Formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river

Feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors. We describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized Isère River in France. The channel was laterally confined with embankments and mostly straightened. From the beginning of the 1970s to the end of the 1990s, alternate bars were progressively but heavily colonized by vegetation. This context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions. Based on a GIS analysis of aerial photographs (between 1948 and 1996), we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age, size and mobility. Field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars. A highly significant statistical association of geomorphological and vegetation variables (RV of co-inertia analysis = 0.41, p < 0.001) explained 95% of the variability in just one axis, supporting the existence of very strong feedback between geomorphological changes (i.e. the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest, and vegetation succession). Such dynamics reflect the fluvial biogeomorphological successions model, as described by the authors earlier. © 2020 John Wiley & Sons, Ltd.     

Biogeomorphology in the marine landscape: Modelling the feedbacks between patches of the polychaete worm Lanice conchilega and tidal sand waves

Tidal sand waves are dynamic bedforms found in coastal shelf seas. Moreover, these areas are inhabited by numerous benthic species, of which the spatial distribution is linked to the morphological structure of sand waves. In particular, the tube-building worm Lanice conchilegais of interest as this organism forms small mounds on the seabed, which provide shelter to other organisms. We investigate how the interactions between small-scale mounds (height ∼dm) and large-scale sand waves (height ∼m) shape the bed of the marine environment. To this end, we present a two-way coupled process-based model of sand waves and tube-building worm patches in Delft3D. The population density evolves according to a general law of logistic growth, with the bed shear stress controlling the carrying capacity. Worm patches are randomly seeded and the tubes are mimicked by small cylinders that influence flow and turbulence, thereby altering sediment dynamics. Model results relate the patches with the highest worm densities to the sand wave troughs, which qualitatively agrees with field observations. Furthermore, the L. conchilegatubes trigger the formation of sandy mounds on the seabed. Because of the population density distribution, the mounds in the troughs can be several centimetres higher than on the crests. Regarding sand wave morphology, the combination of patches and mounds are found to shorten the time-to-equilibrium. Also, if the initial bed comprised small sinusoidal sand waves, the equilibrium wave height decreased with a few decimetres compared to the situation without worm patches. As the timescale of mound formation (years) is shorter than that of sand wave evolution (decades), the mounds induce (and accelerate) sand wave growth on a similar spatial scale to the mounds. Initially, this leads to shorter sand waves than they would be in an abiotic environment. However, near equilibrium the wavelengths tend towards their abiotic counterparts again. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Landforms as extended composite phenotypes

Biotic influences on geomorphology (and vice‐versa) are ubiquitous. This paper explores whether landforms may be extended (composite) phenotypes of biota, based on four criteria: process–form relationships between biota and landforms; evolutionary synchrony; selective pressure via ecosystem engineering and niche construction; and positive feedback benefitting the engineer organism(s). Coral reefs, peat bogs, biomantles, insect mounds, grassland soils, salt marshes, mangrove swamps, and some vegetation‐dependent sand dune types clearly meet these criteria. Karst landforms, meandering rivers, and tree uprooting pit‐mound systems meet the first three criteria, but positive feedback to engineer organisms has not been established. Research in biogeomorphology will surely identify other extended phenotypes. Implications are that biological evolution will continue to drive landscape metamorphosis, the appearance of new landform types, and presumably the disappearance of extended phenotypes associated with extinct species. Independently of extended phenotypes, tightly‐coupled geomorphological–ecological interactions such as coevolution, and biogeomorphic forms of ecosystem engineering and niche construction are common. The toposphere, encompassing Earth's landforms, is partly a biotic construct. Some elements would be present in an abiotic world, but the toposphere would not exist in anything resembling its contemporary state without a biosphere. This raises important questions with respect to Earth system evolution. The bio, litho‐, atmo‐, hydro‐, topo‐, and pedospheres coevolve at the global scale. Major biotic events have driven revolutions in the other spheres, but the atmosphere and the global hydrological system seem to have been relatively steady‐state at the global scale. The toposphere and pedosphere have not. This suggests that perhaps landforms and soils provide the major mechanisms or degrees of freedom by which Earth responds to biological evolution. Landforms and soils may thus be the ‘voice’ of the biosphere as it authors planetary change, even if clear biotic signatures are lacking. Copyright © 2015 John Wiley & Sons, Ltd.     

