Impacts of hydropower-induced flow alterations on composition and diversity of riparian vegetation in the Western Himalayas: A case study in Uttarakhand, India

The increasing demand for water and energy resources has led to widespread dam construction,particularly in ecologically sensitive regions like the Himalayan Range.This study focuses on the Uttarakhand state in the Western Himalayas,where hydroelectric projects(HEPs)have significantly altered river flow regimes.The research investigates the impact of flow alterations on the composition and structure of riparian vegetation in the Garhwal Himalayas,specifically analysing four rivers regulated by hydroelectric projects.Utilizing the paired-reach comparison method,control(undisturbed),diverted(downstream of barrage/dam),and altered flow conditions(downstream of water outlet)were examined.The research reveals diverse and unique riparian ecosystems,with 89 genera and 113 taxa identified,showcasing the dominance of families like Asteraceae and Lamiaceae.The study unveils the structural importance of key species such as Berberis asiatica and Artemisia nilagirica.The density,diversity,and richness of shrub and herb species vary significantly across flow conditions.Notably,altered flow conditions demonstrate resilience in vegetation structure,while diverted conditions exhibit decreased species richness and density.The study emphasizes the importance of nuanced environmental flow management for mitigating adverse effects on riparian biodiversity in the fragile Himalayan region.These findings contribute to the global discourse on dam impacts and riparian ecology,shedding light on the complexities of this dynamic relationship in a vulnerable ecosystem.

Riparian habitat quality as an indicator of land use/land cover effects on riverine water quality

Riparian land use/land cover(LULC)plays a crucial role in maintaining riverine water quality by altering the transport of pollutants and nutrients.Nevertheless,establishing a direct relationship between water quality and LULC is challenging due to the multi-indicator nature of both factors.Water quality encompasses a multitude of physical,chemical,and biological parameters,while LULC represents a diverse array of land use types.Riparian habitat quality(RHQ)serves as an indicator of LULC.Yet,it remains to be seen whether RHQ can act as a proxy of LULC for assessing the impact of LULC on riverine water quality.This study examines the interplay between RHQ,LULC and water quality,and develops a comprehensive indicator to predict water quality.We measured several water quality parameters,including pH(potential of hydrogen),TN(total nitrogen),TP(total phosphorus),T_(water)(water temperature),DO(dissolved oxygen),and EC(electrical conductivity)of the Yue and Jinshui Rivers draining to the Han River during 2016,2017 and 2018.The water quality index(WQI)was further calculated.RHQ is assessed by the InVEST(Integrated Valuation of Ecosystem Services and Tradeoffs)model.Our study found noticeable seasonal differences in water quality,with a higher WQI observed in the dry season.The RHQ was strongly correlated with LULC compositions.RHQ positively correlated with WQI,and DO concentration and vegetation land were negatively correlated with T_(water),TN,TP,EC,cropland,and construction land.These correlations were stronger in the rainy season.Human-dominated land,such as construction land and cropland,significantly contributed to water quality degradation,whereas vegetation promoted water quality.Regression models showed that the RHQ explained variations in WQI better than LULC types.Our study concludes that RHQ is a new and comprehensive indicator for predicting the dynamics of riverine water quality.

Effects of phosphorus fertilizer application rate on transformation processes of phosphorus fractions in the purple alluvial soil of a riparian zone

