Riparian Restoration Projects Research Articles

Environmental drivers for riparian restoration success and ecosystem services supply in Mediterranean agricultural landscapes

Riparian forests nestled in agricultural landscapes represent a small proportion in crop-intensive areas, while contributing remarkably to their biodiversity. This biodiversity supports several ecological processes crucially involved in the supply of ecosystem services (ES) complementary to that provided by agricultural lands and also relevant for designing biodiverse and multifunctional landscapes. Riparian forest is one of the most threatened ecosystems due to land-use intensification and associated water extraction, especially in Mediterranean semi-arid areas, and proper evaluation of the success of riparian restoration projects is usually lacking. Furthermore, there is little empirical evidence of the effects of riparian restoration on ES supply. In this study, we first investigated the effect of hydrological and soil features on survival and growth of saplings planted in degraded riparian areas in two Mediterranean watersheds. Then, we evaluated how riparian restoration affected the supply of ES, comparing nine regulating and supporting ES on these restored areas with other riparian areas spanning a gradient of conservation status, and with other natural and agricultural land-uses in the same watershed.We found that restoration success mainly depended on water table depth, soil salinity and soil nutrients (namely Mg+2 and Olsen P). Moreover, we detected an antagonistic interaction between the latter two, and a synergetic interaction between water table depth and soil salinity. Forest patches provided meaningful regulating and supporting ES in agricultural landscapes. In particular, riparian restoration zones increased the supply of regulating and supporting ES (water purification, habitat provision, microclimate regulation and soil C storage) in comparison with degraded natural land-uses and crops. Nevertheless, they were still far from the magnitude and range of ES provided by mature riparian forests. These results highlight the importance of focusing management practices on conserving riparian forest patches and restoring the degraded ones to reconcile agricultural production with the maintenance or enhancement of ES in agricultural Mediterranean landscapes.

Study of the Effects of Ten-Year Microclimate Regulation Based on Different Vegetation Type Combinations in a City Riparian Zone

Ecological engineering construction is the main method for urban riparian landscape restoration. Continuous ecological environmental monitoring can reflect the effects of engineering construction and can provide a scientific basis for the improvement of engineering technology. However, the evaluation of riparian ecological engineering mainly focuses on the water environmental function and biodiversity conservation function after the construction period. Studies on the long-term evaluation of regional microclimate regulation and human settlement improvement are limited. In this paper, an ecological restoration project along the Yitong River in northern China was selected as the research object. Temperature, relative humidity and wind speed under different vegetation type combinations were monitored in the riparian ecological engineering construction during the first, second, third and tenth years. The temperature–humidity index (THI) was selected to evaluate human comfort and the improvement effect of microclimate was assessed for different vegetation type combinations. The results showed that vegetation type combinations can play a good role in regulating the microclimate and human comfort. The riparian ecological restoration project achieved a stable function for microclimate regulation in the third year. There was no significant regulation difference between tree–shrub–herb and tree–herb combinations. To realize the optimization of ecological benefits, economic benefits and social benefits, the tree–herb combination can be appropriately increased, and the tree–shrub–herb can be reduced in the application of ecological engineering. Microclimate regulation is an important achievement in engineering construction effects and can be regarded as one of the indices to evaluate the effect of ecological restoration.

Feed the bees and shade the streams: riparian shrubs planted for restoration provide forage for native bees

