David M. Merritt

USDA Forest Service

Willows are an important component of western riparian zones as their roots stabilize streambanks, their overstory mediates stream temperature, and aquatic biota use their stems and leaves as forage and build- ing material. We evaluated 1894 stream reaches in the Inland Pacific Northwest for the presence of wil- lows and detected one or more willow...

• Understanding the current distribution of riparian plant species is essential for predicting their expansions or contractions in response to flow alterations due to climate changes or direct human actions. Riparian vegetation flow response guilds are assemblages of species that have common functional traits and are hypothesised to respond similar...

Riparian zones are the paragon of transitional ecosystems, providing critical habitat and ecosystem services that are especially threatened by global change. Following consultation with experts, 10 key challenges were identified to be addressed for riparian vegetation science and management improvement: (1) Create a distinct scientific community by...

Riparian ecosystems are among the most diverse terrestrial ecosystems on all continents on Earth. Geologic and ecoregional setting, the form and distribution of water and sediment supply, connectivity, and the regional species pool govern the physical form, the seasonal and interannual flow and sediment regime, together define the possibilities and...

Ecosystems are defined, studied, and managed according to boundaries constructed to conceptualize patterns of interest at a certain scale and scope. The distinction between ecosystems becomes obscured when resources from multiple origins cross porous boundaries and are assimilated into food webs through repeated trophic transfers. Ecosystem compart...

Overcoming challenges of water scarcity necessitates creative flow management approaches that account for multiple, potentially competing water needs of plants and animals in river ecosystems. Mechanistic multispecies models can guide decision making by evaluating trade‐offs associated with flow regimes designed for specific ecosystem outcomes befo...

The southern Rocky Mountains serve as the headwaters of the West, providing water to agriculture, industry, recreation, and millions of people in 17 western states. Eighty percent of the water draining land managed by the United States Department of Agriculture Forest Service (Forest Service) is from snowmelt. The demand for this water continues to...

Riparian areas are among the most ecologically diverse terrestrial ecosystems but make up <2% of landscape area in southwestern USA. Many species of resident and neotropical migratory birds utilize riparian habitats for breeding, foraging, and nesting. We quantified vegetation composition and structure to predict bird guilds on Wild and Scenic port...

Within arid regions riparian forests support high bird diversity compared to surrounding uplands. In these same regions, water demands for agriculture, urbanization, and recreation have altered the structure and composition of riparian forests and degraded bird habitat. Along rivers, plants with similar responses to flood disturbance and water avai...

Altering stream flows and groundwater have modified how streams are connected to riparian floodplain vegetation. This disconnection has led to the proliferation of non-native and invasive woody plant species and altered habitat complexity. Squamate vertebrates such as lizards and snakes, and amphibians such as frogs and toads, are important food we...

Overcoming the physical limits of dam operations under nonstationarity will require creative approaches to flow management and modeling approaches that forecast the effects of management actions on multiple ecosystem components simultaneously. Using a novel multispecies modeling approach, we investigated the cross-ecosystem effects of environmental...

Patterns of riparian vegetation are strongly influenced by hydrology and fluvial processes. However, valley form and processes (rates of runoff and erosion and deposition), channel planform and cross-sectional form and slope are influenced by the presence, physiognomy, structure, distribution and abundance of vegetation, as well. The interrelations...

More than a century of dam construction and water development in the western United States has led to extensive ecological alteration of rivers. Growing interest in improving river function is compelling practitioners to consider ecological restoration when managing dams and water extraction. We developed an Ecological Response Model (ERM) for the...

As the climate warms, we can’t restore waterways to pristine condition, but models can predict potential changes, argue Jonathan D. Tonkin, N. LeRoy Poff and colleagues. As the climate warms, we can’t restore waterways to pristine condition, but models can predict potential changes, argue Jonathan D. Tonkin, N. LeRoy Poff and colleagues. Fish that...

Understanding how novel biological assemblages are structured in relation to dynamic environmental regimes remains a central challenge in ecology. Demographic approaches to modeling species assemblages show promise because they seek to represent fundamental relationships between population dynamics and environmental conditions. In dryland rivers, r...

The natural hydrologic processes that create and maintain the diversity of aquatic and riparian habitats along the World's streams and rivers have been profoundly altered by humans. Diversion of surface water to support production agriculture in arid and semi-arid regions has degraded ecosystems but also created potential habitat along and in canal...

