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Difficulties have hampered bioassessment in southern European rivers due to limited reference data and the unclear impact of multiple interacting stressors on plant communities. Predictive modelling may help overcome this limitation by aggregating different pressures affecting aquatic organisms and showing the most influential factors. We assembled a dataset of 292 Mediterranean sampling locations on perennial rivers and streams (mainland Portugal) with macrophyte and environmental data. We compared models based on multiple linear regression (MLR), boosted regression trees (BRT) and artificial neural networks (ANNs). Secondarily, we investigated the relationship between two macrophyte indices grounded in distinct conceptual premises (the Riparian Vegetation Index — RVI, and the Macrophyte Biological Index for Rivers — IBMR) and a set of environmental variables, including climatic conditions, geographical characteristics, land use, water chemistry and habitat quality of rivers. The quality of models for the IBMR was superior to those for the RVI in all cases, which indicates a better ecological linkage of IBMR with the stressor and abiotic variables. The IBMR using ANN outperformed the BRT models, for which the r-Pearson correlation coefficients were 0.877 and 0.801, and the normalised root mean square errors were 10.0 and 11.3, respectively. Variable importance analysis revealed that longitude and geology, hydrological/climatic conditions, water body size and land use had the highest impact on the IBMR model predictions. Despite the differences in the quality of the models, all showed similar importance to individual input variables, although in a different order. Despite some difficulties in model training for ANNs, our findings suggest that BRT and ANNs can be used to assess ecological quality, and for decision-making on the environmental management of rivers. [ABSTRACT FROM AUTHOR]

Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper, we present an overview of current trends and future directions in aquatic plant research in the early twenty first century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrates the global relevance of aquatic plant research in the early twenty first century but also the many challenges that this burgeoning scientific discipline must address. [ABSTRACT FROM AUTHOR]

Patterns of native and exotic species richness and cover were examined together with the composition of species assemblages along a typical Mediterranean river and across its floodplain. Major goals were to characterize species distribution regarding diverse environmental and habitat features, and to explore floodplain landforms relations using plant assemblages and invasion responses as biological indicators of aquatic–terrestrial connectivity. A floristic survey was undertaken during May and early June 1998 in six sites of a southern Iberian basin. Vegetation data were gathered from three transects in three landforms: inundated and frequently flooded banks (FF), infrequently flooded valley floors (IF), and rarely flooded higher floodplains (RF). We used 2×2 m plots to record each species present and visual estimates of percentage cover of each species. Cover of native and exotic species assemblages were also estimated for each plots, for the transects, and for the landforms. The total number of vascular plant species found was 287 of which only 26 were exotic. Despite the high environmental and geomorphological variability, the hierarchical classification showed that species composition varied across the floodplain, rather than along the river. The IF and RF landforms were the most species-rich, both for native and exotic species group, whereas the cover trends of exotic and native plant species were opposed, with exotics being consistently more abundant in FF, and native cover increasing towards RF landforms. We found positive correlations between native and exotic species richness on the floodplain scale, and on a smaller scale in FF and IF landforms, thus supporting the hypothesis that in aquatic and riparian ecosystems of semi-arid landscapes, species-rich communities are preferentially colonized by exotic species. However, this pattern was not consistently coupled with a high cover of exotic species, and it was not sustained for the dry areas of the RF landforms. [ABSTRACT FROM AUTHOR]

Functional diversity indices are increasingly being used to describe plant community assembly processes and ecosystem functioning. However, their relevance for predicting alterations in ecosystem functioning of riparian plant communities is still largely unknown. We investigated the functional patterns of riparian forests along environmental gradients, using biological and environmental data from 189 well-preserved riverine locations in mainland Portugal. We calculated functional diversity indices (e.g. Richness, Redundancy, Divergence) for four riparian forest types, namely the Alder woodlands, Ash woodlands, Tree-heath shrublands and Mediterranean shrublands, using their plant species composition and 25 plant functional traits. We used multiple linear regression to predict the effect of the environment in the functional structure of riparian forests and ultimately evaluate the resilience of the riparian forests to environmental fluctuations. We found that Mediterranean shrublands have a significantly higher Functional Richness and a lower Functional Redundancy in comparison to the other riparian forest types. Both regional and habitat variables were important for predicting the functional diversity of riparian forests, with varying patterns according to forest types. In particular, we found that the redundancy of Mediterranean shrublands is mostly affected by precipitation, suggesting their potential vulnerability to climate change in the study area. Our results suggest the usefulness of functional diversity measures for conservation and monitoring the ecological functioning of riparian forests. [ABSTRACT FROM AUTHOR]