With evidence of pollinator declines and an increasing focus on restoration, interest is growing in investigating floral resources for native bees. Although native bees forage on shrubs, few studies have explored the pollinator communities of native shrubs and none have examined shrub‐pollinator interactions in riparian areas of the northwestern United States. Life history traits of shrubs may make them particularly important resources for bees, especially in early spring—a key point in the lifecycle of many bee species. We conducted extensive hand‐net surveys over 2 years in a large riparian restoration project in the Pacific Northwest to understand bee‐flowering plant interactions with the aim of guiding future restoration efforts. Although forb blooming stem abundance and richness were higher than that of shrubs in spring, 57% of bees observed foraging were on willow (Salix spp.), a commonly planted riparian shrub. Season‐long, bee community composition on shrubs differed from that of forbs. Bee species diversity was highest on wax currant (Ribes cereum) and willow in early spring (April) and on black hawthorn (Crataegus douglasii) and mallow ninebark (Physocarpus malvaceus) later (i.e., June – July). Some bees showed a strong preference for wax currant and black hawthorn, both of which are more resistant to ungulate herbivory than other shrubs. Our results suggest that riparian restoration practitioners could consider using shrubs that provide forage to a diverse community of pollinators and improve stream health by shading and stabilizing banks. Planting bee‐friendly shrubs can help accomplish multiple restoration goals and leverage limited restoration funding.

Guiding riparian management in a transboundary watershed through high resolution spatial statistical network models

The United States Environmental Protection Agency and the Houlton Band of Maliseet Indians (HBMI) built a stream temperature spatial statistical network (SSN) model for the Meduxnekeag Watershed. The headwaters of the Meduxnekeag Watershed are in Maine, United States of America and the outlet is in New Brunswick, Canada, creating an additional challenge because many datasets are constrained to political boundaries. The release of the High-Resolution National Hydrology Dataset Plus included transboundary watersheds and enabled creation of fine resolution (1:24,000) SSN temperature models consistent with management scales for riparian buffers. SSN models were developed for July, August, and September median stream temperatures and the growing season maximum (GSM). Fitted SSN models had relatively high R2 values (0.88–0.96) and all final models included significant parameters for shade-attenuated solar radiation, reference flow, air temperature, and bankfull depth or width. Fitted models predicted stream temperatures during a dry (2010) and wet (2011) year. Monthly models predicted the fewest cold water (<19.0 °C) reaches in July with 28% in the dry and 68% in the wet year. September had >99% cold water reaches, and August results were intermediate between July and September. GSM predictions found 81% of stream reaches could not support salmonid survival (>27.0 °C) in the dry year and 59% of the reaches were warmwater (22.5–27.0 °C) in the wet year. The model was used to predict stream temperatures following restoration scenarios of a forested 30-m or 90-m buffer of stream segments bordered by agricultural or developed land. The restoration scenarios expanded cold water habitat based on monthly median temperatures and decreased the habitat area with GSM above survival thresholds, with little difference in effectiveness of the two buffer widths. These results will guide riparian restoration projects by the HBMI to expand habitat for cold water fishes.

Mapping legal authority for terrestrial conservation corridors along streams.

Wildlife corridors aim to promote species’ persistence by connecting habitat patches across fragmented landscapes. Their implementation is limited by patterns of land ownership and complicated by differences in the jurisdictional and regulatory authorities under which lands are managed. Terrestrial corridor conservation requires coordination across jurisdictions and sectors subject to site‐specific overlapping sources of legal authority. Mapping spatial patterns of legal authority concurrent with habitat condition can illustrate opportunities to build or leverage capacity for connectivity conservation. Streamside areas provide pragmatic opportunities to leverage existing policy mechanisms for riverine and terrestrial habitat connectivity across boundaries. Conservation planners and practitioners can make use of these opportunities by harmonizing actions for multiple conservation outcomes. We formulated an integrative, data‐driven method for mapping multiple sources of legal authority weighted by capacity for coordinating terrestrial habitat conservation along streams. We generated a map of capacity to coordinate streamside corridor protections across a wildlife habitat gap to demonstrate this approach. We combined values representing coordination capacity and naturalness to generate an integrated legal‐ecological resistance map for connectivity modeling. We then computed least‐cost corridors across the integrated map, masking the terrestrial landscape to focus on streamside areas. Streamside least‐cost corridors in the integrated, local‐scale model diverged (∼25 km) from national‐scale least‐cost corridors based on naturalness. Spatial categories comparing legal‐ and naturalness‐based resistance values by stream reach highlighted potential locations for building or leveraging existing capacity through spatial coordination of policy mechanisms or restoration actions. Agencies or nongovernmental organizations intending to restore or maintain habitat connectivity across fragmented landscapes can use this approach to inform spatial prioritization and build coordination capacity. Article impact statement: Combined mapping of legal authority and habitat condition reveals capacity to coordinate actions along streams for clean water and wildlife.

