Russian Olive

Elaeagnus angustifolia

Summary 6

Elaeagnus angustifolia, commonly called silver berry,oleaster,Russian olive, or wild olive, is a species of Elaeagnus, native to western and central Asia, from southern Russia and Kazakhstan to Turkey and Iran. It is now also widely established in North America as an introduced species.

Impacts and control 7

More info for the terms: avoidance, climax, codominant, competition, cover, density, facilitation, fire management, invasive species, litter, natural, nonnative species, restoration, root crown, shrub, shrubs, tree

Impacts: There is varied and somewhat limited empirical evidence available demonstrating Russian-olive's impacts upon native ecosystems in North America; however, some evidence suggests that Russian-olive replaces native vegetation, altering vegetation structure and reducing wildlife habitat for some species. Additionally, some authors have suggested that Russian-olive can alter stream hydrology and nutrient cycling [180], although this has not been tested in natural settings.

Russian-olive is often invasive in riparian areas, which are often impacted by a plethora of human-induced disturbances. "Riparian ecosystem functions have been altered, reduced, or lost among the cascading effects of river management actions on many western rivers. Because ecosystems are complex and replete with interconnected, confounding factors, it can be difficult to quantify losses and function, and to sort out causes and effects. Riparian nonnative invasives appear to be a single symptom or facet of a complex, systemic resource allocation problem" [171].

Rankings: Several agencies and organizations rank Russian-olive as invasive to varying degrees. The USDA, Forest Service, Eastern Region ranks Russian-olive as "highly invasive" (nonnative plants that invade natural habitats and replace native species), based on information from lists, botanists, and ecologists from 15 of the 20 states in that region [183]. Conversely, Russian-olive is ranked as an "occasionally invasive species" (plants that generally do not affect ecosystem processes but may alter plant community composition by outcompeting one or more native plant species) by the Virginia Department of Conservation and Recreation. These are plants that often establish in areas severely disturbed by events such as ice storms, windthrow, or road construction, and spread slowly or not at all from disturbed sites [192]. Russian-olive is ranked as a "Category 2 species" (nonnative plant species that are suspected to be invasive or are known to be invasive in limited areas of the Southern Region) by the Southern Region of the US Forest Service, as reported by the Southeast Exotic Pest Plant Council. Category 2 species will typically persist in the environment for long periods once established and may become invasive under favorable conditions, thus posing a potential risk to the integrity of natural plant communities in parts of the region [184]. The California Invasive Plant Council (Cal-IPC) lists Russian-olive among the most invasive wildland pest plants in California. These are " documented as aggressive invaders that displace natives and disrupt natural habitats" [32]. However, there is no information in the literature specifically describing distributions and impacts of Russian-olive in California. At a given site, Russian-olive may be present as scattered individuals, within multi-species canopies, or in monotypic stands [96]. Russian-olive is said to displace and/or have the potential to displace native climax species in many parts of the western US such as the Platte River drainage of Nebraska [47] and other prairie river floodplains [140]; marshlands in South Dakota [137]; the Rio Grande Basin in New Mexico [33,91,123,128], and other river drainages in the Southwest [128].

Several characteristics give Russian-olive an advantage in the communities it invades, including high seed production and viability, seed longevity, seed dispersal by birds and mammals, vegetative reproduction following injury, drought and salt tolerance, and the ability to establish in the absence of disturbance in late successional communities (see Botanical And Ecological Characteristics). These characteristics allow Russian-olive to replace some dominant, native riparian species that can no longer germinate, establish, and persist under conditions imposed by river impoundment (e.g. increased salinity, reduced flooding, and water table declines) and other impacts of human development [4,19,45,64,81,91,111,112,113,123]. Native riparian trees tend to be pioneers, dependent on physical disturbance for recruitment [23,96,156]. Flow regulation resulting in reduced flood peaks and point bar accretion rate, in addition to land clearing, livestock grazing, beaver cutting, ice damage, and fire, along with nonnative species invasions, are all implicated in the decline of native woody vegetation in riparian ecosystems in the western US [30,61,67,134,160,171,174]. These same site conditions and processes that lead to the decline of native species concurrently provide ideal site conditions for Russian-olive establishment and eventual dominance [50,111,112,140,156,188]. Russian-olive is both a partial cause and a symptom of native species declines [91].

