Complex Undisturbed Riparian Zones Are Resistant to Colonisation by Invasive Alien Plant Species

Riparian vegetation entraps macroplastics along the entire river course: implications for eco-safety activities and mitigation strategies

Macroplastic litter causes detrimental effects on freshwater biota affecting human health. Despite the significant role of rivers in transporting plastic waste, most plastics remain in fluvial ecosystems, accumulating in infrastructure, river sediment, and (riverbank) vegetated areas. However, the entrapment of plastics by riparian vegetation was overlooked, particularly in upper and middle river courses. For the first time, we aimed to quantify the entrapment of plastics by riparian vegetation along the entire river course. Sampling riparian areas in the upper, middle, and lower river courses in central Italy, we found 1,548 macrolitter items, with vegetation entrapping 93.9% of total litter. Riverbank and riparian plastics acted as long-term indicators of river plastics. We emphasized the trapping efficiency at the species level highlighting that the best plastic trapper species were trees, shrubs and reeds (Populus spp., Salix spp., Rubus ulmifolius, Phragmites australis, and Ficus carica), blocking 85.4% of the total macrolitter entrapped by plants. Plastic pieces, bags, bandages, sanitary items, and packaging were among the most trapped types. Furthermore, vegetation in the lower river course exhibited greater plastic entrapment compared to the upper and middle courses, following the fact that all the river courses contribute to plastic pollution. Recognizing the potential of riparian vegetation as a valuable ecosystem service in trapping macroplastics, further research should explore the characteristics and structures of riparian communities involved in this process. By developing eco-safe practices and mitigation strategies based on these findings, we might contribute significantly to managing, conserving, and restoring riverine ecosystems.

Spatial Distribution Pattern and Risk Assessment of Invasive Alien Plants on Southern Side of the Daba Mountain Area

The southern side of the Daba Mountain area is a hotspot of global biodiversity and an essential barrier promoting ecological security. However, knowledge about the distribution status and transmission pathways of invasive alien species (IAS) in this area is limited. We counted the IAS on the southern side of the Daba Mountain area through sample transects and analyzed the factors affecting their spatial distribution. We also assessed IAS risk using the analytic hierarchy process (AHP), which found 64 IAS belonging to 23 families and 53 genera. Around rivers and roads, the results showed a vertical two-way dispersal pattern. Human and environmental factors, such as a very dense transportation network, can affect the distribution pattern of IAS. AHP assessed 43 IAS (67.19%), primarily distributed in villages and towns, as being of high or medium risk. High- and medium-risk IAS should be the focus of invasion prevention and control, and priority should be given to controlling the spread of IAS around rivers and roads.

Study of the Effects of Ten-Year Microclimate Regulation Based on Different Vegetation Type Combinations in a City Riparian Zone

Ecological engineering construction is the main method for urban riparian landscape restoration. Continuous ecological environmental monitoring can reflect the effects of engineering construction and can provide a scientific basis for the improvement of engineering technology. However, the evaluation of riparian ecological engineering mainly focuses on the water environmental function and biodiversity conservation function after the construction period. Studies on the long-term evaluation of regional microclimate regulation and human settlement improvement are limited. In this paper, an ecological restoration project along the Yitong River in northern China was selected as the research object. Temperature, relative humidity and wind speed under different vegetation type combinations were monitored in the riparian ecological engineering construction during the first, second, third and tenth years. The temperature–humidity index (THI) was selected to evaluate human comfort and the improvement effect of microclimate was assessed for different vegetation type combinations. The results showed that vegetation type combinations can play a good role in regulating the microclimate and human comfort. The riparian ecological restoration project achieved a stable function for microclimate regulation in the third year. There was no significant regulation difference between tree–shrub–herb and tree–herb combinations. To realize the optimization of ecological benefits, economic benefits and social benefits, the tree–herb combination can be appropriately increased, and the tree–shrub–herb can be reduced in the application of ecological engineering. Microclimate regulation is an important achievement in engineering construction effects and can be regarded as one of the indices to evaluate the effect of ecological restoration.

Guiding restoration of riparian ecosystems degraded by plant invasions: Insights from a complex social-ecological system in the Global South

Restoring riparian ecosystems in human-dominated landscapes requires attention to complexity, and consideration of diverse drivers, social actors, and contexts. Addressing a Global North bias, this case study uses a mixed-method approach, integrating historical data, remote sensing techniques and stakeholder perceptions to guide restoration of a river in the Western Cape, South Africa. An analysis of aerial photographs of the riparian zone from 1953 to 2016 revealed that although anthropogenic land conversion happened primarily before the 1950s, several land use and land cover classes showed marked increases in area, including: waterbodies (+ 1074%), urban areas (+ 316%), alien weeds (+ 311%) and terrestrial alien trees (+ 79%). These changes have likely been driven by land fragmentation, disturbance, and agricultural intensification. Stakeholder interviews revealed that despite the clear need for restoration, several barriers exist to successful implementation; these stem from inadequate financial resources, inappropriate funding models, institutional challenges, and a lack of techno-scientific knowledge. We give several recommendations to overcome these barriers.

