Botanical description: This description covers characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [22,42]).
Thorny-olive is a multistemmed, freely branched, dense shrub [22,37,42]. It may reach 25 feet (7.6 m) tall and 15 feet (4.6 m) wide [15,37]. Once established, thorny-olive produces prolific, fast-growing stem sprouts, which allow shrubs to increase in size and "scramble" through neighboring vegetation [22,37]. Stem bark is armed with "rather nasty", 2- to 3-inch (5-8 cm) long thorns [15]. Leaves are simple, evergreen, arranged alternately, and typically measure 1.6 to 4 inches (4-10 cm) long and less than half as wide [15,42]. The undersides of leaves are ashy white and flecked with brown scales [60]. Thorny-olive produces tubular flowers that are about 1 cm long and occur in clusters of up to 3 [37]. Fruits are single-seeded drupes that are 1 to 1.5 cm long [37,42].
Thorny-olive is not native to the United States but was introduced from Asia in 1830 [15,22]. As of 2011, escaped populations were suspected nearly throughout the southeastern United States from Kentucky and Virginia south to Louisiana and Florida [37]. Thorny-olive may also occur in natural areas of Massachusetts and Washington DC [54]. Plants Database provides a map of thorny-olive's US distribution.
Since its introduction as an ornamental, thorny-olive has frequently been planted in hedgerows and along highways [15,37,57]. It has also been used to revegetate mine sites [41,50]. Because thorny-olive grows densely even in harsh conditions, it was "extensively" planted in highway medians in the Southeast. As of 2000, the Virginia Department of Transportation had been planting thorny-olive along roadways for about 20 years [57]. Thorny-olive was also used in highway medians in Texas [16]. Around 1970 in eastern Kentucky, thorny-olive was planted on surface mine spoils and because establishment was successful and surival high, it was recommended for further use in mine reclamation [41]. On a coal surface-mined area in Laurel County, Kentucky, thorny-olive was still present and described as growing well or increasing 18 years after planting [50].
Reports on the extent of invasive populations of thorny-olive in the United States were rare, although surveys provided cover estimates in southern forests and indicated US range expansions. Forest Inventory Analysis data from 12 southern states in 2008 indicated that thorny-olive occupied an estimated 6,107 acres (2,471 ha) in forests in 6 states. It was most widespread in forests of Georgia (3,380 acres (1,368 ha)) and South Carolina (about 2,000 acres (800 ha)) [38]. In Florida, thorny-olive was known outside of cultivation only in the panhandle until about 2000, when it was reported in Alachua and Marion counties [28]. In 2003, it was reported as an escape in St Lucie County, 160 miles (250 km) south of Marion County [39]. In 1997, thorny-olive was reported as infrequent but spreading on the barrier islands of northern North Carolina [47].
Potential for postfire establishment and spread: Without more information about the conditions conducive to successful seedling emergence, the potential for thorny-olive establishment and spread in burned areas is unknown. However, likely long-distance seed dispersal by birds means that postfire monitoring for thorny-olive may be necessary even in areas lacking a nearby seed source.
Preventing postfire establishment and spread: Preventing invasive plants from establishing in weed-free burned areas is the most effective and least costly management method. This may be accomplished through early detection and eradication, careful monitoring and follow-up, and limiting dispersal of invasive plant propagules into burned areas. General recommendations for preventing postfire establishment and spread of invasive plants include:
For more detailed information on these topics, see the following publications: [3,8,23,53].
Use of prescribed fire as a control agent: Without more information about the vegetative regeneration capacity and postfire response of thorny-olive, the potential for using prescribed fire to control it is unclear.
Altered fuel characteristics: Changes in fuel characteristics or related fire regime characterisitics in habitats invaded by thorny-olive were not described in the available literature (2011).
Thorny-olive occurs in a variety of sites including disturbed, undisturbed, sunny, and shady locations [12,37,60]. In South Carolina, thorny-olive occurs in the mountains, Piedmont, and Coastal Plain regions [46].
Climate: In the United States, thorny-olive is hardy to USDA Hardiness zones 6 to 10, where the average annual minimum temperatures range from -10 °F to 35 °F (-23 to 2 °C) [15,21]. Once established, thorny-olive tolerates heat, wind, coastal conditions, and drought [21,30].
Elevation: Thorny-olive primarily occurs at elevations of less than 3,300 feet (1,000 m) in China [59]. Elevation ranges for thorny-olive habitats in the United States were not reported.
Soils: A variety of soil types, textures, and conditions are tolerated by thorny-olive. Horticultural references indicate that thorny-olive grows on occasionally wet, alkaline to acidic clays, sands, or loams [21]. Well-drained saline soils are also tolerated [30]. Once established, thorny-olive has "considerable" drought tolerance [15].