Once established, Russian-olive may further hinder recruitment of native cottonwood and willow on some sites [47,112]. For example, where Russian-olive occurs as a major understory component along the Rio Grande River, from Espanola to south of Belen, New Mexico, it will continue to spread through the woodland, contributing to stabilization of the riverbanks against future flooding, and thus further limit opportunities for cottonwood regeneration [91]. Similarly, in a comparison of the free-flowing Yellowstone River and the flow-regulated Marias River in eastern Montana, Lesica and Miles [111,112,113] found cottonwood establishment and dominance was not precluded by Russian-olive on the upper reaches of the Yellowstone River where flooding and new channel development continuously create new habitat for cottonwood establishment. However, cottonwood may eventually be replaced by Russian-olive on the Marias River as old cottonwoods die on upper terraces and young cottonwoods on low terraces are removed by beaver or livestock or shaded by less palatable species [111,112,113].

Russian-olive dominance may further lead to reduced species diversity. Russian-olive stands tend to be less diverse both structurally and compositionally than surrounding communities [91,128]. In Montana, for example, undisturbed colonizing and established cottonwood communities support as many as 114 and 58 plant species, respectively, compared to only 29 species in Russian-olive stands [81,140]. Altered structural and compositional plant diversity may lead to lower wildlife diversity.

Wildlife: The impact of Russian-olive invasions upon wildlife species is variable, site specific, and often debated. Also see the Importance to Livestock and Wildlife section of this report. Anecdotal evidence and observations by managers suggest that several species may be affected by Russian-olive invasion, although in some cases it is unclear whether impacts are caused by Russian-olive itself, or by changes in the ecosystem as a whole. Although Russian-olive has been promoted for use in wildlife habitat plantings, there has been relatively little research on its use by native animals [96].

Knopf and Olson [103] suggest that naturalization of Russian-olive on floodplains in the Rocky Mountains has provided additional wildlife habitat between riparian cottonwood forests and adjacent grass-dominated uplands. In some cases Russian-olive may provide important structural habitat for wildlife species by forming an intermediate-height canopy layer that is lacking in some native riparian forest communities. It may also increase the spatial extent of woody habitat by establishing on the outer edge of native riparian forests, providing additional habitats, especially for those avian species that are associated with tall shrub vegetation. Bird species richness and alpha diversity in monotypic Russian-olive stands were intermediate to those of native riparian and native upland vegetation types in Colorado, Idaho and Utah [103]. However, in some cases Russian-olive forms dense, monotypic stands that replace native communities on floodplains (see above), thus altering and potentially reducing habitat options for wildlife [91,137,140]. Some authors suggest that the displacement of native floodplain forest by Russian-olive can result in loss of habitat for species such as cavity-nesting and insectivorous birds [25,103,112,137,168].

Some researchers have examined Russian-olive's relative usefulness to wildlife as compared with native plant species it replaces, with mixed results. Several studies indicate that Russian-olive is utilized to varying degrees, and with varying degrees of success, by many avian species along the Rio Grande River [110,204], the Gila River [168], the Columbia River (Hudson 2000, as cited by [168]), and the Snake River [25]. However, results and related inference from several studies indicate avoidance of Russian-olive and/or a preference for native plant species by, for example, primary and secondary cavity nesters [168], neotropical migrants (Hudson 2000, as cited by [168]), greater prairie-chicken ([McCarthy et al 1997] and references therein), ducks [70], and foreign guilds in winter [25]. Additionally, Brown [25] found that species richness, abundance and density were greater in willow than in Russian-olive habitats, and all foraging guilds avoided Russian-olive in the breeding season along the Snake River in Idaho.

