Flood Disturbance Research Articles

Riparian vegetation of ephemeral streams

Ephemeral streams are abundant in drylands, yet we know little about how their vegetation differs from surrounding terrestrial zones and about their projected response to regional warming and drying. We assessed plant communities at seven ephemeral streams (and terrestrial zones) distributed among three climatic settings in Arizona. Compared to terrestrial zones, riparian zones had similar herbaceous cover but greater woody vegetation volume. They supported more plant species, with several woody taxa restricted to the ephemeral zone (consistent with the idea that herbaceous plants are rain-dependent while riparian trees rely on runoff stored in stream sediments). Their herbaceous communities had high compositional overlap with terrestrial zones and may sustain regional diversity as droughts intensify. Presumably owing to periodic flood disturbance, riparian plant communities had greater evenness than terrestrial zones, many of which were dominated by Eragrostis lehmanniana. Patterns along the climatic gradient suggest that increasing aridity will reduce the number of herbaceous (and total) plant species within riparian zones (110 species per stream in semihumid settings, 88 in semiarid, 48 in arid) and drive compositional shifts from perennials grasses and forbs to annuals. Hotter and drier conditions will drive sharp declines in herbaceous cover, converting riparian savanna to xeroriparian scrubland.

Stream network geomorphology mediates predicted vulnerability of anadromous fish habitat to hydrologic change in southeast Alaska.

In rivers supporting Pacific salmon in southeast Alaska, USA, regional trends toward a warmer, wetter climate are predicted to increase mid- and late-21st-century mean annual flood size by 17% and 28%, respectively. Increased flood size could alter stream habitats used by Pacific salmon for reproduction, with negative consequences for the substantial economic, cultural, and ecosystem services these fish provide. We combined field measurements and model simulations to estimate the potential influence of future flood disturbance on geomorphic processes controlling the quality and extent of coho, chum, and pink salmon spawning habitat in over 800 southeast Alaska watersheds. Spawning habitat responses varied widely across watersheds and among salmon species. Little variation among watersheds in potential spawning habitat change was explained by predicted increases in mean annual flood size. Watershed response diversity was mediated primarily by topographic controls on stream channel confinement, reach-scale geomorphic associations with spawning habitat preferences, and complexity in the pace and mode of geomorphic channel responses to altered flood size. Potential spawning habitat loss was highest for coho salmon, which spawn over a wide range of geomorphic settings, including steeper, confined stream reaches that are more susceptible to streambed scour during high flows. We estimated that 9-10% and 13-16% of the spawning habitat for coho salmon could be lost by the 2040s and 2080s, respectively, with losses occurring primarily in confined, higher-gradient streams that provide only moderate-quality habitat. Estimated effects were lower for pink and chum salmon, which primarily spawn in unconfined floodplain streams. Our results illustrate the importance of accounting for valley and reach-scale geomorphic features in watershed assessments of climate vulnerability, especially in topographically complex regions. Failure to consider the geomorphic context of stream networks will hamper efforts to understand and mitigate the vulnerability of anadromous fish habitat to climate-induced hydrologic change.

Recovery of benthic primary producers from flood disturbance and its implications for an altered flow regime in a tropical savannah river (Australia)

Flood disturbances in the Australian tropical savannah occur annually during the wet season and play a central role in shaping river ecosystems. We examined the recovery of benthic primary producer biomass from wet season (January to March) flood disturbances in the Daly River. Recovery occurs during the subsequent period of predominately groundwater-fed flow. A 3.3km long reach comprising a pool-run-pool-run sequence was surveyed on four dates for four plant groups: periphytic microalgae, visible filamentous Spirogyra spp., macroalgal Chara and Nitella spp., and the vascular macrophyte Vallisneria nana. Benthic primary producers had low resistance to flood disturbance, with the exception of V. nana which most likely survived through resistant rhizomes and leaves. Recovery following flood disturbance is possible when riverbed PAR exceeds the compensation irradiance of the primary producers, which occurs during the wet to dry season transition (April, May) as depth declines and water clarity improves. The total biomass of primary producers increased from 0.5gdryweightm−2 in June to 15g dry weight m−2 in November, indicating significant recovery. The temporal sequence of primary producer domination, from microalgae to macroalgae to V. nana, reflected plant size and growth rates. Inter-annual variability of wet season floods and dry season base-flows are hypothesized to affect the resistance and recovery of the four plant groups. Imposed on this natural variability, water resource developments will reduce flows, although this may be offset to a limited extent by more frequent flood disturbances of high magnitude caused by climate change.