Development of a carbon calculator tool for riparian forest restoration

AbstractAim(s)Methods for estimating carbon sequestration in riparian forest biomass are needed to qualify riparian restoration and conservation projects for funding through carbon credits. As part of a proposed accounting methodology for California's cap‐and‐trade system, we described five riparian vegetation associations and created a tool to predict their rates of carbon accumulation under different restoration and land‐use scenarios.LocationCalifornia, USA.MethodsWe assembled a database of 654 forest inventory plots of known age (3–108 years) from replanted and naturally recruiting California riparian forests. We then used detrended correspondence analysis and agglomerative hierarchical clustering to detect vegetation structure in the plots and delineate distinct forest types. We used allometric equations to estimate biomass from individual trees’ diameters and calculate total biomass for each plot. Next, we fitted sigmoid growth functions to the plot biomass data to generate expected values for live‐tree biomass over a 100‐year period for each forest type. Finally, we created an algorithm to match user‐inputted data for an intended restoration project with a look‐up table that predicts carbon accumulation appropriate to the user's scenario.ResultsCalifornia riparian vegetation was divided into willow scrub, cottonwood–willow, mixed riparian, upland riparian and riparian woodland types. Total carbon sequestration in riparian vegetation and soil varied from 75.7 to 137.4 Mg C/ha at 30 years post‐restoration and from 95.1 to 175.8 Mg C/ha 100 years after stand initiation. Vegetation types dominated by taller, more shade‐tolerant trees developed more slowly than scrubby and pioneer stands, but came to a higher maximum biomass. Our models put riparian biomass accumulation in the range of the few extant literature values for mediterranean systems, but uncertainties are high, and soil carbon may be underestimated.ConclusionsOur workflow and methods should be transferable to the development of carbon accounting tools for any other woody vegetation type. However, our difficulty in finding appropriate published data for the analysis suggests a critical need for field surveys appropriate to biomass estimation in woodland and forest communities not exploited for timber. The most important measurements are the age of the stand and a census of tree species, height and diameter.

Assessing the effectiveness of riparian restoration projects using Landsat and precipitation data from the cloud-computing application ClimateEngine.org

Riparian vegetation along streams provides a suite of ecosystem services in rangelands and thus is the target of restoration when degraded by over-grazing, erosion, incision, or other disturbances. Assessments of restoration effectiveness depend on defensible monitoring data, which can be both expensive and difficult to collect. We present a method and case study to evaluate the effectiveness of restoration of riparian vegetation using a web-based cloud-computing and visualization tool (ClimateEngine.org) to access and process remote sensing and climate data. Restoration efforts on an Eastern Oregon ranch were assessed by analyzing the riparian areas of four creeks that had in-stream restoration structures constructed between 2008 and 2011. Within each study area, we retrieved spatially and temporally aggregated values of summer (June, July, August) normalized difference vegetation index (NDVI) and total precipitation for each water year (October-September) from 1984 to 2017. We established a pre-restoration (1984–2007) linear regression between total water year precipitation and summer NDVI for each study area, and then compared the post-restoration (2012–2017) data to this pre-restoration relationship. In each study area, the post-restoration NDVI-precipitation relationship was statistically distinct from the pre-restoration relationship, suggesting a change in the fundamental relationship between precipitation and NDVI resulting from stream restoration. We infer that the in-stream structures, which raised the water table in the adjacent riparian areas, provided additional water to the streamside vegetation that was not available before restoration and reduced the dependence of riparian vegetation on precipitation. This approach provides a cost-effective, quantitative method for assessing the effects of stream restoration projects on riparian vegetation.

