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Datasheet

Tamarix ramosissima (saltcedar)

Summary

  • Last modified
  • 22 June 2017
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Preferred Scientific Name
  • Tamarix ramosissima
  • Preferred Common Name
  • saltcedar
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • T. ramosissima possesses numerous inherent physiological characteristics that make it adapted to natural or modified riparian ecosystems and make it appear to be more aggressive and better adapted to the invade...

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Pictures

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PictureTitleCaptionCopyright
Tamarix ramosissima (saltcedar); invasive habit. Haystack Rock, Oregon, USA. August, 2005.
TitleInvasive habit
CaptionTamarix ramosissima (saltcedar); invasive habit. Haystack Rock, Oregon, USA. August, 2005.
Copyright©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); invasive habit. Haystack Rock, Oregon, USA. August, 2005.
Invasive habitTamarix ramosissima (saltcedar); invasive habit. Haystack Rock, Oregon, USA. August, 2005.©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); foliage. USA.
TitleFoliage
CaptionTamarix ramosissima (saltcedar); foliage. USA.
Copyright©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); foliage. USA.
FoliageTamarix ramosissima (saltcedar); foliage. USA.©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); close view of foliage. USA.
TitleFoliage
CaptionTamarix ramosissima (saltcedar); close view of foliage. USA.
Copyright©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); close view of foliage. USA.
FoliageTamarix ramosissima (saltcedar); close view of foliage. USA.©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); flowers. USA.
TitleFlowers
CaptionTamarix ramosissima (saltcedar); flowers. USA.
Copyright©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); flowers. USA.
FlowersTamarix ramosissima (saltcedar); flowers. USA.©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); close view of flowers. USA.
TitleFlowers
CaptionTamarix ramosissima (saltcedar); close view of flowers. USA.
Copyright©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); close view of flowers. USA.
FlowersTamarix ramosissima (saltcedar); close view of flowers. USA.©Leslie J. Mehrhoff/University of Connecticut/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); seedling carpet in a stream bed. Oregon, USA. August, 2009.
TitleSeedlings
CaptionTamarix ramosissima (saltcedar); seedling carpet in a stream bed. Oregon, USA. August, 2009.
Copyright©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); seedling carpet in a stream bed. Oregon, USA. August, 2009.
SeedlingsTamarix ramosissima (saltcedar); seedling carpet in a stream bed. Oregon, USA. August, 2009.©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); close view of seedling carpet in a stream bed. Oregon, USA. August, 2009.
TitleSeedlings
CaptionTamarix ramosissima (saltcedar); close view of seedling carpet in a stream bed. Oregon, USA. August, 2009.
Copyright©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Tamarix ramosissima (saltcedar); close view of seedling carpet in a stream bed. Oregon, USA. August, 2009.
SeedlingsTamarix ramosissima (saltcedar); close view of seedling carpet in a stream bed. Oregon, USA. August, 2009.©Eric Coombs/Oregon Department of Agriculture/Bugwood.org - CC BY 3.0 US
Diorhabda elongata (Mediterranean tamarisk beetle); D. elongata, a Chrysomelid leaf beetle native to China, is a natural enemy of saltcedar (Tamarix spp.).
TitleNatural enemy
CaptionDiorhabda elongata (Mediterranean tamarisk beetle); D. elongata, a Chrysomelid leaf beetle native to China, is a natural enemy of saltcedar (Tamarix spp.).
Copyright©Robert D. Richard/USDA APHIS PPQ/Bugwood.org - CC BY 3.0 US
Diorhabda elongata (Mediterranean tamarisk beetle); D. elongata, a Chrysomelid leaf beetle native to China, is a natural enemy of saltcedar (Tamarix spp.).
Natural enemyDiorhabda elongata (Mediterranean tamarisk beetle); D. elongata, a Chrysomelid leaf beetle native to China, is a natural enemy of saltcedar (Tamarix spp.).©Robert D. Richard/USDA APHIS PPQ/Bugwood.org - CC BY 3.0 US

Identity

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Preferred Scientific Name

  • Tamarix ramosissima Ledeb. (1829)

Preferred Common Name

  • saltcedar

Other Scientific Names

  • Tamarix altaica Ndz. (1925)
  • Tamarix eversmanni Presl ex Ledeb.
  • Tamarix eversmannii Presl ex Bge.
  • Tamarix galica var. pallasii Dyer (1874)
  • Tamarix gallica var. micrantha Ledeb. (1843)
  • Tamarix odessana Stev. ex Bge. (1852)
  • Tamarix pallasii
  • Tamarix pallasii var. brachytachys Bge.
  • Tamarix pallasii var. minutiflora Bge.
  • Tamarix pallasii var. odessana (Stev. ex Bge.) Schmalh. (1895)
  • Tamarix pallasii var. ramosissima (Ledeb.) Bge.
  • Tamarix pallasii var. tigrensis Bge.
  • Tamarix pendandra Pall. (1788) nom. illegit.
  • Tamarix pentandra subsp. tigrensis (Bge.) Hand.-Mazz. (1913)

International Common Names

  • English: salt-cedar; tamarisk; tamarix
  • Spanish: pinebete
  • French: tamaris à cinq étamines

Local Common Names

  • Germany: Sommertamariske; Tamariske, Fünfmännige; Tamariske, Kaspische; Tamariske, Sommer-
  • Israel: ashel
  • Italy: tamarice a cinque stami
  • South Africa: perstamarisk (Afrikaans); pink tamarisk

EPPO code

  • TAAPE (Tamarix ramosissima)

Summary of Invasiveness

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T. ramosissima possesses numerous inherent physiological characteristics that make it adapted to natural or modified riparian ecosystems and make it appear to be more aggressive and better adapted to the invaded native ecosystems of western North America than are the native plant communities (DeLoach et al., 2000). T. ramosissima has an extremely high reproduction rate, the ability to produce seeds over a very long time period (throughout the growing season), very efficient means of seed dispersal, the ability to reproduce vegetatively as well as by seed, and mechanisms for rapid seed germination and seedling establishment. T. ramosissima and related Tamarix spp. qualify under 10 of the 12 characteristics of the 'ideal weed' discussed by Baker (1974). T. ramosissima is listed as a federal noxious weed in the USA (USDA-NRCS, 2007) and is included in the 100 of the 'World's Worst' invaders (ISSG, 2007).

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Tamaricales
  •                         Family: Tamaricaceae
  •                             Genus: Tamarix
  •                                 Species: Tamarix ramosissima

Notes on Taxonomy and Nomenclature

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The placement of Tamarix in the family Tamaricaceae has never been questioned among taxonomists. However, the relationship of the Tamaricaceae to higher taxonomic categories has been a topic of considerable uncertainty. Spichiger and Savolainen (1997), based on molecular systematics, drastically rearranged the placement of some families in Cronquist's Violales (Cronquist, 1981, 1988). The new arrangement placed the Tamaricaceae and Frankeniaceae together in the two-family order Tamaricales. Thus, the only plants closely related to Tamarix are in two small genera, Myricaria in Eurasia and Reaumuria in Asia (family Tamaricaceae), and the larger genus Frankenia (family Frankeniaceae). The latest monographer of the genus (Baum, 1978) described 54 Tamarix species, though the subgeneric sections and series were not supported by genetic analyses (Gaskin and Schaal, 2003).

