment were also correlated. In the restored side‐arms of the river Rhine, phosphorus‐rich sediment seems to be important in the recolonization dynamics, as it was linked to higher species richness, whereas nitrogen played a role in the colonization patterns as a growth limiting factor.     

亚高寒草甸植物群落种多度分布关系及相似性对氮磷添加的响应

以青藏高原亚高寒草甸为研究对象,采用随机区组设计,通过连续4a添加N、P,研究了不同施肥(N、P、N+P)处理下群落物种丰富度、种多度分布模式以及群落相似性的变化特征。结果显示:(1)N、N+P连续添加4年后,随N素添加水平的增加,草地植物群落物种丰富度逐渐降低(P0.001);种多度分布曲线的斜率逐渐增大;N+P添加处理对植物群落物种丰富度和种多度分布(SAD)曲线的影响较单独N添加处理更显著,如N15P15处理下群落物种丰富度的降幅最大,达对照群落的65.5%;(2)单一N或N+P处理中,不同添加量间的植被组成趋异,而相同添加量的植被组成趋同(stress level=0.152);(3)N、N+P添加引起刷状根的丛生型禾本科植物逐渐在植物群落中占据优势;(4)P素添加对群落物种丰富度、种多度分布曲线、群落相似性和不同生长型组成及比例的影响不显著;(5)植物生长型特征和N/P添加处理可解释56.97%植物群落的物种多度分布特征。这些结果表明:亚高寒草甸地区N添加引起植物群落组成的重新排序、优势种的变化、SAD曲线逐渐陡峭,群落的相似性增加;N富集时,添加P素会增加N素的利用效率,且群落结构受N、P供应水平的影响。     

Spatial and temporal patterns of species richness in a riparian landscape

Aim To test for control of vascular plant species richness in the riparian corridor by exploring three contrasting (although not mutually exclusive) hypotheses: (1) longitudinal patterns in riparian plant species richness are governed by local, river‐related processes independent of the regional species richness, (2) riparian plant species richness is controlled by dispersal along the river (longitudinal control), and (3) the variation in riparian plant species richness mirrors variation in regional richness (lateral control). Location The riparian zones of the free‐flowing Vindel River and its surrounding river valley, northern Sweden. Methods We used data from three surveys, undertaken at 10‐year intervals, of riparian reaches (200‐m stretches of riverbank) spanning the entire river. In addition, we surveyed species richness of vascular plants in the uplands adjacent to the river in 3.75‐km² large plots along the same regional gradient. We explored the relationship between riparian and upland flora, and various environmental variables. We also evaluated temporal variation in downstream patterns of the riparian flora. Results Our results suggest that local species richness in boreal rivers is mainly a result of local, river‐related processes and dispersal along the corridor. The strongest correlation between species richness and the environment was a negative one between species number and soil pH, but pH varied within a narrow range. We did not find evidence for a correlation between species richness on regional and local scales. We found that the local patterns of species richness for naturally occurring vascular plants were temporally variable, probably in response to large‐scale disturbance caused by extreme floods. Most previous studies have found a unimodal pattern of species richness with peaks in the middle reaches of a river. In contrast, on two of three occasions corresponding to major flooding events, we found that the distribution of species richness of naturally occurring vascular plants resembled that of regional diversity: a monotonic decrease from headwater to coast. We also found high floristic similarity between the riparian corridor and the surrounding landscape. Main conclusions These results suggest that local processes control patterns of riparian species richness, but that species composition is also highly dependent on the regional species pool. We argue that inter‐annual variation in flood disturbance is probably the most important factor producing temporal variability of longitudinal species richness patterns.     

