9.14 Reciprocal Relations between Riparian Vegetation, Fluvial Landforms, and Channel Processes

Merritt, David M.

doi:10.1016/b978-0-12-374739-6.00239-6

Cited by 37 publications

(26 citation statements)

References 160 publications

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“…Riparian vegetation is structured by hydrogeomorphic processes operating at a hierarchy of scales (from watersheds to reaches), but also influences the operation of such processes through feedback mechanisms (Merritt 2013). For example, large wood accumulation alters local hydraulics and the subsequent deposition of sediment that forms islands that provide suitable germination sites for new riparian communities that stabilize the landform (Wohl 2013).…”

Section: Discussionmentioning

confidence: 99%

Multi‐scale environmental filters and niche partitioning govern the distributions of riparian vegetation guilds

et al. 2015

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Across landscapes, riparian plant communities assemble under varying levels of disturbance, environmental stress, and resource availability, leading to the development of distinct riparian life‐history guilds over evolutionary timescales. Identifying the environmental filters that exert selective pressures on specific riparian vegetation guilds is a critical step in setting baseline expectations for how riparian vegetation may respond to environmental conditions anticipated under future global change scenarios. In this study, we ask: (1) What riparian plant guilds exist across the interior Columbia and upper Missouri River basins? (2) What environmental filters shape riparian guild distributions? (3) How does resource partitioning among guilds influence guild distributions and co‐occurrence? Woody species composition was measured at 703 stream reaches and each species' morphological and functional attributes were extracted from a database in four categories: (1) life form, (2) persistence and growth, (3) reproduction, and (4) resource use. We clustered species into guilds by morphological characteristics and attributes related to environmental tolerances, modeling these guilds' distributions as a function of environmental filters—regional climate, watershed hydrogeomorphic characteristics, and stream channel form—and guild co‐existence. We identified five guilds: (1) a tall, deeply rooted, long‐lived, evergreen tree guild, (2) a xeric, disturbance tolerant shrub guild, (3) a hydrophytic, thicket‐forming shrub guild, (4) a low‐statured, shade‐tolerant, understory shrub guild, and (5) a flood tolerant, mesoriparian shrub guild. Guilds were most strongly discriminated by species' rooting depth, canopy height and potential to resprout and grow following biomass‐removing disturbance (e.g., flooding, fire). Hydro‐climatic variables, including precipitation, watershed area, water table depth, and channel form attributes reflective of hydrologic regime, were predictors of guilds whose life history strategies had affinity or aversion to flooding, drought, and fluvial disturbance. Biotic interactions excluded guilds with divergent life history strategies and/or allowed for the co‐occurrence of guilds that partition resources differently in the same environment. We conclude that the riparian guild framework provides insight into how disturbance and bioclimatic gradients shape riparian functional plant diversity across heterogeneous landscapes. Multiple environmental filters should be considered when the riparian response guild framework is to be used as a decision‐support tool framework across large spatial extents.

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Section: Discussionmentioning

confidence: 99%

Multi‐scale environmental filters and niche partitioning govern the distributions of riparian vegetation guilds

et al. 2015

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“…Defining guilds and functional groups of plants allows generalization of patterns between plants and their environment that can be transferrable between systems (Merritt, ). Evette et al .…”

