Do invasive alien plants really threaten river bank vegetation? A case study based on plant communities typical for Chenopodium ficifolium-An indicator of large river valleys.
ABSTRACT: Riparian zones are very rich in species but subjected to strong anthropogenic changes and extremely prone to alien plant invasions, which are considered to be a serious threat to biodiversity. Our aim was to determine the spatial distribution of Chenopodium ficifolium, a species demonstrating strong confinement to large river valleys in Central Europe and an indicator of annual pioneer nitrophilous vegetation developing on river banks, which are considered to be of importance to the European Community. Additionally, the habitat preferences of the species were analysed. Differences in the richness and abundance of species diagnostic for riverside habitats, as well as the contribution of resident and invasive alien species in vegetation plots along three rivers differing in terms of size and anthropogenic impact were also examined. Finally, the effect of invaders on the phytocoenoses typical for C. ficifolium was assessed. The frequency of C. ficifolium clearly decreased with an increasing distance from the river. Among natural habitats, the species mostly preferred the banks of large rivers. The vegetation plots developing on the banks of the three studied rivers differed in total species richness, the number and cover of resident, diagnostic and invasive alien species, as well as in species composition. Our research indicates that abiotic and anthropogenic factors are the most significant drivers of species richness and plant cover of riverbank vegetation, and invasive alien plants affect this type of vegetation to a small extent.
Project description:Background:Conventional river engineering operations have a substantial influence on the fluvial ecosystem. Regulation and channelization generally reduce the physical heterogeneity of river beds and banks and the heterogeneity of habitats. They determine the character, diversity and species richness of plant communities. The effect of river regulation on vegetation has been repeatedly investigated, but few studies have been conducted within reaches of previously regulated rivers. The aim of this work is to expand and current knowledge about the impact of dredging on the vegetation of a regulated section of a lowland river. Materials & Methods:The study included pre-dredging (1 year before) and post-dredging surveys (results 1 and 2 years after dredging). The vegetation was analysed in terms of species composition, origin of species, life forms, distribution of Grime's life strategies, and selected ecological factors. The Shannon-Wiener biodiversity index (H) and evenness were also analysed in each year of the study. The impact of dredging on the vascular flora was assessed by 'before-after-control-impact' (BACI) analysis. Results:The number of species and biodiversity as measured by the Shannon-Wiener index (H) increased in the analysed section of the river valley. However, enrichment of the flora was observed only on the floodplain, on the surface of the deposited dredging material, while the number of species in the river channel decreased, as dredging of the river bed and levelling of the banks had markedly reduced habitat diversity. Although species richness in the second year after the dredging approached the values recorded before the intervention, the absence of particularly species or phytocenoses associated with shallow river banks and sandbars was still observed. The change in habitat conditions and the destruction of the vegetation cover during the dredging enabled penetration by numerous previously unrecorded alien species of plants and apophytes. There was a perceptible increase in the role of therophytes in the flora. It is worth noting that the number of alien species and therophytes declined significantly in the second year after the dredging. Analysis of the proportions of species representing various life strategies showed that previously unrecorded species with the type R (ruderal) life strategy had appeared, representing by pioneer species occurring in frequently disturbed habitats. There was also a marked increase in the share of species representing the mixed C-R (competitive-ruderal) strategy, occurring in habitats with low levels of stress, whose competitive abilities are limited by repeated disturbances. By the second year after the dredging, however, these changes were largely no longer observed. Conclusions:Through appropriate maintenance of the regulated river, it can be rapidly recolonized by vegetation after the procedure, but it may lead to the loss of some species and phytocoenoses.
Project description:Urban rivers have been overlooked as they are regarded as unnatural with poor ecological conditions to support aquatic life. This dataset presents the abundance and taxa richness of macroinvertebrates collected in an urban Palmiet River, which showed highly variable stretches with respect to water quality and physical habitat availability. A YSI 556 MPS handheld multiparameter instrument was used to measure physical variables of the water, whereas samples were taken using sampling bottles and kept in the fridge prior to nutrient analysis. Habitat assessment was carried out following the integrated habitat assessment score (IHAS) protocol. Macroinvertebrates were collected using modified SASS5 protocol, where stone, vegetation, and gravel sand, and mud biotopes were sampled. Macroinvertebrates were identified to family levels, and abundance and taxa richness were calculated. This data affirms the capacity of urban rivers to harbor aquatic biota and to self-purify along the longitudinal gradient. The data further attest that the response of urban rivers to anthropogenic activities does not differ from natural streams, and the assemblage of macroinvertebrates is driven by water quality and physical habitat. Moreover, the role played by anthropogenic litter in the absence of natural habitat is stressed. Lastly, this data can guide urban ecologists when designing studies for highly variable urban river systems as it illustrates the dynamics of urban ecosystems and their potential to harbor aquatic biota.