A field experiment on surface-mined sites in eastern Kentucky indicates that thorny-olive growth and survival may be better in neutral than acidic conditions. Four years after establishment, thorny-olive survival was 63%, and shrubs averaged 5.7 feet (1.7 m) tall on spoils with a pH of 3.8 and phosphorus levels of 1.1 ppm. On spoils with greater pH (7.2) and phosphorus levels (2.7 ppm), thorny-olive survival was 100%, and shrubs averaged 7.8 feet (2.4 m) tall [41].
While it seems that dense, rapid, and sometimes climbing growth would inevitably shade other vegetation, reduce native plant recruitment, and restrict human and animal movements, the citations that suggest such [11,35] lack documentation of these effects. Some suggest that thorny-olive could hybridize with other oleasters (Elaeagnus spp.) in the United States [35], but hybrids were not reported in the reviewed literature.
Although impacts have not been documented in any detail, many southern states treat thorny-olive as a serious threat to native plant communities. When invasive shrubs of Kentucky were compared, thorny-olive had many characteristics in common with the most widespread invasive shrubs, suggesting it could become widespread in the state [7]. As of 2008, thorny-olive was considered a severe threat by the South Carolina Exotic Pest Plant Council. Severe threat species are those known to severely threaten the composition, structure, or function of natural areas [46]. Thorny-olive is also listed as a moderate or significant threat to natural areas by other southern states including Tennessee [49], Georgia [20], and Florida [18].
Control: Studies involving the control of thorny-olive were generally lacking, but there are some recommendations with regard to the timing of control. Control measures prior to fruit ripening are recommended to limit seed dispersal [11]. Defoliation control measures may be more successful in the fall than in the spring. In a nursery study, all thorny-olive plants survived spring defoliation, and growth of spring-defoliated plants was not significantly different from that of controls. However, just 3 of 8 plants survived fall defoliation in "good condition" [32].
Control of biotic invasions is most effective when it employs a long-term, ecosystem-wide strategy rather than a tactical approach focused on battling individual invaders [36]. In all cases where invasive species are targeted for control, no matter what method is employed, the potential for other invasive species to fill their void must be considered [9].
Prevention: Establishment and spread of thorny-olive may be prevented by restricting its sale and use for landscape and roadside plantings in or near invasible habitats. As of 2009, thorny-olive was still available for sale in nurseries. The use of thorny-olive in ornamental, hedgerow, and roadside plantings is a major means for dispersal [11,37]. In a 1984 edition of the Pacific Horticulture magazine, thorny-olive was highlighted as an "excellent plant for the California landscape" [30], an area in which it may not occur outside of cultivation (as of 2011).
It is commonly argued that the most cost-efficient and effective method of managing invasive species is to prevent their establishment and spread by maintaining "healthy" natural communities [36,44] (e.g., avoid road building in wildlands [52]) and by monitoring several times each year [27]. Managing to maintain the integrity of the native plant community and mitigate the factors enhancing ecosystem invasibility is likely to be more effective than managing solely to control the invader [25]. Weed prevention and control can be incorporated into many types of management plans, including those for logging and site preparation, grazing allotments, recreation management, research projects, road building and maintenance, and fire management [53]. See the Guide to noxious weed prevention practices [53] for specific guidelines in preventing the spread of weed seeds and propagules under different management conditions.
Fire: For information on the use of prescribed fire to control this species, see Fire Management Considerations.
Cultural control: No information is available on this topic.
Physical or mechanical control: Some suggest that aggressive tillage or mowing may control thorny-olive [35], but others report that mechanical control of thorny-olive is slow and labor intensive [11]. These methods may not be appropriate for wildland management.
Biological control: As of 2011, no biological control agents had been tested or released for control of thorny-olive. There are few known thorny-olive pests in the United States [11].
Biological control of invasive species has a long history that indicates many factors must be considered before using biological controls. Refer to these sources: [55,58] and the Weed control methods handbook [51] for background information and important considerations for developing and implementing biological control programs.
Chemical control: The following references: [11,35,38] provide some guidelines for chemical control of thorny-olive. Byrd and Westbrooks [11] suggest that chemical control of thorny-olive can be slow, and signs of effectiveness may not be visible for "some time" after herbicide treatments. Herbicides are effective in gaining initial control of a new invasion or a severe infestation, but they are rarely a complete or long-term solution to weed management [10]. See the Weed control methods handbook [51] for considerations on the use of herbicides in natural areas and detailed information on specific chemicals.
Integrated management: No information is available on this topic.Based on the little information available (as of February 2011), thorny-olive occupies a greater
diversity of habitats in its nonnative than its native range.
Native habitats: In Asia, thorny-olive is primarily reported in open areas or shrublands. The Flora of China indicates that thorny-olive occurs on open slopes, along roadsides, and in thickets [59]. In limestone areas of Skikoku, Japan, thorny-olive
is common in Quercus phillyraeoides-Pittoporum tobira scrub [61].