From plant neighbourhood to landscape scales: how grazing modifies native and exotic plant species richness in grassland

The interactive effect of grazing and soil resources on plant species richness and coexistence has been predicted to vary across spatial scales. When resources are not limiting, grazing should reduce competitive effects and increase colonisation and richness at fine scales. However, at broad scales richness is predicted to decline due to loss of grazing intolerant species. We examined these hypotheses in grasslands of southern Australia that varied in resources and ungulate grazing intensity since farming commenced 170 years ago. Fine-scale species richness was slightly greater in more intensively grazed upper slope sites with high nutrients but low water supply compared to those that were moderately grazed, largely due to a greater abundance of exotic species. At broader scales, exotic species richness declined with increasing grazing intensity whether nutrients or water supply were low or high. Native species richness declined at all scales in response to increasing grazing intensity and greater resource supply. Grazing also reduced fine-scale heterogeneity in native species richness and although exotics were also characterised by greater heterogeneity at fine scales, grazing effects varied across scales. In these grasslands patterns of plant species richness did not match predictions at all scales and this is likely to be due to differing responses of native and exotic species and their relative abundance in the regional species pool. Over the past 170 years intolerant native species have been eliminated from areas that are continually and heavily grazed, whereas transient, light grazing increases richness of both exotics and natives. The results support the observation that the processes and scales at which they operate differ between coevolved ungulate—grassland systems and those in transition due to recent invasion of herbivores and associated plant species.     

先锋种丰富度对边坡植被群落特征及其护坡效益的影响

乡土植物灌木化建植是高速公路边坡防护的重要途径。以成渝高速(G85)永川段为例,以西南地区两种典型的边坡绿化初始配置"慈竹(Neosino calamus affinis)+野牛草(Buchloe dactyloides)"、"棉槐(Amorpha fruticosa)+紫羊茅(Festuca rubra)"为基础,分别与马棘(Indigofera pseudotinctoria Mats.)、黄荆(Vitex negundo)、狗牙根(Cynodon dactylon)、芒(Miscanthus sinensis)等路域优势种以不同方式组合,研究一定立地条件下初始绿化植物(先驱植物)的丰富度对边坡植被群落生长发育、早期演替行为及护坡性能的影响。结果表明:1)先驱植物丰富度可直接影响边坡植被的成坪时间、生物量积累:相同建植条件(边坡条件、播种密度等)下,先锋种种类越多,成坪时间就越短,被积累的生物量也越多;2)先锋种数量与群落的生物多样性水平有关(R20.954):相同演替阶段内,先锋种越多,群落的多样性水平(如物种丰富度、Shannon-Wiener指数、Pielou指数)则越高;3)群落中物种多样性水平与植被的护坡性能密切相关(R20.998):多样性水平越高,植被的蓄水、保土能力越强,边坡内径流系数、土壤侵蚀模数越小。可见,在边坡条件、播种密度等建植条件与建植措施一致的情形下,提高初始绿化植物的物种数可有效改善边坡植被的护坡性能。     

珠三角河网浮游植物物种丰富度时空特征

对2012年珠三角河网浮游植物物种丰富度的时空特征进行了系统阐析。季节上,枯水期的物种丰度差异大,丰水期差异小;空间上,广州周边及河网中部个别站位的总种数高于其他站位。不同季节的空间特征显示,枯水期的物种丰度自西江沿线、河网中部、广州周边呈递增趋势;而丰水期呈现三角洲两侧的物种丰富度高于河网中部。各类群相对组成结果显示,硅藻在枯水季节占绝对优势,丰水期优势下降;空间上广州周边站位硅藻百分比明显低于其他站位。分析原因,径流相关的补充和稀释作用和水体搅动引起的底层藻类的悬浮补充不仅影响物种丰富度的季节变动,也影响不同类群的相对组成;水体交换能力和营养盐分别是决定丰水期和枯水期物种丰富度空间分布的关键因素。     

The river domain: why are there more species halfway up the river?

Biologists have long noted higher levels of species diversity in the longitudinal middle‐courses of river systems and have proposed many explanations. As a new explanation for this widespread pattern, we suggest that many middle‐course peaks in richness may be, at least in part, a consequence of geometric constraints on the location of species’ ranges along river courses, considering river headwaters and mouths as boundaries for the taxa considered. We demonstrate this extension of the mid‐domain effect (MDE) to river systems for riparian plants along two rivers in Sweden, where a previous study found a middle‐course peak in richness of natural (non‐ruderal) species. We compare patterns of empirical richness of these species to null model predictions of species richness along the two river systems and to spatial patterns for six environmental variables (channel width, substrate fineness, substrate heterogeneity, ice scour, bank height, and bank area). In addition, we examine the independent prediction of mid‐domain effects models that species with large ranges, because the location of their ranges is more constrained, are more likely to produce a mid‐domain peak in richness than are species with small ranges. Species richness patterns of riparian plants were best predicted by models including both null model predictions and environmental variables. When species were divided into large‐ranged and small‐ranged groups, the mid‐domain effect was more prominent and the null model predictions were a better fit to the empirical richness patterns of large‐ranged species than those of small‐ranged species. Our results suggest that the peak in riparian plant species richness in the middle courses of the rivers studied can be explained by an underlying mid‐domain effect (driven by geometric constraints on large‐ranged species), together with environmental effects on richness patterns (particularly on small‐ranged species). We suggest that the mid‐domain effect may help to explain similar middle‐course richness peaks along other rivers.     