The weedy species of Tamarix in North America, small trees or shrubs, include a complex of four very similar species: T. ramosissima, T. chinensis, T. canariensis and, occasionally, T. gallica, plus the distinct T. parviflora, and their hybrids. These species are all deciduous. The distinctive, large evergreen tree, athel (T. aphylla) is also becoming weedy at a few locations (Barnes et al., 2004). Four other species have been introduced that are known only as ornamentals or that have become weakly naturalized (Baum, 1967; Crins, 1989). Recent DNA analyses throw some doubts on the value of the morphological differences by which some species are separated, but the current assumption is that the main invasive entity in North America is a hybrid of T. ramosissima with T. chinensis, while other entities include a hybrid between T. canariensis and T. gallica and the distinct species, T. parviflora and T. aphylla (Gaskin and Schall, 2002, 2003). These authors also comment that although the ranges of the Asian species, T. ramosissima and T. chinensis, overlap in China, hybrids have not been recorded from that region.

The common name 'saltcedar' derives from the superficial resemblance of the leaves to Juniperus which is commonly called 'cedar' in the USA and the salt glands that excrete excess salts from saline ground water taken up by the roots. It is frequently used for all the weedy, decidous, small trees or shrubs of Tamarix in the USA and Mexico. The large, evergreen T. aphylla is often distinguished by using the common name 'athel'.

This datasheet provides specific data on T. ramosissima and information common to the group of four similar species that have been introduced into North America (T. ramosissima, T. chinensis, T. canariensis and T. gallica). Specific information on the other three Tamarix species can be found in separate datasheets. Where data refer strictly to T. ramosissima, the full species name is used, while the term 'saltcedars' generally refers to the wider range of weedy species in the genus.

Description

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Of the genus:

Tamarix species are either true trees with a well developed trunk (e.g. T. aphylla) or shrubs (Baum, 1978). The North American saltcedars are small trees or shrubs, often multi-stemmed, 2-5 (1-10) m tall depending on water availability and latitude/elevation, deciduous (except for T. aphylla) and with attractive pink, usually terminal inflorescences. Tamarix spp. are usually deep rooted, with a tap root reaching to 30 m deep and lateral roots to 50 m long that can produce adventitious buds, especially when covered by shifting sand. Some species therefore are excellent dune binders (Baum, 1978).

In the North American saltcedars, the young branches are usually flexible and willowy. The bark of young branches varies from reddish-brown, to brown, blackish-brown, dark purple, grey or black, and are glabrous (Baum, 1978). The older branches, with heavy bark, often shredded, grey or brownish, may reach 10-15(-20) cm diameter, although trees with single trunks to 30 cm diameter are not uncommon in old stands along rivers in southwestern USA. Adventitious buds in the crown area sprout when the upper part of the plant is killed or injured (as with mechanical control); new sprouts may grow 2-3 m in 1 year. The leaves of saltcedars are small and bract-like (vaginate in T. aphylla; Baum, 1978) superficially resembling those of Juniperus. The foliage often turns a golden-orange colour in the autumn.

The inflorescence is racemose, often paniculately branched, and borne on the ends of green, current-year branches (aestival), either densely congested or loosely scattered on the common axis, often intermingled with foliage twigs on the basal portion; or they come out directly from previous-year branches (vernal) or with both aestival and vernal flowers (Baum, 1978). In the American introduced saltcedars, the foliage appears first followed by the flowers (aestival) except in T. parviflora where the flowers appear first (vernal) and in dense clusters along the stems. The flower parts are of major taxonomic value at the species level. Characters include the length, structure and shape of the bracts; the arrangement of the sepals; the persistence of the androecium, including the number of stamens and their insertion in the disk and the shape of the discal lobes at the base of the flower that supports the stamens and ovary. The ovaries usually consist of three, sometimes four, and rarely five carpals and stigmas, the number varying in a single raceme, and the shape varying within a species. The shape of the pollen grains is also of some taxonomic value. The fruit is a many-sided capsule with many tiny seeds. North American Tamarix species have five stamens and five petals, except for T. parviflora which has four. The flowers are small, with petals 1-2 mm long, and pink (except that T. aphylla has white flowers). The fruit is a small 3-valved capsule, and seeds are very small and bear an apical pappus of hygroscopic hairs; but are of little taxonomic value.

Of T. ramosissima:

T. ramosissima is a shrub or shrubby tree, 1-5(-6) m high, with reddish-brown bark, entirely glabrous. Leaves sessile with narrow base, 1.5-3.5 mm long. Aestival inflorescences densely composed of racemes, the vernal ones usually simple, loose and not as common as the aestival ones, often vernal-aestival. Racemes 1.5-7 cm long, 3-4 mm broad. Bracts longer than pedicels, triangular-trullate to narrowly trullate (trowel-shaped, wider below the middle), acuminate, with margins more or less denticulate, mainly in their lower part. Pedicels shorter than calyx. Calyx pentamerous. Sepals narrowly trullate, acute, or the outer two ovate to narrowly trullate-ovate and the inner trullate-ovate and broader than the outer, irregularly denticulate to erose, 0.5-1 mm long, not connate at base. Corolla pentamerous, persistent. Petals, dark to pale pink, 1-1.75 mm long, obovate to broadly elliptic-obovate, inequilateral. Androecium consisting of a single shorl of stamens (haplostemonous), with five antesepalous stamens (inserted opposite the sepals); insertion of filaments hypodiscal (inserted below the nectary disc); disc holophic, its lobes usually strongly emarginate. Flowering occurs from May to October (Baum, 1978). In the USA, trees grow to 10 m high in good habitats, inflorescences typically 20-40 cm long with racemes on loosely and paniculately branched terminals of branches, sometimes intermixed with foliage in the proximal part of the inflorescence.

Plant Type

Top of page Broadleaved
Perennial
Seed propagated
Shrub
Tree
Vegetatively propagated
Woody

Distribution

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Tamarix is an ancient genus that originated during the Cretaceous Period in the Turanian and Middle Asian deserts, where it specialized in saline soils of riparian areas (Rusanov, 1949; Kovalev, 1995), from present day Iran and Afghanistan, to Turkmenistan and southern Kazakhstan (Baum, 1978). Recent information indicates that the centre of origin probably should not include India but should include western China. The genus has radiated to eastern China (Liu and Zhang, 1987; Ma, 1988; Li, 1990), to Mongolia and Korea, into India, and across the Middle East to the eastern Mediterranean areas where a secondary major centre of speciation developed, and across southern Europe to Spain, across northern Africa to Morocco and Senegal, and through eastern Africa to southern Africa (Baum, 1978). Baum (1978) recognized 54 species, none of which occur naturally in the Western Hemisphere nor in Australia. Although widespread and sometimes abundant in small areas within its natural distribution in Asia, Africa and southern Europe, Tamarix spp. are, in none of those areas considered invasive or noxious weeds. However, a few species have been introduced into North America and Australia, especially in deserts and semi-arid areas with high soil salinity, and have become highly invasive and damaging weeds.

