Riparian Plant Communities Research Articles

Riparian plant community structure and assembly processes differed by variations in riverbank curvatures: implications for restoring habitats along the Three Gorges Reservoir

Abstract A meandering riverbank plays a vital role in maintaining natural river ecosystems, providing habitats for riparian vegetation. However, dams have significantly altered riverbank shapes. To restore the riparian ecosystems, it is imperative to understand how different riverbank curvatures influence them. This study aims to uncover the ecological impacts of riverbank curvature on the structure and assembly process of plant communities in the riparian zone of the Yangtze River, regulated by the Three Gorges Dam (TGD) in China. We categorized the riparian zones into four types: cove, lobe, wavy, and linear shapes. We documented the composition and diversity of riparian plant communities. Our findings revealed that wavy and cove riverbanks exhibited greater species diversity (with Shannon-Wiener diversity index values 1.5 times higher) compared to communities along linear riverbanks. Furthermore, the analysis of functional traits indicated that wavy riverbanks promoted the differentiation of plant functional traits, thus enhancing ecosystem functions, with functional dispersion index (FDis) values 1.3 times higher than those of linear riverbanks. Significant variations in the assembly of riparian communities were also observed among different riverbanks, with standardized effect size (SES) values indicating a higher degree of niche differentiation in cove riverbanks (SES = 0.4) compared to linear riverbanks (SES = -0.6). These results highlight the ecological importance of diverse riverbank curvatures in influencing the diversity, structure, and assembly of riparian communities along waterway. In conclusion, this study underscores the necessity of maintaining or restoring various natural morphological curvatures when rehabilitating riparian communities along rivers impacted by human activities.

Cynodon dactylon and Sediment Interaction in the Three Gorges Reservoir: Insights from a Three-Year Study

Sediment deposition is critical in maintaining riparian plant communities by providing essential nutrients and posing growth challenges. This study focuses on Cynodon dactylon, a dominant clonal species in the riparian zones of the Three Gorges Reservoir, and its interaction with sediment deposition over three years. Results indicated an average sediment deposition depth of 2.85 cm in the lower riparian regions. Observations revealed that C. dactylon coverage increased progressively at lower elevations despite its dominance diminishing with rising elevation levels. Additionally, positive linear correlations between C. dactylon coverage and sediment deposition depths were identified during flood periods, underscoring the species’ role in enhancing sediment deposition. These findings suggest that C. dactylon plays a significant role in sediment accumulation, which may bolster its growth and survival prospects during subsequent growing cycles. The study highlights the importance of riparian vegetation, mainly perennial clonal species like C. dactylon, in promoting sediment accumulation and contributing to the stability and functionality of riparian ecosystems.

Correlation Analysis of Riparian Plant Communities with Soil Ions in the Upper, Middle, and Lower Reaches of Heihe River Midstream in China

Correlation Analysis of Riparian Plant Communities with Soil Ions in the Upper, Middle, and Lower Reaches of Heihe River Midstream in China

Two-stage channels can enhance local biodiversity in agricultural landscapes

Field drainage causes habitat loss, alters natural flow regimes, and impairs water quality. Still, drainage ditches often are last remnants of aquatic and wetland habitats in agricultural landscapes and as such, can be important for local biodiversity. Two-stage channels are considered as a greener choice for conventional ditches, as they are constructed to mimic the structure of natural lowland streams providing a channel for drainage water and mechanisms to decrease diffuse loading. Two-stage channels could also benefit local biodiversity and ecosystem functions, but existing information on their ecological benefits is scarce and incomplete. We collected environmental and biological data from six agricultural stream systems in Finland each with consequent sections of a conventional ditch and a two-stage channel to study the potential of two-stage channels to enhance aquatic and riparian biodiversity and ecological functions. Biological data included samples of stream invertebrates, diatoms and plants and riparian beetles and plants. Overall, both section types were highly dominated by few core taxa for most of the studied organism groups. Riparian plant and invertebrate communities seemed to benefit from the two-stage channel structure with adjacent floodplains and drier ditch banks. In addition, two-stage channel sections had higher aquatic plant diversity, algal productivity, and decomposition rate, but lower stream invertebrate and diatom diversity. Two-stage channel construction did not diversify the structure of stream channels which is likely one explanation for the lack of positive effects on benthic diversity. However, both section types harbored unique taxa found only in one of the two types in all studied organism groups resulting in higher local gamma diversity. Thus, two-stage channels enhanced local biodiversity in agricultural landscapes. Improvements especially in aquatic biodiversity might be achieved by increasing the heterogeneity of in-stream habitat structure and with further efforts to decrease nutrient and sediment loads.