Native species recovery after reduction of an invasive tree by biological control with and without active removal

Removal of invasive species is often an important, if not central, component of many riparian restoration projects, however little is known about the response of plant communities following this practice. In particular, active control of the exotic, dominant tree Tamarix spp is often a focus of riparian restoration, much of which occurring against a backdrop of biological control by a folivore beetle. Our research employed controls in both time and space to investigate the impact of active Tamarix removal methods in sites subjected to biological control in 40 sites sampled three times over a period of five years. We found that reduction in Tamarix cover was much greater over time with active means of removal, however the native understory increased both with and without active removal. Importantly, change in the relative cover of understory native species was significantly negatively correlated with change in Tamarix cover, with those sites that received a combination of low-disturbance-mechanical, chemical and bio-control showing greater increases in native understory dominance than those sites with biological control alone or high-disturbance mechanical control. Sites with only bio­control still contained 10% live Tamarix cover >7 yr since the beetle was released there. Taken together, these results suggest that the reduction of this exotic tree, even by biological control that leaves some canopy intact, can facilitate recovery of the native plant community. As such, this study supports the Field of Dreams hypothesis that states that once niches are restored, native plants should be able to recolonize.

Spatial processes structuring riparian plant communities in agroecosystems: implications for restoration

The disruption of hydrological connectivity by human activities such as flood regulation or land-use changes strongly impacts riparian plant communities. However, landscape-scale processes have generally been neglected in riparian restoration projects as opposed to local conditions, even though such processes might largely influence community recovery. We surveyed plant composition of field edges and riverbanks in 51 riparian zones restored by tree planting (565 1-m2 plots) within two agricultural watersheds in southeastern Québec, Canada. Once the effects of environmental variables (hydrology, soil, agriculture, landscape, restoration) were partialled out, three models of spatial autocorrelation based on Moran's eigenvector maps and asymmetric eigenvector maps were compared to quantify the pathways and direction of the spatial processes structuring riparian communities. The ecological mechanisms underlying predominant spatial processes were then assessed by regression trees linking species response to spatial gradients to seed and morphological traits. The structure of riparian communities was predominantly related to unidirectional spatial gradients from upstream to downstream along watercourses, which contributed more to species composition than bidirectional gradients along watercourses or overland. Plant traits selected by regression trees explained 22% of species response to unidirectional upstream-downstream gradients in field edges and 24% in riverbanks, and predominantly corresponded to seed traits rather than morphological traits of the adult plants. Our study showed that even in agriculturally open landscapes, water flow remains a major force structuring spatially riparian plant communities by filtering species according to their seed traits, thereby suggesting long-distance dispersal as a predominant process. Preserving hydrological connectivity at the watershed-scale and restoring riparian plant communities from upstream to downstream should be encouraged to improve the ecological integrity of rivers running through agricultural landscapes.

Riparian community structure and soil properties of restored urban streams

AbstractCommunity assembly and the resulting community structure reflect both local and regional processes. The relative importance, however, of each of these scales in most restoration contexts is unknown. Urban stream restoration, which often involves complete remodelling and replanting of the riparian zone, presents an opportunity to investigate the influences of local and regional processes on community assembly and local and regional biodiversity. Additionally, published outcomes of urban riparian restoration projects, particularly pertaining to plant community composition and soil properties, are lacking in the literature. The aim of this study was to compare the vegetation and soils of paired restored and unrestored urban stream reaches near Baltimore, Maryland. We found that the composition of the mature tree and sapling communities at restored sites differed significantly from that of unrestored sites, indicating that priority effects imposed via planting may dominate subsequent assembly of woody vegetation in urban riparian plant communities, at least in the short term. We also found disparate outcomes for both vegetation and soils at urban stream restoration sites in Baltimore as compared with other studies elsewhere in the mid‐Atlantic United States, but lack of long‐term data or information on specific restoration practices makes it difficult to draw connections between particular techniques and outcomes. Notably, both restored and unrestored reaches in the Baltimore area had very low levels of invasion by exotic tree species, and high levels of Pb and Zn in unrestored reaches and Ca in all reaches reflect the influence of the urban matrix on soil properties. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Effects of submergence in water on seed germination and vigor of the Copaifera lucens (Fabaceae) seedlings