The Old World distributions for the four similar species that are weedy in North America are given by Baum (1978) and Ma (1988) for T. ramosissima, by Baum (1978) and Li (1990) for T. chinensis, and by Baum (1978) for T. canariensis and T. gallica. Gaskin and Schaal (2002) note that even though both T. ramosissima and T. chinensis supposedly occur across China they found the T. ramosissima genotype exclusively west of central China and the T. chinensis genotype exclusively east of central China.

For the exotic Tamarix species in North America, Robinson (1965) and Kartesz and Meacham (1999) give distribution maps. Baum (1967) lists eight naturalized species of Tamarix in the USA: T. africana, T. aphylla, T. aralensis, T. canariensis, T. chinensis, T. gallica, T. parviflora and T. ramosissima; and three species in Canada, including T. ramosissima. Crins (1989) lists all eight of these plus T. tetragyna and T. mascatensis (the latter has not escaped cultivation) in the southeast.

In the USA, Gaskin and Schaal (2002) found that T. ramosissima (especially in the more northern area) and T. chinensis are naturalized over a wide area in the west. The most abundant and widespread Tamarix type is a T. ramosissima x T. chinensis hybrid, ranging from Oklahoma to Washington to California. A T. canariensis/gallica type is also prevalent along the gulf coast of Louisiana and Texas and frequently hybridizes with pure T. chinensis and T. ramosissima in the western half of Texas. Parsons and Cuthbertson (1992) note that T. ramosissima is also naturalised in parts of Australia'.

In Mexico, de León González and Vásquez Aldape (1991) surveyed the distribution of Tamarix in the northeastern states of Chihuahua, Durango, Coahuila, Nuevo León and Tamaulipas, but their species identifications are uncertain. Scudday (1989) found Tamarix in the northwestern states of Sonora and Sinaloa, and E Andress (USDA-APHIS, Barstow, California, USA, personal communication, 2004) found it in Baja California Norte.

Roadside plantings of Tamarix sp. in Buenos Aires Province, Argentina, were found in 1971 (CJ DeLoach, USDA-ARS, Temple, Texas, USA, unpublished observations) and confirmed by Gaskin and Schaal (2003).

T. ramosissima has recently invaded South Africa, where it has become weedy and is damaging grazing lands and natural areas (John Hoffmann, University of Cape Town, South Africa, personal communication, 2004; USDA-NRCS, 2007).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

AfghanistanWidespreadNative Not invasive Baum, 1978
ArmeniaRestricted distributionNative Not invasive Baum, 1978
AzerbaijanRestricted distributionNative Not invasive Baum, 1978
China
-GansuWidespreadNative Not invasive Baum, 1978
-Nei MengguRestricted distributionNative Not invasive Baum, 1978
-NingxiaPresentNativeUSDA-ARS, 2007
-QinghaiPresentNativeUSDA-ARS, 2007
-TibetPresentNativeUSDA-ARS, 2005
-XinjiangWidespreadNative Not invasive Baum, 1978
Georgia (Republic of)WidespreadNative Not invasive Baum, 1978
IranWidespreadNative Not invasive Baum, 1978
IraqRestricted distributionNative Not invasive Baum, 1978
KazakhstanWidespreadNative Not invasive Baum, 1978
Korea, Republic ofPresentNativeUSDA-ARS, 2007
KyrgyzstanWidespreadNative Not invasive Baum, 1978
MongoliaWidespreadNative Not invasive Baum, 1978
PakistanPresentNativeUSDA-ARS, 2007
QatarPresentAbulfatih et al., 2002
TajikistanWidespreadNative Not invasive Baum, 1978
TurkeyRestricted distributionNative Not invasive Baum, 1978
TurkmenistanWidespreadNative Not invasive Baum, 1978
UzbekistanWidespreadNative Not invasive Baum, 1978

Africa

South AfricaPresentIntroduced Invasive USDA-ARS, 2007

North America

Canada
-SaskatchewanPresent, few occurrencesIntroducedKartesz and Meacham, 1999
MexicoRestricted distributionIntroducedMissouri Botanical Garden, 2007Baja and Sonora
USAWidespreadIntroduced1823 Invasive Robinson, 1965
-ArizonaWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-ArkansasPresentIntroducedUSDA-ARS, 2007
-CaliforniaWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-ColoradoWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-GeorgiaPresentIntroducedUSDA-ARS, 2007
-IdahoRestricted distributionIntroduced Invasive Baum, 1967; Crins, 1989
-KansasWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-LouisianaPresentIntroducedUSDA-ARS, 2007
-MississippiPresentIntroducedUSDA-ARS, 2007
-MissouriPresentIntroducedMissouri Botanical Garden, 2007
-MontanaWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-NebraskaWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-NevadaWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-New MexicoWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-North DakotaRestricted distributionIntroduced Invasive Baum, 1967; Crins, 1989
-OklahomaWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-OregonRestricted distributionIntroduced Invasive Baum, 1967; Crins, 1989
-South CarolinaPresentIntroducedUSDA-ARS, 2007
-South DakotaRestricted distributionIntroduced Invasive Baum, 1967; Crins, 1989
-TexasWidespreadIntroduced Invasive Baum, 1967
-UtahWidespreadIntroduced Invasive Baum, 1967; Crins, 1989
-VirginiaPresentIntroducedUSDA-ARS, 2007
-WashingtonRestricted distributionIntroduced Invasive Baum, 1967; Crins, 1989
-WyomingWidespreadIntroduced Invasive Baum, 1967; Crins, 1989

South America

ArgentinaPresentIntroducedGaskin and Schaal, 2003; Missouri Botanical Garden, 2007

Europe

ItalyPresentIntroducedMissouri Botanical Garden, 2007
Russian Federation
-Russia (Europe)PresentNativeUSDA-ARS, 2007
-Southern RussiaRestricted distributionNativeBaum, 1978
UkrainePresentNativeUSDA-ARS, 2007

Oceania

AustraliaPresentIntroducedUSDA-ARS, 2007
-Australian Northern TerritoryPresentIntroducedRoyal Botanic Gardens Sydney, 2007
-New South WalesPresentIntroduced Invasive ISSG, 2005; Royal Botanic Gardens Sydney, 2007
-QueenslandPresentIntroducedRoyal Botanic Gardens Sydney, 2007
-South AustraliaPresentIntroducedRoyal Botanic Gardens Sydney, 2007
-TasmaniaPresentIntroducedRoyal Botanic Gardens Sydney, 2007
-VictoriaPresentIntroducedRoyal Botanic Gardens Sydney, 2007
-Western AustraliaPresentIntroducedRoyal Botanic Gardens Sydney, 2007

