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Non-native shrub species in the genus Tamarix (saltcedar, tamarisk) have colonized hundreds of thousands of hectares of floodplains, reservoir margins, and other wetlands in western North America. Many resource managers seek to reduce saltcedar abundance and control its spread to increase the flow of water in streams that might otherwise be lost to evapotranspiration, to restore native riparian (streamside) vegetation, and to improve wildlife habitat. However, increased water yield might not always occur and has been substantially lower than expected in water salvage experiments, the potential for successful revegetation is variable, and not all wildlife taxa clearly prefer native plant habitats over saltcedar....
Invasion by Tamarix (L.) can severely alter riparian areas of the western U.S., which are globally rare ecosystems. The upper Verde River, Arizona, is a relatively free-flowing river and has abundant native riparian vegetation. Tamarix is present on the upper Verde but is a minor component of the vegetation (8% of stems). This study sought to determine whether riparian vegetation characteristics differed between sites where Tamarix was present and sites where Tamarix was absent during the invasion of the upper Verde. We hypothesized that herbaceous understory and woody plant communities would differ between Tamarix present and absent sites. Our hypothesis was generally confirmed, the two types of sites were different....
Groundwater is a key driver of riparian condition on dryland rivers but is in high demand for municipal, industrial, and agricultural uses. Approaches are needed to guide decisions that balance human water needs while conserving riparian ecosystems. We developed a space-for-time substitution model that links groundwater change scenarios implemented within a Decision Support System (DSS) with proportions of floodplain vegetation types and abundances of breeding and migratory birds along the upper San Pedro River, AZ, USA. We investigated nine scenarios ranging from groundwater depletion to recharge. In groundwater decline scenarios, relative proportions of tall-canopied obligate phreatophytes (Populus/Salix, cottonwood/willow)...
Environmental flows have become important restoration tools on regulated rivers. However, environmental flows are often constrained by other demands within the river system and thus typically are comprised of smaller water volumes than the natural flows they are meant to replace, which can limit their functional efficacy. We review environmental flow programs aimed at restoring riparian vegetation on four arid zone rivers: the Tarim River in China; the Bill Williams River in Arizona, U.S.; the delta of the Colorado River in Mexico; and the Murrumbidgee River in southern Australia. Our goal is to determine what worked and what did not work to accomplish restoration goals. The lower Tarim River in China formerly formed...
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This data release presents observations of riparian vegetation, topography, sediment quality, and river corridor geomorphology in four river reaches of the Lower Virgin River extending downstream 62 river kilometers (rkm) from near the town of Littlefield (AZ) and the Arizona-Nevada border at rkm 119. Methods included field observations and analysis of remotely-sensed data before (2010) and after (2011-2012) a 40-year return period flood (December 2010, at the gaging station “Virgin River near Littlefield” (USGS gage #09415000)). The data release includes four .csv files related to field observations: UTM coordinates of field transect locations; vegetation and geomorphology; species codes; and sediment quality....
Tamarix spp. removal has been proposed to salvage water and allow native vegetation to recolonize western U.S. riparian corridors. We conducted wide-area studies on the Lower Colorado River to answer some of the scientific questions about Tamarix water use and the consequences of removal, combining ground surveys with remote sensing methods. Tamarix stands had moderate rates of evapotranspiration (ET), based on remote sensing estimates, averaging 1.1 m/yr, similar to rates determined for other locations on the river and other rivers. Leaf area index values were also moderate, and stands were relatively open, with areas of bare soil interspersed within stands. At three Tamarix sites in the Cibola National Wildlife...
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Invasion by the non-native tree Tamarix has led to implementation of restoration projects aimed at maintaining the ecological integrity of many riparian communities in the southwestern United States. These restoration efforts may include Tamarix removal, manipulation of hydrologic regimes, and active revegetation of native species. The goal of this study was to determine which site characteristics are correlated with restoration success, defined in terms of reductions of undesirable species such as Tamarix and establishment of desirable, native species. To accomplish this, vegetative and environmental data were collected at 28 sites in the southwestern United States where active revegetation was completed after...
Saltcedars (Tamarix spp., Tamaricaceae) (SC), are exotic, invasive shrubs to medium trees native to the Old World. In riparian ecosystems of the western United States, SC replaces native plant communities, degrades wildlife habitat, reduces biodiversity, alters stream channel morphology, uses large quantities of groundwater, increases wildfire frequency, reduces recreational and agricultural usage, and probably has contributed to the decline of many wildlife and fish species. In recent years, the southwestern willow flycatcher (Empidonax trailii extimus) (sw WIFL) has begun nesting extensively in SC in some of its major breeding areas in Arizona, but not in other areas, since SC has replaced its native willow nest...
Characterizing avian diet is complex, especially for generalist insectivores, as food resources can vary over space and time, and individuals of different sexes and ages may consume different food. We examined diet of a generalist insectivore, the Southwestern Willow Flycatcher (Empidonax traillii extimus), at Roosevelt Lake in central Arizona from 2000 to 2004, determined from 344 fecal samples. We found that five prey categories accounted for 70% of the proportional abundance in flycatcher diet: Hymenoptera, Diptera, Cicadellidae, Coleoptera, and Formicidae, although the relative amounts of these and other taxa differed significantly among years. We detected no differences in diet between sexes of adults, but...