Other studies and reports indicate less certainty about the role and/or impacts of Russian-olive for native wildlife species. The threatened southwestern willow flycatcher, for example, nests in native vegetation where available but also nests in thickets dominated by Russian-olive and saltcedar, and individuals of both species are used as nesting substrates ([188] and references therein). High-elevation (>6,200 feet (1,900 m)) breeding sites are typically dominated by native trees and shrubs, although Russian-olive is a major habitat component at some high-elevation breeding sites in New Mexico. From the standpoint of flycatcher productivity and survivorship, the suitability of nonnative-dominated habitats is unknown. Flycatcher productivity is lower in nonnative dominated sites compared with native-dominated sites in some locations, and higher in others. It is unclear whether factors such as patch size may have greater effects on flycatcher productivity at those sites. Details are given in the southwestern willow flycatcher recovery plan [188]. Results presented by Kelly and others [100] and Gazda and others [70] also do not seem to support the conjecture that nonnative shrubs in riparian areas provide lower-quality habitat for birds, and Russian-olive does provide a food source for many birds. The role of Russian-olive in native wildlife habitat is unclear for many species [168,204].

For small mammals, species richness was greater in Russian-olive stands than in the native riparian and upland vegetation types (low species richness, intermediate diversity) in Colorado, Idaho and Utah [103]. Native beavers primarily use cottonwood trees while rarely using Russian-olive or tamarisk along several rivers in eastern Montana [111,112,113]. Thus, beavers create areas of lower competitive stress for Russian-olive by felling dominant cottonwoods. Most beaver damaged cottonwoods were cut off at the base, while damage to Russian-olive was usually confined to 1 or 2 basal limbs. Growth rates of both Russian-olive and tamarisk were substantially higher where beavers had reduced the cottonwood canopy cover. Managers wishing to reintroduce beavers should consider the potential effect on invasive plants; it may be best to control invasives before reintroducing beavers [113].

Hydrogeology/Nutrient cycling/Other: Some authors have suggested that Russian-olive influences hydrogeomorphic processes, for example by increasing floodplain roughness in habitats where woody vegetation would otherwise not occur (Tickner et al 2001, as cited by [96]), and contributing to stabilization of riverbanks against flooding [91]. There is not, however, literature available that addresses this issue.

As a nitrogen-fixing plant species, Russian-olive has high leaf nitrogen content [153], and leaves and leaf litter of Russian-olive tend to have higher nitrogen content than native species in the communities it invades. Thus, Russian-olive may contribute substantial amounts of additional nitrogen to invaded ecosystems ([96] and references therein). Nodular nitrogenase activity in Russian-olive varies with season and site conditions [206], thus the impacts of an Russian-olive as a novel N-fixing plant in some communities probably also vary. Royer and others [153] found slow processing rates of Russian-olive leaves (compared to natives) in some Idaho streams, and suggested that slowed litter processing might alter local and downstream aquatic communities. However, studies of degradation rates of Russian-olive leaf litter have been inconclusive regarding system nitrogen inputs. So, while invasion by Russian-olive may affect ecosystem nutrient levels, no studies have yet demonstrated this in invaded communities [96].

There is little quantitative information on the historic and present-day spread of Russian-olive, ecological factors that may limit the geographical range of Russian-olive, or its potential for range expansion in western North America. Lesica and Miles [112] approximate a 10-year lag before newly established Russian-olive individuals become reproductively mature in eastern Montana, and Katz and Shafroth [96] suggest inherently slow rates of spatial spread for species such as Russian-olive that possess relatively large, primarily vertebrate-dispersed seed. There is also no published information on competition or facilitation between Russian-olive and co-occurring species. More research is needed on these topics to better understand the potential impacts of Russian-olive in particular plant communities under specific site conditions [96].

Control: Detailed control prescriptions are beyond the scope of this review; however, an understanding of what kills or damages Russian-olive may provide insight into how Russian-olive responds to injury, and therefore its potential response to fire. For more detailed management techniques and prescriptions, refer to cited references, the Russian-olive Element Stewardship Abstract, or the Weed control methods handbook.