Effects of phosphorus(P)fertilizer application rate on soil transformation processes of P fraction are still unclear in the riparian zone.Purple alluvial soils in the riparian zone of the Three Gorges Reservoir were collected to conduct a 21-day incubation executed by two hydrological environments(drying and flooding)and ten application rates of P fertilizer.Transformation percentages of P fertilizer(TPPF)were calculated as content differences of soil P fractions between fertilizer addition and none fertilizer addition divided by soil total P increases caused by fertilizer addition.TPPF to inorganic P extracted by sodium hydroxide(NaOH-Pi)and hydrochloric acid(HCl-Pi)increase by 20.91%(9.71%)and 24.26%(40.72%)under the drying(flooding)environment.Instead,TPPF to the other fractions decrease.Phosphorus fertilizer input mainly has indirect positive and negative effects on organic P via precipitated P under the drying and flooding environments and finally has indirect positive effects on labile P(p<0.001).Percentage changes of water-soluble inorganic P(H2O-Pi)and HCl-Pi under the flooding environment are higher than that under the drying environment,and percentage changes of organic P extracted by sodium hydrogen carbonate(Na HCO3-Po)and NaOH-Pi show an opposite trend(p<0.01).?(differences in soil P fraction content between flooding and drying incubations)H2O-Pi is negatively correlated with?NaHCO3-Po,and?NaHCO3-Po is positively correlated with?NaOH-Pi(p<0.001).In conclusion,P fertilizer is transformed more into precipitated P than into other P fractions with an application rate increase.Phosphorus fertilizer input mainly increases organic P via precipitated P under the drying environment and decreases organic P via precipitated P under the flooding environment,and organic P is further transformed into labile P.With P fertilizer input,P release caused by flooding is derived from NaHCO3-Po release triggered by NaOH-Pi release.The results can be helpful for the understanding of P fertilizer migration processes from the riparian zone soil to the Three Gorges Reservoir under rain leaching and flooding.

Land Use and Environmental Gradients Influence on Riparian Woody Plant Diversity and Structure in Lake Manyara Watershed Ecosystem, Tanzania

Riparian vegetations are important in supporting ecological connectivity between aquatic and terrestrial ecosystems. The structure and species composition of riparian woody plants have been subjected to multiple forces with varying degree of influences. This study examined the influence of land use and environmental gradient to the structure and composition of the riparian woody plants in northern Tanzania. A total of 270 plots were surveyed for woody plant species in the riparian ecosystems and later analysed to determine the influence of land use categories (homegarden, crop field, woodlot, open canopy forest, and closed canopy forest) and environmental variables (temperature, precipitation, elevation and slope) to the species richness, abundance, and stand parameters. Basal area was higher in woodlots, homegardens and crop fields than in the open and closed canopy forests;and as expected the reverse was true for the number of stocking density. Correlation among stand parameters with environmental variables varied significantly. Species richness and species abundance were negatively correlated to precipitation, temperature and elevation, while stocking density and basal area were positively correlated to precipitation. The study recommends continual retentions of trees on farm, further promoting of agroforestry interventions and sustainable utilization of woody plants in open and close canopy forests.

Characteristics,classification and ordination of riparian plant communities in the Three-Gorges areas

Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparian plant communities distributed along the gradient of moisture.

Distribution pattern of rare plants along riparian zone in Shennongjia Area

Due to the importance of riparian zone in maintaining and protecting regional biodiversity, increasingly more ecologists paid their attentions to riparian zone and had been aware of the important effects of riparian zone in basic study and practical management. In this study, 42 sampling belts (10 m?00 m) parallel to the bank of Xiangxi River at different elevations in Shennongjia Area were selected to investigate the riparian vegetation and rare plants. 14 species of rare plants were found distributing in riparian zone, accounting for 42.4% of the total rare plant species in Shennongjia Area. The main distribution range of the 14 rare plant species was the evergreen and deciduous mixed broadleaved forest at elevation of 1200-1800 m, where, species diversity of plant community was the maximum at the moderate elevation. The analysis of TWINSPAN divided the 14 rare species into 3 groups against the elevation, namely low elevation species group, moderate elevation species group, and high elevation species group. The analysis of DCA ordination showed similar results to that of TWINSPAN. In the paper, the authors discussed the reasons forming the distribution pattern of rare plant species, and pointed out that the important function of riparian zone on rare plant species protection.