Nonnative habitats: In the southeastern United States, thorny-olive is reported in shaded woodlands as well as open, disturbed sites. In North Carolina, thorny-olive occurred in oak-hickory (Quercus-Carya spp.) woodland understories [4], urban riparian forests [56], maritime evergreen forests [31], and ruderal habitats within the longleaf pine (Pinus palustris) ecosystem [45]. In northeastern Tennessee, thorny-olive occurred within and at the edges of woodlands [26]. In Alabama, it was reported in parks, rights-of-way, and managed forests, as well as natural areas [1,17]. In Alabama's Pike County Pocosin Nature Preserve, thorny-olive occurred in hardwood ravines, which were the least disturbed of the Preserve's habitats. Common overstory species in the hardwood ravines included yellow-poplar (Liriodendron tulipifera), southern magnolia (Magnolia grandiflora), American beech (Fagus grandifolia), and white ash (Fraxinus americana) [14]. In St Lucie County, Florida, thorny-olive occurred in
dry pine woods [39].
Although thorny-olive seedlings have been observed, information regarding the best conditions for successful seedling establishment were not reported in the reviewed literature (February 2011). In Atlanta, Georgia, and Clemson, South Carolina, thorny-olive seedlings were observed beneath older conspecifics [13], suggesting that thorny-olive is likely to persist where established.
Plant growth: Thorny-olive grows "very rapidly". Shoots may grow 3 to 4 feet (0.9-1.2 m) in a single growing season [5]. In a nursery study, stem diameter of thorny-olive increased 5% within 2 growing seasons after planting. Shrubs defoliated in the spring had stem diameter increases of 183% after 2 growing seasons [32].
Elaeagnus pungens is a species of flowering plant in the family Elaeagnaceae, known by the common names thorny olive,[1] spiny oleaster[2] and silverthorn; also by the family name "oleaster". It is native to Asia, including China and Japan. It is present in the southeastern United States as an introduced species, a common landscaping and ornamental plant, and sometimes an invasive species.[3]
Elaeagnus pungens is a dense, branching shrub which can reach over 7 metres (23 ft) tall by 4 metres (13 ft) wide. It sprouts prolifically from its stem, spreading out and twining into adjacent vegetation. Parts of the stem are covered in thorns which can be up to 8 centimetres (3.1 in) long. The evergreen, alternately-arranged leaves are up to 10 centimetres (3.9 in) long but under 5 centimetres (2.0 in) wide. The undersides are silvery white with brown flecks. Tubular flowers are borne in clusters of up to three.[3] The flowers are yellowish or white and are sweet-scented.[4] The fruit is a drupe up to 1.5 centimetres (0.59 in) long which contains one seed.[3] It is reddish with silver scales.[4] Blooming occurs in the autumn and fruit develops during the spring. The plant grows quickly, with shoots growing over one meter per season. The growth has been described as "aggressive", with shoots extending many meters into neighboring treetops. The seeds are dispersed by birds.[3]
In China this plant occurs on hillsides and in thickets. In Japan it grows in scrub dominated by Quercus phillyraeoides and Pittosporum tobira. This plant was introduced to the United States from Asia in 1830. It has been used extensively as a landscaping plant. Its densely packed, spreading form has proved useful along roadsides and highway medians. It was also used to revegetate abandoned mining sites in Kentucky and other areas. It took hold easily and still persists in these places. It also spread into the wild, having escaped cultivation. In North Carolina it has been reported from longleaf pine forests, urban and maritime forests, and oak-hickory woodlands. In Alabama it grows in urban areas and in protected, natural habitats as a weed. The South Carolina Southern Weed Science Society places it as an invasive species in their local area.[5]
Despite its invasive potential, E. pungens is widely cultivated as a garden plant in temperate regions. It tolerates varied environmental conditions, including heat, cold, wind, coastal conditions, shade, and full sun. It is very drought-tolerant. It can grow in varied soil types, including those found at mine spoils.[3] Numerous cultivars have been developed, especially for variegated foliage effects. Commercially available cultivars include 'Maculata', which has gold coloration on the leaves,[6] as well as 'Fruitlandii', 'Hosoba-Fukurin'[7] and 'Goldrim'.[8]
Elaeagnus × submacrophylla, formerly known as E. × ebbingei, is a hybrid between E. macrophylla and E. pungens. The hybrid and its cultivars are also grown in gardens as ornamental plants.[9]
Many birds feed on the fruits of the shrub. Birds are most attracted to the plants that produce the most fruit.[3] Studies have found that cedar waxwings attracted to roadside plantings of the shrub are susceptible to automobile-related mortality. In Brazos County, Texas between 8 March and 5 April 1981, researchers counted 298 cedar waxwings that had been killed while trying to get fruits from thorny-olive shrubs growing along one highway.[3]
Elaeagnus pungens is a species of flowering plant in the family Elaeagnaceae, known by the common names thorny olive, spiny oleaster and silverthorn; also by the family name "oleaster". It is native to Asia, including China and Japan. It is present in the southeastern United States as an introduced species, a common landscaping and ornamental plant, and sometimes an invasive species.