Effects of Ecological Restoration on Degraded Riparian Plant Communities

Riparian areas are the transitional zones between terrestrial and aquatic ecosystems. Riparian have been experienced serious river channelization, riparian hardening and other anthropogenic activities. These disturbances result in degradation of ecological function and reduction of biodiversity of riparian ecosystems. There are many ecological engineering to restore riparian ecosystems in China. The research results of this article indicate that species richness and the Shannon-Wiener diversity index were: restored sites > natural sites > channelized sites, and biomass of natural sites was significantly lower than that of restored and channelized sites. The reason is that river channelization severely changed the composition and structure of plant communities and decreased plant diversity in riparian zone. Practicable ecological restoration measures could effectively reconstruct the plant communities and improved plant diversity in the channelized riparian zones.

Does restoring apex predators to food webs restore ecosystems? Large carnivores in Yellowstone as a model system

AbstractModification of food webs is a frequent cause of shifts in ecosystem states that resist reversal when the food web is restored to its original condition. We used the restoration of the large carnivore guild including gray wolves (Canis lupis), cougars (Felis concolor), and grizzly bears (Ursus arctos horribilis) to the northern range of Yellowstone National Park as a model system to understand how ecosystems might resist reconfiguration after the restoration of apex predators to the food web. The absence of wolves, cougars, and grizzly bears for nearly a century from the northern range was the primary cause of dramatic changes in riparian plant communities. Willows (Salix spp.) were suppressed in height by intense browsing by the dominant herbivore, elk (Cervus canadensis). The loss of activity by beavers (Castor canadensis) coincided with the loss of tall willows. We hypothesized that intense elk browsing interrupted the mutualism between willow and beavers: ecosystem engineering by beavers was a critical component of willow habitat and tall willows were a critical component of habitat for beavers. This interruption made riparian communities resilient to the disturbance caused by the restoration of apex predators. We hypothesized further that reductions in elk browsing attributable to reductions in elk population size were not sufficient to prevent the suppression of willow growth. To test these hypotheses, we conducted a 20‐year, factorial experiment that crossed simulated beaver dams with the exclusion of browsing. We found that willows grew to heights expected for restored communities only in the presence of dams and reduced browsing. Willows experiencing ambient conditions remained well below this expectation. We found no difference in heights or growth rates of willows in experimental controls and willows in 21 randomly chosen sites, confirming that the results of the experiment were representative of range‐wide conditions. A reorganized community of large herbivores was implicated in the suppression of willow growth. We conclude that the restoration of large carnivores to the food web failed to restore riparian plant communities on Yellowstone's northern range, supporting the hypothesis that this ecosystem is in an alternative stable state caused primarily by the extirpation of apex predators during the early 20th century.

The Effects of Legacy Sediment Removal and Floodplain Reconnection on Riparian Plant Communities

Stream restoration includes a number of different approaches intended to reduce sediment and nutrient export. Legacy sediment removal (LSR) and floodplain reconnection (FR) involve removing anthropogenically derived sediment accumulated in valley bottoms to reconnect incised streams to their floodplains. These projects also present an opportunity to create high-quality riparian and wetland plant communities and provide information about the early stages of wetland vegetation development and succession. We surveyed vegetation immediately after restoration at three sites and at three additional sites 1–3 years post-restoration to determine how LSR/FR affects riparian plant communities. Restoration increased the prevalence of hydrophytic herbaceous species at all sites, suggesting these projects successfully reconnected the stream to the floodplain. Pronounced decreases in woody basal area and stem density likely also influenced an increase in native and graminoid species after restoration. Only 16% of the indicator species identified for restored reaches were planted as part of the restoration, suggesting the local seed bank and other seed sources may be important for vegetation recovery and preservation of regional beta diversity. Although vegetation quality increased after restoration in reaches with initially low-quality herbaceous vegetation, vegetation quality did not improve or decreased after restoration in reaches with higher-quality vegetation before restoration. The practice of LSR/FR has the potential to improve the quality of some riparian vegetation communities, but the preservation of high-quality forested areas, even if they are atop legacy sediment terraces, should be considered, particularly if reductions in nutrient export do not offset losses in tree canopy.