There is limited published research addressing effective techniques to control or remove Russian-olive from invaded sites. Caplan [34] and Edelen and Crowder [59] present case studies of effective Russian-olive control in New Mexico and Washington, respectively. Tu [180] discusses a variety of control approaches for Russian-olive and provides examples of Russian-olive management on Nature Conservancy preserves. Stannard and others [163] and Deiter [49] assess a variety of suppression methods, including mechanical and chemical approaches. Important considerations for Russian-olive management include age of Russian-olive individuals, timing relative to population establishment and seed set, size of Russian-olive populations, and site conditions, including land use.

Awareness and prevention are probably the most effective tools for managing against Russian-olive invasion. In Montana, for example, invasion by Russian-olive is relatively recent and ongoing, receiving important impetus from domestic plantings [111]. Land managers should be aware of Russian-olive in the area surrounding their management unit. If Russian-olive is present, monitoring for Russian-olive seedling establishment is an important prevention practice. Discourage adjacent landowners from planting Russian-olive if possible. When Russian-olive is already established in an area, it is important to employ control measures where they will be most effective (e.g., where the native vegetation has some chance of recovering).

Control of Russian-olive is difficult once trees are mature, so early detection and rapid response are important [49,180]. Similarly, large, well-established stands of Russian-olive are nearly impossible to eradicate throughout an entire watershed, whereas small patches of Russian-olive can be adequately controlled using a variety of control methods [180]. Additionally, removal of Russian-olive should be undertaken before seeds are fully developed to prevent further spread of seeds [49]. Stevens and Ayers [165] report that heightened awareness, modest field efforts, and early detection have resulted in the control of Russian-olive and other nonnative species in the Grand Canyon.

When planning Russian-olive control, integrating several approaches will likely be necessary, depending on the size, age, and extent of the population. Mowing, cutting, burning, excavation, spraying, girdling, and bulldozing have all been used to reduce aboveground Russian-olive biomass, with varying degrees of success. Russian-olive removal can be labor-intensive and expensive, especially in the 1st year of large-scale removal [180]. Most published accounts of effective Russian-olive suppression employ chemical treatment, either alone or combined with mechanical techniques [49]. Cultural control, in the sense of managing for natives, is an important consideration.

Russian-olive control approaches and successes may differ between riparian areas on free-flowing rivers and streams, where native species have a better chance of re-establishment, and more heavily managed areas along regulated rivers. Where a dynamic disturbance regime maintains most of the active floodplain in early-successional vegetation, only a small proportion of the riparian zone will remain undisturbed long enough to become fully stocked with Russian-olive. Russian-olive is more likely to become dominant in reaches where the riparian zone in less dynamic or where the stream is more entrenched or has been artificially channelized. Consequently, the latter are the places where control measures may have a more long-term benefit [112].

Successful long-term control of Russian-olive requires that all control sites be continually monitored and follow-up treatments applied for several years, since Russian-olive sprouts following injury [180]. Lesica and Miles [112] suggest that, because most Russian-olive invasions in eastern Montana occur over a period of several decades, eradication of mature trees every 10 years or of all plants every 30 years may be effective strategies for controlling Russian-olive in those areas. Rate of spread of Russian-olive probably varies among regions, so this approach may not be effective in some areas.

Prevention: Once established, Russian-olive is difficult to control and nearly impossible to eradicate. Therefore planting of Russian-olive should be eliminated due to its tendency to persist and spread in some areas, and the inevitable costs associated with long-term control [79,81]. Prevention involves awareness and education, working with adjacent landowners and managers to remove Russian-olive from plantings and prevent additional plantings, providing alternative species for planting in areas where Russian-olive is commonly used, managing livestock grazing to minimize damage to native species, maintaining natural disturbance regimes (i.e. seasonal flooding) in riparian areas, and minimizing other human induced disturbances.