The effect of overstorey proteas on plant species richness in South African mountain fynbos

Two South African mountain fynbos sites, similar in drainage, elevation, slope angle, slope aspect and soil type but with differing fire histories, were studied to measure how the effect of high densities of overstorey proteas in one fire cycle affects the α-diversity levels of the plant community in the following fire-cycle, how their repeated absence due to several short fire-cycles affects their species richness and finally, at what spatial scale such patterns are most appropriately measured. High prefire canopy cover percentages and densities of overstorey proteas increase the postfire α-diversity of understorey species. In addition, the increase in species richness observed occurred for all higher plant life history types present. At sites where one or more short fire cycles resulted in the repeated absence of overstorey proteas, the number of plant species present in the understorey was lower than at a site where overstorey proteas persisted. These results are dependent on the spatial scale at which the α-diversity of understorey species is measured. At small quadrat sizes (< 5 m²), overstorey proteas decrease the number of understorey species present, while at larger quadrat sizes (100 m²) higher species richness is observed. The contradiction in conclusions when α-diversity is measured at different spatial scales can be attributed to the patchiness of fynbos communities. Overstorey proteas play an important role in maintaining the patchiness component of fynbos communities by diminishing the effect of understorey resprouting species, making available regeneration niches for the maintenance of plant species richness. Where small quadrats are used, the effect of patchiness on the dynamics of the mountain fynbos community is lost. Thus, it is the fire history prior to the last fire and how it affects overstorey proteas that is important in the determination of α-diversity levels in mountain fynbos plant communities.     

Hydrologic effects on riparian vegetation in a boreal river: an experiment testing climate change predictions

Climate change is expected to alter the magnitude and variation of flow in streams and rivers, hence providing new conditions for riverine communities. We evaluated plant ecological responses to climate change by transplanting turfs of riparian vegetation to new elevations in the riparian zone, thus simulating expected changes in water‐level variation, and monitored the results over 6 years. Turfs moved to higher elevations decreased in biomass and increased in species richness, whereas turfs transplanted to lower elevations gained biomass but lost species. Transplanted plant communities responded slowly to the new hydrologic conditions. After 6 years, biomass of transplanted turfs was statistically indistinguishable from target level controls, but species richness and species composition of transplants were intermediate between original and target levels. By using projections of future stream flow according to IPCC climate change scenarios, we predict likely changes to riparian vegetation in boreal rivers. Climate‐driven hydrologic changes are predicted to result in narrower riparian zones along the studied Vindel River in northern Sweden towards the end of the 21st century. Present riparian plant communities are projected to be replaced by terrestrial communities at high elevations as a result of lower‐magnitude spring floods, and by amphibious or aquatic communities at low elevations as a result of higher autumn and winter flows. Changes to riparian vegetation may be larger in other boreal climate regions: snow melt fed spring floods are predicted to disappear in southern parts of the boreal zone, which would result in considerable loss of riparian habitat. Our study emphasizes the importance of long‐term ecological field experiments given that plant communities often respond slowly and in a nonlinear fashion to external pressures.     

