Francisca C. Aguiar

Human-disturbed landscapes: effects on composition and integrity of riparian woody vegetation in the Tagus River basin, Portugal

SUMMARY Human activities within fluvial corridors and surrounding landscapes have persistently stressed riparian ecosystems, particularly in Iberian Mediterranean-type streams. The impact of human disturbance relative to natural environmental factors in shaping riparian vegetation is still poorly understood. Both regional variables (such as altitude and precipitation), and site-specific characteristics (such as substrate and riverbank modifications) were analysed as potential determinants of riparian vegetation patterning to determine the relative influences of the diverse land-use types and environmental factors on the composition (including floristic species richness and percentage cover of trees, shrubs and woody climbers) and integrity (width of riparian woods and patterns of longitudinal continuity) of riparian woods in eight river basins of the Tagus fluvial system (Portugal).Therewaspatchyestablishmentofriparian woods, with generally low average width and low species richness, as well as significant inter-basin differences and upstream-downstream variations in riparian features. Species distribution was clearly determined by environmental factors, such as human disturbance on the riverbanks and geological background, and the environmental variables and the land use in the river valley partially explained the integrity of riparian woody vegetation. The results highlight the predictive capability of reach-level features; it appears that, linked with the geomorphological and climate context, small-scale human disturbances on riparian corridorsplayamajorroleinexplainingtheremaining biological variability.

Relative Influence of Environmental Variables on Macroinvertebrate Assemblages from an Iberian Basin

The composition of macroinvertebrate assemblages was studied at 31 sites in the Sado basin, a lowland area with intermittent rivers located in southern Portugal. Riparian features of the sites, including bankfull width, composition, cover, shade, and relative amount of tree debris, were also measured, and local and basin abiotic variables were determined. Woody vegetation in the Sado basin was species poor and was dominated by the ash Fraxinus angustifolia, the alder Alnus glutinosa, and the willows Salix alba and S. salvifolia. The study sites included a broad range of cover and riparian longitudinal integrity. Macroinvertebrate assemblages revealed low levels of richness (4-29 taxa, average 17.6) and Shannons diversity (0.65-2.87 bits, average 1.89), and were dominated by species or groups (especially chironomids) that tolerate organic pollution and habitat disturbance. Assemblages were composed of collector-gatherers (5.4-100%, average 58.1), and to a lesser extent collector-filterers (0-81.3%, average 14.1) and shredders (0-25.5%, average 10.6). Partial canonical correspondence analysis was used to relate the macroinvertebrate assemblages to the riparian characteristics of a site and to local and basin abiotic variables. Out of 8 riparian variables, overhanging tree shade, total tree cover, and abundance of F. angustifolia and A. glutinosa were significant predictors of assemblage variation. Of the 21 abiotic variables considered, only conductivity, distance from source, and the average number of flowless summer months were significant predictors of assemblage variation. Total macroinvertebrate variation was divided into portions that were: 1) explained solely by abiotic variables (∼14%); 2) explained solely by riparian variables (∼18%); 3) explained by both riparian and abiotic variables (∼2%); and 4) unexplained (∼66%). Riparian features had greater influence than other environmental characteristics on the composition of macroinvertebrate assemblages in the Sado basin, perhaps because riparian features are closely related to food types.

Plant invasions in the rivers of the Iberian Peninsula, south-western Europe: A review

Aquatic and riparian ecosystems are known to be highly vulnerable to invasive alien species (IAS), especially when subjected to human-induced disturbances. In the last three decades, we have witnessed a growing increase in plant invasions in Portugal and Spain (Iberian Peninsula, south-western Europe), with very detrimental economic, social and ecological effects. Some of these species, such as the giant reed (Arundo donax L.) and the water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub.), number among the worlds worst weeds. We present an appraisal of this invasive alien river flora and the most problematic aquatic weeds. We review various aspects of invasion ecology, including spatial and temporal patterns of invasion, species invasiveness, species traits of invasive weeds, and relationships between human disturbance in rivers and surrounding areas and invasibility, and contextualize them in overall state-of-the-art terms. We also acknowledge the use of IAS as bioindicators of the ecological quality of rivers, wetlands and riparian zones. Remote-sensing tools and Geographic Information Systems for detecting and monitoring IAS in Iberian rivers are presented.