Interannual controls on riparian plant health in a dryland river

AbstractRiparian zones in drylands provide important refugia for plants but depend on groundwater and thus are subject to local temporal and spatial variability in abiotic controls. In lieu of costly field‐based sampling, we used readily available data to establish site–scale interannual relationships among riparian plant health and the abiotic factors that control their water balance for a historically persistent wetland adjoining the Santa Clara River in southern California, USA. Non‐linear generalized additive model (GAM) analysis of plant health, represented using the normalized difference vegetation index (NDVI), confirmed robust relationships among plant health and various geomorphological and hydrological factors over multi‐decadal timeframes, including years since last high‐flow event, intra‐year groundwater elevation changes and magnitude of 2‐year cumulative surface water inflows. Geomorphic controls are related to years with high flows that cause extensive scour and deposition that re‐set riparian plant communities. Relationships with dry‐season groundwater declines reflect direct plant access to sub‐surface moisture. Hydrological dependence via cumulative inflow magnitude indicates the dependency of groundwater elevations on sufficient winter recharge to prevent precipitous groundwater decline. GAMs‐based inflection point analysis of surface water inflows versus groundwater elevations confirmed that the cumulative magnitude of multi‐year inflows is critical in avoiding catastrophic groundwater declines and that large flood events drive groundwater recovery. We show that abiotic controls on plant health can be derived from readily available data and that non‐linear analysis better represents the complexity of these scalar controls. Our analysis has relevance for ecosystem management of human‐altered rivers and climate change adaptation.

Plant–plant interactions vary greatly along a flooding gradient in a dam-induced riparian habitat

Plant–plant interactions under extreme environmental stress are still controversial. The stress gradient hypothesis (SGH) proposes that facilitation prevails under extreme environmental stresses, while an alternative view states that facilitation collapses or even switches back to competition at the extreme end of stress gradients. However, how the relationship between plant–plant interaction and periodic extreme flooding stress varies and its underlying mechanism are still unclear in a dam-regulated riparian ecosystem. We established a controlled experiment using two dominant species pairs (Cynodon dactylon–Cyperus rotundus and C. dactylon–Xanthium sibiricum) in the water level fluctuating zone of the Three Gorges Dam to examine their growth responses to the periodic extreme flooding stress. The results showed that as flooding stress increased, the competitive effect of C. dactylon on X. sibiricum shifted to facilitation, whereas the effect of X. sibiricum on C. dactylon maintained a strong inhibition. The plant height of X. sibiricum was the most important driver of the interaction between X. sibiricum and C. dactylon along the flooding gradient. The net effect of C. dactylon on C. rotundus shifted from neutral to negative, and the inhibitory effect of C. rotundus on C. dactylon became stronger at the extreme end of flooding stress. The root biomass of the two species was the key trait regulating their interaction with increasing flooding stress. Overall, the SGH was partially supported along our periodic extreme flooding stress gradient. Aboveground resource (light) might be the dominant factor driving the response of the interaction between annual plants and perennial clonal plants to periodic flooding stress, whereas belowground resource (water and nutrients) was probably the dominant factor for perennial clonal plants. Our study will help to further understand the environmental responses of plant–plant relationships and their regulatory mechanism, and the succession of riparian plant communities under extreme environmental changes, providing a basic theoretical basis and data support for the ecological restoration and management of riparian wetland vegetation.

Divergence of Seed Mass in Riparian Plant Communities Dominated by Filtering and Random Processes

Restoration of degraded riparian zones is the primary challenge for ensuring the sustainability of watershed ecosystems. An essential aspect of this endeavor is gaining a deep understanding of how riparian plant communities are assembled. The main focus of this study was to investigate how riparian plant communities respond to varying levels of flooding stress along the Three Gorges Reservoir (TGR) in China’s Yangtze River. To accomplish this, we calculated the diversity of plant taxonomy, traits and phylogeny, and used a null model to reflect the plant community assembly rules within the riparian zones along the TGR. The riparian zones were divided into four regions based on water regime: the fluctuating backwater area, the permanent backwater area, mainstream and tributaries of the TGR, covering the reservoir area of 1084 km2 with 180 sampling sites surveyed. Our results showed that within the permanent backwater area of the tributaries, the gradient variation in taxonomic and trait diversity of the riparian community was strongly aligned with the varying levels of flooding stress, which suggests that strong environmental selection plays a significant role in this section. Furthermore, through analysis of phylogenetic and trait structures based on the null model, we found that environmental filtering and random processes were the primary mechanisms shaping plant communities in the riparian zones across the entire study area. However, by further examining single traits, we found that seed mass was the sole trait displaying noteworthy divergence in the riparian communities throughout the study area. This finding highlights that seed mass appears as a pivotal divergent trait in the herb succession stage of the riparian communities that is strongly governed by filtering and random processes. In conclusion, we recommend prioritizing seed mass differences in ecological restoration efforts for herb succession in flooding-stressed riparian communities. This approach is crucial for enhancing source utilization, facilitating community assembly, and improving overall recovery outcomes.