Biogeomorphology: diverse,integrative and useful

Biogeomorphology is an umbrella term given to a highly‐active research area within geomorphology that focusses on the many and varied interactions and feedbacks between organisms and the physical Earth. In the last 25 years this interest has developed and diversified to include the direct and indirect influences of microorganisms, plants, animals and humans on earth surface processes and landform dynamics, and the roles of geomorphology in ecological functioning, resilience and evolution. This Commentary introduces a virtual special issue of 16 research papers and three ‘State of Science’ pieces, illustrating the diversity of the field, its continued theoretical and conceptual progression, and the applied relevance of biogeomorphological science in tackling environmental problems. Collectively, these papers demonstrate the merits of – and opportunities for – biogeomorphology as an inherently integrative science in understanding and managing the complexity of living landscapes. Copyright © 2016 John Wiley & Sons, Ltd.     

Solifluction meets vegetation: the role of biogeomorphic feedbacks for turf‐banked solifluction lobe development

Vegetation is an important factor influencing solifluction processes, while at the same time, solifluction processes and landforms influence species composition, fine‐scale distribution and corresponding ecosystem functioning. However, how feedbacks between plants and solifluction processes influence the development of turf‐banked solifluction lobes (TBLs) and their geomorphic and vegetation patterns is still poorly understood. We addressed this knowledge gap in a detailed biogeomorphic investigation in the Turtmann glacier foreland (Switzerland). Methods employed include geomorphic and vegetation mapping, terrain assessment with unmanned aerial vehicle (UAV) and temperature logging. Results were subsequently integrated with knowledge from previous geomorphic and ecologic studies into a conceptual model. Our results show that geomorphic and vegetation patterns at TBLs are closely linked through the lobe elements tread, risers and ridge. A conceptual four‐stage biogeomorphic model of TBL development with ecosystem engineering by the dwarf shrub Dryas octopetala as the dominant process can explain these interlinked patterns. Based on this model, we demonstrate that TBLs are biogeomorphic structures and follow a cyclic development, during which the role of their components for engineer and non‐engineer species changes. Our study presents the first biogeomorphic model of TBL development and highlights the applicability and necessity of biogeomorphic approaches and research in periglacial environments. Copyright © 2016 John Wiley & Sons, Ltd.     

Channel and vegetation recovery from dredging of a large river in the Gulf coastal plain,USA

Anthropogenic impacts in large rivers are widely studied, but studies of recovery once a disturbance has stopped are uncommon. This study examines the biogeomorphic recovery of a 40-km river corridor on the mid-Apalachicola River, Florida following the cessation of dredging, disposal, and snag removal in 2002. This failed navigation project resulted in vegetation losses (~166 ha between 1941 and 2004), river widening, and increased point bar areas. We used paired sets of imagery for a 10-year period during the recovery process at two different flow levels to assess sand bar change, land cover change, and their spatial variations. Most large sand bars decreased significantly in area due to growth of pioneer species, typically from the bankside of the bar. Mean bar area shrank 0.17 and 0.20 ha for the 30th and 1st percentile flows, respectively. For the entire study area, both water-level comparisons showed gains in vegetation (23.36 and 15.83 ha), compensated by losses in the extent of water (16.83 and 8.55 ha) and sand bar losses (6.53 and 7.28 ha). Overall, these gains during the 10-year passive recovery period are equivalent to ~15% of the vegetation losses that resulted from the navigational dredging. As found in other studies, most of the pioneer vegetation grew approximately 2 m relative elevation above the low-water surface. The initial length of the tree line and the area of herbaceous growth both had a significant and positive relationship with the area of new vegetation growth over the study interval. As parts of the river are healing, reduced channel capacity from narrowing and tree growth will benefit the floodplain. As elsewhere, understanding of a river's biogeomorphology, hydrology, and disturbance history can help in selecting appropriate recovery metrics to further advance the understanding and management of disturbed floodplains. © 2020 John Wiley & Sons, Ltd.     