History of Introduction and Spread

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Saltcedars were introduced into the USA as ornamentals, first recorded in a nursery in New Jersey in 1837. They were reported in California 2 years later and apparently were widely planted as an ornamental, for windbreaks (especially T. aphylla), and by government agencies for stream bank stabilization (Robinson, 1965). Saltcedars invaded many western riverine systems between the 1890s and 1930s. They increased in abundance rapidly from the 1930s through the 1950s, by which time they had occupied most of the available and suitable habitat in its central area of the North American distribution in Arizona, New Mexico and western Texas (Christensen, 1962; Horton, 1977). Spread into more outlying areas (Wyoming, Montana, Oklahoma, Kansas and northern Mexico) occurred later and is still continuing in several areas, apparently at a rapid rate. Robinson (1965) estimated the areas infested at 360,000 ha in 1960, with a projection of 526,000 ha of riparian land infested by 1970. Since then, several river valleys have been measured more precisely (Hildebrandt and Ohmart, 1982; Anderson and Ohmart, 1984; Hink and Ohmart, 1984) but no nationwide estimates have been made. Most of these measurements mapped and summed the area covered in various vegetation community types. These community-structural types contain varying amounts of saltcedar, so that the total amount cannot be easily determined. Probably, more than 800,000 ha are infested today. Remote sensing by satellite imagery or low-level aerial photography has good potential for measuring saltcedar on a watershed scale (Everitt and DeLoach, 1990). However, the foliage of saltcedars so far cannot be distinguished from other vegetation except in late autumn when the saltcedar turns a golden orange colour. The shade of colour varies by date and location, making large-area mapping difficult. Many thousands of hectares have been cleared by government agencies since 1960, but maintaining them requires continuing effort and regrowth is common.

Saltcedars now infest most river bottoms and lakeshores from the central Great Plains (ca. 100°W) to the Pacific and from Montana into northern Mexico, except for Washington State (invasive in the east of the state), western Oregon and the higher mountain areas (Robinson, 1965). Infestations are most dense in the more southern areas from western Texas and western Kansas to the Pacific, especially along the larger rivers. In California desert areas, saltcedars have now become established at remote mountain springs, streams and washes, where no signs of human disturbance are apparent, many kilometres away from the Colorado River, and sometimes long distances from, and at higher elevations above, infested or disturbed areas (Neill, 1985; Barrows, 1998; Lovich and DeGouvernain, 1998).

Risk of Introduction

Top of page The major risk is from the introduction of cuttings by tourists for planting ornamentals, although the interception of cuttings by the port inspectors may be efficient.

Habitat

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Saltcedars, being facultative phreatophytes, grow mainly in riparian habitats: in broad floodplains of rivers, along permanent or intermittent streams, around lakes and reservoirs, and at a depth to water table of 1-5 m. They can also grow (less densely) on upland areas or with their roots out of contact with the water table. They can grow in a wide variety of soils, and in both saline and fresh soils. They do not prefer saline soils but can tolerate salinity, giving them a competitive advantage over most plants which cannot.

Habitat List

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CategoryHabitatPresenceStatus
Littoral
Coastal areas Principal habitat Natural
Coastal areas Principal habitat Productive/non-natural
Terrestrial-managed
Disturbed areas Secondary/tolerated habitat Harmful (pest or invasive)
Managed forests, plantations and orchards Secondary/tolerated habitat Harmful (pest or invasive)
Managed grasslands (grazing systems) Secondary/tolerated habitat Harmful (pest or invasive)
Rail / roadsides Secondary/tolerated habitat Harmful (pest or invasive)
Rail / roadsides Secondary/tolerated habitat Productive/non-natural
Urban / peri-urban areas Present, no further details Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Arid regions Secondary/tolerated habitat Harmful (pest or invasive)
Arid regions Secondary/tolerated habitat Natural
Arid regions Secondary/tolerated habitat Productive/non-natural
Deserts Secondary/tolerated habitat Harmful (pest or invasive)
Deserts Secondary/tolerated habitat Natural
Deserts Secondary/tolerated habitat Productive/non-natural
Natural forests Present, no further details Harmful (pest or invasive)
Natural grasslands Present, no further details Harmful (pest or invasive)
Riverbanks Principal habitat Harmful (pest or invasive)
semi-natural/Scrub / shrublands Secondary/tolerated habitat Harmful (pest or invasive)
Wetlands Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

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The list of plants, both indigenous and introduced, that are displaced by saltcedar invasions would include virtually every plant known in riparian areas of the western USA and northern Mexico. The invasion and domination of native riparian plant communities most often follows the recession of flood waters or wildfires, which kill the native plants, and then allows the saltcedar seedlings to establish without competition.

Biology and Ecology

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Genetics

The chromosome number is 2n=24 for all species of the genus so far investigated (Baum, 1978).

Gaskin and Schaal (2002, 2003) have conducted an extensive DNA comparison of many species of the genus based on field collections by Gaskin throughout most of the Tamarix distribution in the Old World, and compared them with specimens of weedy species from many locations in the western USA. Gaskin found no hybrids in the Old World, although a few records are reported in the literature.

Gaskin and Schaal (2002), using introns selected from both chloroplastic and nuclear DNA, identified a strong concentration of haplotype 2/genotype 2/2 (= T. chinensis) in eastern China; also of haplotype 1/genotype 1/1 in eastern Kazakhstan and Turkmenistan (= T. ramosissima) and with scattered populations in Georgia and Azerbaijan and in Iran and Iraq. Haplotype 7 (not identified to species) was found in eastern Kazakhstan, Turkmenistan and Georgia and Azerbaijan, and genotype 12/12 (also not identified to species) was found in Azerbaijan.

Gaskin and Schaal (2003) identified four invasive genetic entities of Tamarix in the USA: T. aphylla, T. parviflora, and two entities that could not be defined at the species level but represented a T. ramosissima/T. chinensis entity and a T. gallica/T. canariensis entity. They also found evidence for hybridization between T. ramosissima, T. canariensis and T. gallica and T. aphylla which adds to the confusion in identification.

A comparison with US genotypes (Gaskin and Schaal, 2002) revealed that T. ramosissima was the dominant species in Montana, Wyoming, Nevada and southern California, and in a few sites in Oklahoma, Texas and Arizona. T. chinensis was the dominant species in Texas (especially western Texas) and New Mexico, with some sites in several other states. The T. ramosissima x T. chinensis hybrid was the most common genotype in New Mexico and was common in Oklahoma, Nevada, California and Montana. The unidentified 12/12 genotype and hybrids with T. ramosissima or T. chinensis were uncommon but found in nearly all western states. Hybrids with haplotype 7 were found in Idaho.

These species/hybrid complexes usually cannot be distinguished morphologically in the field. Some species or hybrids predominate and may be the only form in some areas but in other areas several species and hybrids may occur at the same site.

Physiology and Phenology

The follow relates to Tamarix spp. invasive in the USA.