Riparian Buffers as a Critical Landscape Feature: Insights for Riverscape Conservation and Policy Renovations

Riparian zones are critical for functional integrity of riverscapes and conservation of riverscape biodiversity. The synergism of intermediate flood-induced disturbances, moist microclimates, constant nutrient influx, high productivity, and resource heterogeneity make riparian zones disproportionately rich in biodiversity. Riparian vegetation intercepts surface-runoff, filters pollutants, and supplies woody debris as well as coarse particulate organic matter (e.g., leaf litter) to the stream channel. Riparian zones provide critical habitat and climatic refugia for wildlife. Numerous conservation applications have been implemented for riparian-buffer conservation. Although fixed-width buffers have been widely applied as a conservation measure, the effectiveness of these fixed buffer widths is debatable. As an alternative to fixed-width buffers, we suggest adoption of variable buffer widths, which include multiple tiers that vary in habitat structure and ecological function, with each tier subjected to variable management interventions and land-use restrictions. The riparian-buffer design we proposed can be delineated throughout the watershed, harmonizes with the riverscape concept, thus, a prudent approach to preserve biodiversity and ecosystem functions at variable spatial extents. We posit remodeling existing conservation policies to include riparian buffers into a broader conservation framework as a keystone structure of the riverscape. Watershed-scale riparian conservation is compatible with landscape-scale conservation of fluvial systems, freshwater protected-area networks, and aligns with enhancing environmental resilience to global change. Sustainable multiple-use strategies can be retrofitted into watershed-scale buffer reservations and may harmonize socio-economic goals with those of biodiversity conservation.

Macrophyte communities as indicators of the ecological status of drainage canals and regulated rivers (Eastern Poland)

Macrophytes are one of the biological elements for assessing the ecological status. Macrophyte communities were studied in six artificial (drainage canal and ditches) or modified watercourses (regulated rivers). In order to assess the ecological status of the watercourses, studies were carried out with the use of the Macrophyte Index for Rivers (MIR) proposed in the Water Framework Directive. Macrophyte communities were mainly represented by helophytes (12 species in total), and the highest percentage area cover (50-75% of the site) was observed for pleustophytes (Lemna spp.). Macrophytes communities were affected by the gradients of hydromorphological (canal modification, flow type, and shading) and parameters water quality (nutrients and water transparency). The relationships were highly species-specific. In accordance with the MIR values, the ecosystems were classified as having poor (drainage canal), moderate (regulated rivers), or good (drainage ditches) ecological status.

The Relationships of Habitat Conditions, Height Level, and Geographical Position with Fruit and Seed Traits in Populations of Invasive Vine Echinocystis lobata(Cucurbitaceae) in Central and Eastern Europe

In climbing plants, fruits can be formed at different heights, depending on the height of external support. However, the effect of height on fruit and seed traits in invasive vines of Cucurbitaceae has not been intensively studied so far. In Europe, Echinocystis lobata, a North American member of Cucurbitaceae, is considered one of the most abundant invasive alien plants spreading in natural riparian forests, thickets, and tall herbs, whereas it is a rare species in urban woodlands. In this study, we tested the variability of selected fruit and seed traits of E. lobata in connection with habitat origin (natural, semi-natural, and anthropogenic), habitat type (using the EUNIS habitat classification), height (the distance between the fruit and the ground), and geographical position. The study was conducted in 2018 in 65 sites located in Latvia, Lithuania, Poland, and Slovakia. In each study site, a random sample of 10 fresh mature fruits of E. lobata was collected from subsequent 0.50 m intervals of height. The length, the width, and the weight of the fresh fruits, as well as the total number of seeds and number of undeveloped seeds per fruit, were examined. Moreover, the well-developed seeds from selected study sites were weighed. The statistical analysis showed the significant effect of habitat origin, habitat type, and height on most of the studied fruit and seed traits. The largest range of height (from 0.00 to 4.00 m) was observed in two types of habitats (F—heathland, scrub, and tundra; and G—woodland, forest, and other wooded land). The total number of seeds per fruit was positively correlated with the length, width, and weight of the fresh fruits. The fruits were a little heavier and bigger in natural habitats located in the northeast of the study area. The distribution of fruits at different heights may contribute to better dispersal of seeds by animals and wind, and may also better protect the seeds from being eaten by granivorous animals. The defence against seed-eating animals is expected to be stronger in semi-natural habitats, as well as on banks and shores of inland surface waters, where the seed production is the highest. The influence of seed traits on seed germination and seedling survival in various habitats and their importance in the invasiveness of E. lobata require further study.

Diversity of Macrophytes and Environmental Assessment of the Ljubljanica River (Slovenia)

The present research aimed to determine the diversity of macrophyte taxa in the Ljubljanica River and its relationship with environmental parameters. In each of the 19 river sections, the presence and abundance of plant taxa were recorded, and basic physical and chemical parameters were measured. Additionally, selected environmental parameters were assessed using a modified version of the Riparian, Channel and Environmental (RCE) method. We compared the obtained data set with survey data from the year 2004. In 2019, a total of 34 macrophyte taxa were recorded. The dominant taxa with the highest abundance were Sparganium emersum, Callitriche sp., and the invasive alien species Elodea canadensis. The species richness and diversity of macrophytes decreased with distance from the source, an increase in pH, and alterations of the riverbed structure due to interference in the riverine ecosystem in the lower part of the Ljubljanica River and its catchment. The comparison of 2004 and 2019 surveys revealed a decrease in the overall presence and abundance of P. natans and in the frequency of occurrence of the species Myriophyllum spicatum and an increase in the presence and abundance of the invasive alien species Elodea canadensis.