Response of riparian plant community to landscape matrix differs by taxonomic and functional diversity: Implications for the planning of riparian landscapes regulated by dams

Local plant communities are embedded within the landscape matrix, and thus, diversity of these communities is largely determined by the spatial pattern of surrounding land-use. However, it is not yet clear how taxonomic and functional diversity within riparian plant communities respond differently to the landscape matrix at different scales, and whether and how these landscape-scale responses can be shaped by flooding conditions in the riparian landscape. This study is based upon field surveys of riparian plant communities in a total of 136 quadrats exposed to two different levels of flooding intensity along the reservoir formed by the Three Gorges Dam (TGD). We investigated the relationship between plant diversity of riparian communities and the surrounding landscape at different scales, which examined how the diversity, in terms of both plant taxonomy and functional traits, was affected by the landscape matrix at 15 different spatial scales ranging from 200 m to 3000 m in increments of 200 m around each sampling site. Furthermore, the community diversity in response to the landscape matrix under different levels of flooding intensity was also examined. Our findings suggested that trait-based functional diversity was more closely related to the landscape matrix at all 15 scales examined, compared to taxon-based diversity. The dispersal trait was found to be more susceptible to landscape connectivity across the matrix. Further, both types of diversity responded more strongly to landscape configurational metrics than compositional metrics. In addition, we observed that, in the communities exposed to high flooding intensity, the two types of diversity tended to have more consistent responses to the landscape matrix compared to those exposed to low flooding intensity. We concluded that while the landscape matrix had different effects on taxonomic and functional diversity, the high flooding intensity could lessen their differences in the riparian landscape. Our findings revealed that the robust local environmental filtering process, which affects the diversity of riparian communities, could lead to both diversity components exhibiting similar responses to the landscape matrix in riparian landscapes.

Long-term changes in the riparian vegetation of a large, highly anthropized river: Towards less hygrophilous and more competitive communities

Vegetation resurvey has proven effective in understanding long-term trajectories of plant communities. Combined with information related to ecological preferences and ecological strategies of plants, this framework can provide insight into the dynamics of communities and associated ecological processes over several decades. By comparing old and recent vegetation surveys, we sought to understand how past changes in flow and sediment regimes along a 100-km reach of the Rhône river still influence the structure of riparian plant communities. Specifically, we studied variations in the mean and dispersion values of light, nutrient availability and soil moisture, as well as of competitors, stress tolerators and ruderals, at the community scale over four decades and along connectivity and productivity gradients. Results showed that communities were composed of more hygrophilous and heliophilous species in old surveys and that this decrease in soil moisture and light over time was broadly consistent along environmental gradients. In response to these environmental changes, the ecological strategies of riparian vegetation have evolved into more competitive and less stress-tolerant communities. This was illustrated by the decline of the pioneer species Salix alba, but the increase in several post-pioneer woody species. Given that these changes were observed on almost all the plots studied, irrespective of their position along the connectivity and productivity gradients, our results reflect to some extent an overall evolution of the system towards more mature and closed successional stages. Thus, over a period of 40-years, and probably due to the legacy effects of anthropogenic modifications to flow and sediment regimes that have favored more stable riparian environments, a directional shift of riparian communities towards more advanced successional stages was highlighted. In a context where past and present anthropogenic stressors are accumulating, we infer that these changes in riparian ecosystem properties are probably irreversible and represent a major challenge for restoration.

