Restoring natural fluvial dynamics is fundamental for sustaining biodiversity and functional integrity of river and floodplain ecosystems. In Central Europe, however, pervasive river regulation and bank protection have greatly impaired ecosystem functioning and many water bodies fail to achieve a good ecological status within the European Water Framework Directive. The “Free Moving Rivers” approach seeks to restore the ecological integrity of rivers and floodplains by creating appropriate conditions for natural fluvial dynamics. Principal goals of the approach include removing artificial constraints on river processes and expanding the river corridor to restore natural river habitats and structures. Lacking, however, are complementary tools that evaluate and predict changes to ecosystem services (ESSs) after implementation. Here, we describe a case study of the Ammer river in Bavaria, Germany, to (i) calculate the extent of the “Free Moving Rivers” corridor, and (ii) assess changes to ESSs of a proposed river restoration measure under two alternative land‐use scenarios. To do this, we apply the River Ecosystem Service Index (RESI), whereby individual ESSs are assessed in a spatially explicit way. We show how a proposed implementation of the “Free Moving Rivers” approach enhances three investigated ESSs: flood retention, sediment balance and habitat provision. We conclude that RESI is a potentially useful tool with wide applicability for restoration planning that synthesises floodplain complexity in such a way that facilitates decision making.

We determined how the interaction between geomorphic processes and vegetation development enables tipping points in braided rivers. We performed vegetation monitoring and succession modelling on the restored Kleblach side channel at the Upper Drava River (Austria) to assess long-term trends in vegetation succession and landform development. Two alpine pioneer plant species, the German Tamarisk (Myricaria germanica) and the Dwarf bulrush (Typha minima), were used to assess the ecosystem consequences of succession. Vegetation rapidly developed on initially open sites; 14 years after restoration, approximately 60% of the study area was characterized by stable succession phases. Even a major flood event in the near future would not reduce the dense vegetation cover. This indicates that a stable, dense vegetation cover can lead to a permanent transition from a dynamic braided to a stable single-channel river without major morphological changes, which we interpret as “biogeomorphic tipping point”. The result is a significant reduction in the indicator species’ habitats, preventing them from maintaining a resilient population in the long term. Thus, maintaining process regimes with high hydro- and morphodynamics is critical for preserving the valuable braided river ecosystems. The idea of “biogeomorphic tipping points” contributes to the process-based conservation and restoration of braided rivers globally.

Riparian softwood forests support numerous ecological functions and high biodiversity. In the context of the LIFE+ Traisen project, a non-regulated new riverbed for the lower Traisen River (“New Traisen”) was created within an artificially lowered floodplain corridor. Using vegetation monitoring from 2014 to 2021, we determined (i) the role of Solidago gigantea in the establishment of softwood forests, (ii) the habitat parameters (such as flooding height, fine substrate layer thickness, and vegetation cover) that impact the establishment and growth of woody plants, and (iii) the successional phase at which woody plants become established, as well as the potential creation of new germination habitats. During early succession, the softwood species, as light-tolerant pioneer species, colonized the open sites together with S. gigantea and subsequently established a floodplain softwood forest. Unexpectedly, we observed negative forest development only when the S. gigantea cover exceeded 90%. Neither the habitat parameters nor S. gigantea cover significantly impacted tree occurrence. However, we highlight the need for optimum habitat parameters for softwood forest development in early succession phases, ideally before S. gigantea forms dense, monospecific stands. Tailored monitoring strategies are needed to guide the succession of such semi-aquatic habitats toward the development of the desired habitat type.

Riverine landscapes are shaped by the feedbacks between hydrological, geomorphological and ecological processes. These feedbacks occur across multiple scales, from the scale of single plants modifying the hydraulic forces around it to the formation of landforms like islands which in turn lead to the emergence of specific river types such as braided or anastomising. Over the past years, the field of biogeomorphology has significantly improved the understanding of the interaction of vegetation and hydro-morphological processes. Despite recent scientific progress, research gaps remain. In particular, it is still poorly understood, how processes happening on small scales, such as sedimentation in the lee of an individual plant or a piece of large wood, lead to the emergence of landforms and reach scale river types and how – vice versa – the specific landform pattern within river types foster small scale processes. The concept of Panarchy considering a number of adaptive cycles linking the different scales of the fluvial biogeomorphic system is a promising candidate for analyzing cross-scale vegetation-hydromorphology feedbacks. However, developing methods for quantitative studies is still an ongoing challenge in biogeomorphological research.We introduce an empirical approach for filling this research gap driven by a combination of field mapping and state-of-the-art remote sensing taking the Naryn River, a large free flowing river in Kyrgyzstan, as a case study. In the field, we map vegetation traits and geomorphic characteristics and link them to the stages of the biogeomorphic succession concept. Then, we utilize the computational potential of the “Terrabyte” cloud computing platform of the German Aerospace Center (DLR) to analyze temporally dense time series from the Sentinel-1 and -2 archives. To map vegetation and hydro-geomorphic characteristics (vegetation height, density, biomass, share of bare sediment, grainsize, duration of inundation) and to assess how these biogeomorphic traits change over time, we make use of the capabilities of the recently available foundational deep learning model “Clay” as state-of-the-art artificial intelligence method in earth observation. This enables river corridor scale analysis of the spatial-temporal dynamics of hydro-geomorphic disturbance, rejuvenation potential (windows of opportunity), vegetation growth as well as the emergence of biogeomorphic feedback windows and therefore tracking the biogeomorphic succession. This gives us the possibility to study adaptive cycles on different scales and construct Panarchies for different river types occurring along the Naryn River. Our approach is a significant step towards the quantification of biogeomorphic feedbacks across multiple scales and advances the empirical understanding of the role of scale dependence of biogeomorphic feedbacks which lead to the emergence of riverine landscape pattern.

