Quantifying the effect of riparian forest versus agricultural vegetation on river meander migration rates,central Sacramento River,California, USA

Riparian forest vegetation is widely believed to protect riverbanks from erosion, but few studies have quantified the effect of riparian vegetation removal on rates of river channel migration. Measured historical changes in a river channel centreline, combined with mapped changes in floodplain vegetation, provide an opportunity to test how riparian vegetation cover affects the erodibility of riverbanks. We analysed meander migration patterns from 1896 to 1997 for the central reach of the Sacramento River between Red Bluff and Colusa, using channel planform and vegetation cover data compiled from maps and aerial photography. We used a numerical model of meander migration to back‐calculate local values for bank erodibility (i.e. the susceptibility of bank materials to erosion via lateral channel migration, normalized for variations in near‐bank flow velocities due to channel curvature). A comparison of migration rates for approximately 50 years before and after the construction of Shasta dam suggests that bank migration rates and erodibility increased roughly 50%, despite significant flow regulation, as riparian floodplains were progressively converted to agriculture. A comparison of migration rates and bank erodibilities between 1949 and 1997, for reaches bordered by riparian forest versus agriculture, shows that agricultural floodplains are 80 to 150% more erodible than riparian forest floodplains. An improved understanding of the effect of floodplain vegetation on river channel migration will aid efforts to predict future patterns of meander migration for different river management and restoration scenarios. Copyright © 2004 John Wiley & Sons, Ltd.     

Valley floor landscape change following almost 100 years of flood embankment abandonment on a wandering gravel‐bed river

Critical to restoring the nature conservation value of many river corridors is an understanding of how alluvial landscapes will respond to cessation of river management and land use practices that have previously degraded the environment. This paper analyses changes in valley floor landforms and vegetation patch dynamics, in relation to fluvial disturbance, over a period of almost 100 years following flood embankment abandonment on a wandering gravel‐bed river, namely the River Tummel, Scotland. Such rivers were once typical of many draining upland areas of northern maritime Europe. Prior to abandonment the valley floor landscape was agriculturally dominated and the river for the most part was single thread confined between flood embankments. The pattern of landform change and vegetation patch development over time following a decision in 1903 not to maintain embankments was tracked by geomorphic and land cover mapping utilizing successive sets of aerial photography for the period 1946 to 1994. A historical context for these changes was also feasible because the channel planform in 1900 and earlier channel planform changes dating back to 1753 were known due to the availability of old maps and earlier geomorphic studies. The land cover mapping was validated by comparison of results produced from the interpretation work on the 1994 aerial photographs with the field‐based UK National Vegetation Classification protocol. The findings of the study illustrate that bordering the River Tummel fluvial landforms and vegetation patch mosaics, presumably resembling those that occurred before valley floor land use intensification, evolved in less than 50 years after flood embankment abandonment with a resultant increase in habitat diversity. The change relates primarily to flood‐induced channel planform change and moderate levels of fluvial disturbance. The general significance of this change to plant species diversity on the valley floor of the River Tummel and elsewhere is discussed as is possible implications of the upstream impoundment and scenarios for climatically induced changes in flood frequency and magnitude. The overall outcome is the strong possibility that simple changes in river management and land use practices could result in re‐establishment of the nature conservation value of similar river corridors in Europe over the medium term without active restoration efforts. Copyright © 2002 John Wiley & Sons, Ltd.     