Landscape Design of Majiagou Riparian Small Park in Harbin City:Wuxing Park

This paper analyzed landscape status of the area where Majiagou Riparian Small Park in Harbin City-Wuxing Park was constructed, explained the park's design concept, overall structure layout, landscape and function division, planting design, ecological planning and so on. The purpose of the design was to create for people an urban park with reasonable layout, distinct division, ecological function, historical memory and distinctive feature.

Agricultural non-point nitrogen pollution control function of dierent vegetation types in riparian wetlands: A case study in the Yellow River wetland in China

Riparian wetland is the major transition zone of matter, energy and information transfer between aquatic and terrestrial ecosystems and has important functions of water purification and non-point pollution control. Using the field experiment method and an isotope tracing technique, the agricultural non-point nitrogen pollution control function of different vegetation types in riparian wetland was studied in the Kouma Section of the Yellow River. The results showed that the retention of agricultural non-point nitrogen pollution by riparian wetland soil occurs mainly in top 0-10 cm layer. The amount of nitrogen retained by surface soils associated with three types of vegetation are 0.045 mg/g for Phragmites communis Trin Linn, 0.036 mg/g for Scirpus triqueter Linn, and 0.032 mg/g for Typha angustifolia Linn, which account for 59.21%, 56.25%, and 56.14% of the total nitrogen interception, respectively. Exogenous nitrogen in 0-10 cm soil layer changes more quickly than in other layers. One month after adding KISNO3 to the tested vegetation, nitrogen content was 77.78% for P communis Trin, 68.75% for T. angustifolia, and 8.33% for S. triqueter in the surface soil. After three months, nitrogen content was 93.33% for P. communis Trin, 72.22% for S. triqueter, and 37.50% for T. Angustifolia. There are large differences among vegetation communities respecting to purification of agricultural non-point nitrogen pollution. The nitrogen uptake amount decreases in the sequence： new shoots ofP. communis Trin （9.731 nag/g） 〉 old P. communis Trin （4.939 mg/g） 〉 S. triqueter （0.620 mg/g） 〉 T. angustifolia （0.186 mg/g）. Observations indicated that the presence of riparian wetlands as buffers on and adjacent to stream banks could be recommended to control agricultural non-point pollution.

Vitality variation and population structure of a riparian forest in the lower reaches of the Tarim River,NW China

Since 2000, the Chinese government has implemented emergency water diversion measures to restore the damaged riparian forest ecosystem with dominant tree species Euphrat poplar(Populus euphratica Oliv.)at the lower reaches of the Tarim River. In the present study, comparative analysis of variations in the vitality of P. euphratica trees were made using 2005 and 2010 data to illustrate the revitalization process of riparian forest. Poplar trees within 300 m of the riverbed were positively revitalized, while the vitality of trees farther than 300 m from the river decreased. Population structure was studied to demonstrate the development of poplar community. In the first belt, the class structure for the diameter at breast height(DBH) of P. euphratica fit a logistic model, and the 2nd, 3rd and 4th belt curve fittings were close to a Gaussian model; in other plots they were bimodal. Cluster analysis of the composition of the DBH class of poplar trees demonstrated that those within 16–36 cm DBH were the most abundant(58.49% of total) in study area, under 16 cm of DBH were second(31.36%), and trees >40 cm DBH were the least abundant(10.15%). More than 80% of the trees were young and medium-sized, which means that the poplar forest community in the vicinity of the lower Tarim River is at a stable developmental stage. The abundance of juvenile trees of P. euphratica in the first and second measuring belts was 12.13% in 2005 and increased to 25.52% in 2010, which means that the emergency water transfer had a positive impact on the generation of young P. euphratica trees in the vicinity of the river.

