Elaeagnus angustifolia
(Russian olive)

E. angustifolia, the Russian olive, is one of several species of Elaeagnus that has proven invasive. It is native to temperate Eurasia but has become especially invasive in riverine areas in the western USA, and is increasingly common in areas already invaded by exotic saltcedars (Tamarix spp.), displacing native vegetation. E. angustifolia has a tendency to spread to areas where it is not desired, necessitating careful monitoring of sites planted with this species as once established, it is difficult to control and nearly impossible to eradicate. It can interfere with agricultural practices, displace native riparian vegetation and choke irrigation ditches. Delaney et al. (2013) has reviewed possible biological control strategies in North America. Vaughan and Mackes (2016) noted that the cost of removal could be defrayed by the sale of wood for artisan use due to its attractive grain and colour.

E. angustifolia is native to parts of eastern Europe and Asia, and is an important deciduous species of arid and semi-arid areas of northwestern China. It is present in central Europe though the exact western limits of its native range are open to speculation.

It is a declared B list noxious weed in Colorado and a Class C noxious weed in New Mexico, and is on noxious weed lists on a number of other states where present and invasive, e.g. California, or where not yet invasive, e.g. Connecticut (USDA-NRCS, 2008). Noting its presence on species lists for reforestation, and its value in parts of the native range means it may continue to be introduced. It should also be monitored where introduced but not yet invasive.

E. angustifolia occupies many habitats in its native range, including mountainous areas, plains, sands, and desert. Where introduced, it is commonly found growing along floodplains, river banks, stream courses, marshes and irrigation ditches in the western states of the USA, and in desert or dry (<_st13a_metricconverter _w3a_st="on" productid="150 mm">150 mm annual rainfall) areas of western Asia. It is highly invasive along riverine areas in the western USA. It is also noted as present around oases in North Africa (Dommergues et al., 1999). Vegetation types where it is noted as invasive in the USA include natural forests, natural grasslands, desert scrub and savanna, though a very thorough review is included by Zouhar (2005).

Reproductive Biology

Flowering mainly takes place in May and June while fruits ripen during August to October. Fruits are retained on trees throughout the winter providing a valuable food source for birds (Bartha and Csiszár, 2008). Flowers are insect pollinated (Zouhar, 2005), and trees produce seed after 3-5 years, with birds and small mammals dispersing them in their droppings. The seeds can remain viable for up to 3 years and are capable of germinating over a broad range of soil types (Knopf and Olson, 1984), and germination is enhanced by stratification in moist sand for 90 days at 41°C (Vines, 1960). It bears few fruits if the annual precipitation is over 400 mm. E. angustifolia is mainly established from seed, although cuttings are used in areas with sufficient moisture. Brock (2003) found that the average number of seeds in the seed bank averaged 336-494 seeds/m² for five sites assessed, with fresh and viable seeds comprising 63% of the seed bank, with the remaining 37% of seeds considered old and with low or no germination potential.

Physiology and Phenology

E. angustifolia is a fast-growing tree, up to 1.8 m per year, and is nitrogen-fixing. A thorough review by Katz and Shafroth (2003) highlights the ecological characteristics enabling its invasiveness, including an adaptation to semiarid riparian habitats, lack of intense pressure from herbivores, and tolerance of the competitive effects of established vegetation. We believe that the success of this species is at least partly due to its ability to take advantage of the reduced levels of physical disturbance that characterize riparian habitats downstream from dams. Control of E. angustifolia is likely to be most promising where natural river flow regimes remain relatively intact (Katz and Shafroth, 2003).