According to the USDA, NRCS [186], seed or plants of Russian-olive are available through several suppliers throughout the US, and Russian-olive is not identified as an invasive species on their list. Similarly, Carty [39] recommends 10 drought resistant trees, Russian-olive among them, for planting. While he does mention that Russian-olive is nonnative, considered invasive, and displaces native species across much of the Southwest, he also says, "as long as it's not allowed to spread, it can fill a variety of drought resistant niches." This is the type of misinformation that land managers must contend with when discouraging individuals and organizations from planting "horticulturally desirable" species such as Russian-olive [39]. As long as this type of information and these plant products are available, prevention of new introductions is difficult.

Choosing noninvasive landscape ornamentals to plant at sites near natural areas can help prevent the spread of Russian-olive [52]. In the Southern Region, Russian-olive is classified as a "Category 2" species. Therefore planting is prohibited in areas where ecological conditions would favor invasiveness and is discouraged elsewhere. They suggest consulting the forest botanist, plant ecologist, or forest noxious weed coordinator for alternative native and/or noninvasive species [184]. Stannard and others [163] provide a list of native, woody species that could be planted instead of Russian-olive in the northern Great Plains.

The potential benefits of Russian-olive to landowners for windbreaks, soil stabilization and ornamental plantings must be weighed against potential negative impacts to native communities [140]. Winter [148] recommends working with landowners and managers to remove Russian-olive from shelter belts and tree plantings, and to recommend desirable, native species for future plantings in Minnesota.

Lack of natural regeneration of native species in western riparian areas may be due, in part, to cattle grazing in the Great Plains and cattle and elk grazing in the Southwest [134]. When browsing among the multispecies patches of seedlings that germinate on bare sediments after floods, livestock feed upon the more palatable cottonwoods and willows, thus favoring dominance of tamarisk and Russian-olive. Additionally, mature Russian-olive exhibits several traits that allow it to thrive in grazed habitats, including sharp thorns, which increase in density if the tree is cut back, and large seeds that may enhance the survival of seedlings following browsing. These adaptations may contribute to spread of Russian-olive into heavily-grazed meadows and pastures ([188] and references therein). Initial Russian-olive seedling establishment may be prevented in an area with targeted grazing, granivory (using animals that would eat Russian-olive seedlings and/or seeds), or temporary inundation [96].

Water diversion, groundwater pumping [91,170], and sand and gravel mining also impact native species regeneration in the Southwest [134,170]. Hydrologic alterations have been implicated in the widespread decline of some riparian forest types and in facilitating invasions by opportunistic nonnative species ([96] and references therein). Indeed, it is likely that reduced levels of fluvial disturbance downstream from dams favor invasion of Russian-olive [95,111,112,156]. Current interest in changing river-flow management strategies to restore native fish [151] and/or native riparian forest [123] provides hope for the possible control of invasive riparian plant species via restoration of ecosystem processes (also see FEIS review on tamarisk). At present, it is unclear how prescribed flows might influence the spread or abundance of Russian-olive. Ideally, river flow regimes designed to improve regeneration and survival of native riparian forest species will also limit the success of nonnative invaders [96].

Integrated management: Integrated management includes considerations of not only killing the target weed, but also of establishing desirable species and maintaining weed-free systems over the long-term. Factors to be addressed before a management decision is made include inventory and assessment to identify the target weed and determine the size of the infestation(s); assessment of nontarget vegetation, soil types, climatic conditions, and important water resources; and an evaluation of the benefits and limitations of control methods [129].

On Hempstead Plains in Uniondale, New York, where Russian-olive and other nonnative trees and shrubs are present, restoration has been attempted to re-establish the prairie matrix. Controlled burns, mowing, herbicides and reintroduction of native species have all been used, but no results were given [131].

Deiter [49] reports that the most effective means of Russian-olive control employs a combination of pulling out small individuals from moist soil using a weed wrench, and cutting larger individuals at ground level and then immediately applying a small amount of herbicide to the cut stumps. Similarly, Caplan [34] describes controlling small (<4 inches (10 cm) diameter) Russian-olive stems with a mulching tractor and controlling large stems with cutting and immediate application of triclopyr. Several annual follow-up applications of herbicide to the foliage of root sprouts were also required 34. In general, any initial control method requires at least some ongoing suppression of stem and root sprouts and of new recruitment from seed [59,96,163].