CATCHMENT CHARACTERISTICS AND PLANT RECRUITMENT FROM SEDIMENT IN STREAM AND MEADOW HABITATS

Streams and rivers constitute a dense network with a large interface to the surrounding landscape and are thus highly susceptible to anthropogenic pressures related to land‐use activities in adjacent riparian and upland areas. In the present study, we investigated the influence of catchment characteristics on potential propagule and species recruitment from sediment in lowland stream ecosystems. We tested the following hypotheses: (1) catchment characteristics affect species recruitment from stream sediment in both stream and riparian habitats and (2) recruitment of species associated with undisturbed fen‐meadow habitats is higher in places with natural vegetation in the riparian zones. A large number of wetland species emerged from the stream sediment and sediment recruitment and therefore can act as an important dispersal corridor for common species in stream ecosystems. The recruited propagules were dominated by terrestrial species, but amphibious and aquatic species also appeared, particularly in the artificial stream channels. These included among others species within the genera Ranunculus sp., Callitriche sp. and Potamogeton sp. The large between‐site differences in land‐use characteristics in the riparian zones of the studied stream reaches, both locally and along upstream reaches, were not reflected in species recruitment from the stream sediments. Thus, most recruited species were common and widely distributed, and they were dominated by species with ruderal and competitive life history strategies, whereas only few species associated with fen‐meadow vegetation were recruited. From these findings, we infer not only that hydrochorous dispersal of species can be a potential efficient dispersal vector in agricultural landscapes but also that limitations can exist as to which species can be recruited. We suggest that further studies are performed to elucidate this issue further. Copyright © 2012 John Wiley & Sons, Ltd.     

Restoration of riparian vegetation on a mountain river degraded by historical mining and grazing

Riparian ecosystems in montane areas have been degraded by mining, streamflow alterations, and livestock grazing. Restoration of ecological and economic functions, especially in high-elevation watersheds that supply water to lower elevation urban and agriculture areas is of high priority. We investigated the response of riparian vegetation and bank stability following channel treatments and riparian habitat restoration along a segment of the upper Arkansas River south of Leadville, Colorado. The study area has been historically degraded by heavy-metal mining and is designated a U.S. Superfund site. Additionally, trans-basin water diversions and livestock grazing have contributed to channel widening and altered vegetation composition and cover. We used a before-after-control impact study design in four reaches with varied contamination and grazing history to assess restoration success. Before restoration, streambanks were dominated by graminoids and total vegetation cover varied among reaches with willow cover less than 16% in three reaches. Post-restoration, changes in total vegetation cover fell short of projected goals, but willow cover was greater than 20% in all study reaches. The increase in woody cover likely contributed to reduced erosion and vegetation encroachment post-restoration. Differences in functional group cover among reaches persisted post-restoration and may be attributed to soil contamination levels and low willow seed rain and dispersal. These results highlight the importance of setting realistic restoration goals based on elevation and past land use. We recommend further remediation of fluvial tailings with low vegetation cover and continued monitoring of willow height and cover to determine if further restoration activities are needed.     

Vegetation community response to hydrologic and geomorphic changes following dam removal

Dam removal can restore fish passage, natural flow regimes, sediment transport in streams, dispersal of organic matter, and drift of aquatic insects. However, dam removal also impacts the riparian vegetation, with both immediate and delayed responses. In this study, we measure vegetation change at the Merrimack Village Dam site on the Souhegan River in Merrimack, NH, USA. The August 2008 removal caused a ~3‐m drop in water level and rapid erosion of impounded sediment, with ~50% removed in the first 3 months. Terrace, floodplain, and wetland communities were surveyed in summer 2007, 2009, 2014, and 2015. Temporal change was quantified using Analysis of Similarity on the Bray–Curtis dissimilarity matrix. Only herbaceous vegetation closest to the river channel and in the off‐channel wetland changed significantly. The herbaceous plots directly adjacent to the impoundment eroded to bare sand in 2009, but by 2014, the original riparian fringe community had re‐established in the newly developed floodplain. Between 2007 and 2014, the off‐channel wetland area changed from aquatic species to a stable terrestrial community that persisted without significant change in 2015. The vegetation response was greatest in areas with the largest geomorphic and hydrologic change. These included the channel margin where erosion and bank slumping created an unstable scarp. The mid‐channel island and off‐channel wetland were strongly affected by the lowered water table. However, large unvegetated areas never persisted nor did the areal coverage of invasive species expand, which are two frequent concerns of dam removal stakeholders.     