Herbaceous angiosperms, pteridophytes and shrubs cocktail for rapid ground cover for soil and water bioengineering in the Caribbean

Among the Nature-based Solutions currently spreading worldwide, soil and water bioengineering techniques, are used to stabilize hill slopes, earth embankment, and riverbanks. They consist in the use of living plants, sometimes coupled with dead materials, to control erosion and restore ecosystems.These approaches remain to be adapted to Neotropics and particularly to the Caribbean Islands biodiversity hotspot. The success of soil and water bioengineering designs depends on the selection of suitable native plant species and considering the hydrodynamic and geotechnical processes. In the Caribbean, data are available concerning woody species but are still lacking for the other constitutive components of riparian plant communities. The objective of this study was to identify the riparian forest understory species best suited for use in SWBE at their establishment phase. In a three-month ex situ experiment, we measured the survival rate, biomass production and root growth of propagules (cuttings and bulbils) of eleven native Caribbean species (5 herbs, 4 pteridophytes, 2 shrubs) occurring naturally in a variety of riparian environments. All the herb and shrub species studied displayed growth vigour adequate for a successful inclusion in soil and water bioengineering techniques. Among herbs, Commelina diffusa, Hymenachne amplexicaulis and Sphagneticola trilobata performed the best. Gynerium sagittatum and Dieffenbachia seguine, despite their slower growth and root development, remain suitable. Regarding the two shrubs, Ludwigia octovalvis gave better results than Clidemia hirta. Among the pteridophytes, Adiantum latifolium, Thelypteris reticulata and particularly Lycopodium cernuum appeared poorly suited to soil and water bioengineering. Acrostichum danaeifolium was the best-performing pteridophyte. These first experimental results focusing on the propagation and establishment of native herbs, pteridophytes and shrubs, allowed to identify a diversity of species of interest as cuttings for soil and water bioengineering and practical clues for their use in the Neotropics.

Flooding Depth and Flooding Duration with the Zonation of Riparian Plant Communities in the Three Gorges Reservoir of China

The hydraulics of flows, especially the flooding process, influence the patterns of riparian plant zonation. Different characteristics of the flooding process should be analyzed to correlate plant zonation with flooding due to their different effect modes. The effects of flooding characteristics on riparian plants have yet to be studied, especially in the field. Thus, two elements of the flow regime, flooding duration and depth, were analyzed in relation to the riparian plants of the Three Gorges Reservoir. The taxonomic indices and the functional diversity of the riparian plants in three seasons in 2019 and the corresponding inundation character were surveyed. Our results showed that the riparian plant diversity and functional diversity varied by season. A significant negative relationship between plant diversity and flooding depth was observed, while flooding duration was not a significant predictor in different seasons. The greater explanatory capacity of flooding depth than that of flooding duration suggests that flooding depth could be a better indicator of the zonation of the riparian vegetation in this area. Concerning the vital component of flow hydraulics, growing opportunities to study flooding depth and strategies that consider both flooding time and flooding depth in a reservoir should be offered, as they will assist in refining process-based river restoration.

The accumulation of anthropogenic stressors induces a progressive shift in the ecological preferences and morphological traits shared by riparian plant communities

Abstract In riverine ecosystems, human‐induced stressors related to flow regulation and bank stabilisation have accumulated over time. The restoration of these highly anthropised ecosystems has become a major issue over the last few decades, with ambitious stated objectives. However, while the individual impact of flow regulation and channelisation on river functioning has been extensively studied, the response of ecological communities to multiple co‐occurring human‐induced stressors remains largely unexplored. Using a sampling design based on five river reaches in the Rhône catchment, ranging from unregulated in flow and bedload transport to intensively regulated reaches, we sought to understand how the accumulation of anthropogenic stressors influenced the functional response of riparian plants communities on gravel bars. By using 12 ecological and morphological traits, we performed a classification analysis to construct six riparian guilds and investigated whether their representativeness, as well as the mean value of individual traits, varied with increasing levels of anthropogenic stressors. Species cover and redundancy in several guilds increased or decreased significantly with increasing pressures. Thus, the guild of small taproot herbs with low nutrient and soil moisture requirements (xero‐oligotro‐taproot species guild) and the guild of taproot herbs adapted to very bright and dry conditions (mesoxero‐mesotro‐taproot species guild) dominated the unregulated reaches with active bedload transport. Conversely, regulated reaches with stabilised baseflow and inactive transport were dominated by the guild of flood‐tolerant trees (hygro‐perennial tall species guild) and the guild of vegetatively reproducing and flood‐tolerant perennial herbs (hygro‐perennial clonal species guild). Analysis of individual traits revealed a shift in environmental conditions, from full light to shade tolerance and from dry to humid, with increasing anthropogenic stressors. In response to this decrease in drought levels, plants traits shifted from annual to perennial species, from sexual to vegetative strategies and from taproots to a fibrous root system. Our results highlight the accumulated effects that anthropogenic stressors can have on riparian communities, inducing a progressive shift in certain traits related to life history, reproductive strategies, and drought adaptations. This effect on a set of shared traits reveals the strong influence that human infrastructures can have on the ecological niche of species and the morphological adaptations of riparian vegetation. From an applied point of view, and for highly anthropised rivers, our results suggest that restoration actions targeting a single stressor will not be sufficient to reorient riparian plant communities towards an ecological state closer to reference systems. Since human‐induced stressors have often deeply altered the flow and sediment regimes of rivers, a more integrated approach based on the restoration of erosion and flooding processes is essential to allow the expression of a wider diversity of riparian plant communities and habitats.