Habitat heterogeneity drives bird species richness, nestedness and habitat selection by individual species in fluvial wetlands of the Paraná River, Argentina

We assessed the relationship between habitat heterogeneity and bird species richness and composition within wetlands of the floodplain of the Middle Parana River, Argentina. Given the high habitat heterogeneity in these wetland systems, we sought to determine whether (i) there was a positive relationship between bird species richness and habitat heterogeneity; (ii) whether bird species richness was associated with certain types of individual habitat types; (iii) whether there was a pattern of species nestedness and turnover between sites as a function of habitat heterogeneity and composition, respectively; and (iv) whether individual species exhibited associations with habitat heterogeneity. Point counts were used to survey birds at 60 sites. We estimated the area of eight habitat types found within a 200-m radius from the centre of each site and calculated number and Pielou's evenness of habitat types. These indices, together with area proportion of each habitat type, were used as explanatory factors of bird species richness in linear regression models. Habitat heterogeneity per se rather than area of individual habitat types was a more important predictor of species richness in these fluvial wetlands. Sites with more habitat types supported more bird species. Results showed that individual bird species were associated with different habitat types and, therefore, sites that contained more habitat types contained more species. Number of habitat types accounted for species nestedness between sites whereas composition of habitat types accounted for species turnover between sites. Results suggest that selection of heterogeneous sites by individual species could help explain the positive heterogeneity–species richness relationship. Our findings highlight the importance of habitat heterogeneity per se resulting from flood disturbances in maintaining bird richness in fluvial systems.

Coupled Hydrological/Hydraulic Modelling of River Restoration Impacts and Floodplain Hydrodynamics

Channelization and embankment of rivers has led to major ecological degradation of aquatic habitats worldwide. River restoration can be used to restore favourable hydrological conditions for target species or processes. However, the effects of river restoration on hydraulic and hydrological processes are complex and are often difficult to determine because of the long-term monitoring required before and after restoration works. Our study is based on rarely available, detailed pre-restoration and post-restoration hydrological data collected from a wet grassland meadow in Norfolk, UK, and provides important insights into the hydrological effects of river restoration. Groundwater hydrology and climate were monitored from 2007 to 2010. Based on our data, we developed coupled hydrological/hydraulic models of pre-embankment and post-embankment conditions using the MIKE-SHE/MIKE 11 system. Simulated groundwater levels compared well with observed groundwater. Removal of the river embankments resulted in widespread floodplain inundation at high river flows (>1.7 m3 s−1) and frequent localized flooding at the river edge during smaller events (>0.6 m3 s−1). Subsequently, groundwater levels were higher and subsurface storage was greater. The restoration had a moderate effect on flood peak attenuation and improved free drainage to the river. Our results suggest that embankment removal can increase river–floodplain hydrological connectivity to form a more natural wetland ecotone, driven by frequent localized flood disturbance. This has important implications for the planning and management of river restoration projects that aim to enhance floodwater storage, floodplain species composition and biogeochemical cycling of nutrients. © 2016 The Authors. River Research and Applications Published by John Wiley & Sons Ltd.

Fluvial Corridor Changes Over Time in Regulated and Non‐Regulated Rivers (Upper Esla River, NW Spain)

AbstractOver the last decades, rivers and fluvial corridors have been noticeably modified from their natural conditions. In general, damming and other in‐channel human interventions have been traditionally considered as the main drivers of change. However, recent studies highlight the influence of climate, hillslope and floodplain cover changes over fluvial corridor dynamics. The present study illustrates the channel morphology and riparian vegetation responses observed in three gravel bed rivers located in the Upper Esla River, north‐west of Spain. The entire study catchment was exposed to afforestation changes and farmland abandonment during the last decades, and two of the rivers are regulated by large dams. Analysis of historical orthophotos at different periods between 1956 and 2011 allowed quantifying channel narrowing, reduction of braiding index and vegetation encroachment along the three rivers. Field reconnaissance of landforms and vegetation structure along transects showed significant differences in species composition and age structure between the non‐regulated reach, where recruitment of Salicacea pioneer species existed, and the regulated reaches where mature and late‐seral species were much more abundant. These responses were consistent with reductions in mean annual discharge in all rivers and with flood disturbance decrease and summer minimum flow increase that were observed in the regulated rivers. Copyright © 2016 John Wiley & Sons, Ltd.