Project description:The study of changes in species richness and composition along rivers has focused on large spatial scales. It has been ignored that in different sections of the river (high mountain area, middle zone, and mouth of the river) the specific environmental conditions can generate different longitudinal patterns of the species richness and composition. In this study, we determine whether species richness and composition of the riparian plant communities change along a mountain river and whether these changes are related to environmental variables. We expect an increase in species richness and turnover along the river, that the upstream communities would be a subset of the downstream communities, and that such would be related to edaphic and hydrologic conditions. To test this, we sampled three strata of the riparian vegetation (upper: individuals with <1 cm of ND, middle: individuals with >1 cm of ND, low: individuals with >1 m tall) in a set of 15 sites that we place along a mountain river. Additionally, we recorded topographic, hydrological, morphological, and soil variables. We performed correlation analyzes to determine whether changes in species richness and turnover were related to increased distance to the origin of the river. Also, we obtained the nestedness and evaluated the importance of environmental variables with GLM, LASSO regression, and CCA. With the increase in distance, the species richness decreases in the upper stratum, but not in the middle and the low stratum (although the highest values were observed near the origin of the river), the turnover increase in all strata and the upstream communities were not a subset of the downstream communities. The changes in species richness and composition were related to topographic (altitude), hydrological (flow), and edaphic (conductivity and pH) variables. Our results indicate that at small spatial scales the patterns of richness and composition differ from what has been found at larger spatial scales and that these patterns are associated with environmental changes in the strong altitude gradients of mountain rivers.
Project description:Anthropogenic disturbance and distinctive geochemistry have resulted in rocky desertification in many karst regions of the world. Seed banks are crucial to vegetation regeneration in degraded karst ecosystems characterized by a discontinuous distribution of soil and seasonal drought stress. However, the dynamics of seed banks across one complete series of secondary succession and the underlying mechanisms remain unclear. We selected eight typical stages during secondary succession, conducted aboveground vegetation survey and collected 960 soil samples in the Guiyang karst landscape of China. Seed density, species richness and plant life forms in seed banks were determined via the germination method. The results indicated that the seed density in seed banks before and after field seed germination was significantly different among most succession stages. Community succession had impacts on the seed density of seed banks before and after field seed germination. Seed density ranged from 1,042 seedlings.m<sup>-2</sup> in evergreen broadleaf forests to 3,755 seedlings.m<sup>-2</sup> in the herb community, which was a relatively high density. The seed density and similar species composition between the seed banks and vegetation declined with succession from early to later stages. Species richness in seed banks was highest in middle succession stages and increased with increasing species richness of aboveground vegetation. The species richness of the five life forms in the seed banks showed different variations across these succession stages. The conservation of diverse aboveground vegetation can maintain the diversity of seed banks for restoration.
Project description:Biogeographical barriers formed by natural forces over billions of years have been substantially disrupted by human activity, particularly in recent centuries. In response to these anthropogenic changes, global homogenization of biota is observed at an ever-increasing rate, causing environmental and economic losses as well as emerging health risks. Identifying factors underlying alien species richness is essential for prevention of future introductions and subsequent spread. In this study, we examined the effects of environmental and human-related factors on distribution of alien animal species richness in the Czech Republic (Central Europe). We compiled a set of maps showing the level of invasion of six categories of alien animal species in each of 628 grid cells (ca. 12.0 × 11.1 km) covering the Czech Republic. Relationships between alien species richness and 12 variables characterizing climatic conditions, topography, land cover, and human population size were calculated using the generalized least squares method. Species richness of all alien species, of invertebrates, and of terrestrial species showed the strongest positive relationship with mean annual temperature, while the number of black and grey (proposed prominent invaders) and aquatic species was most closely related to the presence of large rivers. Alien vertebrates showed a strong negative relationship with annual precipitation. The highest alien animal species richness was found in and near large population centers and in agricultural landscapes in warm and dry lowlands. The gateways for alien aquatic species are rather large rivers over sport fishing and aquaculture import. Compiled maps create a powerful visual communication tool, useful in development of programs to prevent future introductions.
Project description:One of the simplest questions in riverine science remains unanswered: "What determines the width of rivers?" While myriad environmental and geological factors have been proposed to control alluvial river size, no accepted theory exists to explain this fundamental characteristic of river systems. We combine analysis of a global dataset with a field study to support a simple hypothesis: River geometry adjusts to the threshold fluid entrainment stress of the most resistant material lining the channel. In addition, we demonstrate how changes in bank strength dictate planform morphology by exerting strong control on channel width. Our findings greatly extend the applicability of threshold channel theory, which was originally developed to explain straight gravel-bedded rivers with uniform grain size and stable banks. The parsimonious threshold-limiting channel model describes the average hydraulic state of natural rivers across a wide range of conditions and may find use in river management, stratigraphy, and planetary science.