Hygroscopic hairs allow the seeds to germinate rapidly (half germinate within 24 hours after wetting). The seeds do not survive the winter in nature. No insects, birds or other animals appear to feed on the tiny seeds.

Young et al. (2004) found that seed of T. ramosissima from the Walker River Delta, Nevada, USA, germinated well over a broad range of temperatures: 0-35°C cold period and 10-35°C warm period; and moderately at 5-35°C cold and 40°C warm. Seeds collected in mid-summer germinated at higher temperatures than those collected in late spring.

Seedlings establish most efficiently on silt bars as flood waters recede. Densities of young seedlings in silt banks may average over 950/m² and may reach a few thousand/m² but most die during the first year (Hopkins and Tomanek, 1957). The small plants allocate resources primarily to the roots, which are able to grow rapidly downward and maintain contact with moisture as the silt bars dry. The roots can reach a depth of 75 cm at 10 weeks and first-year plants, only 10 cm high, may have roots 2 m deep (Smith et al., 1998). In 3 years, lateral roots can extend for 3-6 m and tap roots to 5 m deep (Merkel and Hopkins, 1957). Roots of mature plants sometimes extend 50 m laterally and 30 m deep. The tap roots grow down to the water table but not into the water, then spread laterally above the water table or above impenetrable layers (Gary, 1963).

Saltcedar reaches its maximum transpiration rate in late morning and maximum carbon dioxide assimilation and photosynthesis at 44% of full sunlight. It substantially reduces transpiration by stomatal closure during the hottest part of the day, thus conserving water with little loss in photosynthesis. The 23-28°C optimum for photosynthesis is well below the 40-45°C maximum in mid-afternoon (Anderson, 1982).

Reproductive Biology

Saltcedars produce attractive, nectar-producing flowers that are insect pollinated. Flowering in the USA begins in mid-spring, and reaches a peak in late spring, but continues at a lower rate into the autumn, sometimes with a second smaller peak in August. The flowers produce phenomenal quantities of tiny seeds, estimated at more than 600,000 on some small to medium sized plants and 100,000,000 on some large, healthy plants (Bowser, 1957). The pappus enables the seed to disperse easily for long distances by wind or by floodwaters. The seeds do not survive the winter to the next spring season which limits dispersal.

When branches are buried during floods, they may form adventitious roots and then new plants. Plants are easily propagated by stem cuttings during the spring and early summer, but drying will kill them (Gary and Horton, 1965).

Environmental Requirements

In the Old World, T. ramosissima is adapted to a very wide range of temperatures, from 45°C or more in summer to -20°C or less in winter. T. parviflora and T. canariensis are native in the Mediterranean area with a milder climate. The native range of T. chinensis in eastern China is from 35° to 40°N. In North America, saltcedars have invaded similar climatic zones, from northern Mexico (25°N) to Montana (48°N).

Saltcedars are facultative phreatophytes that thrive with their roots in contact with the water table. They can also grow by utilizing only soil moisture without contact with the water table, and they can withstand conditions of low soil moisture, and therefore they can grow on upland areas after seedlings establish after rains (Smith et al., 1998). However, upland plants usually do not grow in dense thickets as in riparian areas. This characteristic allows them to survive in areas of great watertable fluctuations such as along reservoir shores or during severe droughts.

Plants can survive up to 70 days of complete submergence and up to 98 days if part of the canopy is exposed (Warren and Turner, 1975); however, seedlings can be killed by 30 days submergence (Horton et al., 1960; Gladwin and Roelle, 1998).

Saltcedars also are facultative halophytes. They do not require saline habitats but are able to use saline ground water by excreting the excess salts through leaf glands. Saltcedars can grow well at salinities up to 10,000 p.p.m. and can survive and grow at a reduced rate up to 36,000 p.p.m. (Jackson et al., 1990). By comparison, willows (Salix spp.) and poplars/cottonwoods (Populus spp.) grow poorly or die at salinities above 1500-2000 p.p.m. Waisel (1972) studied the biology of halophytes (including Tamarix) in Israel, and Bean and Russo (1988) comment that T. ramosissima has a higher tolerance of salinity that T. chinensis and is found under more saline conditions than the latter.

Saltcedars probably grow best in silty alluvial soils but they can grow on a wide range of soil textures from clay to sand, and at relatively high pH levels, and at elevations from sea level up to 2500 m.

Saltcedars are fire adapted and resprout readily from the basal stem buds after the above-ground plant has burned (Busch and Smith, 1992). Regrowth can reach 3 m high the first year after burning. They are resistant to livestock and wildlife herbivory for other reasons as well, because the high tannin content makes the foliage unpalatable, although young seedlings may be heavily browsed.

Climate

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ClimateStatusDescriptionRemark
A - Tropical/Megathermal climate Tolerated Average temp. of coolest month > 18°C, > 1500mm precipitation annually
As - Tropical savanna climate with dry summer Tolerated < 60mm precipitation driest month (in summer) and < (100 - [total annual precipitation{mm}/25])
Aw - Tropical wet and dry savanna climate Tolerated < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
B - Dry (arid and semi-arid) Preferred < 860mm precipitation annually
BS - Steppe climate Preferred > 430mm and < 860mm annual precipitation
BW - Desert climate Preferred < 430mm annual precipitation
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)

Air Temperature

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Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) -20
Mean maximum temperature of hottest month (ºC) 50

Rainfall

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ParameterLower limitUpper limitDescription
Mean annual rainfall751000mm; lower/upper limits

Rainfall Regime

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Soil Tolerances

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Soil drainage

  • free
  • impeded
  • seasonally waterlogged

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • infertile
  • saline
  • shallow
  • sodic

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Agdistis tamaricis Herbivore Leaves
Amblypalpis olivierella Herbivore Stems
Chionaspis etrusca Herbivore Leaves
Colposcenia aliena Herbivore Leaves
Coniatus steveni Herbivore Leaves
Coniatus tamarisci Herbivore Leaves
Corimalia tamarisci Herbivore Fruits/pods
Cryptocephalus sinaita Herbivore Leaves
Diorhabda elongata Herbivore Leaves
Eustigmatia tamaricina Herbivore Leaves
Liocleonus clathratus Herbivore Roots
Opsius stactogalus Herbivore Leaves
Ornativalva heluanensis Herbivore Leaves
Parapodia sinaica Herbivore Stems
Psectrosema album Herbivore Stems
Psectrosema noxium Herbivore Stems
Trabutina mannipara Herbivore Leaves/Stems
Trabutina serpentina Herbivore Leaves/Stems

Notes on Natural Enemies

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Most of the following comments and the list of natural enemies relate to T. ramosissima. Several surveys have identified insect species collected from saltcedars in the USA: a few species by Hefly (1937) in Oklahoma, 56 species by Hopkins and Carruth (1954) in Arizona, and 159 species by Liesner (1971) and Watts et al. (1977) in New Mexico. Glinski and Ohmart (1984) found high populations of the native Apache cicada (Diceroprocta apache) in stands of saltcedar in southeastern Arizona; the nymphs are general feeders on the roots of several riparian plants. Stevens (1985) listed 145 species, including those listed by the previous workers. He found that the number of individual insects was slightly greater on willow (Salix spp.), and the number of insect species was much greater on willow, but that insect biomass was greater on saltcedar. Except for Apache cicada, none of the native North American insect species caused more than sporadic and slight damage to saltcedar.