Section: Introductionmentioning

confidence: 99%

Modeling the functional influence of vegetation type on streambank cohesion

Polvi

Wohl

Merritt

2014

Earth Surf Processes Landf

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The important role of vegetation in adding cohesion and stabilizing streambanks has been widely recognized in several aspects of fluvial geomorphology, including stream restoration and studies of long‐term channel change. Changes in planform between braided, meandering, and anabranching forms have been attributed to the impacts of vegetation on hydraulic roughness and bank stability. However, these studies focus either on flume studies where analog vegetation is used, or case studies featuring one species, which is commonly invasive. We present functional differences of bank‐stabilizing root characteristics and added cohesion, with vegetation categorized as woody and non‐woody and by the vegetation groups of trees, shrubs, graminoids, and forbs. We analyzed root morphology and tensile strength of 14 species common to riparian areas in the southern Rocky Mountains, in field sites along streambanks in the montane and subalpine zones of the Colorado Front Range. Using the vegetation root component (RipRoot) of a physically‐based bank stability model (BSTEM), we estimated the added cohesion for various sediment textures with the addition of each of the 14 species. Significant differences exist between woody and non‐woody vegetation and between the four vegetation categories with respect to the coefficient of the root tensile strength curve, lateral root extent, and maximum root diameter. Woody vegetation (trees and shrubs) have higher values of all three parameters than non‐woody species. Tree roots add significantly more cohesion to streambanks than forb roots. Additionally, rhizomes may play an important role in determining the reach‐scale effects of roots on bank stabilization. Differences in root characteristics and added cohesion among vegetation categories have several important implications, including determining the likelihood of planform change, developing guidelines for the use of bank‐stabilizing vegetation, and linking the effect of vegetation to geomorphic structure that can benefit ecosystem functioning. Copyright © 2014 John Wiley & Sons, Ltd.

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“…However, some questions about the effectiveness of this restoration technique remain unsolved. First, the gravel bars that were sampled in the restored segment are still too young to project whether they will contribute to the habitat complexity described in theoretical succession models for natural riparian forests, which consists of a shifting mosaic of forest patches of different ages (Corenblit et al, 2007;Johnson et al, 1976;Merritt, 2013). We believe, though, that given that the migration of the channel is still limited, succession in these sites will be recurrently truncated by flooding disturbance and they will remain in a juvenile stage.…”

Section: Lessons Learned From Upscaling Channel Widening To Entire Rimentioning

confidence: 99%

Dismantling artificial levees and channel revetments promotes channel widening and regeneration of riparian vegetation over long river segments

Martínez-Fernández

González

López-Almansa

et al. 2017

Ecological Engineering

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Longitudinal structures manipulation can re-activate channel migration and thus restore flood-dependent riparian plant communities in human-constrained floodplains. However, it has been rarely implemented over long restored river segments and has been infrequently assessed while taking into account river conditions prior to restoration. This study describes the morphological and vegetation response to this type of restoration in a project completed in 2012 along a 21.6 km river segment in the Orbigo River (NW Spain). Land cover changes and channel planform evolution in the restored segment were compared with a downstream non-restored (control) segment and to an upstream unregulated (reference) segment before (2011) and shortly after (2014) the restoration implementation. Riparian vegetation was surveyed in 18 gravel bars of the three river segments four years after restoration completion (2016). The restored segment presented the largest increase of active channel area. Rejuvenation of landforms predominated over transition toward mature stages (succession) in the restored and the reference segment, while succession predominated in the control segment. The sinuosity and braiding indexes in the restored segment increased much more than in the reference and, especially, than in the control segment. Riparian plant communities that colonized gravel bars in the restored segment resembled those found in the unregulated segment and slightly differed from that found in the non-restored segment. Withinsegment variability was much higher, indicating the dependence of riparian plant communities on local processes. Although positive, our results showed that the high stability of floodplain areas in the human-constrained rivers of industrialized societies limits the short-term effectiveness of longitudinal structures manipulation as a restoration strategy. We also showed that assessments using relatively simple aerial photointerpretation and vegetation surveys in pioneer habitats can illustrate trajectories in river restoration projects shortly after their completion. Long-term monitoring of the geomorphic trajectory and associated plant communities, however, will help define the timing of future additional interventions to assure the natural resilience of riparian habitats.

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9.14 Reciprocal Relations between Riparian Vegetation, Fluvial Landforms, and Channel Processes

Cited by 37 publications

References 160 publications

Multi‐scale environmental filters and niche partitioning govern the distributions of riparian vegetation guilds

Multi‐scale environmental filters and niche partitioning govern the distributions of riparian vegetation guilds

Modeling the functional influence of vegetation type on streambank cohesion

Dismantling artificial levees and channel revetments promotes channel widening and regeneration of riparian vegetation over long river segments

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