A Multi‐scale,Hierarchical Model to Map Riparian Zones

Riparian zones are important for their contribution to biodiversity and ecosystem services, especially in the western USA where riparian zones occupy a small proportion of the landscape but support a majority of the biodiversity. However, few accurate datasets of riparian zone locations are available over broad spatial extents, and cost efficient methods to map riparian zones at fine spatial resolutions do not currently exist. We created a multi‐scale, hierarchical, and process‐guided method to map the location of riparian zones using readily available, national datasets. We demonstrate the applicably of this straightforward method in the Southern Rockies Ecoregion, where we mapped both current riparian zones (the riparian zone that is not strongly modified by human land uses and is assumed to support natural riparian vegetation) and potential riparian zones (the area that would likely support natural riparian vegetation in the absence of human activity). The overall accuracy of our method for potential and current riparian zones was 92%. The Southern Rockies Ecoregion is composed of 3.1% (±0.3%) potential and 2.5 (±0.2%) current riparian zones, indicating that roughly 21.0% (±0.5%) of riparian zones have been removed by human activities. This modelling approach can be used to create detailed maps of riparian zones to inform regional conservation and management decision‐making, and the methods can be applied to different regions at multiple scales from small watersheds to a national analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

Novel plant communities limit the effects of a managed flood to restore riparian forests along a large regulated river

Dam releases used to create downstream flows that mimic historic floods in timing, peak magnitude and recession rate are touted as key tools for restoring riparian vegetation on large regulated rivers. We analysed a flood on the 5th‐order Green River below Flaming Gorge Dam, Colorado, in a broad alluvial valley where Fremont cottonwood riparian forests have senesced and little recruitment has occurred since dam completion in 1962. The stable post dam flow regime triggered the development of novel riparian communities with dense herbaceous plant cover. We monitored cottonwood recruitment on landforms inundated by a managed flood equal in magnitude and timing to the average pre‐dam flood. To understand the potential for using managed floods as a riparian restoration tool, we implemented a controlled and replicated experiment to test the effects of artificially modified ground layer vegetation on cottonwood seedling establishment. Treatments to remove herbaceous vegetation and create bare ground included herbicide application (H), ploughing (P), and herbicide plus ploughing (H + P). Treatment improved seedling establishment. Initial seedling densities on treated areas were as much as 1200% higher than on neighbouring control (C) areas, but varied over three orders of magnitude among the five locations where manipulations were replicated. Only two replicates showed the expected seedling density rank of (H + P) > P > H> C. Few seedlings established in control plots and none survived 1 year. Seedling density was strongly affected by seed rain density. Herbivory affected growth and survivorship of recruits, and few survived nine growing seasons. Our results suggest that the novel plant communities are ecologically and geomorphically resistant to change. Managed flooding alone, using flows equal to the pre‐dam mean annual peak flood, is an ineffective riparian restoration tool where such ecosystem states are present and floods cannot create new habitat for seedling establishment. This problem significantly limits long‐term river and riparian management options. Copyright © 2010 John Wiley & Sons, Ltd.     

Influences of valley form and land use on large river and floodplain habitats in Puget Sound

In this paper, we use a system‐wide census of large river and floodplain habitat features to evaluate influences of valley form and land use on salmon habitats along 2,237 km of river in the Puget Sound region of Washington State, USA. We classified the study area by geomorphic process domains to examine differences in natural potential to form floodplain habitats among valley types, and by dominant land cover to examine land use influences on habitat abundance and complexity. We evaluated differences in aquatic habitat among strata in terms of metrics that quantify the length of main channels, side channels, braid channels, and area of wood jams. Among geomorphic process domains, habitat metrics standardized by main channel length were lowest in canyons where there is limited channel migration and less potential to create side channels or braids, and highest in post‐glacial and mountain valleys where island‐braided channels tend to form. Habitat complexity was lower in glacial valleys (generally meandering channels) than in post‐glacial valleys. Habitat abundance and complexity decreased with increasing degree of human influence, with all metrics being highest in areas classified as forested and lowest in areas classified as developed. Using multiple‐year aerial photography, we assessed the ability of our methods to measure habitat changes through time in the Cedar and Elwha Rivers, both of which have recent habitat restoration activity. We were able to parse out sources of habitat improvement or degradation through time, including natural processes, restoration, or development. Our investigation indicates that aerial photography can be an effective and practical method for regional monitoring of status and trends in numerous habitats.     