Shallow groundwater nitrogen responses to different land use managements in the riparian zone of Yuqiao Reservoir in North China

This field study investigated the nitrogen concentrations in the shallow groundwater from an ephemeral stream and four land uses： cropland, two-year restored （2yr） and five-years restored （Syr） woodlands, fishponds, and the nitrogen flux in the riparian zone of Yuqiao Reservoir. The groundwater nitrate-N concentrations in cropland were the highest among the four land uses. Total dissolved nitrogen （TDN） and nitrate-N concentrations in the 2yr woodland were significantly （p 〈 0.05） higher than in 5yr woodland. The lowest nitrogen concentrations were detected in fishponds. Nitrate-N was the main form in cropland and 2yr woodland, whereas both nitrate-N and dissolved organic nitrogen （DON） were the main species in 5yr woodland and fishponds. But, ammonium-N was the main form in the ephemeral stream. During the rainy season, the groundwater flow with dissolved nitrogen drains from upland into the reservoir along the hydraulic gradient. The woodland between the cropland and reservoir could act as a buffer to retain shallow groundwater nitrogen. The dominant form of ammonium-N in the groundwater TDN pool in ephemeral stream indicated that nitrogen from the village and orchard in upland flowed into the reservoir via subsurface flow. The fishpond was not an important pollution source for nitrogen transfer via shallow groundwater.

Restoring environmental flows and improving riparian ecosystem of Tarim River

Rapid population growth and artificial oasis enlargement did pose great threat to the natural riparian ecosystems of Tarim River and caused seriously ecological deterioration and greater desertification of the Tarim River Basin in the second half of 20 century. Restoration of the endangered riparian ecosystem requires that environmental flow should be restored through restricted and uncontrolled flow diversion irrigation in tributary areas. Implementation of such restriction needs further the basin-wide reallocation of water resources through a set of engineering and non-engineering measures taken to ensure the water requirement in the tributary and maintain effective flows in Tarim River. As one of evolving HELP (Hydrology for Environment, Life and Policy) basins, the article first presents an overview of hydrology, socio-economic development and ecosystem evolution of the Tarim River Basin. Then, those measures for restoring and maintaining environmental flow are reviewed and analyzed along with its applicability and validity. The issues emerging in implementing those measures are also explored, and then the conclusions were summarized. Lessons learned could provide a good example for other basins under similar conditions.

Effects of soil moisture regimes on growth and photosynthesis of the riparian plant Bolboschoenus planiculmis

Plants distributed in riparian regions experience frequent episodes of flooding and drought between years, and hence, riparian plants need to be flood- and drought-tolerant. Riparian plants possess various traits to survive flooding, while their sensitivity to drought has received less attention. To investigate the growth and photosynthetic responses of a riparian species （Bolboschoenus planiculmis） to flooding and drought, plants of this species were subjected to 60-d flooding or drought stress under greenhouse conditions. Growth and photosynthetic traits were measured at the end of the treatments. As well, we determined the efficiency of photosynthetic apparatus in mature leaves. Plants of B. planiculmis adequately adjusted their growth and photosynthetic traits under both flooding and drought conditions. Flooding did not affect the above-ground growth of B. planiculmis. Increased growth of roots and rhizomes and the generation of new tubers suggested a high ability of below-ground lateral growth by capturing resources under flooding conditions. Enhanced photosynthetic capacity, retained leaf pigment concentrations and chlorophyll a fluorescence capacity indicated photosynthetic adaptation to flooding. In contrast, drought significantly decreased the above-ground growth of B. planiculmis, especially the leaves, thereby minimizing water loss due to transpiration. Its increased root to shoot ratio and ＂phalanx＂ asexual propagation pattern might enhance soil water uptake ability. Although the functional leaves of B. planiculmis could retain their leaf pigment concentrations, as well as photosynthesis and chlorophyll a fluorescence, the total biomass of plants decreased, which may be a consequence of the reduced leaf area, suggesting adverse effects by drought. Therefore, both growth and photosynthetic responses of B. planiculmis are likely to contribute to the ability of this species to thrive in riparian regions, but remain susceptive to drought.