Many riparian ecosystems in Mediterranean Europe are affected by land use and flow alteration by dams. We focused on understanding how these stressors and their components affect riparian forests in the region. We asked the following questions: (1) Are there well‐defined, responsive riparian guilds? (2) Do dam‐induced streamflows determine abundanc...

Riverine ecosystems are governed by patterns of temporal variation in river flows. This dynamism will change due to climate change and the near-ubiquitous human control of river flows globally, which may have severe effects on species distributions and interactions. We employed a combination of population modelling and network theory to explore the...

Riparian areas are hotspots of biological diversity that may serve as high quality habitat for fish and wildlife. The National Riparian Core Protocol (NRCP) provides tools and methods to assist natural resource professionals in sampling riparian vegetation and physical characteristics along wadeable streams. Guidance is provided for collecting basi...

Hierarchical frameworks are useful constructs when exploring landscape- and local-scale factors affecting patterns of vegetation in riparian areas. In drylands, which have steep environmental gradients and high habitat heterogeneity, landscape-scale variables, such as climate, can change rapidly along a river's course, affecting the relative influe...

The functional trait framework, an ecological tool powerful for its simplicity and ability to facilitate modeling and generalization across environmental gradients, can capture the interactions between ecological and physical processes that shape riparian ecosystems. We demonstrate that ecological-response traits that describe how a plant will resp...

Wetland indicator status (WIS) describes the habitat affinity of plant species and is used in wetland delineations and resource inventories. Understanding how species-level functional traits vary across WIS categories may improve designations, elucidate mechanisms of adaptation, and explain habitat optima and niche. We investigated differences in s...

Comparisons of community-level functional traits across environmental gradients have potential for identifying links among plant characteristics, adaptations to stress and disturbance, and community assembly. We investigated community-level variation in specific leaf area (SLA), plant mature height, seed mass, stem specific gravity (SSG), relative...

Trait-based approaches to vegetation analyses are becoming more prevalent in studies of riparian vegetation dynamics, including responses to flow regulation, groundwater pumping, and climate change. These analyses require species trait data compiled from the literature and floras or original field measurements. Gathering such data makes trait-based...

Modeling riparian plant dynamics along rivers is complicated by the fact that plants have different edaphic and hydrologic requirements at different life-stages. With intensifying human demands for water and continued human alteration of rivers, there is a growing need for predicting responses of vegetation to flow alteration, including responses r...

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...

Plant functional types (or guilds) increasingly are being used to predict vegetation response to global changes. Continued human population growth coupled with projected warmer and drier climate will alter the hydrologic regimes of many arid‐zone rivers, including intermittent rivers. We aimed to identify (i) woody plant guilds associated with dist...

Maximum flood extent--a key data need for disaster response and mitigation--is rarely quantified due to storm-related cloud cover and the low temporal resolution of optical sensors. While change detection approaches can circumvent these issues through the identification of inundated land and soil from post-flood imagery, their accuracy can suffer i...

The Colorado River in Grand Canyon has undergone major changes in riparian habitat since the closure of Glen Canyon Dam. Adaptive management of the current regulated river ecosystem requires a means to link flow with riparian vegetation response. Riparian vegetation-flow response guilds provide a potential tool to mechanistically link flow attribut...

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. Identifying the environmental filters that exert selective pressures and favor specific vegetation guilds within riverscapes is a critical s...

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. Identifying the environmental filters that exert selective pressures and favor specific vegetation guilds within riverscapes is a critical s...

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. Identifying the environmental filters that exert selective pressures and favor specific vegetation guilds within riverscapes is a critical s...

Flow diversions are widespread and numerous throughout the semi‐arid mountains of the western United States. Diversions vary greatly in their structure and ability to divert water, but can alter the magnitude and duration of base and peak flows, depending upon their size and management. Channel geometry and riparian plant communities have adapted t...

Over the past decades, we have assisted to an increasing understanding of the effects of regulated-flow conditions on aquatic ecosystems. However, the responses to altered flows of the ecotonal ecosystems remain a long-standing chal-lenge in the Mediterranean regions. This is probably due to the multiple pressures that in-fluence directly and indir...