Reptile community responses to native and non‐native riparian forests and disturbance along two rivers in Arizona

Aridland riparian forests are undergoing compositional changes in vegetation and wildlife communities due to altered hydrology. As flows have been modified, woody vegetation has shifted from native‐tree dominated to non‐native and shrub encroached habitats. Squamate vertebrates such as lizards and snakes are important food web links in riparian ecosystems of the Sonoran Desert. However, little is known about how these communities might respond as riparian forests transition from native tree dominated habitats to open xeroriparian woodlands. We used pitfall arrays deployed across three types of riparian forest to document reptile community patterns, measure vegetation, and produce species‐habitat models. Riparian forests differed on the basis of habitat composition and physiognomy. Two types, cottonwood‐willow (Populus‐Salix) and mesquite (Prosopis) stands, were characterized by high woody species richness. The third type, non‐native saltcedar (Tamarix) stands, had high densities of woody debris and greater canopy coverage. Results show that lizards were common and abundances greatest in cottonwood‐willow, especially for arboreal species. Species‐habitat models for three of five lizard species indicated a negative association to saltcedar‐invaded habitat and no species appeared to select saltcedar‐dominated habitat. Mesquite was an intermediate habitat between upland and riparian, and supports high species diversity. A wildfire in the cottonwood‐willow forest disproportionately affected abundance of ground‐foraging whiptail (Aspidoscelis) lizards; whereas, abundance of arboreal spiny (Sceloporus) species was unchanged. Expected drivers from climate and water use could transition cottonwood forests to other woody‐dominated types. Our results suggest that mesquite woodlands would provide higher quality habitat for riparian reptiles compared to non‐native saltcedar stands.     

Vegetation development and restoration potential of drained reservoirs following dam removal in Wisconsin

Dam removal is potentially a powerful tool for river and riparian restoration. However, long‐term studies on the fate of former reservoirs do not exist, limiting assessment of the utility of dam removal as a means of riparian restoration. We took advantage of the decades‐long legacy of dam removals in Wisconsin to determine human uses of drained reservoirs and to evaluate vegetation establishment and species replacement at these sites. More than half of the 30 dam removal sites in southern Wisconsin over the past 47 years were used as commercial areas, parks and agricultural land, and active riparian restoration occurred on only two sites. For the 13 sites that were allowed to revegetate on their own, plants established in the first growing season and cover was very high at all sites in 2001. Species diversity and frequency (defined as percentage of sampled quadrats where a species is present) of trees were positively correlated with time since removal. No relationship existed between site age and frequencies of other growth forms, nor were there significant relationships between site age and the number or frequency of introduced species. However, mean frequency of introduced species was 75% per site and several sites were dominated by the introduced grass Phalaris arundinacea. Frequency of P. arundinacea was negatively correlated with number of native forbs, and lowest species diversity occurred on sites dominated by P. arundinacea. Ordination analyses revealed substantial site‐to‐site variation in vegetation that was weakly associated with gradients of site location, age, area, and soil phosphorus. Thus, temporal vegetation dynamics following dam removal were site‐specific. Rapid revegetation demonstrates the potential of these sites for riparian restoration. However, if dam removal is used as a means of restoring native riparian communities, then approaches must be tailored to individual sites and will need to focus on techniques to minimize establishment of aggressive invading species. Copyright © 2006 John Wiley & Sons, Ltd.     