Braided rivers represent extraordinary wetland ecosystems due to their high disturbance regimes. Their riparian vegetation needs to be adapted to these harsh conditions. At the same time, braided river systems are sensitive to changes in the underlying environmental factors. Additionally, their open gravel and sand banks represent germination sites for invasive alien plant species. There is a risk that invasive species can spread over large areas and thus alter river reaches, even leading to morphological changes in the entire river system.The aim of this study was to identify similarities and differences in the key functional traits and strategies of invasive alien plants compared to the dominant native plant species in braided rivers around the world. The analysis of what makes invasive species more successful than the native species was carried out in seven globally distributed mountain regions with braided rivers, including parts of the European Alps, the mediterranean Vjosa river system, Iceland, Alaska, Patagonia, Central Asia, and New Zealand. Studied river system cover different climate zones, with varying degrees of human influence.We used a plot design (10m by 10m) covering all occurring biogeomorphic succession phases (Corenblit et al. 2007) in the investigated river reaches. In each plot, we recorded general information on the habitat conditions and vegetation characteristics. We combined the field data with response and effect trait data from the TRY trait database (Kattge et al. 2020). The traits of the dominant native and invasive alien plant species were compared using a PCA analysis to reveal differences in trait combinations that can explain the success of invasive species.First findings indicate that successfully invading alien species enter the braided river systems in the pioneer succession phase and comprise traits for dealing with the high hydromorphodynamic disturbances, for example a short lifespan. They have rather smaller specific leaf area and plant height. By decreasing the disturbance impact through dense vegetation cover and trapping of fine sediment they push their growing areas to the following biogeomorphic succession phase. Here, especially invasive ecosystem engineer species improve their own growing conditions and may create dense vegetation covers in the formerly open active channel.Across our study areas, a wide range of the magnitude of plant invasion was visible: While in the Alaskan rivers with extreme arctic to boreal climate and low human impact no invasive alien plants occured, the braided rivers in the intensively agriculturally used Canterbury region on New Zealand's South Island were highly invaded. Here, many formerly sparsely vegetated active channels were densely covered with alien species and the later succession phases prevailed. ReferencesCorenblit, D., Tabacchi, E., Steiger, J., & Gurnell, A. M. (2007). Reciprocal interactions and adjustments between fluvial landforms and vegetation dynamics in river corridors: a review of complementary approaches. Earth-Science Reviews, 84(1-2): 56-86.Kattge, J., Bönisch, G., Díaz, S., Lavorel, S., Prentice, I. C., Leadley, P., Tautenhahn, S., & Werner, G., et al. (2020). TRY plant trait database - enhanced coverage and open access. Global Change Biology, 26(1): 119-188. doi:10.1111/gcb.14904

The remote sensing model ‘Google4Habitat’ (Egger et al. 2024) enables large-scale vegetation classification based on freely available satellite imagery in combination with ground truth data. In a current project, it was further developed to predict hydrogeomorphology-driven vegetation succession phases at the Naryn River in Kyrgyzstan. This river has high hydrologic and morphologic dynamics over its entire length of 600 km (Betz et al. 2023). Additionally, drought stress due to the continental climate of Central Asia causes specific succession pathways (Lauermann et al. 2024). This makes the Naryn an interesting case study for demonstrating the capabilities of the ‘Google4Habitat’ model for analyzing the spatial pattern of vegetation communities and their biogeomorphic implications.The ‘Google4Habitat’ model runs on the Google Earth Engine platform. By using globally available satellite data together with recorded reference points for each classified habitat type, it performs a spatial and temporal analysis for each habitat. Specifically, Sentinel-2 scenes from one year are selected and monthly spectral values and vegetation indices are calculated. Orthophotos are integrated and texture parameters are added. Pixel values at training points are used to create the classification model (358 collected in the field, supplemented by 987 points from aerial image interpretation), which is then validated, evaluated, and used to create the classification map of the study area. To obtain precisely delineated habitat maps, a segmentation of habitat structures is carried out based on a high resolution orthophoto. Then, the classification map is intersected with the segments and final habitat types are assigned using zonal statistics. The habitat map is intersected with the three succession series delineated on the orthophoto and area balances are created.On the Naryn River, nine different habitat types were obtained using this supervised classification approach. The freshly to moderately dry sites of the sedimentation series are characterized by pioneer vegetation located within the active channel, Salix-Myricaria shrub, and softwood riparian forests of varying ages with Populus talassica, as well as extensive Hippophae shrubs. The shallow sites of the aggradation series are, however, much more sparsely vegetated than the sedimentation series and are characterized by the presence of Tamarix ramosissima. Both series end with an Artemisia steppe. Finally, the siltation series is characteristic of the former side arms that are in the process of silting up and are particularly dominated by Typha minima and Phragmites australis.ReferencesBetz, F., Lauermann, M., & Egger, G. (2023). Biogeomorphology from space: Analyzing the dynamic interactions between hydromorphology and vegetation along the Naryn River in Kyrgyzstan based on dense satellite time series. Remote Sensing of Environment, 299, 113890.Egger, G., Preinstorfer, S., Kollmann, M., Becker, I., Izquierdo-Verdiguier, E. & Paul, P. (2024). Google4Habitat - a novel method for remote sensing-based habitat classification using Google Earth Engine. Carinthia II, 3/1, 8–28.Lauermann, M., Heckmann, T., Poeppl, R., Egger, G., Eichel, J. & Betz, F. (2024). How does Hydrological Connectivity Influence Fluvial Biogeomorphic Succession in Semiarid Regions? A Case Study from the Naryn River in Kyrgyzstan, Central Asia. AGU Fall Meeting 2024, Poster No. 1302, EP43C-1302.