Background: Stream flow is a fundamental driver of riparian plant communities. The increasing need for water resources to manifold purposes (hydropower energy, agriculture, industry, urban use) resulted in a widespread disturbance of flow regimes, with regulation by dams having a major impact in fluvial and riparian landscapes. There is increasing...

Background & Aim: Alteration of flow regimes by dams causes shifts in the composition and diversity as well as the trait syndromes of streamside plant communities [1]. There is still a limited knowledge of riparian strategies to streamflow regulation and moreover to different dam operations. Such an understanding would enable us to more strategical...

Background/Question/Methods Along lowland streams in the western United States, reproduction of cottonwood trees (Populus spp.) is dependent on floods that provide substrate for germination space and moisture for seedling survival. The Middle Rio Grande in central New Mexico is heavily regulated by dams and diversions, which have restricted the o...

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 hyd...

The biological control agent (tamarisk leaf beetle, Diorhabda spp.) is actively being used to defoliate exotic saltcedar or tamarisk (Tamarix spp.) in riparian ecosystems in western USA. The Virgin River in Arizona and Nevada is a system where tamarisk leaf beetle populations are spreading. Saltcedar biocontrol, like other control methods, has the...

To enable assessment of risks of water management to riparian ecosystems at a regional scale, we developed a quantile-regression model of abundance of broadleaf cottonwoods (Populus deltoides and P. fremontii) as a function of flood flow attenuation. To test whether this model was transferrable to narrowleaf cottonwood (Populus angustifolia), we me...

QuestionsAre seed release and hydrochory of riparian plants coupled with seasonal flood pulses for a river with bimodal flows? What phenological hydrochore guilds are present? How representative of riparian vegetation are hydrochores? What is the role of hydrochory in riparian plant community composition in arid land streams? LocationVerde River, c...

This chapter explores the impact of hydrology and fluvial geomorphology on the distribution and abundance of Tamarix as well as the reciprocal effects of Tamarix on hydrologic and geomorphic conditions. It examines whether flow-regime alteration favors Tamarix establishment over native species, and how Tamarix stands modify processes involved in th...

This chapter focuses on the restoration of riparian systems in the context of Tamarix control-that is, Tamarix-dominated sites are converted to a replacement vegetation type that achieves specific management goals and helps return parts of the system to a desired and more natural state or dynamic. It reviews research related to restoring native rip...

Patterns of riparian vegetation are strongly influenced by hydrology and fluvial processes. However, valley form and processes (rates of runoff and erosion and deposition), channel planform, and cross-sectional form and slope are influenced by the presence, physiognomy, structure, distribution, and abundance of vegetation, as well. The interrelatio...

Tamarix spp. are introduced shrubs that have become among the most abundant woody plants growing along western North American rivers. We sought to empirically test the long-held belief that Tamarix actively displaces native species through elevating soil salinity via salt exudation. We measured chemical and physical attributes of soils (e.g., salin...

Restoration projects can have varying goals, depending on the specific focus, rationale, and aims for restoration. When restoration projects use project-specific goals to define activities and gauge success without considering broader ecological context, determination of project implications and success can be confounding. We used case studies from...

The relationship between riparian vegetation and changes in fluvial processes as a response to flow diversion is not well understood. Water extraction affects the hydrologic flow regime (i.e., magnitude, duration, and frequency of flows) reducing peak and base-flows, which could negatively impact riparian vegetation. Vegetation communities are temp...

Increasing human populations have resulted in aggressive water development in arid regions. This development typically results in altered stream flow regimes, reduced annual flow volumes, changes in fluvial disturbance regimes, changes in groundwater levels, and subsequent shifts in ecological patterns and processes. Balancing human demands for wat...

Background/Question/Methods In the American Southwest, cottonwood (Populus spp.) forests cover a small percentage of the landscape but are highly valued for their aesthetic appeal and ecological services. Cottonwoods require specific hydrological conditions for survival and reproduction and are less fire-tolerant than other woody species. These c...

Background/Question/Methods To what extent are seed maturation and hydrochory of riparian plant species coupled with timing of flood events? Some riparian plants show tight coupling between regeneration phenology and seasonal flood timing, but patterns have not been described for most taxa. Such knowledge is important for predicting recruitment b...