As global climate change affects recharge and runoff processes, stream flow regimes are being altered. In the American Southwest, increasing aridity is predicted to cause declines in stream base flows and water tables. Another potential outcome of climate change is increased flood intensity. Changes in these stream flow conditions may independently affect vegetation or may have synergistic effects. Our goal was to extrapolate vegetation response to climate-linked stream flow changes, by taking advantage of the spatial variation in flow conditions over a 200 km length of the San Pedro River (Arizona). Riparian vegetation traits were contrasted between sites differing in low-flow hydrology (degree of stream intermittency)...
1. Riparian vegetation in dry regions is influenced by low-flow and high-flow components of the surface and groundwater flow regimes. The duration of no-flow periods in the surface stream controls vegetation structure along the low-flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape...
Drastic alterations to river hydrology, land use change, and the spread of the nonnative shrub, tamarisk (Tamarix spp.), have led to the degradation of riparian habitat in the Colorado River Delta in Mexico. Delivery of environmental flows to promote native cottonwood (Populus spp.) and willow (Salix spp.) recruitment in human-impacted riparian systems can be unsuccessful due to flow-magnitude constraints and altered abiotic–biotic feedbacks. In 2014, an experimental pulse flow of water was delivered to the Colorado River in Mexico as part of the U.S.-Mexico binational agreement, Minute 319. We conducted a field experiment to assess the effects of vegetation removal, seed augmentation, and environmental flows, separately...
Biological control of invasive saltcedars (Tamarix spp.) in the western U.S. by exotic tamarisk leaf beetles, Diorhabda spp., first released in 2001 after 15 years of development, has been successful. In Texas, beetles from Crete, Greece were first released in 2004 and are providing control. However, adults alight, feed and oviposit on athel (Tamarix aphylla), an evergreen tree used for shade and as a windbreak in the southwestern U.S. and México, and occasionally feed on native Frankenia spp. plants. The ability of tamarisk beetles to establish on these potential field hosts was investigated in the field. In no-choice tests in bagged branches, beetle species from Crete and Sfax, Tunisia produced 30–45% as many...
Managing streamflow is a widely-advocated approach to provide conditions necessary for seed germination and seedling establishment of trees in the willow family (Salicaceae). Experimental flow releases to the Colorado River delta in 2014 had a primary objective of promoting seedling establishment of Fremont cottonwood (Populus fremontii) and Goodding's willow (Salix gooddingii). We assessed seed germination and seedling establishment of these taxa as well as the non-native tamarisk (Tamarix spp.) and native seepwillow shrubs (Baccharis spp.) in the context of seedling requirements and active land management (land grading, vegetation removal) at 23 study sites along 87 river km. In the absence of associated active...
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The data release presents observations of riparian vegetation, topography, and ground cover in two river reaches of the Upper Colorado River within a river segment extending 208 river kilometers (rkm), from near the Colorado/Utah border to the confluence of the Green River. Methods included field observations and analysis of the plant community five times over eight years in the fall of 2010, 2012, 2013, 2015 and 2017, encompassing a second cycle of biocontrol-induced dieback of invasive Tamarix spp. shrubs. The data release includes four .csv files related to field observations: UTM coordinates of field transects; vegetation, topography and ground surface information at the pinpoint level and at the transect level;...
Aim A regional analysis was used to explore the influence of river regulation on the dominance of non-native, invasive shrubs and trees. We addressed the following questions: (1) How do large dams affect hydrological parameters that influence riparian vegetation? (2) How do flow regimes affect the dominance of non-native woody species? (3) How do changes in flow regimes affect the dominance of non-native woody species? Location South-western USA. Methods We sampled the canopy cover of woody species on 179 point bars along seven non-dammed and thirteen dammed river segments. Wilcoxon rank sum tests were used to determine differences between flow parameters in dammed and non-dammed rivers. We used correlation analyses...
Ground-water and surface flow depletions are altering riparian ecosystems throughout the southwestern United States, and have contributed to the decline of forests of the pioneer trees Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow). On some rivers, these forests have been replaced by shrublands of Tamarix ramosissima (tamarisk), a drought-tolerant species from Eurasia. The physiological response of these three riparian plant species to decreases in water availability is well studied, but little attention has been given to shifts in community and population structure in response to declines in surface flow and ground-water levels. Based on study of 17 sites spanning a hydrologic gradient,...
Restoration of salt-affected soils is a global concern. In the western United States, restoration of salinized land, particularly in river valleys, often involves control of Tamarix, an introduced species with high salinity tolerance. Revegetation of hydrologically disconnected floodplains and terraces after Tamarix removal is often difficult because of limited knowledge regarding the salinity tolerance of candidate native species for revegetation. Additionally, Tamarix appears to be non-mycorrhizal. Extended occupation of Tamarix may deplete arbuscular mycorrhizal fungi in the soil, further decreasing the success of revegetation efforts. To address these issues, we screened 42 species, races, or ecotypes native...


map background search result map search result map Success of Active Revegetation after Tamarix Removal in Riparian Ecosystems of the Southwestern United States: A Quantitative Assessment of Past Restoration Projects Riparian vegetation, topography, sediment quality, and river corridor geomorphology in the Lower Virgin River, Nevada and Arizona, before (2010) and after (2011-2012) a 40-year return period flood Riparian vegetation, topography, and ground cover constituents along the Upper Colorado River near Moab, UT (2010-2017) Riparian vegetation, topography, sediment quality, and river corridor geomorphology in the Lower Virgin River, Nevada and Arizona, before (2010) and after (2011-2012) a 40-year return period flood Riparian vegetation, topography, and ground cover constituents along the Upper Colorado River near Moab, UT (2010-2017) Success of Active Revegetation after Tamarix Removal in Riparian Ecosystems of the Southwestern United States: A Quantitative Assessment of Past Restoration Projects