Digging deep for diversity: riparian seed bank abundance and species richness in relation to burial depth

相似文献   

Ectomycorrhizal fungal diversity and saprotrophic fungal diversity are linked to different tree community attributes in a field‐based tree experiment

Exploring the link between above‐ and belowground biodiversity has been a major theme of recent ecological research, due in large part to the increasingly well‐recognized role that soil microorganisms play in driving plant community processes. In this study, we utilized a field‐based tree experiment in Minnesota, USA, to assess the effect of changes in plant species richness and phylogenetic diversity on the richness and composition of both ectomycorrhizal and saprotrophic fungal communities. We found that ectomycorrhizal fungal species richness was significantly positively influenced by increasing plant phylogenetic diversity, while saprotrophic fungal species richness was significantly affected by plant leaf nitrogen content, specific root length and standing biomass. The increasing ectomycorrhizal fungal richness associated with increasing plant phylogenetic diversity was driven by the combined presence of ectomycorrhizal fungal specialists in plots with both gymnosperm and angiosperm hosts. Although the species composition of both the ectomycorrhizal and saprotrophic fungal communities changed significantly in response to changes in plant species composition, the effect was much greater for ectomycorrhizal fungi. In addition, ectomycorrhizal but not saprotrophic fungal species composition was significantly influenced by both plant phylum (angiosperm, gymnosperm, both) and origin (Europe, America, both). The phylum effect was caused by differences in ectomycorrhizal fungal community composition, while the origin effect was attributable to differences in community heterogeneity. Taken together, this study emphasizes that plant‐associated effects on soil fungal communities are largely guild‐specific and provides a mechanistic basis for the positive link between plant phylogenetic diversity and ectomycorrhizal fungal richness.     

Testing the impact of climate variability on European plant diversity: 320,000 years of water-energy dynamics and its long-term influence on plant taxonomic richness

Models examining the present-day relationship between macro-scale patterns in terrestrial species richness and variables of water and energy demonstrate that a combined water–energy model is a good predictor of richness in mid-to-high latitude regions. However, the power of the individual water and energy variables to explain this richness through time has never been explored. Here, we assess how well energy and water can predict long-term variations in plant richness using a 320 000-year fossil pollen data set from Hungary. Results demonstrate that a combined water–energy model best explains the variation in plant diversity through time. However, this long temporal record also demonstrates that amplitude of energy variation appears to be a strong determinant of richness. Decreased richness correlates with increased climate variability and certain species appear to be more susceptible according to their ecological traits. These findings have important implications for predicting richness at times of increasing climate variability.     

Vascular plant species richness along latitudinal and altitudinal gradients: a contribution from New Zealand temperate rainforests

Vascular plant species richness is known to often decrease with both increasing latitude and increasing altitude. However, a number of studies have shown the reverse trend and the primary cause of these gradients remains unknown. In the present work, generalized linear models were used to assess the relative importance of latitude and altitude as well as of a number of other factors (mean annual precipita-tion, slope, substrate and forest type) on species richness in temperate rainforests of New Zealand. The effect of Southern beech ( Nothofagus spp.) as dominant canopy species on total species richness was shown to be much smaller than postulated in most previous studies. Within the region studied, altitude had by far the strongest effect on species richness. This effect was independent of latitude and was significant for woody but not for herbaceous vegetation.     

Biological invasion hotspots: a trait‐based perspective reveals new sub‐continental patterns

Invader traits (including plant growth form) may play an important, and perhaps overlooked, role in determining macroscale patterns of biological invasions and therefore warrant greater consideration in future investigations aimed at understanding these patterns. To assess this need, we used empirical data from a national‐level survey of forest in the contiguous 48 states of the USA to identify geographic hotspots of forest plant invasion for three distinct invasion characteristics: invasive species richness, trait richness (defined as the number of the five following plant growth forms represented by the invasive plants present at a given location: forbs, grasses, shrubs, trees, and vines), and species richness within each growth form. Three key findings emerged. 1) The hotspots identified encompassed from 9 to 23% of the total area of our study region, thereby revealing many forests to be not only invaded, but highly invaded. 2) Substantial spatial disagreement among hotspots of invasive species richness, invasive trait richness, and species richness of invasive plants within each growth form revealed many locations to be hotspots for invader traits, or for particular growth forms of invasive plants, rather than for invasive plants in general. 3) Despite eastern forests exhibiting higher levels of plant invasion than western forests, species richness for invasive forbs and grasses in the west were respectively greater than and equivalent to levels found in the east. Contrasting patterns between eastern and western forests in the number of invasive species detected for each growth form combined with the spatial disagreement found among hotspot types suggests trait‐based variability in invasion drivers. Our findings reveal invader traits to be an important contributor to macroscale invasion patterns.     