Evaluating Riparian Plant Communities After Restoration of Plains Bison in the Northern Great Plains of Montana

Restoration of plains bison (Bison bison bison) in the northern Great Plains has been controversial for a variety of reasons, including the public concern that bison will supplant cattle on public rangelands. Riparian zones are among the most biologically rich areas within rangelands, but they are highly sensitive to disturbances such as grazing, leading to the public perception that riparian vegetation communities will be negatively impacted by year-round bison grazing compared with the norm of seasonal cattle grazing. Our objective was to evaluate the vegetation community and soil compaction conditions of areas in the northern Great Plains of Montana, where bison have been restored 5−10 yr as year-round grazers, compared with adjacent sites where cattle have been retained as seasonal grazers. Out of the 24 variables we assessed, only 2 significantly differed between the grazer treatments within our study's time frame and stocking rates. Native species diversity was significantly higher in the bison-grazed treatment (F[1,1,5.98] = 8.16, P = 0.03), and woody height heterogeneity was twice as high in the bison-grazed treatment than the cattle-grazed treatment (F[1,5.97]= 5.81, P = 0.05). Although longer-term studies are required, our findings indicate that year-round bison grazing under the current stocking rates did not degrade riparian vegetation communities compared with seasonal cattle grazing and rather benefitted some aspects of the plant community.

Hydrochorous Seed Transport in the Lower Traisen River before and after Riverbed Restoration.

Hydrological restoration was carried out in a Lower Traisen, a small river within the floodplain of the Danube. The main goal was the reestablishment of typical riparian plant communities by using the potential of natural dispersal processes. We studied the transport of plant diaspores in the river water before and after the reconstruction of the riverbed. Aquatic seed traps were placed upstream and downstream of the restoration site. We identified the transported species and tested the viability of propagules. Functional species traits were analyzed to predict the probability of successful hydrochorous dispersal and changes in the transport pool due to the restoration. One-third of the local species pool was detected as being diaspores in the river. We observed a significant increase of ruderal species and neophytes, while the competitors and stress-tolerant competitors declined. Hydrochory is an important dispersal pathway for numerous plant species in the study area, including those without specific adaptations to this vector. Hydrochorous transport appears to be a sink for large-seeded species, primarily adapted to endozoochory. Follow-up management should be recommended to control the invasive species and to improve the structural and biological diversity of the Traisen Valley by supporting target species, which are also represented in the transport pool.

Flood changed the community composition and increased the importance of stochastic process of vegetation and seed bank in a riparian ecosystem of the Yellow River

Changes in riparian plant community composition and species richness are anticipated as a result of future projected increases in the risk of flood disasters in riparian ecosystems, but the extent and direction of these changes remain uncertain. In this study, we established four blocks comprising six plots in each block to investigate communities of vegetation and seed banks before and after flooding the middle and lower reaches of the Yellow River to investigate how flood influenced the indicator species, alpha diversity, community composition, and community assembly process. The study found that Symphyotrichum subulatum and Rumex acetosa were the indicator species for pre- and post-flood vegetation, as well as for the seed bank. Furthermore, there was a significant increase in all three alpha diversity indices (Shannon-wiener Index; H, Simpson diversity index; D, and Species richness; S) for both the vegetation and seed bank following the flood event. Our analysis of community assembly revealed that the flood event had a notable effect on the relative importance of different processes driving vegetation and seed bank dynamics. Specifically, according to the species composition assembly analysis, we observed a significant increase in the relative importance of stochastic process but decreased in determined process in vegetation. However, the results of multiple regression on matrices indicated the environmental filtering can hardly explain the deterministic process which the patterns of pre-flood vegetation composition were largely controlled by biological interactions, particularly competition among species. Therefore, the reduction of competitive pressures accompanied with the uncertainty of upstream seed banks make local riparian ecosystem more vulnerable to ecological invasions (after the recorded flood event, the invasive species Bidens pilosa was observed to successfully establish). This vulnerability highlights the need for effective protection and management strategies to ensure the long-term sustainability of riparian ecosystems in the middle and lower reaches of the Yellow River.