IntroductionFlow Regimes Structure Ecological ComplexityFlow Regimes as a Management TargetSummaryReferences

Wetlands and riparian areas are unique landscape elements that perform a disproportionate role in landscape functioning relative to their aerial extent on the landscape. The purpose of this guide is to provide a general foundation for the reader in several interrelated disciplines for the purpose of enabling him/her to characterize and quantify the...

Supplementary information to: Non-natives: 141 scientists object Full list of co-signatories to a Correspondence published in Nature 475, 36 (2011); doi: 10.1038/475036a. Daniel Simberloff University of Tennessee, Knoxville, Tennessee, USA. dsimberloff@utk.edu Jake Alexander Institute of Integrative Biology, Zurich, Switzerland. Fred Allendorf Univ...

Delineation of riparian zones along mountain streams is complicated by substantial longitudinal variability in gradient and valley geometry and the lack of a floodplain along many stream reaches. We propose an approach to defining and delineating riparian zones based on site-specific geomorphic features and process domains, as well as the distribut...

It is well established that the roots of riparian vegetation add tensile strength to stream banks, thus reducing bank erosion and undercutting. Bank stability models that add the mechanical strength of riparian roots, based on root tensile strength and density, contribute to the understanding of vegetation-enhanced bank strength. However, for land...

The spatial distribution and temporal availability of propagules fundamentally constrain plant community development. This study experimentally tested several hypotheses about the relative roles of wind and water dispersal in colonization and development of riparian communities along rivers. Through controlling the source of propagules (dispersed b...

Hydrochory, or the passive dispersal of organisms by water, is an important means of propagule transport, especially for plants. During recent years, knowledge about hydrochory and its ecological consequences has increased considerably and a substantial body of literature has been produced. Here, we review this literature and define the state of th...

1. Riparian vegetation composition, structure and abundance are governed to a large degree by river flow regime and flow‐mediated fluvial processes. Streamflow regime exerts selective pressures on riparian vegetation, resulting in adaptations (trait syndromes) to specific flow attributes. Widespread modification of flow regimes by humans has result...

1. The flow regime is a primary determinant of the structure and function of aquatic and riparian ecosystems for streams and rivers. Hydrologic alteration has impaired riverine ecosystems on a global scale, and the pace and intensity of human development greatly exceeds the ability of scientists to assess the effects on a river‐by‐river basis. Curr...

The primary intent of this document is to provide the science assessment called for under The Saltcedar and Russian Olive Control Demonstration Act of 2006 (Public Law 109–320; the Act). A secondary purpose is to provide a common background for applicants for prospective demonstration projects, should funds be appropriated for this second phase of...

Tamarix ramosissima is a naturalized, nonnative plant species which has become widespread along riparian corridors throughout the western United States. We test the hypothesis that the distribution and success of Tamarix result from human modification of river‐flow regimes. We conducted a natural experiment in eight ecoregions in arid and semiarid...

Background/Question/Methods Removal of non-native, invasive plants from riparian areas throughout the western United States is widespread and expensive, yet the ecological yield on such investments is extremely variable. The objectives of non-native species removal efforts range from salvaging water (through reducing evapotranspiration) and minimi...

Streamfl ow on the North Fork Cache La Poudre River, a tributary of the South Platte River in north-central Colorado, has been modifi ed by impoundments for a century. A proposed expansion of the largest reservoir on the North Fork, Halligan Reservoir, presents an opportunity to modify dam operation to achieve environmental fl ows that sustain the...

The combined influence of tree-clearing, road construction, snowmaking, and machine-grading can cause increased flow and sediment loads along streams in or adjacent to commercial ski resorts. These changes to stream channels can increase bank failures, bed material size, pool scour, and, in extreme cases, channel incision. We used field data from t...

The basic patterns and processes of steep channels remain poorly known relative to lower-gradient channels. In this analysis, characteristics of step-pool, plane-bed, and pool-riffle channels are examined using a data set of 335 channel reaches from the western United States, Nepal, New Zealand, and Panama. We analyzed differences among the three c...

Global biodiversity in river and riparian ecosystems is generated and maintained by geographic variation in stream processes and fluvial disturbance regimes, which largely reflect regional differences in climate and geology. Extensive construction of dams by humans has greatly dampened the seasonal and interannual streamflow variability of rivers,...