Project description:This study explores the potential effects of alien fishes on the native fish community, well-being, and tropic preferences in selected rivers of Klang Valley, Malaysia. Following the Aquatic Species Invasiveness Screening Kit assessment, most of the alien fishes (80%) are invasive. The alien species occurrences correlated positively (<i>p</i> < 0.05) with poor water quality, such as rivers with high ammonia-nitrogen and nitrite, but negatively with phosphate and dissolved oxygen. Anthropogenic characteristics, such as rivers with high pollution levels and ease of accessibility to the fish habitat, are mainly associated positively (<i>p</i> < 0.05) with the occurrences of alien fish species. In general, the results of fish stomach contents analyses and their associated indices, together with stable carbon and nitrogen isotopes, revealed domination by alien fishes or diet overlaps between both alien and native fish species. This finding indicates that alien fishes benefited from the impacts of the anthropogenic activities in their surrounding habitats, while their plasticity in feeding habits might help them to invade, survive, and dominate in the rivers of Klang Valley, Malaysia.
Project description:Riverine environments have been threatened by anthropogenic perturbations worldwide, whereby their fish assemblages have been modified by habitat changes and nonendemic species invasions. We assessed changes in fish assemblages by comparing the species presence in historical and contemporary fish data in the Yellow River from 1965 to 2015. The temporal change in species assemblages was found with increased nonendemic species and fewer natives. Fish species richness of the river declined 35.4% over the past fifty years. Moreover, the decreased mean Bray-Curtis dissimilarity among reaches suggested that the fish assemblages of different reaches in the Yellow River were becoming more similar over time. However, temporal patterns of fish assemblages varied among reaches. In the upper Yellow River, higher species richness and more invasive species were found than those in the historical record, while the lower reaches experienced significant species loss. Dam constructions, exotic fish invasions, and flow reductions played the vital role in structuring the temporal fish assemblages in the Yellow River. It is suggested that river basins which experienced different types and levels of stressors by anthropogenic perturbations can produce varied effects on their temporal trends of species assemblages.
Project description:Cohesive floodplain sediment and vegetation are both thought to cause meandering river patterns. Our aims are to compare the isolated and combined effects of mud and vegetation on river planform and morphodynamics in the setting of intermediate-sized valley rivers. We use a numerical model for century-scale simulation of flow, sediment transport and morphology coupled with riparian vegetation settlement, growth and mortality as functions of species traits on which flow resistance depends. Mud fluxes were predicted by excess shear stress relations in combination with the active layer formulation. We found that valley-flooding water levels increase with vegetation density, causing a higher braiding intensity rather than meandering tendency. The shear stress during floods carves channels through the muddy floodplain surface. Higher mud concentration, on the other hand, increases floodplain aggradation, reduces the overbank flow frequency and ultimately causes formation of a single-thread channel. Vegetation causes mud to deposit closer to the river channel as a levee, showing that mud sedimentation and vegetation settling mutually enhance floodplain formation. However, mud and vegetation counteract in two ways. First, vegetation enhances floodplain accretion, which ultimately increases plant desiccation for high mud concentrations. Second, vegetation increases the tendency of periodic chute cutoffs in valleys. The chute cutoffs locally reset the landscape and create new windows of opportunity for the vegetation. Surprisingly, in systems with a high mud concentration this causes hysteretic loops of vegetation cover and delayed mud deposition. Ramifications for the interpretation of Palaeozoic fluvial facies are that even rootless vegetation, capturing cohesive mud closer to the river channel to form thicker floodplain on the point bar, can enhance the tendency to meander and, under high mud supply, form stable channels. However, meandering is more unlikely in narrower valley rivers with higher vegetation density.
Project description:Alien species are a major component of human-induced environmental change. Variation in the numbers of alien species found in different areas is likely to depend on a combination of anthropogenic and environmental factors, with anthropogenic factors affecting the number of species introduced to new locations, and when, and environmental factors influencing how many species are able to persist there. However, global spatial and temporal variation in the drivers of alien introduction and species richness remain poorly understood. Here, we analyse an extensive new database of alien birds to explore what determines the global distribution of alien species richness for an entire taxonomic class. We demonstrate that the locations of origin and introduction of alien birds, and their identities, were initially driven largely by European (mainly British) colonialism. However, recent introductions are a wider phenomenon, involving more species and countries, and driven in part by increasing economic activity. We find that, globally, alien bird species richness is currently highest at midlatitudes and is strongly determined by anthropogenic effects, most notably the number of species introduced (i.e., "colonisation pressure"). Nevertheless, environmental drivers are also important, with native and alien species richness being strongly and consistently positively associated. Our results demonstrate that colonisation pressure is key to understanding alien species richness, show that areas of high native species richness are not resistant to colonisation by alien species at the global scale, and emphasise the likely ongoing threats to global environments from introductions of species.