However, five natural enemies from the Old World have been accidentally introduced on saltcedar in the USA. These are a small leafhopper (Opsius stactogalus), two scale insects (Chionapsis etrusca and C. gilli) and two eriophyiid mites. The leaf hopper is often very abundant and C. etrusca is sporadically abundant, and both may cause substantial damage (Liesner, 1971; Sun, 1999; McConnell et al., 2004).

In a 3-year comparison of insect populations on saltcedar compared with native willows (Salix spp.), poplar/cottonwood (Populus spp.) and seepwillow baccharis (Baccharis salicifolia) in northwestern and southwestern Texas and southern New Mexico, USA, both species diversity and populations of native herbivorous insects (immature specimens and adults) were significantly greater on the native plants than on saltcedar. Only the exotic leafhopper (Opsius stactogalus) was more abundant on saltcedar. Although many nectar and pollen feeding insects were abundant on saltcedar flowers, all of these developed as immatures on nearby native plants. Saltcedar, therefore, is a much poorer food resource for insectivorous birds and other small animals than are native plants (A Knutson, Texas Cooperative Extension, Dallas and David Thompson, New Mexico State University, Las Cruces, USA, unpublished data, 2004).

From the Old World, Kovalev (1995) listed 25 insect genera that have co-evolved with and are completely or mostly specific to the genus Tamarix. Their host plants sometimes included the genus Myricaria or rarely Reaumuria, both in the family Tamaricaceae (that do not occur in North America), but never the genus Frankenia in the family Frankeniaceae. Most of these insects could be candidates for biological control. In faunistic studies, 59 species of insects that attack Tamarix spp. were listed in Kazakhstan (Mityaev, 1958), 52 in Georgia (Lozovoi, 1961), 105 in central Asia (Sinadskii, 1968), and 92 in Italy (Zocchi, 1971). Kovalev (1995) reviewed these and other records and listed 325 species from the former USSR that fed only on plants in the family Tamaricaceae, 75% of which were specific on Tamarix and most of which attack T. ramosissima but probably not T. aphylla. Other surveys specifically identified potential biocontrol agents for introduction into the USA; with 220 species listed from Israel, Turkey, Iran, and western India (Gerling and Kugler, 1973), 26 from Turkey (Pemberton and Hoover, 1980) and 190 from Pakistan (Habib and Hassan, 1982).

USDA-ARS researchers at Temple, Texas, and Albany, California, USA, together with others from France, Israel, Turkmenistan, Kazakhstan and China have tested, or are continuing to test, 15 species of insect for introduction as biological control agents of saltcedar (DeLoach et al., 1996).

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)

Saltcedars disperse naturally and very efficiently by means of the huge quantity of small windblown or waterborne seeds. They also can disperse to a limited extent by the rooting of plant parts that wash downstream in floods.

Vector Transmission (Biotic)

The seeds are not dispersed by birds or other animals, either through the alimentary canal or attached to fur or feathers.

Agricultural Practices

Saltcedars seldom grow in agricultural fields where they might otherwise be dispersed with baled hay, seeds crops, etc., and the seeds would probably be blown out by harvesting machinery but these seeds probably only rarely or never establish.

Intentional Introduction

After dispersal by wind and water, the next greatest means of dispersal is probably the sale of ornamental plants by nurserymen, and the secondary spread of windblown seeds or cuttings from these plants. Dispersal from plantings for streambank erosion control or for windbreaks has also occurred.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Disturbance Yes
Habitat restoration and improvementMain reason for introduction Yes Yes
Hedges and windbreaksAnd along roads Yes Gaskin and Schaal, 2003
Landscape improvement Yes Yes Gaskin and Schaal, 2003
Nursery tradeStill on sale Yes
Ornamental purposesIntroduction and local spread Yes
ResearchFor species trial Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsSmuggled flowers, cuttings Yes
Containers and packaging - woodCuttings, whole plants Yes
Floating vegetation and debris Yes
Water Yes
Wind Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark
Fruits (inc. pods) seeds
Leaves whole plants
Roots whole plants
Stems (above ground)/Shoots/Trunks/Branches
True seeds (inc. grain) seeds
Plant parts not known to carry the pest in trade/transport
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx
Growing medium accompanying plants
Seedlings/Micropropagated plants
Wood

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Negative
Crop production Negative
Cultural/amenity Negative
Economic/livelihood Negative
Environment (generally) Positive and negative
Fisheries / aquaculture Negative
Forestry production Negative
Human health Negative
Livestock production Negative
Native fauna Negative
Native flora Negative
Rare/protected species Negative
Tourism None
Trade/international relations None
Transport/travel Negative

Impact

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The greatest economic losses caused by saltcedars relate to the large losses of streamflow and ground water, especially in arid areas of the western USA and in northern Mexico. This entire area is experiencing severe water shortages for agricultural irrigation and for municipal use. The major cities of southern California and Arizona are all experiencing water rationing, the Texas/New Mexico water compact is in default, and the water treaty between the USA and Mexico is in default. Many farmers in these and other states have been forced to discontinue irrigating large parts of their land at great loss of income and the threat of economic ruin. The US Bureau of Reclamation in Albuquerque, New Mexico estimates that one-third of the total amount of water allowed to be taken from the Rio Grande is used by saltcedar (S Hansen, US Bureau of Reclamation, Albuquerque, New Mexico, USA, personal communication, 2002). Zavaleta (2000) estimated water losses from saltcedar at US $133 to 285 million annually, and this does not include losses in Mexico. Saltcedar also reduces water quality by increasing the salinity of stream flow and ground water.

The increased frequency of wildfires caused by saltcedar damages fences and sometimes farm buildings, other buildings and kills livestock. These damages are probably relatively small and economic analyses are not known.

Saltcedars cause economic losses by reducing the utilization of parks and natural areas by hunters, fishers, campers, bird watchers, wildlife photographers and others (USDI Fish and Wildlife Service, 1988). In an attempt at determining the proportion of losses caused by saltcedar, DeLoach (1989) estimated losses to these non-consumptive, recreational-type uses in Arizona, USA, at US$29.5 million and in New Mexico at probably US$15.8 million annually, and twice that if the value of the time of the participants were included.