Changes to herbaceous plant communities on a regulated desert river

Riparian plant communities are shaped by gradients of disturbance intensity and frequency and resource availability. Reservoir operation can alter the composition and abundance of riparian vegetation by changing the flood regime and by trapping fine sediments and associated nutrients within the reservoir system. We examined differences in herbaceous species richness, abundance and composition in Populus‐Salix stands along an unregulated and regulated reach of a river in semi‐arid Arizona, contrasted flood inundation frequency and edaphic conditions (soil moisture, nutrients and texture) between the reaches, and interpreted the vegetation differences in light of observed differences in environmental conditions. Flooding frequency was similar between reaches, but the proportion of fine textured soils in the unregulated reach was nearly double that of the regulated reach and soil nutrient levels were up to three times higher in the unregulated reach. Herbaceous cover and richness were consistently lower in the regulated reach, with between‐reach differences greatest during dry seasons. These patterns suggest that an edaphic‐based change in resource availability is the principal pathway by which river damming is altering herbaceous vegetation in this system. Our results demonstrate that sediment transport within riparian corridors is important for maintenance of herbaceous communities and that restoration of flow regimes alone may be insufficient to restore herbaceous flora on some regulated reaches. Copyright © 2008 John Wiley & Sons, Ltd.     

PAST AND PREDICTED FUTURE CHANGES IN THE LAND COVER OF THE UPPER MISSISSIPPI RIVER FLOODPLAIN,USA

This study provides one historical and two alternative future contexts for evaluating land cover modifications within the Upper Mississippi River (UMR) floodplain. Given previously documented changes in land use, river engineering, restoration efforts and hydro‐climatic changes within the UMR basin and floodplain, we wanted to know which of these changes are the most important determinants of current and projected future floodplain land cover. We used Geographic Information System data covering approximately 37% of the UMR floodplain (3232 km²) for ca 1890 (pre‐lock and dam) and three contemporary periods (1975, 1989 and 2000) across which river restoration actions have increased and hydro‐climatic changes have occurred. We further developed two 50‐year future scenarios from the spatially dependent land cover transitions that occurred from 1975 to 1989 (scenario A) and from 1989 to 2000 (scenario B) using Markov models. Land cover composition of the UMR did not change significantly from 1975 to 2000, indicating that current land cover continues to reflect historical modifications that support agricultural production and commercial navigation despite some floodplain restoration efforts and variation in river discharge. Projected future land cover composition based on scenario A was not significantly different from the land cover for 1975, 1989 or 2000 but was different from the land cover of scenario B, which was also different from all other periods. Scenario B forecasts transition of some forest and marsh habitat to open water by the year 2050 for some portions of the northern river and projects that some agricultural lands will transition to open water in the southern portion of the river. Future floodplain management and restoration planning efforts in the UMR should consider the potential consequences of continued shifts in hydro‐climatic conditions that may occur as a result of climate change and the potential effects on floodplain land cover. Published 2011. This article is a U.S. Government work and is in the public domain in the USA.     

Riparian Vegetation Communities of the American Pacific Northwest are Tied to Multi‐Scale Environmental Filters

Riparia surrounding low‐order streams are dynamic environments that often support distinct biodiversity. Because of their connection to nearby uplands, riparian vegetation communities at these streams respond to many environmental filters—climatic, physical, chemical or biotic factors—that restrict what species can occur at a given location from within larger regional species pools. In this study, we examined how environmental filters originating at the landscape, watershed and reach scales correspond to riparian plant community composition across the interior Columbia and upper Missouri River basins, USA. We correlated riparian vegetation to environmental filters, identified unique communities and partitioned the variance within riparian vegetation data among filters originating at different scales. Riparian vegetation composition was strongly correlated to landscape‐scale filters including elevation, precipitation and temperature. Watershed‐scale filters such as grazing and reach filters indicative of fluvial setting were also correlated to vegetation composition, often differentiating communities with similar landscape settings. We identified 10 distinct vegetation communities. Forested communities occurred at higher elevation, moderate gradient reaches with high mean annual precipitation. Shrub–forb systems corresponded to fluvial and watershed disturbances and occurred within climates that could preclude forest establishment. Meadows corresponded to high water tables and/or high grazing activity. Variance partitioning showed that landscape‐scale filters explained the most variance within vegetation communities. Global change will alter many of the environmental filters that drive vegetation. Vegetation change may occur rapidly if local filters (e.g. fluvial process) change rapidly or may occur more slowly if larger‐order filters (e.g. climate) change slowly and without influencing local hydrogeomorphic filters. By identifying filter–vegetation relationships at large spatial scales, hypotheses can be constructed on how riparian vegetation communities may change under future environmental conditions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

