To date, no survey on the diverse channel patterns existing prior to the major phase of river regulation in the mid‐19th–early 20th century has been elaborated at the scale of the whole European Alps. The present paper fills this knowledge gap. The historical channel forms of the 143 largest Alpine rivers with catchments larger than 500 km² (total length 11,870 km) were reconstructed based on maps dating from the 1750s to 1900. In the early 19th century, one‐third of the large Alpine rivers were multi‐channel rivers. Single‐bed channels oscillating between close valley sides were also frequent in the Alps (28%). Sinuous and even more so meandering channels were much rarer. Historical river patterns generally followed an upstream–downstream gradient according to slope condition, floodplain width and distance from the sources. The local occurrence of certain channel patterns, however, primarily reflected the tectonic/orographic conditions. Multi‐channel reaches were widespread within the whole Alpine area, alternating with confined and oscillating reaches. This demonstrates that most areas were mainly transport‐limited rather than supply limited. Sinuous and meandering reaches were more frequent in the north‐eastern Alps and were characterized by lower denudation rates and less sediment delivery.Channel straightening caused the loss of about 510 km of river course length, equivalent to 4.3% of the historical extent. Multi‐channel stretches are currently a mere 15% of their historical length, and 45% of the larger Alpine rivers are intensively channelized or have been transformed into reservoirs. Channelization measures differed from one country to another. Human pressures directly affected both local channel geometry and the upstream controls (i.e., sediment supply). Accordingly, individual multi‐channel reaches also evolved into single‐thread channels without any local human interventions.

Context: Large near-natural rivers have become rare in Europe, a fact reflected in the high conservation status of many riverine ecosystems. While the Balkan still harbors several intact river corridors, most of these are under pressure from planned hydropower constructions. Unfortunately, there is little information available on the hydromorphodynamics and biota of Balkan rivers under threat. Objectives: We present a synthesis of research on the Vjosa in Southern Albania. Here, longitudinal continuity in water flow, undisturbed sediment transport and intact fluvial dynamics are still maintained, but threatened by two large dams planned in its downstream section. We intend to provide a first multidisciplinary inventory of this river system as an example of the knowledge base required for sound water management decisions in the Balkans. Methods: Based on field work of a multidisciplinary consortium of scientists from Albania and other countries conducted from 2017 onwards, we summarize the most important findings on geomorphology of the riverine landscape, habitat turnover rates, vegetation ecology and selected animal taxa. Results: We found evidence that significant areas (86%) of the river corridor are covered by habitats listed in Annex 1 of the European Union Habitats Directive. These are associated with a high number of threatened biota. Conclusions: Our findings underscore the value of the Vjosa as one of the few remaining reference sites for dynamic floodplains in Europe and as a natural laboratory for interdisciplinary research. We emphasize that such multidisciplinary studies are a prerequisite for informed evaluation of potential impacts caused by hydropower plants.

Many riparian ecosystems in European temperate regions have lost their inherent, highly dynamic character due to human-induced impacts such as river channelization and flow regulation. The lower course of the Allier River (France) is one of the last remaining free meandering river segments, and thus, constitutes an opportunity to investigate riparian succession processes of a dynamic, temperate river system. We analyzed (i) the dynamics of the succession phases based on eight sets of aerial images of the riparian corridor over the last five decades (1967-2014), (ii) the dominant succession trajectories and (iii) their relation with the Allier River flow regime. Results revealed that the study site was characterized by a shifting habitat mosaic between 1967 and 2005, whilst floods did not change the overall habitat composition of the riparian corridor but their distribution in space. After the year 2005, progression and retrogression processes have been drastically reduced, with an increase of stability (i.e. no more channel migration and neither progression nor retrogression of patches), and a concomitant reduction of high and moderate magnitude floods. This study depicts a clear threshold of trajectory change in succession processes since the beginning of the 21^st century and facilitates a better understanding of future trajectories under current global climate change.

The large flood pulse of the Amazon basin is a principal driver of environmental heterogeneity with important implications for ecosystem function and the assembly of natural communities. Understanding species ecological response to the flood pulse is thus a key question with implications for theories of species coexistence, resource management, and conservation. Yet these remain largely undescribed for most species, and in particular for trees. The large flood pulse and high tree diversity of the Negro River floodplain makes it an ideal system to begin filling this knowledge gap. We merged historical hydrologic data with 41 forest inventories under variable flooding conditions distributed across the Negro River basin, comprising a total area of 34 ha, to (i) assess the importance of flood duration as a driver of compositional variation, (ii) model the response curve shapes of 111 of the most frequent tree species in function of flood duration, and (iii) derive their niche properties (optima and tolerance). We found that flood duration is a strong driver of compositional turnover, although the majority site-to-site variation in forest composition still remains unexplained. About 73% of species responded to the flood duration gradient, exhibiting a diversity of shapes, but most frequently skewed. About 29% of species were clearly favored by flood durations >120 days year^–1, and 44% of species favored by shorter floods. The median niche breadth was 85 flood days year^–1, corresponding to approximately 30% of the flood duration gradient. A significant subset of species (27%) did not respond to flooding, but rather exhibited wide tolerance to the flood gradient. The response models provided here offer valuable information regarding tree species differential capacity to grow, survive, and regenerate along an ecologically important gradient and are spatially valid for the Amazon Negro basin. These attributes make them an appealing tool with wide applicability for field and experimental studies in the region, as well as for vegetation monitoring and simulation models of floodplain forest change in the face of hydrologic alteration.