Structural and functional responses of riparian vegetation to human disturbance: performance and spatial scale-dependence

Successful protection, enhancement and management of surface inland waters require bioassessment and monitoring of ecological quality, as recognized by the Water Framework Directive (WFD; EU/2000/60). In the present paper, we aimed at assessing the response to disturbance of structural and functional components of the riparian ecosystem in order to develop a plant-based index of biotic integrity (Riparian Vegetation index, RVI). Further, the implications of Mediterranean conditions and the spatial scale dependency in the index performance and its component metrics were investigated and discussed. Aquatic and bankside plant species were sampled at more than 400 sites of Portuguese rivers, in Spring-Summer of 2004 and 2005. Over 300 plant attributes were pre-screened to select 32 candidate metrics. Both single stressors and composite stressor indices were used in this study. Two spatial scale-approaches were evaluated: the Local River Type - LRT - which follows the Portuguese river typology, and the Regional River Type - RRT -, which clusters the LRT into North and South types. Compo- sition (e.g. cover and number of alien and endemic species) and functional metrics associated with life cycle and reproduction (e.g. numbers of perennial species), or with trophic status (e.g. proportion of nitrophyllous species) were the most responsive to disturbance across types. Overall, the RVI displayed a reliable response to disturbance; although the local approach has a higher discriminatory effi ciency, the macro scale approach had a more consistent response to multifaceted human disturbances and a more robust performance, essential for environmental-decision making. Results substantiate the hypothesis that plant-based indices of integrity are scale-dependent, an important consideration in the development of typological-adapted methods either for the WFD implementation or for other assessment and monitoring purposes. Future work is required to calibrate the index for inter-annual variability in plant structure and composition, which is especially relevant in Mediterranean-type rivers.

Comparability of river quality assessment using macrophytes: A multi-step procedure to overcome biogeographical differences

This paper exposes a new methodological approach to solve the problem of intercalibrating river quality national methods when a common metric is lacking and most of the countries share the same Water Framework Directive (WFD) assessment method. We provide recommendations for similar works in future concerning the assessment of ecological accuracy and highlight the importance of a good common ground to make feasible the scientific work beyond the intercalibration. The approach herein presented was applied to highly seasonal rivers of the Mediterranean Geographical Intercalibration Group for the Biological Quality Element Macrophytes. The Mediterranean Group of river macrophytes involved seven countries and two assessment methods with similar acquisition data and assessment concept: the Macrophyte Biological Index for Rivers (IBMR) for Cyprus, France, Greece, Italy, Portugal and Spain, and the River Macrophyte Index (RMI) for Slovenia. Database included 318 sites of which 78 were considered as benchmarks. The boundary harmonization was performed for common WFD-assessment methods (all countries except Slovenia) using the median of the Good/Moderate and High/Good boundaries of all countries. Then, whenever possible, the Slovenian method, RMI was computed for the entire database. The IBMR was also computed for the Slovenian sites and was regressed against RMI in order to check the relatedness of methods (R(2)=0.45; p<0.00001) and to convert RMI boundaries into the IBMR scale. The boundary bias of RMI was computed using direct comparison of classification and the median boundary values following boundary harmonization. The average absolute class differences after harmonization is 26% and the percentage of classifications differing by half of a quality class is also small (16.4%). This multi-step approach to the intercalibration was endorsed by the WFD Regulatory Committee.

Invasive river plants from Portuguese floodplains : What can species attributes tell us?

Biological traits of aquatic and riparian plants were compared among invasive and non-invasive groups of species from both native and exotic taxa in Portuguese fluvial systems. Twenty-six riparian and aquatic species were selected and their frequency of occurrence and foliar percentage cover was analysed at 401 sampling sites on the main catchments of Central and Southern Portugal. Canonical correspondence analysis and a hierarchical clustering were applied to the species traits data set. No typical invader profile emerged from the analyses. However, some specific attributes were clearly related to the alien and native plant invasiveness, such as vegetative reproduction, fragment viability and life span. The results of the present work could help with the early detection of invasive plant species in Portuguese fluvial corridors.

Invasibility patterns of knotgrass (Paspalum distichum) in Portuguese riparian habitats.

Spatial patterns of the exotic riverine knotgrass (Paspalum distichum L.) were examined in Mediterranean river basins in Southwestern Iberia. The major goals of this study were to assess the degree of invasibility of riparian habitats by this species and to determine the influence of environmental factors and human-induced disturbances that this knotgrass has on both the landscape and the habitat scales. The present study demonstrates the ability of knotgrass to invade riparian habitats in Portuguese freshwater ecosystems. However, most of the spatial variation of the knotgrass cover seemed to be driven by local factors, such as fine sediment enrichment and the fragmentation of riparian woods, and by other anthropogenic interferences in relation to both the fluvial system and the surrounding landscape. Nomenclature: Knotgrass, Paspalum distichum L. #3 PASDS. Additional index words: Exotic species, human disturbances, environmental variables, PASDS, Mediterranean basin.