滨海湿地生物地貌学进展及在生态修复中的应用展望

生物地貌学研究生物过程和地貌过程之间的双向交互作用,是一门新兴的交叉学科。早期的生物地貌学关注陆地生态系统,近期海岸带成为生物地貌学研究的热点地区,尤其是滨海湿地(如盐沼、红树林)成为研究生物地貌学过程和机理的重要区域。本文回顾了生物地貌学研究的概念、历史发展和方法,选取滨海湿地作为生物地貌学的主要研究对象,并就其研究方向、重要因素以及核心机制展开综述。最后对生物地貌学在海岸带生态系统修复工作中的应用进行梳理,分析了生物地貌学在红树林修复、滨海盐沼湿地修复和互花米草入侵防控上的应用展望。     

Biogeomorphology: understanding different research approaches

Geomorphologists and ecologists commonly employ different scientific approaches to data collection and validation. Ecologists often employ a more statistics‐based approach, whereas geomorphologists place less emphasis on replication and significance testing and more often focus on multiple‐parameter measurements and theoretical reasoning. These differences in approach could slow down collaboration between the fields and hinder integration in biogeomorphology. Such integrated research is necessary, however, if both fields are to benefit from the knowledge and experience of the other. Copyright © 2010 John Wiley & Sons, Ltd.     

The strength of biogenic sand reefs: Visco-elastic behaviour of cement secreted by the tube building polychaete Sabellaria alveolata, Linnaeus, 1767

Mechanical properties of the biomineralised cement from tube-building marine worms are poorly known. Secreted from an organ connected to the polychaetes specialised glands, the cement glues sand grains and calcareous shell fragments of a given size and, on a larger scale, ensures the resistance of the reef to waves. In this study, three kinds of mechanical tests were performed with worm tubes to establish the nature of the cement behaviour. Results obtained show that cement behaves like a visco-elastic material. This property allows the tubes to dissipate the mechanical energy from the waves to which they are subject and to reduce the mechanical stress transmitted inside the tubes to the polychaetes. Comparison of “fresh” and “dry” cements highlights that the visco-elastic behaviour of the cement is maintained after five years. The viscosity of the cement is therefore not related to moisture but to its chemical composition. More generally, these results offer a better understanding of the role of cement on worm reefs strength and their persistence in the geological record.     

Influence of inclination and permeability of solitary woody riparian plants on local hydraulic and sedimentary processes

The role of solitary woody riparian plants with respect to local erosion and deposition of sediments is investigated. A focus is laid on the characteristics ‘inclination’ and ‘permeability’ of the plant's projected frontal area. Therefore, two experimental studies using cylindrical obstacles were carried out in a laboratory flume, one aiming at inclination, the other at permeability. The first series revealed that the total amount of mobilized sediment around the cylinder on average decreased by 8–10% per 5° increasing inclination in streamwise direction. Locations of maximum scour depth simultaneously shifted downstream. A horseshoe vortex system, causing the frontal and lateral scouring, ceased to exist below inclinations of 25–30°. The second series revealed that with increasing permeability, frontal scour incision is delayed, and the eroded sediment volume is significantly reduced. With permeable obstacles, two system states were observed: first, frontal scouring with leeside deposition at higher flow velocities and, second, moderate leeside scouring at lower flow velocities. For up‐scaling and comparison, a field study focussing on fluvial obstacle marks at poplars and willows in secondary channels of the River Loire was additionally conducted. A modified analytical model enabled us to quantify the amount of deposited sediments leeside of the plants. Leeside sediment ridges are significantly stabilized and have a higher preservation potential when covered by pioneer vegetation. Under such conditions, they may indeed induce the development of stable islands. Eventually, ‘sediment ridge width’ turned out to be a suitable indicator for leeside deposited sediment volume, irrespective of spatial scale. Copyright © 2012 John Wiley & Sons, Ltd.