Riparian Plant Research Articles

Carbon Fixation and Oxygen Release Capacity of Typical Riparian Plants in Wuhan City and Its Influencing Factors

In order to explore the carbon fixation and oxygen release capabilities of riparian plants in Wuhan, the photosynthetic rate (Pn) and morphological indicators of 13 typical riparian plants in the middle section of the Xunsi River in Wuhan were measured by portable photosynthesis apparatus. The daily carbon fixation and oxygen release of each plant at different scales were calculated, and the carbon fixation and oxygen release capacity and its influencing factors were analyzed. The results show that: (1) according to the biological characteristics, the daily carbon fixation and oxygen release capacity per unit leaf area was higher in herbaceous than in trees; the daily carbon fixation and oxygen release capacity per plant, per projected area, and per land area were higher in trees than in herbaceous. (2) The plant with the strongest ability of daily carbon fixation and oxygen release per unit leaf area was Ruellia brittoniana, and the weakest was Triadica sebifera; the plant with the strongest ability of daily carbon fixation and oxygen release of a single plant was Metasequoia glyptostroboides, and the weakest was Lolium perenne; the plant with the strongest ability of daily carbon fixation and oxygen release per land area was Metasequoia glyptostroboides, and the weakest was Alternanthera sessilis. (3) The carbon fixation and oxygen release ability of 13 plant species was analyzed by cluster analysis based on per unit leaf area, per plant, and per land area; ten species of herbaceous plant could be divided into three grades and three species of trees into two grades. This study provides a theoretical reference for the selection and application of riparian zone vegetation in Wuhan, and provides a scientific basis for the evaluation of riparian zone ecological benefits.

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.

Along the river: Longitudinal patterns of functional and taxonomic diversity of plants in riparian forests

AbstractQuestionsThe River Continuum Concept (RCC) predicts a gradual shift of functional adaptations of organisms along the longitudinal (upstream–downstream) gradient, as well as the maximization of the biotic diversity in mid‐reaches. Although this theoretical framework was originally developed for stream macroinvertebrates, we tested whether such a pattern can also be observed in riparian plant communities.LocationThe study was conducted in the upper catchments of the San and Wisłoka Rivers in southeastern Poland. In both catchments, very well preserved riparian forests occur continuously along both rivers.MethodsWe studied the cover of plant species in riparian forests across two river networks. We analyzed the taxonomic and functional diversity indices, as well as community‐weighted means of functional traits in relation to the plots' positions in the catchments.ResultsThe functional richness and divergence displayed unimodal patterns of increasing values in the mid‐reaches. The patterns of taxonomic diversity were similar, but some plots in the lowest reaches were more diverse than expected, forming an additional increase in diversity. The observed patterns were largely in line with the predictions of RCC. We discovered a significant decrease in the specific leaf area and an increase in the height of herbaceous plants in communities along a longitudinal gradient. There was also a shift in the dispersal syndromes, toward a higher importance of zoochory in the lower reaches.ConclusionsThe study shows that plant communities in natural riparian forests show continuous species turnover along the longitudinal gradient that, along with the longitudinal shift of abiotic factors, creates patterns that are known from theoretical predictions.

Impact of water supply on the restoration of the severely damaged riparian plants along the Tarim River in Xinjiang, Northwest China

Restoring degraded ecosystems in drylands is challenging because of low precipitation and high evapotranspiration. Water availability determines the existence and spatiotemporal distribution patterns of key endangered species struggling to survive in the severely damaged desert riparian ecosystem of the lower Tarim River (LTR) in NW China. Ecological water flow restoration measures with high costs and uncertainties have been implemented since 2000. The key task for scientists is to assess the success and drawbacks of this restoration project and propose specific recommendations for stakeholders to optimize the ecological benefits of the project in a cost-effective manner. In this study, Landsat time-series data from 1990 to 2020 were used to extract vegetation index values from river corridors along the LTR and explore the spatiotemporal patterns of desert riparian forest (DRF) vegetation. Based on land use and surface water data, we extracted the interannual spatial distribution range of vegetation and surface water, and selected several sample plots to demonstrate the influence of surface water and groundwater on vegetation change trends. The study results showed the following. 1) From 1990 to 1999, the vegetation slowly degraded; from 2000 to 2012, the extent of vegetation restoration was approximately 1 km from the river; and from 2013 to 2020, the extent of vegetation restoration at the Yingsu and Karday sections increased to 4.5–6.0 km, while that at the Arghan and Yiganbujima sections remained within 1 km from the river. 2) The vegetation growth rate increased substantially and was spatially heterogeneous when the groundwater level reached 4.0–5.0 m and was influenced by surface water divergence; the average vegetation expansion rates per square km for P1–P4 were 0.017 km2/a, 0.011 km2/a, 0.005 km2/a, and 0.002 km2/a, respectively. 3) Flooding by surface water was the main driver of vegetation expansion when groundwater was stable and elevations in surface vegetation area were often accompanied by the spreading of surface water. Surface water was significantly correlated with vegetation cover and normalized difference vegetation index (NDVI) (Water pixels–Vegetation cover [P1: R2 = 0.57, P < 0.001; P2: R2 = 0.45, P < 0.01]; Water pixels–NDVI [P1: R2 = 0.22, P < 0.05; P2: R2 = 0.40, P < 0.01]). The increase in surface vegetation has alleviated the desertification process in the LTR, and the survival of the poplar has been mitigated. The results of this paper can help decision makers to formulate reasonable ecological water conveyance strategies and realize sustainable management of DRF ecosystems in arid zones.