The relevance of bryophytes in the macrophyte-based reference conditions in Portuguese rivers

The identification of macrophyte reference communities represents a significant challenge in Mediterranean zones, where few aquatic taxa exist compared to other regions of the world. In the highly seasonal rivers of Portugal, we explored the contribution of bryophytes to enhance the compositional and ecological characterization of reference conditions. We performed partitioning, classification, and ordination analyses and obtained eight groups of bryophytic assemblages explained by water availability and quality. Groups A, B, and H assemblages are type-specific of the inland areas of the northern eco-region, reflecting the neutral minerotrophic currents with summer low currents. Groups C and D are type-specific of acidic oligotrophic shifting currents dependent of precipitation events in the mountainous streams of the North Atlantic eco-region. Groups E, F, and G are widespread in continental northern, central, and southern zones in neutral and highly mineralized watercourses with seasonal dryness. We propose bryophytes as a tool in the characterization of the reference conditions for two main reasons: (i) many of the recorded taxa are capable of withstanding the natural seasonal desiccation, and (ii) the type-specific bryophytes have perennial life-strategies and can be assessed at any time of year as a support for other type-specific macrophytes in compositional assessments of reference conditions.

Spectral separability of riparian forests from small and medium-sized rivers across a latitudinal gradient using multispectral imagery

Spectral discrimination between riparian forests is a challenging issue due to the inherent complexity of species composition and the high spatial structural variability of these vegetation types. This study aimed to evaluate spectral separability among riparian forests, in small and medium-sized river catchment areas, in three bioclimatic zones of Portugal (temperate, transitional, and Mediterranean). We also assess the spectral differences using only the dominant riparian woody species in each riparian forest class, namely Alnus glutinosa, Salix salviifolia, and Nerium oleander. Pixel values were extracted from high-resolution airborne multispectral imagery (red, green, blue, and near-infrared, 50 cm pixels) of 26 riparian forests located in the three bioclimatic zones. Spectral separability was calculated using the transformed divergence (TD) distance. Discriminant analysis (DA) was used to select the bands that contribute most to the spectral separability and for the classification accuracy assessment of the riparian forests. Species composition and percentage of canopy closure were collected for all the riparian forests in a field campaign and subjected to hierarchical clustering in order to validate the spectral separability analyses. Optical traits derived from field data were used to interpret the spectral differences between riparian forest classes. The greatest spectral separability was observed between the temperate and the Mediterranean riparian forest classes. Global classification accuracy for the DA was 86.3% for riparian forest classes along medium-sized rivers and 70.1% in small-sized ones. The high floristic and spatial structure variability was responsible for the misclassification errors that occurred between the transitional and the other riparian forest classes. The spectral separability using only the dominant species was greater than that obtained using the overall species assemblages of the riparian forests. Alnus glutinosa had the highest level of classification accuracy, and this may be related to its peculiar yellowish-green tone. DA also revealed that all spectral bands were needed in order to distinguish the riparian forest classes. This study provided evidence that the spectral discrimination of riparian forests can be explained on the basis of differences in species composition and cover, and by a convergence of optical traits, at both leaf and canopy levels. Spectral signatures of these riparian forests and related spectral signatures of key species are useful tools for evaluating the floristic deviations of actual riparian forests from their near-natural benchmarks.

Relations Between River Plant Richness in the Portuguese Floodplains and the Widespread Water Knotgrass (Paspalum Paspalodes)

The distribution and invasive status of the amphibious plant Paspalum paspalodes (water knotgrass) are observed. The P. paspalodes distribution clearly shows that it is an invasive plant established in Portugal, which has never before been recorded as invasive in Portugal. The purpose of our study is to determine the various stages of invasion of this plant on a large biogeographical scale, in five basins or groups of floodplain river basins belonging to five Portuguese regions covering the principal floodplains of the south and centre of the country. The composition of the river plant community in terms of structure and species richness was obtained from a data set of 401 sites. In some cases, water knotgrass could be a threat for particular river flora and consequently for the integrity of the river system. In other cases, it occurs in highly degraded places, where other taxa considered as invasive plants and/or indicators of degraded ecosystems are present. The pattern of invasion of P. paspalodes is discussed in relation to risk assessment for the other river plants and compared to the North European invasion processes of P. paspalodes. We conclude that the evolution of the distribution of this predominant Portuguese water plant has to be carefully followed in some of the studied floodplains, as well as its North European distribution limits. In-depth survey should be carried out to relate the current biogeographical changes to the hypothesis of indication in climate changes.