Harsh habitats? Waterfalls and their faunal dynamics in tropical Australia

There are few studies of the ecology of waterfalls despite their being prominent landscape features and of ecological interest because of their physical characteristics. We compared invertebrate assemblages of 5 waterfalls in the Australian Wet Tropics over 12–18 mo. Waterfall assemblages were distinct from those of riffles and bedrock, with some taxa particularly abundant on waterfalls (e.g. Simuliidae, Hydropsychidae) and others restricted to them (e.g. Blephariceridae, Pyralidae), and supported more species than bedrock but fewer than riffles. Differences among waterfalls related to differences in discharge, shade and habitat complexity. Waterfalls comprised a complex of microhabitat patches, with high-flow smooth, high-flow rough, vertical and spray zones most prevalent and distinguishable by gradient, roughness, water velocity, depth and invertebrate assemblages. In high-flow microhabitats rheophilic taxa (e.g. Simuliidae) were prevalent, while in the spray zone a range of madicolous taxa (e.g. various Coleoptera) occurred. Within microhabitats, temporal change was moderate, with stable composition over 12 months. Flood disturbance had limited effect on assemblages, as large flows overshot steep surfaces; drought may be more of a threat because recovery is hindered by isolation and lack of hyporheic refugia. Given their isolation, limited extent and distinctive fauna, waterfalls merit special conservation attention.

Time and Intensity Weighted Indices of Fluvial Processes: a Case Study from the Kootenai River, USA

AbstractWithin riparian landscapes, river flows and stages determine habitat gradients from less to more dynamic, and these support different plant species and their life history stages that are adapted to specific positions along these gradients. The gradients are characterized by physical processes that vary in magnitude and duration, and these shape the riparian vegetation communities. Consequently, natural riparian ecosystems are very dynamic, and the river disturbance regime is essential for sustaining ecosystem health. However, although the importance of disturbance is well accepted, disturbance regimes are poorly understood. This study was undertaken to develop indices capable of characterizing riparian habitats by considering flood magnitude and the elapsed time after flood disturbance, that is, the history that influenced the present vegetation composition. The indices were tested along two reaches of the Kootenai River in Idaho, USA, with braided versus meandering channel forms. The case study spanned a 31‐year period and emphasized two major disturbance components, the morphodynamic influence of velocity and shear stress and the flood or inundation duration. Computed indices were tested for consistency and then used to characterize different riparian vegetation development and succession phases. The statistical analysis revealed high correspondence among the calculated indices and differences across the different successional stages and between the two reaches. This demonstrated the utility of the time and intensity weighted indices to analyse the fluvial patterns that support different riparian vegetation communities, and this could be applicable for riparian management, mitigation, conservation and restoration. Copyright © 2016 John Wiley & Sons, Ltd.

洪水営力による樹木管理後の幼木林動態を踏まえた樹林化抑制手法の考察

Gravel-bed rivers in Japan are now facing a multitude of problems relating to fluvial environment and flood control. These problems include the expansion of river beds with less disturbance by flooding and the growth of the riverine trees and the decrease of high-quality gravel-bed bars and the immobilization of low-flow channel. In particular, the gravel bed river that dominated by vigorous growth of Willows and Robinia pseudo-acacia, sometimes increase the riverine trees by vegetative propagation under the flood disturbance. In addition, expansion of the overgrowth density is likely to occur as the young riverine trees that easily fallen by flood disturbance. In this study, to target the gravel bed of Watarase river that Robinia pseudo-acacia, etc. grows in the river, evaluated the dynamics of young riverine trees after felling, and proposed the excavation shape of gravel-bed bar for forestation suppressing by using flood disturbance.