In Montana, USA, Lesica and Miles (2001) conducted a detailed analysis of E. angustifolia regeneration in invaded riverine areas, concluding that because of its long maturation time and low recruitment rate, invasion there will proceed only slowly compared with many exotics. It occurred in multiple-age stands on terraces along both rivers but was rarely found establishing in recently flood-deposited alluvium, and grew quicker than native species, attaining reproductive maturity at about 10 years of age, and, on average, there was less than one new plant recruited per mature tree per year. Beavers felled a high proportion of native poplars, but E. angustifolia was little damaged. Native riparian forests will be replaced by E. angustifolia as old poplars die on upper terraces or are removed by beavers. Poplar establishment and dominance will not be precluded on rivers where flooding regularly reinitiates primary succession beyond the zone of beaver activity, however, E. angustifolia may preclude poplar recruitment by shading seedlings along streams where flooding does not occur or merely deposits alluvium on top of existing vegetation rather than creating new channels or broad point bars.

Associations

It is a nitrogen-fixing species, in association with Actinomycete fungi, Frankia spp. (Dommergues et al., 1999), that also nodulate Hippophae and Shepherdia, but not by strains that colonize other actinorhizal plants such as Casuarina and Alnus. Inocula is available for Elaeagnus species, although inoculation may not be necessary since most plants spontaneously nodulate in the nursery or upon planting in the field, and unlike Rhizobium, Frankia survive in the soil for long period without the presence of host plants (Baker, 1992). Wei et al. (2017) noted that even under salt stress E. angustifolia has a strong nitrogen fixation ability.

It is a part of several forest types in its native range, including mixed Tamarix-Elaeagnus forests, Elaeagnus-dominated stands, Populus-Elaeagnus woodlands, and Haloxylon woodlands (Zouhar, 2005). Where invasive in western North America, it is commonly found with other exotic invasive species, the saltcedars (Tamarix spp.). Areas invaded are often populated by native poplars (Populus spp., commonly called ‘cottonwoods’ in the USA).

Environmental Requirements

E. angustifolia is a tree of temperature climates with warm summers and cold to very cold winters. According to Bartha and Csiszár (2008) trees can survive frosts of −30°C but some terminal shoot damage may result. Based on simulation studies, Zhang et al. (2018) noted that the dominant climatic factors limiting its potential distribution range in China are annual range of temperature, annual mean temperature, humidity index and coldness index. It is found in a range of environments as it is tolerant of drought and saline, alkaline or infertile soils (Vines, 1960; Olson and Knopf, 1986a, b), having a well-developed root system. It has little preference as to soil type, temperature, or moisture (Zheng et al., 2006). It is commonly found growing along floodplains and where soil water is present such as riverbanks, though it is also found in deserts or dry areas, though it grows slowly if the water table is below 4 m. It is relatively shade-tolerant once established and can withstand competition from other shrubs and trees.

Zheng et al. (2006) report that 10 fungi have been found on members of the genus Elaeagnus, including Aecidium elaeagni which may be host-specific to Elaeagnus spp. and Septobasidium albidum which has a host range that includes E. umbellata as well as species in other genera. Also, 22 arthropods belonging to 10 families of five orders are reported, and the moth, Teia prisca may be specific to E. angustifolia. All natural enemies are listed along with whether they are known to attack the three main invasive Elaeagnus spp., E. angustifolia, E. pungens and E. umbellata.

Animal feed, fodder, forage

• Fodder/animal feed

Environmental

• Agroforestry
• Amenity
• Erosion control or dune stabilization
• Land reclamation
• Ornamental
• Revegetation
• Shade and shelter
• Soil conservation
• Soil improvement
• Wildlife habitat
• Windbreak

Fuels

• Fuelwood

General

• Ornamental

Human food and beverage

• Beverage base
• Fruits
• Honey/honey flora

Materials

• Essential oils
• Fibre
• Gum/resin
• Wood/timber

Medicinal, pharmaceutical

• Traditional/folklore

Pulp

• Short-fibre pulp

Roundwood

• Posts

It has a superficial resemblance to another invasive species, E. umbellata, though they can be separated. The other two genera within the Elaeagnaceae, Hippophae and Shepherdia are also nitrogen fixing, and are very similar to Elaeagnus in general appearance and growth habits (Baker, 1992).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Control

Control is difficult once E. angustifolia trees are mature and populations are well-established, or may even be nearly impossible to eradicate, though Zouhar (2005) thoroughly review management and control methods employed in the USA, which are largely adapted and reported here. Mowing seedlings, cutting, burning, spraying (Diesburg, 1994; Geyer and Long, 1994), girdling and bulldozing have all been attempted, although cutting, followed by either spraying or burning the stumps is the most effective (Olson and Knopf, 1986b).