Economic Impact

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The greatest economic losses caused by saltcedars relate to the large losses of streamflow and ground water, especially in arid areas of the western USA and in northern Mexico. This entire area is experiencing severe water shortages for agricultural irrigation and for municipal use. The major cities of southern California and Arizona are all experiencing water rationing, the Texas/New Mexico water compact is in default, as is the water treaty between the USA and Mexico. Many farmers in these and other states have been forced to discontinue irrigating large parts of their land at great loss of income and the threat of economic ruin. The US Bureau of Reclamation in Albuquerque, New Mexico estimates that one-third of the total amount of water allowed to be taken from the Rio Grande is used by saltcedar (S Hansen, US Bureau of Reclamation, Albuquerque, New Mexico, USA, personal communication, 2002). Zavaleta (2000) estimated water losses from saltcedar at US$133 to 285 million annually, and this does not include losses in Mexico. Saltcedar also reduces water quality by increasing the salinity of stream flow and ground water.

The increased frequency of wildfires caused by saltcedar damages fences and sometimes farm buildings, other buildings and kills livestock. Such damage, however, is probably relatively small and economic analyses are not known.

Saltcedars also cause economic losses by reducing the utilization of parks and natural areas by hunters, fishermen, campers, bird watchers, wildlife photographers and others (USDI Fish and Wildlife Service, 1988). In an attempt at determining the proportion of losses caused by saltcedar, DeLoach (1989) estimated losses to these non-consumptive, recreational-type uses in Arizona, USA, at US$29.5 million and in New Mexico at probably US$15.8 million annually, and twice that if the value of the time of the participants were included.

Environmental Impact

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Dense thickets of saltcedar along streams cause increased sedimentation, bank aggradation, narrowing and deepening of channels, filling in of backwaters, modification or elimination of riffle structure, overgrowth of sand and gravel bars, and changes in turbidity and temperature of the water. Channels are sometimes completely blocked with debris and overbank flooding is more severe (Busby and Schuster, 1971; Burkham, 1972, 1976; Graf, 1978). Saltcedars are probably the greatest users of scarce groundwater in the infested desert ecosystems (reviewed by DeLoach et al., 2000). Estimates of groundwater use from a number of experiments averaged 1676 mm per year along the lower Colorado River near Blyth, California, USA (the hottest area, lowest elevation and longest growing season in the southwestern USA) to 940 mm per year along the middle Rio Grande, New Mexico at a higher elevation and shorter growing season.

Saltcedars increase the natural salinity level by using saline ground water and excreting the excess salts through leaf glands. The salt then drips to the soil surface or falls with the foliage in the autumn, forming a layer of saline litter and soil under the trees in which only saltcedar can survive.

The dry foliage and twigs that accumulate under the deciduous saltcedars are highly flammable. Saltcedar thickets burn more intensely and more frequently than native riparian plant communities in North America (which only rarely burn) (Agee, 1988). This situation, like that of soil salinity, is further worsened by the additional interaction with altered hydrologic cycles below dams, preventing the natural spring floods from washing out the accumulated litter (DeLoach et al., 2000).

Impact: Biodiversity

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In North America, the greatest direct negative environmental impact of the saltcedar invasion is the displacement of native riparian plant communities by dense thickets of saltcedar, that now cover an estimated 800,000 ha of prime bottomlands along major rivers, small streams and lakeshores. Along many major rivers, saltcedar thickets occupy 50-60% of all the vegetative area (summarized by DeLoach, 1991) and 93% on the Pecos River of Texas and New Mexico (Hildebrant and Ohmart, 1982).

The most seriously affected plants are the obligate phreatophytic trees and shrubs, especially poplars/cottonwoods (Populus spp.), willows (Salix spp.), screwbean mesquite (Prosopis pubescens), seepwillow baccharis (Baccharis salicifolia) and a few others. The large (to 20 m tall) stands of poplar/cottonwood trees which formally comprised the dominant upper canopy in most areas, are now reduced to small, scattered trees except for one remaining stand of ca. 115 ha at the confluence of the Bill Williams river of Arizona and the Colorado River. Willows, screwbean mesquite and seepwillow baccharis also have been displaced by saltcedars but to a somewhat lesser extent because they are less sensitive to some of the environmental changes than are poplars/cottonwoods. Some other important plants have been harmed to a lesser extent than the obligate phreatophytes, such as honey mesquite and velvet mesquite (Prosopis glandulosa and P. velutina) and quailbush (Atriplex lentiformis) which can also occupy higher terraces (Wiesenborn, 1995).

One effect of the saltcedar invasion has been to cause some rare plant species to become more rare and some to become endangered. For example, the threatened Pecos sunflower (Helianthus paradoxus) was believed to be extirpated from areas of the Pecos River until saltcedar was cleared, and then it reappeared as a common plant.

The major effect of the saltcedar invasion on native plant communities has been the drastic degradation of wildlife habitat (Kerpez and Smith, 1987, and reviewed by DeLoach et al., 2000). The population of all birds found in saltcedar on the lower Colorado, USA, was only 39% of the levels in native vegetation during the winter and 68% during the rest of the year; and the number of bird species found in saltcedar was less than half that in native vegetation during the winter (Anderson and Ohmart, 1977, 1984). Saltcedar was the most important negatively correlated variable identified with bird populations (Anderson and Ohmart, 1984). Frugivores, granivores and cavity dwellers (woodpeckers, bluebirds and others) are absent, and insectivores are reduced in saltcedar stands (Cohan et al., 1979). At Camp Cady in southern California, the bird population was only 49% as great in saltcedar as in cottonwood/willow/mesquite (Schroeder, 1993). Bird preference for saltcedar was much lower than for native vegetation along the middle Rio Grande, Texas (Engle-Wilson and Ohmart, 1978) and somewhat lower on the middle Pecos River (Hildebrandt and Ohmart, 1982). Recent surveys at release sites in northwestern Texas showed that both the number of birds and the number of bird species per point count were twice as great in 2003 (a dry year) in native vegetation compared to near pure saltcedar stands. In 2004 (a wet year), populations were 37% greater in the native vegetation (T Robbins and K Johnson, USDA-ARS, Temple, Texas, USA, unpublished data, 2002-2004).

Populations of game animals, furbearers and small rodents are lower in saltcedar than in other vegetation types on the Rio Grande of western Texas (Engle-Wilson and Ohmart, 1978) and on the Pecos of New Mexico (Hildebrant and Ohmart, 1982). In Big Bend National Park, Ord's kangaroo rat and beavers have been nearly eliminated because of the saltcedar invasion (Boeer and Schmidly, 1977).

Along the Gila River near Florence, Arizona, Jakle and Gatz (1985) trapped three- to five-times as many lizards, snakes and frogs in native vegetation types as in saltcedar.

DeLoach and Tracy (1997) and Anon. (1995) reviewed 51 listed or proposed threatened and endangered species that occupy western riparian areas infested by saltcedar. These included two mammals, six birds, two reptiles, two amphibians, one arthropod and four plants. Some 34 species of threatened and endangered fish are found in saltcedar infested areas. Their habitat is seriously degraded by reduced water levels, modified channel morphology, silted backwaters, altered water temperature, and probably by reduced and modified food resources. Several of these threatened and endangered species may utilize saltcedar to some extent, but not to a degree that would make it appear important to them or as valuable as the native vegetation it has replaced (Anon., 1995).