Nitrogen fixation by Pueraria lobata as a nitrogen source in the midstream sediment bar of a river

AbstractIt was assumed that the symbiotic N fixation in a floodplain site is highly affected by flood disturbances. To test this hypothesis, we collected soil and plant samples from several quadrats of the midstream flood plain of a relatively steep urbanized river that was subject to a different magnitude of flooding. Soil carbon and nitrogen contents had a significant positive correlation with the elevation of sites; i.e. they negatively correlated with a frequency of flood inundation. Soil pH values ranged between 6.0 and 7.23 at low elevation sites and 5.16 and 6.81 for high elevation sites. There was a significant difference (p < 0.001) in N fixation among sampling points, which suggests that flooding disturbs the process. A pH value of 6.5 is the best for N fixation; N fixation decreases while the pH increases or decreases. Site elevation also directly affected soil characteristics, especially nitrogen and carbon content. The fractionation of 15N value in leaf tissue (δ15N) suggests that N fixation is extensive when the total N (TN) is ≤ 0.3%. Below this TN, Pueraria lobata can derive up to 80% of their TN requirement from the atmosphere. Therefore, it can be concluded that site elevation, or flood pulses, affects the symbiotic N fixation in a floodplain by modifying the edaphic factors. Copyright © 2015 John Wiley & Sons, Ltd.

Tropical insular fish assemblages are resilient to flood disturbance

Periods of stable environmental conditions, favoring development of ecological communities regulated by density‐dependent processes, are interrupted by random periods of disturbance that may restructure communities. Disturbance may affect populations via habitat alteration, mortality, or displacement. We quantified fish habitat conditions, density, and movement before and after a major flood disturbance in a Caribbean island tropical river using habitat surveys, fish sampling and population estimates, radio telemetry, and passively monitored PIT tags. Native stream fish populations showed evidence of acute mortality and downstream displacement of surviving fish. All fish species were reduced in number at most life stages after the disturbance, but populations responded with recruitment and migration into vacated upstream habitats. Changes in density were uneven among size classes for most species, indicating altered size structures. Rapid recovery processes at the population level appeared to dampen effects at the assemblage level, as fish assemblage parameters (species richness and diversity) were unchanged by the flooding. The native fish assemblage appeared resilient to flood disturbance, rapidly compensating for mortality and displacement with increased recruitment and recolonization of upstream habitats.

Large, infrequent disturbance on a regulated river: response of floodplain forest birds to the 2011 Missouri River flood

Floodplain forests are dynamic habitats that support a high diversity and abundance of birds. Periodic flood disturbance is important in the establishment and maintenance of the heterogeneous mosaic of vegetation communities across the riverine landscape. Human suppression of disturbance regimes has been implicated in the decline of bird species in these systems. Because few large rivers are not subject to flood control by dams and levees, opportunities to study avian responses to flood disturbance are limited. A large magnitude, long‐duration flood event on the Missouri River, USA, during the summer of 2011 provided an opportunity to quantify post‐flood changes in forest bird densities and species richness relative to pre‐flood conditions on a riverine floodplain impacted by decades of flow regulation. We surveyed 75 forest sites on two segments of remnant floodplain forest along the Missouri National Recreational River (MNRR) in southeastern South Dakota and northeastern Nebraska and examined changes in density for 35 breeding landbird species from pre‐flood (2009–2010) to post‐flood (2012–2014) periods. We used a repeated measures ANOVA design to test the effects of year on average densities of birds and nesting guilds and confidence intervals to determine changes in densities of individual species and species richness. 19 of 35 focal species declined significantly one year after the flood (2012), but abundances of ten species recovered to pre‐flood densities or higher within two years. In 2012, density declines of six species and density increases of two species were significantly correlated with a decrease in woody vegetation density and percent shrub cover. Average bird densities and the density of shrub nesters rebounded in 2013 to pre‐flood levels and continued to increase through 2014. There were no significant changes in species richness at the level of forest habitat types between sampling years. Our results demonstrate short‐term resilience of floodplain bird species to a major disturbance despite declines in early successional habitat and minimal recovery of woody vegetation.

How to Regenerate and Protect Desert Riparian Populus euphratica Forest in Arid Areas.