BENDING OF SUBMERGED WOODY RIPARIAN VEGETATION AS A FUNCTION OF HYDRAULIC FLOW CONDITIONS

Woody riparian vegetation provides numerous ecological benefits such as stabilizing streambanks, storing and cycling nutrients, shading streams and providing habitat for wildlife. However, vegetation also increases hydraulic roughness and reduces the effective flow area, resulting in an increased water surface elevation for a given streamflow. Balancing the desire to preserve woody vegetation in stream corridors with the need to manage flood risks requires accurate techniques for predicting the influence of vegetation on stream hydraulics. However, this is a challenging problem because woody vegetation responds to the flow field itself by bending and streamlining in response to hydraulic forces. The goal of this study was to predict the bending behaviour of woody riparian vegetation as a function of hydraulic flow conditions. Field tests were performed to elucidate tree biomechanical properties for select riparian taxa of the southwestern USA. Biomechanical results served as input parameters for a numerical algorithm designed to predict tree bending for water velocities likely to be encountered during flood events. Bending simulations revealed appreciable variability in bent tree heights. Variability was likely a manifestation of the extensive variance in plant characteristics and properties inherent in biological specimens. However, no trees were expected to bend to a height lower than approximately 42% of their original height, even in water moving at 2.5 m·s^‐1. The results of this work provide an important first step in an effort to predict a dynamic hydraulic roughness for vegetated channels and floodplains under flood conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

USE OF NATIVE AND NONNATIVE NEST PLANTS BY RIPARIAN‐NESTING BIRDS ALONG TWO STREAMS IN NEW MEXICO

Nonnative plant invasions are a management concern, particularly in riparian forests, but little is known about mechanisms through which they influence vertebrate communities. In the American Southwest, native trees such as cottonwood (Populus spp.) are thought to provide better habitat for breeding birds than nonnative plants, which are more tolerant of human‐altered conditions. To evaluate effects of riparian forest composition on riparian‐nesting birds, we examined nest plant use along two rivers in New Mexico that differed in abundance of nonnative vegetation. Of the nests we observed, 49% along the Middle Rio Grande were constructed in nonnative plants, compared with 4% along the Gila River. Birds in the canopy and cavity‐nesting guilds constructed less than 5% of their nests in nonnative plants along either river. At the Middle Rio Grande, birds in the subcanopy/shrub guild constructed 67% of their nests in nonnative plants. Despite the relatively low availability of cottonwoods, they were used by greater numbers of species than any other woody plant at either river. Riparian obligates and species of conservation concern in the canopy and cavity guilds were especially dependent on cottonwood and Arizona sycamore (Platanus wrightii). Our results show that, although nonnative trees and shrubs support large numbers of nests for certain birds, cottonwoods and other large native trees are disproportionately important to riparian bird communities. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of stream flow intermittency on riparian vegetation of a semiarid region river (San Pedro River,Arizona)