Coordination and adaptation of water processes in Populus euphratica in response to salinity.

Water processes secure plant survival and maintain their ecosystem function. Salinity affects water processes, but the mechanisms remain unclear and may depend on the degree of salinity stress. To improve the understanding of the cooperation of plant organs involved in water processes under salinity stress, we determined hydraulic, gas exchange, and physiological and biochemical parameters in Populus euphratica Oliv. under different salinity stresses. The results suggested that P. euphratica enhanced water transport efficiency in a salinity-stress environment, and the strengthening effect of roots in the water transfer process was greater than that of the aboveground parts. P. euphratica also increased water use efficiency and water transport efficiency in mild and moderate salinity stress (less than 200 mmol/L NaCl) but was adversely affected by heavy salinity stress (more than 300 mmol/L NaCl). Furthermore, P. euphratica increased its water storage by regulating antioxidant enzyme scavenging capacity and osmoregulation, which resulted in coordinated greater water utilization and enhanced water transport among plant organs and indicated that the adverse effects on water processes triggered by salinity stress depended on the extent of salt stress. P. euphratica lessened stress-induced damage and maintained plant productivity by coordination and cooperation of water processes under certain levels of salinity. Research on the coordination and cooperation involving water processes in riparian forests in saline areas provides the scientific basis for riparian plant protection and restoration.

Divergent physiological responses of hydric and mesic riparian plant species to a Colorado River experimental flow

Divergent physiological responses of hydric and mesic riparian plant species to a Colorado River experimental flow

Inundation Tolerance, Rather than Drought Tolerance, Predicts Riparian Plant Distributions Along a Local Hydrologic Gradient

Inundation Tolerance, Rather than Drought Tolerance, Predicts Riparian Plant Distributions Along a Local Hydrologic Gradient

The Euphrates Poplar Responses to Abiotic Stress and Its Unique Traits in Dry Regions of China (Xinjiang and Inner Mongolia): What Should We Know?

At the moment, drought, salinity, and low-temperature stress are ubiquitous environmental issues. In arid regions including Xinjiang and Inner Mongolia and other areas worldwide, the area of tree plantations appears to be rising, triggering tree growth. Water is a vital resource in the agricultural systems of countries impacted by aridity and salinity. Worldwide efforts to reduce quantitative yield losses on Populus euphratica by adapting tree plant production to unfavorable environmental conditions have been made in response to the responsiveness of the increasing control of water stress. Although there has been much advancement in identifying the genes that resist abiotic stresses, little is known about how plants such as P. euphratica deal with numerous abiotic stresses. P. euphratica is a varied riparian plant that can tolerate drought, salinity, low temperatures, and climate change, and has a variety of water stress adaptability abilities. To conduct this review, we gathered all available information throughout the Web of Science, the Chinese National Knowledge Infrastructure, and the National Center for Biotechnology Information on the impact of abiotic stress on the molecular mechanism and evolution of gene families at the transcription level. The data demonstrated that P. euphratica might gradually adapt its stomatal aperture, photosynthesis, antioxidant activities, xylem architecture, and hydraulic conductivity to endure extreme drought and salt stress. Our analyses will give readers an understanding of how to manage a gene family in desert trees and the influence of abiotic stresses on the productivity of tree plants. They will also give readers the knowledge necessary to improve biotechnology-based tree plant stress tolerance for sustaining yield and quality trees in China's arid regions.

Distinct Impact of Drought on Radial Growth at Different Heights and Parts of Populus euphratica in the Oasis at the Hinterland of the Taklimakan Desert

Warming and persistent droughts may exacerbate drought stress in water-scarce areas, thereby negatively affecting tree growth. When riparian plants in arid regions experience severe drought stress, they sacrifice non-dominant branches with less competitive sap flow to improve the sap flow of dominant branches and thus ensure strong plant growth. Populus euphratica is one of the most dominant tree species in the riparian forest ecosystems of inland river basins in arid zones and is a reliable indicator of ecological change because of its diversity in growth and environment. To understand the adaptability of P. euphratica to the environment, the relationship between radial growth and meteorological factors, the growth decline and resistance of different heights and components of P. euphratica, as well as the resilience and resilience after recession were investigated. The results indicated that tree-ring width decreased gradually with increasing height and branching class of P. euphratica. Growth decreased at the bottom of the stem earlier than at the middle and top. Temperature, precipitation, and the Palmer drought index contributed to the growth at the bottom of P. euphratica, while precipitation contributed to growth at the top. The decline in the P. euphratica growth change rate was highly synchronized across heights and parts, with relatively high declines at the bottom and top. There were no significant differences in the recovery values for different heights and parts of P. euphratica, but the resistance, resilience, and relative resilience for the bottom and top were significantly lower than those for the other components, indicating vulnerability in the bottom and top of P. euphratica to drought. The relative resilience gradually decreased with the increase in branching class, and that of the secondary lateral branches at different heights was the lowest. In conclusion, the sensitivity of the top and lateral branches of P. euphratica to drought would cause the phenomenon of “breaking its arm” under drought disturbance in the future.