We analyzed the tolerance of Copaifera lucens seeds to submersion in water to assess the use of this species for direct seeding in riparian forest restoration programs. Seeds were submerged in water for 2, 4, 8, 16 and 32 days or not submerged (control = 0 days of submergence). For the control and at the end of each period of submersion, germination and seedling vigor tests were carried out. For germination tests, seeds were sown in plastic pots containing sand and kept in laboratory conditions. The percentage of seed germination, the germination rate and the average germination time were analyzed. For seedlings, total biomass, leaf area, leaf mass per area and leaf area ratio were analyzed. Submersion time drastically affected the dissolved oxygen content and seed germination. Between 4 and 8 days of submersion there was a decrease from 83.8% to 15.6% in the germination percentage. No seed germination occurred after 16 days of submersion. Although there was a significant decrease in the percentage of seed germination between 4 and 8 days of submersion, seedling vigor was not affected. Seeds of this species were partially tolerant to submersion in water, suggesting that C. lucens is a promising species for direct seeding in riparian forest restoration projects.

Increasing canopy shading reduces growth but not establishment of Elodea nuttallii and Myriophyllum spicatum in stream channels

Submersed macrophytes are often important drivers of instream structure and function, but can be problematic when overabundant. The establishment success, growth rates, and morphology of submersed macrophytes could be affected by alteration of instream light levels during riparian restoration (via removing or planting canopy-forming vegetation), potentially influencing the success of riparian restoration projects aimed at improving aquatic habitats. To examine the effects of canopy shading on two common submersed macrophytes—Elodea nuttallii (native) and Myriophyllum spicatum (non-native)—I conducted experiments in artificial stream channels in two locations in California, USA. Initial establishment of stem fragments of both species was close to 100% in all shade levels, including shade that reduced incident light by 94%. Growth rates of the two species were similar across shade levels, and lowest in the highest shade. Full light appeared to have a photoinhibitory effect on E. nuttallii at the higher elevation site. Higher shade increased the length:biomass ratio and decreased the branching of E. nuttallii. My findings suggest that altering canopy cover during riparian restoration is unlikely to affect the ability of these species to establish, but higher shade levels should slow their growth and create more favorable conditions for other instream organisms.

Factors Determining the Establishment of Plant Zonation In A Southern Californian Riparian Woodland

This paper describes plant zonation in a southern California riparian woodland and identifies the factors responsible for the zonation. Of the 25 common trees and shrubs in the Tijuana River Valley, three were numerically dominant: Baccharis salicifolia (Ruiz & Pav.) Pers., Salix lasiolepis Benth., and Salix gooddingii C. R. Ball, here referred to as BASA, SALA, and SAGO, respectively. Adults of these species displayed significant down-slope zonation, with BASA, SALA, and SAGO most abundant in the High, Intermediate, and Low zone, respectively. Among new recruits, SALA and SAGO seedlings displayed zonation similar to that of adults, indicating that the zonation of SALA and SAGO was established at the time of recruitment. In contrast, BASA seedlings were more broadly distributed than adults; they were abundant in all zones, particularly the Low zone where adults were rare, indicating that the zonation of BASA adults was established post recruitment. For SALA and SAGO, the timing of fruiting and timing of water-level decline were the factors producing adult zonation; the two species had nearly non-overlapping periods of seed production, and this led to zonation of their seedlings on the banks as water levels declined. The seedling zonation was then retained in the adults. Because factors affecting recruitment played an important role in their zonation, these two willow species provide a new example of the supply-side influencing community structure. For BASA, whose seedlings were widely distributed, zonation of adults was the result of poor seedling survivorship in the Low zone during the first winter and poor adult survivorship in the Intermediate zone later. Results of this study can help guide future riparian restoration projects in southern California. Based on the prolific natural recruitment and rapid development of dense, native-dominated stands, use of a natural restoration approach where possible is recommended instead of the more common horticultural approach.