We found that the most suitable flooding disturbance model for regenerating Populus euphratica forest was two to three times per year with a duration of 15–20 days and an intensity of 25–30 m3/s. The flooding should take place during the seed emergence to young tree growth stages, and should be based on flooding experiments and data from vegetation quadrats and ecological water conveyance. Furthermore, we found that tree-ring width index for P. euphratica declined as the groundwater depth increased, and ascertained that the minimum groundwater depths for young trees, near-mature trees, mature trees and over-mature trees were 4.0 m, 5.0–5.4 m, 6.9 m and 7.8 m, respectively. These were derived from a quantitative relationship model between groundwater depth and tree-ring width index. The range for ecological water conveyance volume was 311–320 million m3 in the lower reaches of the Tarim River. This study not only provides a technical basis for sustainable ecological water conveyance in the Tarim River Basin, but also offers a theoretical guide and scientific information that could be used in similar areas to regenerate and protect Populus euphratica around the world.

Assessing the structural adequacy of alternative ecohydrological models using a pattern-oriented approach

The development of environmental system models is challenging because of different disciplinary philosophical approaches to uncertainty in modelling of the terrestrial hydrosphere and ecosphere. We use pattern-oriented modelling to assess model structural adequacy and to select alternative model structures within the hierarchy of a model of flood-groundwater–vegetation interactions. We varied the equation structure of two key model components, flood tolerance and seasonal leaf shedding, and tested how well the model structures reproduced a set of observed patterns: (i) three species coexistence, (ii) species-specific access to groundwater, and (iii) species-specific ability to tolerate flood disturbances. We assessed (a) the role of flood frequency in biomass regulation for modelling of three coexisting species sharing the same water resources, and (b) the effect of alternative process and equation structures on the deviation of hydrological variables (transpiration, groundwater table) from average conditions.Only model structures that explicitly considered the functional relationship between flood events and biomass regulation were able to reproduce the coexistence pattern and the two secondary patterns (ii and iii). The different coexistence mechanisms had little effect on the average transpiration rates and water table depths. However, shallow and deep average groundwater tables, caused by low and high transpiration rates, were modelled more frequently with model structures that intentionally ignored species-specific phenological cycles rather than models which incorporated them. Our findings indicate that, amongst all tested model structures, the most complex one is most plausible and can explain the observed patterns in an environment controlled by the interplay between periods of water deficit and flood disturbance. It reproduced the three observed ecological patterns and enhanced the general understanding of groundwater-dependent ecosystems along ephemeral rivers.

An ecological perspective on floods in Canada

This review presents a summary of the influences of floods on river ecology, both instream and on the adjacent floodplain, mostly in a Canadian context. It emphasizes that ecological impacts and benefits can be highly dependent on flood-generation processes and their magnitude and timing. In Canada, floods can occur under open-water or ice-influenced river conditions. The ecological impacts of floods generated from ice jamming are particularly relevant in Canadian ecosystems due to the potentially higher water levels produced and suspended sediment concentrations that can be detrimental to instream aquatic habitat, but beneficial to floodplains. Large floods provide a major source of physical disturbance. Moderate floods with shorter return periods can be beneficial to aquatic habitats by providing woody debris that contributes to habitat complexity and diversity, by flushing fine sediments and by providing important food sources from terrestrial origins. Floods also influence water-quality variables such as sediment loads, metals and pH, which further influence river ecology. This review points out important links between floods and habitat connectivity and refugia, and the ability of aquatic resources to recover from flood disturbances. The floodplain vegetation also influences bank erosion and channel configuration, as well as many processes contributing to the river ecology, such as allochthonous inputs of carbon, preventing bank erosion, food-web dynamics and other effects. Many species of riparian trees are dependent on floods for reproduction, and floods can limit competitive encroachment of upland vegetation. Floods play a critical role in deltaic environments where high flows provide nutrient supplies and overflows maintain water balances within these environments. Two substantial factors that will likely influence future flood regimes in Canada are climate change and flow regulation. Future research should focus on enhancing our understanding of how floods affect river ecology, including under winter conditions, to better manage important natural resources.