The San Pedro River in the southwestern United States retains a natural flood regime and has several reaches with perennial stream flow and shallow ground water. However, much of the river flows intermittently. Urbanization‐linked declines in regional ground‐water levels have raised concerns over the future status of the riverine ecosystem in some parts of the river, while restoration‐linked decreases in agricultural ground‐water pumping are expected to increase stream flows in other parts. This study describes the response of the streamside herbaceous vegetation to changes in stream flow permanence. During the early summer dry season, streamside herbaceous cover and species richness declined continuously across spatial gradients of flow permanence, and composition shifted from hydric to mesic species at sites with more intermittent flow. Hydrologic threshold values were evident for one plant functional group: Schoenoplectus acutus, Juncus torreyi, and other hydric riparian plants declined sharply in cover with loss of perennial stream flow. In contrast, cover of mesic riparian perennials (including Cynodon dactylon, an introduced species) increased at sites with intermittent flow. Patterns of hydric and mesic riparian annuals varied by season: in the early summer dry season their cover declined continuously as flow became more intermittent, while in the late summer wet season their cover increased as the flow became more intermittent. Periodic drought at the intermittent sites may increase opportunities for establishment of these annuals during the monsoonal flood season. During the late summer flood season, stream flow was present at most sites, and fewer vegetation traits were correlated with flow permanence; cover and richness were correlated with other environmental factors including site elevation and substrate nitrate level and particle size. Although perennial‐flow and intermittent‐flow sites support different streamside plant communities, all of the plant functional groups are abundant at perennial‐flow sites when viewing the ecosystem at broader spatial and temporal scales: mesic riparian perennials are common in the floodplain zone adjacent to the river channel and late‐summer hydric and mesic annuals are periodically abundant after large floods. Copyright © 2005 John Wiley & Sons, Ltd.     

Regulation leads to increases in riparian vegetation,but not direct allochthonous inputs,along the Colorado River in Grand Canyon,Arizona

Dams and associated river regulation have led to the expansion of riparian vegetation, especially nonnative species, along downstream ecosystems. Nonnative saltcedar is one of the dominant riparian plants along virtually every major river system in the arid western United States, but allochthonous inputs have never been quantified along a segment of a large river that is dominated by saltcedar. We developed a novel method for estimating direct allochthonous inputs along the 387 km‐long reach of the Colorado River downstream of Glen Canyon Dam that utilized a GIS vegetation map developed from aerial photographs, empirical and literature‐derived litter production data for the dominant vegetation types, and virtual shorelines of annual peak discharge (566 m³ s^?1 stage elevation). Using this method, we estimate that direct allochthonous inputs from riparian vegetation for the entire reach studied total 186 metric tons year^?1, which represents mean inputs of 470 gAFDM m^?1 year^?1 of shoreline or 5.17 gAFDM m^?2 year^?1 of river surface. These values are comparable to allochthonous inputs for other large rivers and systems that also have sparse riparian vegetation. Nonnative saltcedar represents a significant component of annual allochthonous inputs (36% of total direct inputs) in the Colorado River. We also estimated direct allochthonous inputs for 46.8 km of the Colorado River prior to closure of Glen Canyon Dam using a vegetation map that was developed from historical photographs. Regulation has led to significant increases in riparian vegetation (270–319% increase in cover, depending on stage elevation), but annual allochthonous inputs appear unaffected by regulation because of the lower flood peaks on the post‐dam river. Published in 2010 by John Wiley & Sons, Ltd.     

LONG‐TERM VEGETATION DYNAMICS AFTER HIGH‐DENSITY SEEDLING ESTABLISHMENT: IMPLICATIONS FOR RIPARIAN RESTORATION AND MANAGEMENT

Human disturbances have contributed to the deterioration of many western US rivers in the past century. Cottonwood‐willow communities, present historically along the Colorado River, protect watersheds and provide wildlife habitat, but are now among the most threatened forests. As a result, restoration efforts have increased to re‐establish and maintain cottonwood‐willow stands. While successful establishment has been observed using multiple strategies with varying investments, few projects are evaluated to quantify efficacy and determine long‐term sustainability. We monitored a seeded cottonwood‐willow site over a five‐year period beginning in 2007, with particular interest in how density affected vegetation diversity and stand structure over time. Fremont cottonwood (Populus fremontii) and volunteer tamarisk (Tamarix ramosissma) were the only abundant riparian trees at the site after one year. P. fremontii, compared to T. ramosissma, had higher growth rates, lower mortality, and dominated overstory and total cover each year. Vegetation diversity decreased from 2007–2009, but was similar from 2009–2011 as a result of decreased herbaceous and increased shrub species richness. Diversity was highest in the lowest density class (1‐12 stems/m²), but similar among all other classes (13–24, 25–42, 43+). High initial woody species densities resulted in single‐stemmed trees with depressed terminal and radial growths. Allometry, relating height to DBH at different densities, could prove to be an important tool for long‐term restoration management and studying habitat suitability. Understanding long‐term trends at densely‐planted or seeded sites can benefit restoration managers who aim to establish specific community structure and vegetation diversity for wildlife habitat. Copyright © 2012 John Wiley & Sons, Ltd.     