Levelling the playing field—A case study of how non-market values can compete in policy debates over wastewater allocation in a semi-arid region

In this paper we describe how benefits are transferred from previous non-market valuation research to inform the public policy debate on the allocation of treated wastewater to Riparian Projects in the semi-arid city of Tucson, Arizona, United States. Specifically, we transfer property premiums associated with proximity to riparian habitat to two proposed, and one accidental, urban Riparian Project. The study demonstrates that nearby property owners would likely benefit from wastewater reuse in riparian corridor restoration projects. Furthermore, the variable costs of supplying supplementary treated wastewater to one of the Riparian Projects are covered by incremental property tax revenues. We conclude that there is a window of opportunity to utilize a portion of Tucson's treated wastewater, over half of which is currently discharged at the northern end of the city, for additional in-town riparian restoration projects. Such riparian restoration projects also provide a mechanism for Endangered Species Act compliance.

Creating a catchment scale perspective for river restoration

Abstract. One of the major challenges in river restoration is to identify the natural fluvial landscape in catchments with a long history of river control. Intensive land use on valley floors often predates the earliest remote sensing: levees, dikes, dams, and other structures alter valley-floor morphology, river channels and flow regimes. Consequently, morphological patterns indicative of the fluvial landscape including multiple channels, extensive floodplains, wetlands, and fluvial-riparian and tributary-confluence dynamics can be obscured, and information to develop appropriate and cost effective river restoration strategies can be unavailable. This is the case in the Pas River catchment in northern Spain (650 km2), in which land use and development have obscured the natural fluvial landscape in many parts of the basin. To address this issue we used computer tools to examine the spatial patterns of fluvial landscapes that are associated with five domains of hydro-geomorphic processes and landforms. Using a 5-m digital elevation model, valley-floor surfaces were mapped according to elevation above the channel and proximity to key geomorphic processes. The predicted fluvial landscape is patchily distributed according to hillslope and valley topography, river network structure, and channel elevation profiles. The vast majority of the fluvial landscape in the main segments of the Pas River catchment is presently masked by human infrastructure, with only 15% not impacted by river control structures and development. The reconstructed fluvial landscape provides a catchment scale context to support restoration planning, in which areas of potential ecological productivity and diversity could be targeted for in-channel, floodplain and riparian restoration projects.

Contemporary changes in dissolved organic carbon (DOC) in human‐dominated rivers: is there a role for DOC management?

Summary1. Dissolved organic carbon (DOC) plays a central role in the dynamics of stream and river ecosystems, affecting processes such as metabolism, the balance between autotrophy and heterotrophy, acidity, nutrient uptake and bioavailability of toxic compounds. However, despite its importance to stream processes, restoration and management activities rarely incorporate DOC as a major management criterion.2. Lotic DOC pools reflect terrestrial organic carbon accumulation, transfer to the river channel and aquatic processing. In pristine landscapes, characteristics such as topography, climate, and landscape composition are strong predictors of terrestrial accumulation and transfer. Within aquatic systems, the quantity and form of DOC are altered by a variety of processes including primary production, microbial breakdown, sorption to particles and photodegradation.3. Terrestrial accumulation, transfer and aquatic processing of DOC in agricultural and other human‐dominated landscapes are all subject to substantial change. Consequently, DOC pools in agricultural streams likely differ from historic conditions and now include more labile material and low concentrations of a variety of ubiquitous synthetic organic compounds (e.g. pesticides, antibiotics).4. Although DOC change in agricultural streams and associated ecological consequences are expected to be widespread, current understanding and relevant data needed to manage affected systems are surprisingly scarce.5. Wetland and riparian restoration projects have variable effects on fluvial DOC regimes, but management at this intermediate scale is a realistic compromise between the small extent of most restoration projects and the large spatial scale over which organic carbon impairment occurs.