Soil moisture influences the root characteristics of a herbaceous riparian plant along a regulated river

Soil moisture influences the root characteristics of a herbaceous riparian plant along a regulated river

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.

The impact of flood regime on river floodplain vegetation coverage: Insights from a 30-year Landsat record

The impact of flood regimes on river floodplain vegetation within banks remains poorly understood. In this study, we examined the monthly variation of river floodplain vegetation coverage (RFVC) at a typical reach of the Yangtze River with a 30-year Landsat record. We evaluated its relationships with 13 hydrodynamic characteristic indices. Our results showed that the flow regime alteration associated with dam construction led to an increase in the downstream RFVC every month throughout the year. The maximum specific energy, reflecting both physical and physiological damage effects to riparian plants, was most negatively related to the RFVC after floods (i.e., from September to October) in the whole 30-year period (Adj.R2 = 0.64, p < 0.05). The flood duration with water levels above floodplain vegetation had the most significant negative correlation with RFVC in the post-dam period (Adj.R2 = 0.84, p < 0.05). Also, the change of riparian vegetation area in different elevation zones before and after floods mainly depended on the combined effect of vegetation distribution and flood intensity. Our findings give insights into river floodplain vegetation dynamics and provide scientific support to riparian vegetation modelling.

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.

Quantifying river water contributions to the transpiration of riparian trees along a losing river: lessons from stable isotopes and an iteration method

Abstract. River water plays a critical role in riparian plant water use and riparian ecosystem restoration along losing rivers (i.e., river water recharging underlying groundwater). How to quantify the contributions of river water to the transpiration of riparian plants under different groundwater levels and the related responses of plant water use efficiency is a great challenge. In this study, observations of stable isotopes of water (δ2H and δ18O), 222Rn, and leaf δ13C were conducted for the deep-rooted riparian weeping willow (Salix babylonica L.) in 2019 (dry year) and 2021 (wet year) along the Chaobai River in Beijing, China. We proposed an iteration method in combination with the MixSIAR model to quantify the river water contribution to the transpiration of riparian S. babylonica and its correlations with the water table depth and leaf δ13C. Our results demonstrated that riparian S. babylonica took up deep water (in the 80–170 cm soil layer and groundwater) by 56.5 % ± 10.8 %. River water recharging riparian deep water was an indirect water source and contributed 20.3 % of water to the transpiration of riparian trees near the losing river. Significantly increasing river water uptake (by 7.0 %) and decreasing leaf δ13C (by −2.0 ‰) of riparian trees were observed as the water table depth changed from 2.7 m in the dry year of 2019 to 1.7 m in the wet year of 2021 (p&lt;0.05). The higher water availability probably promoted stomatal opening and thus increased transpiration water loss, leading to the decreasing leaf δ13C in the wet year compared to the dry year. The river water contribution to the transpiration of riparian S. babylonica was found to be negatively linearly correlated with the water table depth and leaf δ13C (p&lt;0.01). The rising groundwater level may increase the water extraction from the groundwater and/or river and produce a consumptive river-water-use pattern of riparian trees, which can have an adverse impact on the conservation of both river flow and riparian vegetation. This study provides new insights into understanding the mechanisms of the water cycle in a groundwater–soil–plant–atmosphere continuum and managing water resources and riparian afforestation along losing rivers.

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.

Temporal and spatial variations of propagule deposition in the riparian zones of mountain rivers

AbstractAlthough dispersal is important for riparian plants, few studies have evaluated the variations of species richness and composition of propagules deposited by different dispersal mechanisms. In the present study, we evaluate the temporal and spatial variations in the diversity of propagules deposited by hydrochory and by other types of dispersal along mountain rivers. We sampled the propagules deposited in the riparian zone on a distance gradient with respect to the site of origin of the rivers in two seasons. We found no differences in the number of propagules between seasons. In the rainy season, we observed a greater number of species deposited by hydrochory, while for other types of dispersal there was a greater number of species in the dry season. Differences in composition were observed for hydrochory but not for other types of dispersal. There were no changes in the number of propagules deposited along the river by hydrochory, while for other types of dispersal an increase was observed in the dry season. A lower number of species deposited by hydrochory along the river was observed during the rainy season. Finally, we observed that turnover increases for other types of dispersal in the dry season but not for hydrochory. The results underline the importance of types of dispersal other than hydrochory in the contribution of propagules dispersed and the temporal and spatial particularities of the hydrochory in mountain rivers.