Functional responses of multitaxa communities to disturbance and stress gradients in a restored floodplain

Summary Trait‐based approaches can reveal the mechanisms through which disturbances or stress impact communities, allowing comparisons of the role of different mechanisms in shaping communities among taxonomic groups. Such information can lead to higher comparability, transferability and predictability of the outcome of restoration projects. However, multitaxa trait‐based approaches were rarely used in the context of ecosystem restoration. We investigated the responses to environmental gradients of seven taxa (vascular plants, staphylinid and carabid beetles, spiders, isopods, diplopods and earthworms) in a restored floodplain using a species traits approach. We assessed the impact of flood disturbances and soil hydric stress on the functional diversity (FD) and community‐weighted mean (CWM) response of traits for each taxon. Ordination of hydrological variables revealed two main gradients. The first was related to the spatiotemporal dynamics of flood disturbances and the second to the average changes in soil hydric conditions. The analysis of CWM revealed that larger, poorly mobile species with narrow ecological tolerances were filtered by regular floods and/or changes in soil hydric conditions. Functional diversity patterns differed between the two gradients: decreasing with increasing flood disturbance, but increasing along the soil hydric stress gradient. This suggests that the mechanisms shaping community composition differ between the two gradients with environmental filtering being dominant with increasing flood disturbances and competition decreasing with more soil hydric stress. Synthesis and applications. Our study shows that the impact of restored flood disturbances and soil hydric stress on plant and invertebrate functional diversity and community‐weighted mean can be positive, negative or more complex depending on the taxonomic group and environmental gradient considered. The patterns can to some extent be explained by the specific characteristics of each group. Larger, poorly mobile species with narrow ecological tolerances were particularly vulnerable to changes in disturbance and stress regime following floodplain restoration. These species may therefore be lost in the initial phases of restoration projects, but other more characteristic species of dynamic floodplains will be favoured. Understanding the consequences of these contrasted responses for biodiversity conservation and ecosystem functioning constitutes the next challenge for ecosystem restoration.

Immediate changes in stream channel geomorphology, aquatic habitat, and fish assemblages following dam removal in a small upland catchment

Dam removal is becoming an increasingly important component of river restoration, with >1100 dams having been removed nationwide over the past three decades. Despite this recent progression of removals, the lack of pre- to post-removal monitoring and assessment limits our understanding of the magnitude, rate, and sequence of geomorphic and/or ecological recovery to dam removal. Taking advantage of the November 2012 removal of an old (~190year-old) 6-m high, run-of-river industrial dam on Amethyst Brook (26km2) in central Massachusetts, we identify the immediate eco-geomorphic responses to removal. To capture the geomorphic responses to dam removal, we collected baseline data at multiple scales, both upstream (~300m) and downstream (>750m) of the dam, including monumented cross sections, detailed channel-bed longitudinal profiles, embeddedness surveys, and channel-bed grain size measurements, which were repeated during the summer of 2013. These geomorphic assessments were combined with detailed quantitative electrofishing surveys of stream fish richness and abundance above and below the dam site and throughout the watershed and visual surveys of native anadromous sea lamprey (Petromyzon marinus) nest sites. Post-removal assessments were complicated by two events: (1) upstream knickpoint migration exhumed an older (ca. late eighteenth century) intact wooden crib dam ~120m upstream of the former stone dam, and (2) the occurrence of a 10–20year RI flood 6months after removal that caused further upstream incision and downstream aggradation. Now that the downstream reach has been reconnected to upstream sediment supply, the predominant geomorphic response was bed aggradation and associated fining (30–60% reduction). At dam proximal locations, aggradation ranged from 0.3 to >1m where a large woody debris jam enhanced aggradation. Although less pronounced, distal locations still showed aggradation with a mean depth of deposition of ~0.20m over the 750-m downstream reach. Post-removal, but pre-flood, bed surveys indicate ~2m of incision had migrated 25m upstream of the former reservoir before encountering the exhumed dam, which now acts as the new grade control, limiting progressive headcutting. Approximately 1000m3 of sediment was evacuated in the first year, with ~67% of the volume occurring by pre-flood, process-driven (e.g., changes in base level) controls. The combination of changes in channel-bed sedimentology, the occurrence of a large magnitude flood, and the emergence of the new crib dam that is a likely barrier to fish movement was associated with major reductions in abundance and richness in sites downstream and immediately upstream adjacent to the former dam in post-removal sampling. At the same time, we documented the presence of four species of fish, including sea lamprey, which were not present above the dam prior to removal, indicating that upstream passage has been achieved; and we also documented lamprey spawning activity at sites immediately below the dam, which had previously been unsuitable owing to an excessively coarse and armored riverbed. Our results point to the importance of interactions between dam removal and flood disturbance effects, with important implications for short- and long-term monitoring and assessment of dam impacts to river systems.