The Influence of Eurasian Beaver (Castor fiber L.) Activity on the Transformation and Functioning of Riparian Phytocoenoses in the Southern Boreal Zone (European Russia)

The reintroduction of Eurasian beaver (Castor fiber L.) results in significant changes in ecosystems. The purpose of this study is to assess the impact of the environment-forming activity of C. fiber on the riparian phytocoenoses of the Raifa forest sector of the Volga-Kama State Nature Biosphere Reserve (Middle Volga region, European Russia) after the reintroduction. Phytoindication methods of ecological–coenotic groups and indicator values were used to assess changes in environmental conditions under the influence of beaver activity. The influence of the beaver reintroduction factor on the increase in the moisture regime (by three points according to the Tsyganov indicator values) and the illumination of habitats, the richness of soils in nitrogen, and the acidity and salt regime of soils (by one point) was revealed. Under the conditions of fodder and construction activities of the beaver, an increase in the proportion of aquatic and wetland groups from 10.2% to 28.2% and boreal plant species from 15.0% to 27.6% was detected. An expansive nature of the change in the degree of landscape occupancy with wetland plants was noted. A decrease in the degree of landscape occupancy (3 to 2 points) of the distribution of ruderal species in the riparian zones of the waterbodies of the reserve due to the activity of the beaver was revealed. Based on phytoindication and ecological–coenotic analyses, it was shown that the reintroduction of C. fiber into the waterbodies of the Raifa forest sector of the reserve is responsible for maintaining the necessary microclimatic conditions for the preservation of natural southern boreal communities. The results obtained can be used for predictive assessment of the influence of the beaver on riparian (small rivers and lakes) plant communities of forest ecosystems in the Middle Volga region of European Russia and other regions of the planet with similar environmental conditions.

Bison influences on composition and diversity of riparian plant communities in Yellowstone National Park

AbstractRiparian zones are among the most biologically diverse ecosystems in the Intermountain West, USA, and provide valuable ecosystem services, including high rates of biotic productivity, nutrient processing, and carbon storage. Thus, their sustainability is a high priority for land managers. Large ungulates affect composition and structure of riparian/stream ecosystems through herbivory and physical effects, via trailing and trampling. Bison (Bison bison) in Yellowstone National Park (YNP) have been characterized as “ecosystem engineers” because of their demonstrated effects on phenology, aboveground productivity of grasses, and woody vegetation structure. Bison have greatly increased in numbers during the last two decades and spend large periods of time in the broad open floodplains of the Northern Range of the Park, where they are hypothesized to have multiple effects on plant species composition and diversity. We sampled indicators of bison use as well as riparian vegetation composition, diversity, and structure along eight headwater streams within YNP's Northern Range. Total fecal density ranged from 333 to 1833 fecal chips and/or piles/ha, stubble heights ranged from 7 to 49 cm, and streambank disturbance ranged from 9% to 62%. High levels of bison use were positively correlated with exotic species dominance and negatively correlated with species richness, native species diversity, willow (Salix spp.) cover, and wetland species dominance. At three sites, the intensity of bison use exceeded recommended utilization thresholds to avoid degradation of streams and riparian zones on public lands. The influences of large herbivores, principally bison, on vegetation composition and structure suggest the cumulative effects of the current densities on the Northern Range are contributing to biotic impoverishment, representing the loss of ecosystem services that are provided by native riparian plant communities. In addition, contemporary levels of bison use may be exacerbating climate change effects as observed through ungulate‐related shifts in composition toward plant assemblages adapted to warmer and drier conditions. However, the resilience of native riparian vegetation suggests that sites currently heavily utilized by bison would have the potential for recovery with a reduction in pressure by this herbivore.