Influencing factors of sediment deposition and their spatial variability in riparian zone of the Three Gorges Reservoir,China

Many factors can affect the sediment deposition and soil erosion process in riparian zone, including terrain, sediment transport and water level fluctuations. Clarifying the factors influencing sediment deposition process in the riparian zone of the Three Gorges Reservoirs is an important problem to determine the key area of sediment deposition and its trend of development in the study area. In order to reveal the influence of these environmental factors on the sediment deposition in riparian zone of the Three Gorges Reservoir, this study investigated 1） the amount of deposited sediment in different environmental conditions, 2） the potential factors affecting sediment deposition in riparian zone of the Three Gorges Reservoir, 3） the relationship between the deposited sediment amount and these factors previously mentioned using correlation analysis, and 4） the influence of human activities considered as an additional factor. This study found that 1） slope gradient, elevation, inundating duration and human activities were the main factors influencing sedimentation in riparian zone of the Three Gorges Reservoir, and 2） the impact of each factor varied with spaces. Specifically, in the upper reach from Jiangjin to Fuling, human activities such as gravel dredging, bank revetment and ports and wharfs constructing disturbed considerable amounts of deposited sediment, as a result, there was no natural law to dictate the distribution. In the middle reach from Fuling to Fengjie, slope gradient and inundating duration were the controlling factors, and the sediment deposition amount was greater in the areas with a gentler slope or lower elevation. Water flow on gentler slopes generally had lower velocity, resulting in more sediment to deposit. Sites with lower elevations would be drowned by sediment-laden flow with a longer duration resulting from hydrologic regime controlled by the operating strategy of the Three Gorges Reservoir, leading to a larger amount of sediment deposition. In the lower reach from Fengjie to Zigni, slope gradient was similar to the middle reach, performing a primary factor, while other factors showed little relationship with sediment amount.

Nighttime sap flow and its driving forces for Populus euphratica in a desert riparian forest, Northwest China

Nighttime sap flow is a potentially important factor that affects whole-plant water balance and water-use efficiency （WUE）. Its functions include predawn disequilibrium between plant and soil water potentials as well as between the increments of oxygen supply and nutrient uptake. However, main factors that drive nighttime sap flow remain unclear, and researches related to the relationship between nighttime sap flow velocity and environmental factors are limited. Accordingly, we investigated the variations in the nighttime sap flow of Populus euphratica in a desert riparian forest of an extremely arid region, Northwest China. Results indicated that P. euphratica sap flow occurred throughout the night during the growing season because of the partial stomata opening. Nighttime sap flow for the P. euphratica forest accounted for 31%-47% of its daily sap flow during the growing season. The high value of nighttime sap flow could be the result of high stomatal conductance and could have significant implications for water budgets. Throughout the whole growing season, nighttime sap flow velocity of P. euphratica was positively correlated with the vapor pressure deficit （VPD）, air temperature and soil water content. We found that VPD and soil water content were the main driving factors for nighttime sap flow of P. euphratica.

Plant diversity and its maintenance in Populus euphratica riparian forests in the Ejina Oasis,China

The dynamic environments in riparian zones support a variety of life-history strategies, which constitute a fundamental mechanism for development and maintenance of biodiversity in riparian forest ecosystems. To demonstrate the effect of life-history strategies on biodiversity, we investigated community-level diversity and its relationship to environmental variability in the riparian Populus euphratica forests of the Ejina Oasis. Communities were divided into 14 associations on the basis of their species impor- tance values. The Simpson＇s index, Shannon-Wiener index, Pielou＇s evenness index and the regional Whittaker＇s index were applied to calculate community diversity. An ordination of the sample plots was carried out by correspondence analysis （CA）. Biodiversity was relatively low across the entire study area, but there was high community diversity （flw = 8.09） due to the spatial heterogeneity of habitats in different plots. In addition, we investigated the relationship between biodiversity and several environmental factors, such as water availability, community components and soil conditions. We conclude that the heterogeneity of soil and water availability drives community diversity patterns in riparian zones and that community-level diversity favors the maintenance of species diversity in the P euphratica forests in the Ejina Oasis.