Cultural control and sanitary measures

Zouhar (2005) suggested that it is unlikely that exotic species will be eradicated from riparian systems in the south-west USA, and that it is also unlikely that simply removing exotics would allow natives to thrive where conditions no longer favour them. Thus, if a return to natural, sustainable conditions may not be possible then it may be necessary to design management techniques such as timed interval flooding and artificial seedbeds, to maintain riparian function. In conclusion for the south-west USA, managing for native species may be more successful than managing against exotic species. Promotion of natural processes such as natural flooding regimes may be important in managing for desirable native species. However, removal of E. angustifolia may only facilitate recovery of native species where natural disturbance processes still function adequately (Zouhar, 2005). On dammed, regulated rivers and areas with intensive livestock grazing, removal or suppression of E. angustifolia will only have temporary effects unless native species are established. Elimination of the stresses such as high salinity and reduced stream flows, that favour exotic plants over native plants may be necessary if native plant communities are to be sustained (Zouhar, 2005).

Physical/mechanical control

Hand-pulling and other manual methods have been attempted with limited success in Arizona, USA (Landis et al., 2006), and ring-barking will also kill older trees (Zouhar, 2005). Also, techniques such as mowing, cutting, girdling, chaining, and bulldozing can suppress E. angustifolia. However, disadvantages can be substantial, including the need for frequent treatment repetition, indiscriminate removal of other species, and severe soil disturbance.

Biological control

CABI initiated a biological control programme against E. angustifolia in 2007, with the primary focus on species that impact the reproductive output without affecting standing trees, due the potential conflict of interest (Weyl et al., 2017). Of the three species currently under study, the Eriophyid mite, Aceria angustifoliae, is the most promising agent with a high level of specificity and preliminary studies suggest a high impact on fruit and ultimately seed production (Weyl et al., 2017). However, to date no biological control agents have been released against this species.

Chemical control

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, and herbicides that have been reported as effective at controlling E. angustifolia to varying degrees include glyphosate, imazapyr, triclopyr, picloram, and 2,4-D (Zouhar, 2005).

Foliar spraying of herbicide has proved successful in some cases although the long-term response is unclear and this approach may be neither feasible nor desirable in many riparian settings, though small seedlings are killed with foliar applications of picloram + 2,4-D. Triclopyr ester is an effecting cut stump treatment if applied within 5 minutes of cutting and on smaller trees, otherwise repeated follow-up passes are required, though stem injections is a useful complement (Zouhar, 2005).

Control by utilization

Noting its high value in China and elsewhere in Asia, it may be wise to look in more detail as the uses of this species, in order to assess if there may be any possibility of control by utilization.

Monitoring and Surveillance

As control of E. angustifolia is difficult once trees are mature, so early detection and rapid response are important, and awareness and prevention are probably the most effective tools for managing against it. Ecological niche modelling also holds promise for the development of control and eradication strategies and for risk assessment for species invasions, including E. angustifolia (Peterson et al., 2003). Although, it is clear that a considerable level of research effort has been applied to woody stemmed, exotic/weed species ecology, an approach involving close coupling between classical mathematical species competition models (Lotka-Volterra) and field management predictive capability may provide a useful first approximation (Chant and Chant, 2004).

18/01/18 Updated by:

Philip Weyl, CABI, Delémont, Switzerland 

29/02/2008 Updated by:

Nick Pasiecznik, Consultant, France