Influence of an exotic grass on benthic macroinvertebrate communities in a tropical rural landscape

Riparian deforestation in rural areas has led to changes in bankside vegetation communities that may have unexpected effects on stream ecosystems. In particular, plants such as grasses can colonize the streambed from adjacent terrestrial habitats, thus altering the physical structure of the streambed and potential influencing macroinvertebrate communities. Here we evaluated if the presence of patches of grasses (Urochloa sp.) on the streambed influenced the structure and composition of macroinvertebrate communities in deforested rural streams. We sampled patches with and without grasses in three low-order streams, in the wet and dry seasons. We recorded higher abundances of macroinvertebrates in patches with grasses in the wet season when compared with bare patches. We also found significant differences in taxonomic and functional feeding group composition between patch types, due to higher overall abundances in patches with grasses, probably due to more food and shelter there. These influences were stronger in the wet season, when in-stream grasses may have provided greater refugia from flood disturbance that occur with increased frequency and intensity. Therefore, although deforestation of rural streams can simplify streambed habitats, in-stream grasses such as Urochloa sp. provide resources that contribute for the maintenance of macroinvertebrate communities.

Hydrological conditions explain variation in wood density in riparian plants of south‐eastern Australia

Summary Wood density is a key plant functional trait which integrates the trade‐offs characteristic to riparian plant ecological strategies. Although high‐density wood is costly to construct, it confers mechanical stiffness to stems, increasing a plant's capacity to withstand flooding, and also enables increased tolerance to water stress. For riparian plants, fluctuations in soil moisture driven by surface hydrology should therefore be an important driver of variation in wood density. We asked the following questions in the study: (1) Does wood density increase with increasing frequency and magnitude of flood disturbance? (2) Does wood density increase with increasing unpredictability of water availability in the riparian zone? (3) Does dispersion of wood density peak at intermediate levels of hydrological disturbance? We surveyed wood density of dominant species at 15 riparian sites along flow‐gauged rivers across south‐eastern Australia. Due to the broad range of hydrological variability associated with Australian river systems, this set of sites functions as a useful model for assessing the response of riparian plants to changing hydrological conditions. We found wood density varied strongly along a single axis of hydrological variability. This axis integrates flood intensity and frequency with metrics of hydrological unpredictability and can be conceptualized as a gradient of environmental harshness, with higher wood density associated with harsher conditions. Synthesis. Our study highlights the importance of hydrological conditions, particularly disturbance and environmental unpredictability, as determinants of ecological strategy in riparian plants. Large, rare flood events in particular appear to favour higher wood density strategies. This is likely to have significant ecological consequences for riparian plant communities in a south‐east Australian context, as well as in other regions where increasing climatic variability and frequency of extreme events are hallmarks of climate change predictions.

Preserving geomorphic data records of flood disturbances

No central database or repository is currently available in the USA to preserve long-term, spatially extensive records of fluvial geomorphic data or to provide future accessibility. Yet, because of their length and continuity these data are valuable for future research. Therefore, we built a public accessible website to preserve data records of two examples of long-term monitoring (40 and 18years) of the fluvial geomorphic response to natural disturbances. One disturbance was ∼50-year flood on Powder River in Montana in 1978, and the second disturbance was a catastrophic flood on Spring Creek following a ∼100-year rainstorm after a wildfire in Colorado in 1996.Two critical issues arise relative to preserving fluvial geomorphic data. The first is preserving the data themselves, but the second, and just as important, is preserving information about the location of the field research sites where the data were collected so the sites can be re-located and re-surveyed in the future. The latter allows long-term datasets to be extended into the future and to provide critical background data for interpreting future landscape changes. Data were preserved on a website to allow world-wide accessibility and to upload new data to the website as they become available. We describe the architecture of the website, lessons learned in developing the website, future improvements, and recommendations on how also to preserve information about the location of field research sites.