Soil nutrients in relation to vertical roots distribution in the riparian zone of Three Gorges Reservoir,China

Since the impoundment of the Three Gorges Reservoir(TGR), the riparian zone has been subjected to numerous environmental changes. This study was conducted to recognize the distribution of grass roots and its impacts on soil nutrients in the water level fluctuation zone of TGR. Roots of four predominant herbaceous plants in the study area, specifically, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, and their corresponding relation with soil nutrient contents were investigated. Root surface area density was determined with Win RHIZO, and the relationships of root distribution with soil depths and soil nutrient contents were studied. The results indicates that most roots are distributed in the top soil layer of 0-10 cm. Estimated root surface area density for the selected grass species ranges from 0.16 to 13.44 cm^2/cm^3, and decreases exponentially with an increase in soil depth. Soil organic matter and total nitrogen contents are significantly lower on bare control area than the corresponding values on the grasslands. Total nutrient contents on grasslands of C. dactylon and H. compressa are higher than those of other grass areas. Root length density and root surface area density are significantly correlated with soil organic matter and total nitrogen content for the four grasslands. The present results suggests that plant roots have significant effects on the distribution of soil nutrients in soil profiles in the riparian zone along the TGR. Nevertheless, additional investigations are needed to reveal the specific interactions between plant roots distribution, soil nutrients and water level fluctuations.

Effects of a Low-Head Dam Removal on River Morphology and Riparian Vegetation: A Case Study of Gongreung River

The long term existence of a low-head dam in the river channel significantly affects river geomorphology and river ecosystem. Because more and more low-head dam structures have deteriorated in recent years, the attention for low-head dam removal is increasing as one of alternatives for river restoration. Thus, this study intends to investigate the impacts of low-head dam removal on river geomorphology and riparian vegetation with developing a quantitative method to predict the changes of river morphology as well as invasion, growth, expansion and destruction of riparian vegetation after a low-head dam removal. To verify the numerical simulation model, the low-head dam removal case in Gongreung River was employed with investigation of low-head dam removal responses on river geomorphology and riparian vegetation. Following the low-head dam removal, the results of monitoring and numerical simulation indicated that new sand bars has formed as well as increasing the extent of existing sand bars in the upstream of the low-head dam. The sand bars have been colonized in a year after the low-head dam removal by grass type plants. After a decade to several decades, the riparian vegetation in sand bars often developed to tree type plants in several low-head dam removal cases. As other cases, Gongreung River also showed the growth of tree type plants in 5 years after the removal.

Geochemical Characteristics of Heavy Metals in Riparian Sediment Pore Water of Songhua River, Northeast China

This study reports the geochemical characteristics of zinc (Zn), copper (Cu), lead (Pb), nickel (Ni), mercury (Hg), iron (Fe), and manganese (Mn) in the riparian sediment pore water of the Songhua River, Northeast China. In total, 36 pore water samples and 18 surface water samples from three typical sections were collected and analyzed in June 2009. Cluster analysis of heavy metals was performed to analyze the pollution sources of the metals. Results showed that Hg concentrations in the pore water were greater than those in the surface water, indicating a potential ability of Hg release from riparian sediment system to river water. However, concentrations of Fe and Mn in the surface water were greater than those in the pore water, demonstrating that the microenvironments of riparian and riverbed sediment systems were quite different. Variations of Zn, Cu, Pb and Ni between the surface and the pore water were different in each section. Most metals had similar horizontal and profile distribution characteristics in the three sections except for Zn and Ni. Hg, Fe and Mn concentrations in the pore water increased gradually with the increase in horizontal distance from water body, in contrast to this, Cu decreased, and Pb presented a fluctuating trend. With the increase in depth, Pb and Fe, Cu and Mn showed the same trends, and Hg showed a variable trend. The above distribution characteristics could mainly be attributed to the properties and the interactions of metals, pH and oxidation-reduction conditions, and the complex pollution sources and hydrologic regime in history. The probable sources of metals include the historical and ongoing discharge of industrial wastewater, mining activities, sewage irrigation for agricultural production, and atmospheric deposition from coal-fired plants.