VEGETATION–LANDFORM ASSEMBLAGES ALONG SELECTED RIVERS IN THE CZECH REPUBLIC,A DECADE AFTER A 500‐YEAR FLOOD EVENT

Rivers with a natural flow regime strongly influence the dynamics of riparian plant communities through hydrological and geomorphological processes. In this study, associations between fluvial landforms and vegetation are investigated on three near‐natural rivers in the Czech Republic a decade after a 500‐year return period flood in July 1997. This extreme disturbance destroyed the anthropogenically modified river channels and created suitable conditions for a range of ecosystems with high diversity and ecological stability. Field surveys were conducted on fluvial landforms (bars, islands, banks, floodplains and terraces) along three ‘renaturalized’ rivers, where no technical modifications had subsequently been made to their channels outside urban areas and the floodplains had been left in a post‐flood state. Vegetation species abundance and 13 environmental variables (topographical, hydrological and soil) were investigated in summer 2007, 10 years after the extreme flood disturbance. The results suggest that the recently created fluvial geomorphic forms are key environmental determinants of riparian vegetation distribution patterns. A range of statistical analyses illustrate that some plant species show predictable patterns of occurrence that correspond with the fluvial forms, supporting a fourfold grouping of herbaceous and woody species and the identification of typical plant communities associated with gravel bars, islands, banks, floodplains and terraces. An investigation of the species richness found on different fluvial landforms showed that the highest number of species occurred on the floodplain and decreased gradually towards the channel bed and towards terraces. Investigation of existing conditions in reaches of rivers with natural dynamics of fluvial processes provides valuable information that can be used as an effective tool for planning restoration strategies and precise management. However, the most important finding of this study is the remarkable establishment of complex river corridor vegetation–landform associations within 10 years of a 500‐year flood that removed the heavily cultivated landscape that had existed before the event. Copyright © 2011 John Wiley & Sons, Ltd.     

SEDIMENT DYNAMICS IN THE RESTORED REACH OF THE KISSIMMEE RIVER BASIN,FLORIDA: A VAST SUBTROPICAL RIPARIAN WETLAND

Historically, the Kissimmee River Basin consisted of a broad nearly annually inundated riparian wetland similar in character to tropical Southern Hemisphere large rivers. The river was channelized in the 1960s and 1970s, draining the wetland. The river is currently being restored with over 10 000 hectares of wetlands being reconnected to 70 river km of naturalized channel. We monitored riparian wetland sediment dynamics between 2007 and 2010 at 87 sites in the restored reach and 14 sites in an unrestored reference reach. Discharge and sediment transport were measured at the downstream end of the restored reach. There were three flooding events during the study, two as annual flood events and a third as a greater than a 5‐year flood event. Restoration has returned periodic flood flow to the riparian wetland and provides a mean sedimentation rate of 11.3 mm per year over the study period in the restored reach compared with 1.7 mm per year in an unrestored channelized reach. Sedimentation from the two annual floods was within the normal range for alluvial Coastal Plain rivers. Sediment deposits consisted of over 20% organics, similar to eastern blackwater rivers. The Kissimmee River is unique in North America for its hybrid alluvial/blackwater nature. Fluvial suspended‐sediment measurements for the three flood events indicate that a majority of the sediment (70%) was sand, which is important for natural levee construction. Of the total suspended sediment load for the three flood events, 3%–16% was organic and important in floodplain deposition. Sediment yield is similar to low‐gradient rivers draining to the Chesapeake Bay and alluvial rivers of the southeastern USA. Continued monitoring should determine whether observed sediment transport and floodplain deposition rates are normal for this river and determine the relationship between historic vegetation community restoration, hydroperiod restoration, and sedimentation. Published in 2011 by John Wiley & Sons, Ltd.