Physical/mechanical: Physical control techniques alone may be suitable for removal of Russian-olive seedlings and saplings, whereas control of larger individuals usually requires application of herbicide or removal of the stump by burning, since cut trees typically sprout from the roots and root crown [52].

Manually removing seedlings and saplings (<4 inches (10 cm) diameter) and their roots is an effective control method. It is most effective when soil is moist. Any remaining exposed roots should be cut off below ground level and buried [49,52,148,180].

Control is difficult once Russian-olive trees mature and populations are well-established. The most effective control method is the cut-stump herbicide treatment 34,49,148,180. Girdling and cutting are not effective controls by themselves, as trees are likely to sprout below the girdled or cut areas or along roots [49].

Techniques such as mowing, cutting, girdling, chaining, and bulldozing can suppress Russian-olive on invaded sites, although the disadvantages to such approaches can be substantial, including the necessity for frequent treatment repetition, the indiscriminate removal of other species, and severe soil disturbance [163]. Additionally, these approaches are not effective without long-term monitoring and follow-up removal of sprouts [180]. Regular cutting in Minnesota tallgrass prairie sites does not kill Russian-olive, but keeps it at "brush height" [148].

Fire: See the Fire Management Considerations section of this summary.

Biological: Research on biological control agents has not been undertaken for Russian-olive [49].

Herbivory does not seem to limit Russian-olive invasion in western North America to any great extent. Reviews indicate that few insects are found on Russian-olive [96,177]. Grasshoppers sometimes consume leaves of young trees as well as the fleshy part of the fruit, but rarely do serious damage [54].

Although domestic livestock browse Russian-olive, the observation that Russian-olive commonly invades grazed meadows and pastures suggests that herbivory does not prevent its survival or limit its spread. Additionally, Russian-olive seedling survival may be enhanced by large seed size, and Russian-olive adults possess several adaptations to deter grazers, including sharp thorns and leaves containing abundant defense compounds ([95] and references therein). On the other hand, granivory by generalist mammals (primarily house mice and deer mice) completely prevented germination of Russian-olive seeds outside of small mammal exclosures in study plots in Colorado [95].

There is a fair amount of literature on the susceptibility and/or immunity of Russian-olive to various diseases (e.g. [54,162]), although none have been proposed as a potential biological control agents.

Chemical: Herbicides may be effective in gaining initial control of a new invasion or a severe infestation, but are rarely a complete or long-term solution to weed management. Use of herbicides may be limited in natural areas, and it is suggested that native species large enough to provide "good structure" be present to fill the niche left by removed Russian-olives [148]. See the Weed control methods handbook for considerations on the use of herbicides in natural areas and detailed information on specific chemicals and techniques. Herbicides that have been reported as effective at controlling Russian-olive to varying degrees include glyphosate, imazapyr, triclopyr, picloram, and 2,4-D.

Foliar spraying of herbicide has provided "successful control" of Russian-olive in some cases, although long-term response is unclear. This approach may be neither feasible nor desirable in many riparian settings ([96] and references therein) due to potential effects on nontarget species, and potential for overspray or drift when applied to large stands [180]. Small seedlings can also be killed with foliar applications of a mixture of picloram and 2,4-D [148]