Estimation of soil reinforcement by the roots of four postdam prevailing grass species in the riparian zone of Three Gorges Reservoir, China

Soil erosion and bank degradation is a major post-dam concern regarding the riparian zone of the Three Gorges Reservoir. The development and succession of vegetation is a main countermeasure,especially to enhance bank stability and mitigate soil erosion by the root system. In this study, the roots of four prevailing grass species, namely, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, in the riparian zone were investigated in relation to additional soil cohesion. Roots were sampled using a single root auger. Root length density（RLD） and root area ratio（RAR） were measured by using the Win RHIZO image analysis system. Root tensile strength（TR） was performed using a manualdynamometer, and the soil reinforcement caused by the roots was estimated using the simple Wu＇s perpendicular model. Results showed that RLD values of the studied species ranged from 0.24 cm/cm3 to20.89 cm/cm3 at different soil layers, and RLD were significantly greater at 0–10 cm depth in comparison to the deeper soil layers（＆gt;10 cm）. RAR measurements revealed that on average 0.21% of the reference soil area was occupied by grass roots for all the investigated species. The measured root tensile strength was the highest for P. paspaloides（62.26MPa） followed by C. dactylon（51.49 MPa）, H.compressa（50.66 MPa）, and H. altissima（48.81MPa）. Nevertheless, the estimated maximum root reinforcement in this investigation was 22.5 k Pa for H.altissima followed by H. compressa（21.1 k Pa）, P.paspaloides（19.5 k Pa）, and C. dactylon（15.4 k Pa） at0–5 cm depth soil layer. The root cohesion values estimated for all species were generally distributed at the 0–10 cm depth and decreased with the increment of soil depth. The higher root cohesion associated with H. altissima and H. compressa implies their suitability for revegetation purposes to strengthen the shallow soil in the riparian zone of the Three Gorges Reservoir. Although the soil reinforcement induced by roots is only assessed from indirect indicators, the present results still useful for species selection in the framework of implementing and future vegetation recovery actions in the riparian zone of the Three Gorges Reservoir and similar areas in the Yangtze River Basin.

Regeneration status of riparian tree species in two sites that differ in land-use in the Okavango Delta,Botswana

Human communities from the Okavango Delta benefit from the services and goods provided by the wetland ecosystem through its riparian vegetation. These include food and timber products used for the construction of shelter and canoes. Despite the importance of riparian tree species in the Delta, their regeneration structure is currently unknown. For riparian trees to be managed sustainably, information on the current regeneration status of the trees under different land uses is needed. The Moremi game reserve (protected area) and Seronga (communal area) were selected for this study on the regeneration of riparian tree species of Croton megalobotrys Müll. Arg, Philenoptera violacea (Klotzsch) Schrire, Senegalia nigrescens (Acacia nigrescens) Oliv and Diospyros mespiliformis Hochst. ex A. Dc. The height of each individual tree was estimated in randomly selected 30 plots (15 from each site) of 20 × 50 m for assignment to five regeneration classes: 0-0.5, 0.5-1, 1-2, 2-4 and >4 m. Linear regression was used to infer regeneration status of each species. An independent-sample Student’s t test was used to determine any significance differences in seedling density/ha and sapling density/ha between different sites at p < 0.05. Diospyros mespiliformis populations had an unstable regeneration structure in both sites, while P. violacea regeneration was stable regardless of land-use type. Croton megalobotrys and S. nigrescens had an unstable regeneration pattern in Seronga, while in Moremi it was stable; thus, the regeneration structure of C. megalobotrys and S. nigrescens is affected by land-use. This result implies that intervention is needed to conserve the two species in Seronga where the current land-use appears to be incompatible with regeneration; D. mespiliformis also needs to be conserved in both Moremi and Seronga.