Restoring habitat for riparian birds in the lower Colorado River watershed: An example from the Las Vegas Wash, Nevada

The success of riparian restoration projects in the arid southwestern U.S. is often measured in terms of vegetation characteristics such as growth, cover, and structure. Among low-elevation riverine environments within the Colorado River watershed, restoration is typically conducted to improve degraded habitats for birds of conservation concern by replacing the exotic tamarisk ( Tamarix ramosissima) with native cottonwoods ( Populus spp.) and willows ( Salix spp.). The working assumption for many restoration practitioners is that replacing exotic plants with native plants will improve habitat quality and will, therefore, benefit birds. Based on data collected at exotic and restored (i.e., native) sites along the Las Vegas Wash, Nevada, not all birds benefit from restoration. Broad measures of community benefit, including benefits to birds of conservation concern and riparian obligate/dependent birds, were not detected. There were, however, some species-specific benefits. Some environmental variables that were associated with exotic and native sites were significant in explaining the composition of the bird community. For example, the richness of forbs and grass-like plants (a proxy of soil moisture), invertebrate mass, and percent shade (a proxy for canopy characteristics) were important. Considering our results and depending on restoration goals, tamarisk replacement projects may not inherently provide benefits to birds.

On improving the science and practice of riparian restoration

On improving the science and practice of riparian restoration

Developing a vision for improved monitoring and reporting of riparian restoration projects

Representatives from agencies involved in natural resource management in the Murray-Darling Basin gathered for a workshop in November 2010 to develop a vision for improved monitoring and reporting of riparian restoration projects. The resounding message from this workshop was that the effectiveness of riparian restoration depends on having sound, documented and agreed evidence on the ecological responses to restoration efforts. Improving our capacity to manage and restore riparian ecosystems is constrained by (i) a lack of ecological evidence on the effects of restoration efforts, and (ii) short-termism in commitment to restoration efforts, in funding of monitoring and in expected time spans for ecosystem recovery. Restoration at the effective spatial scope will invariably require a long-term commitment by researchers, funding agencies, management agencies and landholders. To address the knowledge gaps that constrain riparian restoration in the Basin, participants endorsed four major fields for future research: the importance of landscape context to restoration outcomes; spatio-temporal scaling of restoration outcomes; functional effects of restoration efforts; and developing informative and effective indicators of restoration. To improve the monitoring and restoration of riparian zones throughout the Basin, participants advocated an integrated approach: a hierarchical adaptive management framework that incorporates long-term ecological research.

English

Reed Canarygrass (RCG) is an exceptionally aggressive invader of wetlands and streambanks throughout much of North America and a serious challenge in many riparian restoration projects. RCG generally degrades habitat quality, can outcompete most native grasses and forbs, and can sometimes invade stream channels. Over the last six years, we have used pre-vegetated coir mats for rapid bank stabilization and native plant establishment and to thwart reinvasion by RCG. In this paper, we use field experiments, case studies, and literature to evaluate whether aggressive revegetation can defeat RCG. Our results demonstrate that: (1) successful revegetation of infested sites is possible; (2) although RCG can be excluded for several years, even sites with very successful revegetation are not immune to reinvasion and may require periodic management; and (3) major hurdles include incomplete initial RCG control and poorly understood or challenging hydrology. Factors that favor RCG over native herbaceous plants include rapid spread by seed and rhizomes, high competitive ability, strong response to nutrients and disturbance, broad hydrologic tolerances, resistance to herbicides and other control practices, presence of non-native genotypes, and historical or continuing use as a forage or for bank stabilization. Complete control and replacement of RCG is unrealistic. Decisions about goals and effort for RCG control will depend on RCG abundance in the landscape, project purpose, project sponsors' values, regulatory context, and mandated performance criteria. Depending on the location and agency, RCG may be treated as a regulated noxious weed, an undesirable invasive plant with low value in rating biological integrity, not a concern, or a plant suitable for pastures and other uses. Where minimizing RCG is required, time and resources should be allocated to pre-project RCG control, analysis of site hydrology, intensive revegetation practices, large woody plant material, follow-up RCG control, and monitoring for at least 3 years.