Cut-stump herbicide treatments can be effective if the cut surface is treated with herbicide immediately after cutting. Cuts should be made as close to the ground as possible [49,52,148,180]. In an 80-acre (32 ha) cottonwood gallery forest on the Middle Rio Grande in New Mexico, Russian-olive is the codominant tree in mixed stands. From November 1998 through February 1999, Russian-olive less than 4 inches (10 cm) in diameter were mowed, using mulching tractors, larger trees were cut with chainsaws, and triclopyr ester was applied to the cut stump within 5 minutes of cutting. A second pass was made with mulching tractors to pulverize the remaining tree waste. By summer, 1999, Russian-olive root sprouts occurred throughout the site. Numerous root sprouts were found within close proximity of larger, sprayed stumps, suggesting that the rate of triclopyr used was not effective on stumps exceeding 8 inches (20 cm) in diameter. Triclopyr was applied to leaves of Russian-olive root sprouts each year for 3 subsequent summers. Each follow-up treatment required fewer people and less time. Continued monitoring and spot treatments keeps Russian-olive under control at the site [34].

For trees that do not have to be removed or immediately taken down, exposing more than 50% of the cambium by cutting into the bark with a saw or ax close to ground level and introducing herbicides into the exposed areas is also effective [49]. Deiter [49] reports that injecting herbicide capsules around base of trunk has also been successful for controlling Russian-olive. When injecting herbicides into the cambium of a standing tree, monitoring should occur during the same year to ensure that the entire tree is affected [49].

Conversely, Edelen and Crowder [59] propose killing the top-growth with herbicide (imazapyr), followed by mechanical control of resprouts as an effective alternative to cutting and then mowing resprouts. A project to test this control approach was begun in August 1996 in south-central Washington [59], and resulted in a 90% kill rate (personal communication from Crowder as cited by [180]).

Monitoring for sprouting from cut stumps and/or roots, or seedling establishment should be done for several years following treatment [34,148,163].

Cultural: In all cases of Russian-olive control, it is important that desirable plant species be planted or otherwise cultivated to discourage re-establishment of Russian-olive. Additionally, promotion of natural processes (e.g. natural flooding regimes) may be important to manage for desirable native species. In areas where natural disturbance processes still function, removal of Russian-olive may facilitate recovery of native species. On regulated rivers and areas with intensive livestock grazing, removal or suppression of Russian-olive is likely to be only temporary, unless measures are taken to promote establishment and persistence of native species. Stannard and others [163] and Brock [20] provide lists of species useful for replacement of Russian-olive and rehabilitation of Russian-olive-infested sites.

In southwestern riparian ecosystems, managing for native species may be more successful than managing against nonnative species [171]. Elimination of the stresses, such as high salinity and reduced stream flows, that favor nonnative plants over native plants may be necessary if native plant communities are to be sustained ([188] and references therein). Stromberg and Chew [171] provide some constructive options for restoring functionality to southwestern desert riparian ecosystems. They also indicate that it is unlikely that nonnative species will be eradicated from southwestern riparian systems, but that it is also unlikely that simply removing nonnatives would allow natives to thrive where conditions no longer favor them [171]. Along these lines, Stromberg [170] discusses the ecology, threats and recovery potential of cottonwood and willow in southwestern riparian systems. See the FEIS review on tamarisk for more information on this subject.

Obedzinski and others [134] suggest that in the case of dams and diversions, we may need to accept that a return to natural, sustainable conditions may not be possible, and that we may need to design management techniques, such as timed interval flooding and artificial seedbeds, to maintain riparian function. We may also need to learn the silvics of nonnative species and utilize them according to where they best fit into riparian systems [134].

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  1. (c) Mauricio Mercadante, some rights reserved (CC BY-NC-SA), http://farm9.staticflickr.com/8398/8692200737_d529a3b278_o.jpg
  2. (c) Dan Mullen, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/8583446@N05/2595600156
  3. (c) Le.Loup.Gris, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/d/d5/Elaeagnus_angustifolia_%28habitus%29.jpg
  4. (c) Mauricio Mercadante, some rights reserved (CC BY-NC-SA), http://farm9.staticflickr.com/8542/8693317120_875a0b098b_o.jpg
  5. (c) 2014 Zoya Akulova, some rights reserved (CC BY-NC), http://calphotos.berkeley.edu/cgi/img_query?seq_num=613348&one=T
  6. Adapted by Kate Wagner from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Elaeagnus_angustifolia
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