Flood events overrule fertiliser effects on biomass production and species richness in riverine grasslands

Question: Do severe winter flood events lift the nutrient limitation of biomass production in a river floodplain? How does this affect plant species richness? How long do the effects last? Location: Floodplain grassland on calcareous sandy loam near river Rhine in The Netherlands. Methods: Plots were fertilised with four treatments (control, N, P, N+P) for 21 years; plant species composition, vegetation biomass and tissue nutrient concentrations were determined every year between 1985 and 2005. Results: Fertilisation with N generally increased biomass production and reduced species richness, but these effects varied over time. During the first four years of the experiment, biomass production appeared to be co‐limited by N and P, while N fertilisation dramatically reduced plant species richness; these effects became weaker subsequently. Following two extreme winter floods in 1993–94 and 1994–95 and a drought in spring 1996, the effects of fertilisation disappeared between 1998 and 2001 and then appeared again. Flooding caused an overall reduction in species richness (from c. 24 to 15 species m^‐2) and an increase in biomass production, which were only partly reversed after ten years. Conclusions: Long time series are necessary to understand vegetation dynamics and nutrient limitation in river floodplains, since they are influenced by occasional flood and drought events, whose effects may persist for more than ten years. A future increase in flooding frequency might be detrimental to species richness in floodplain grasslands.     

漫溢干扰过程中微地形对幼苗定居的影响

通过对比漫溢干扰后边坡、坡中和坡底幼苗的物种组成、密度、幼苗周边的环境条件及土壤种子库的差异来分析漫溢干扰过程中,微地形对幼苗定居的影响.结果表明:(1)微地形对幼苗物种组成和生物多样性指数的影响很大.漫溢干扰后,位于边坡、坡中和坡底幼苗的Simpson多样性指数和Mcintosh均匀度指数在0.01的水平上差异极显著,Margalef丰富度指数在0.05的水平上差异显著.(2)微地形对土壤盐分含量影响很大.方差分析的结果表明,除HCO3-和K+外,边坡、坡中和坡底的pH值、C023-、SO24-、Ca2+和Mg2+各指标在0.01的水平上差异极显著;全盐、总盐、Cl-和Na+各指标均在0.05的水平上差异显著.(3)微地形通过改变幼苗定居的环境条件,进而影响幼苗库的物种组成、密度和生物多样性指数.微地形中,幼苗库的各种生态指标均小于对应的土壤种子库的生态指标,从坡底到坡中到边坡,除单位面积上的植被密度外,土壤种子库和幼苗库的各项生态指标的变化趋势均不同.     

Propagule input,transport and deposition in riparian environments: the importance of connectivity for diversity

Question: How important is hydrochory for dispersing propagules along riverbanks and to what extent do the quantity and species composition of deposited propagules reflect the riparian vegetation, represent “new” species that are not present in the vegetation, and vary with river flow and season? Location: River Frome, Dorset, UK. Methods: Over 13 consecutive 6‐week time periods, during which river water levels were continuously monitored, aerial inputs of propagules to riverbanks were sampled using funnels, hydrochorous propagule transport was sampled using drift nets, and deposition across the riverbanks was sampled using astroturf mats. A survey of the riparian vegetation enabled comparison between samples and the standing vegetation, so that “new” species could be identified. Differences in propagule abundance and diversity between sampling methods, time periods and locations were tested using Mann‐Whitney U‐tests and Kruskall‐Wallis ANOVA. DCA established contrasts in the floristic composition of all deposited propagules and “new” propagules between different sample types, time periods and locations. Results: Aerial seed fall generated few propagules of low species richness. Hydrochory introduced large numbers of propagules and new species, resulting in high propagule deposition on the riverbank. The number and diversity of deposited propagules was governed by seasonal patterns of seed release and the hydrological regime. Propagule deposition was significantly greater on the most frequently inundated parts of the riverbank and autumn floods were particularly important for transporting “new” species to the study site and for remobilizing previously released propagules. Conclusions: The abundance and diversity of propagules deposited along riverbanks is dependent upon high river flows, which facilitates connectivity between the channel and the riparian zone.