A very unusual wildlife situation involves the interaction between the proposed biological control programme and the southwestern willow flycatcher (Empidonax trailii extimus) that was listed as endangered in 1995 and that had begun nesting in saltcedar in Arizona (though little or none in neighbouring states) (DeLoach et al., 2000). Extensive population surveys during several years throughout its breeding range revealed that most of the known mortality factors of the flycatcher could be made worse by its association with saltcedar. Yet, in spite of these losses, the birds almost entirely selected saltcedar trees for nesting even in sites where abundant healthy native willows were present. Apparently, the birds had developed a very high preference for the almost ideal branching structure of saltcedar for nest placement.

Risk and Impact Factors

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Impact mechanisms

  • Competition - monopolizing resources
  • Competition - shading
  • Interaction with other invasive species
  • Rapid growth
  • Rooting

Impact outcomes

  • Altered trophic level
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Increases vulnerability to invasions
  • Infrastructure damage
  • Modification of fire regime
  • Modification of hydrology
  • Modification of nutrient regime
  • Modification of successional patterns
  • Monoculture formation
  • Negatively impacts agriculture
  • Negatively impacts cultural/traditional practices
  • Negatively impacts forestry
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
  • Soil accretion
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species

Invasiveness

  • Fast growing
  • Has a broad native range
  • Has high genetic variability
  • Has high reproductive potential
  • Highly adaptable to different environments
  • Highly mobile locally
  • Long lived
  • Pioneering in disturbed areas
  • Proved invasive outside its native range
  • Reproduces asexually
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc

Likelihood of entry/control

  • Difficult to identify/detect in the field
  • Difficult/costly to control
  • Highly likely to be transported internationally deliberately

Uses

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From the time of its introduction in the mid-1800s and probably through the 1920s, T. ramosissima and other saltcedars were widely planted throughout the western USA to control streambank erosion, a major problem in rangelands and natural areas there. In these areas, serious deepening of permanent and intermittent streams has occurred because of overgrazing, droughts and the reduction of vegetative cover. These streams have been deepened by 3-5 m or even more, with the water table being lowered by an equal amount which then leaves the roots of most vegetation unable to reach water. Saltcedars have stopped erosion in many areas but have also narrowed and blocked stream channels and also replaced native willows and other plants that could also protect against erosion (DeLoach, 1991).

Saltcedars are used as occasional ornamental shrubs or small trees, especially in the southwestern states of the USA, because of their attractive flowers and foliage, and tolerance of drought, heat and salinity. Surveys in 77 towns and cities (5556 houses) in Texas, and 36 towns and cities (1851 houses) in Arizona, revealed, however, that only 0.35% of all yard trees are saltcedars. About an equal percentage of trees were of athel (T. aphylla), which is a large (to 20 m high) but low-quality shade tree. However, athel grows only south of 34°N in Arizona, New Mexico and western Texas and south of 31°N in central Texas. (All trees were converted to large-tree equivalents for valuation; CJ DeLoach et al., USDA-ARS, Temple, Texas, USA, unpublished survey, 1987).

In the southwestern USA, saltcedars have only a few relatively minor beneficial uses. From central Texas to southern California they are used to a minor extent for honey production and somewhat more for pollen and colony maintenance by honeybees. The honey is off-colour and off-flavour and is not of table grade but is used in the baking industry. The honey industry in the four states with the greatest extent of saltcedar (New Mexico, Arizona, Utah and Colorado) together amounts to only 4.5% of the total US production (Waller and Schmalzel, 1976). (Texas was not included because data were not available to separate west Texas with the greatest saltcedar infestation from central and eastern Texas with the greatest honey production). In Arizona, one survey of beekeepers ranked saltcedar 7th for honey production and 4th for colony maintenance (GD Waller, Arizona, USA, unpublished report, 1989). However, saltcedar displaces some of the more valuable honey plants such as mesquite (Prosopis spp., the top honey plant), and seepwillow baccharis (Baccharis salicifolia) which helps fill an important gap in nectar and pollen source for colony maintenance in late summer and autumn.

Saltcedars have been used effectively as windbreaks along railroads and other areas since their introduction (Brooks and Dellberg, 1969), however, most of this in the more southern areas is of athel (T. aphylla), because of it being evergreen and a larger tree (Lyles et al., 1984).

On Native American tribal lands, especially in the southwestern USA, saltcedar is used occasionally for firewood, fence posts, small cages, etc. However, it has displaced willows that formerly were used for the same purposes. Nearly all Native Americans discount these values and desire saltcedar control.

Uses List

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Environmental

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

Fuels

  • Charcoal
  • Fuelwood

Human food and beverage

  • Honey/honey flora

Materials

  • Wood/timber

Medicinal, pharmaceutical

  • Source of medicine/pharmaceutical

Ornamental

  • Potted plant

Detection and Inspection

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T. ramosissima is a declared invasive species in many states of the USA, and it is also a declared noxious weed in South Africa, category 1 in Northern, Eastern and Western Cape, category 3 in other parts of South Africa. The major risk is from the further introduction of cuttings by tourists for planting as an ornamental, although the interception of cuttings by port inspectors may be efficient. Tamarix spp. also continue to be introduced and/or planted for erosion control and revegetation in other parts of the world, especially on saline and arid sites, but the potential exists for invasion of neighbouring riparian habitats.

Similarities to Other Species/Conditions

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Tamarix spp. are difficult to differentiate in the field, and also often in the laboratory. Within their native distribution in the Old World, many species of Tamarix can be distinguished by gross morphological characters of the flowers, stems and leaf bracts, or by foliage coloration, time of blooming or shape and size of the plant. However, a group of several species, including T. ramosissima, are quite similar and can be distinguished only by taxonomic specialists, and especially by the structure of the androecium, visible only with a hand lens or dissecting microscope.

The North American introduced species are virtually impossible to identify with certainty in the field, both because of their basic similarity and especially because of the great amount of hybridization between species. Only T. parviflora and T. aphylla can be readily identified and even they produce some hybrids of intermediate form. T. aphylla is a large evergreen tree, to 20 m tall and 1 m trunk diameter, with long, sparsely branched terminal twigs with closely adpressed, vaginate leaves, superficially appearing like long pine needles or Casuarina leaves, with white flowers arranged in a spiral on the raceme, and is cold intolerant. T. parviflora is easily distinguished by having only four stamens and four petals (the other North American introductions have five), in short, densely flowered racemes arranged densely along the stems; the flowers appear before the leaves in the spring. Baum (1968) provides a key which separates T. ramosissima from T. canariensis and T. gallica by the insertion of the filaments between the lobes of the nectary disc (hololophic), while in the other two species they are inserted on the lobes themselves (synlophic). T. chinensis also has filaments alternating with the disc lobes but differs from T. ramisossima in having 'smaller, entire sepals, ovate petals and shorter bracts'. Bean and Russo (1988) emphasise the differences in petal shape - obovate (wider distally) in T. ramosissima and oblong-ovate (narrowed distally) in T. chinensis. Gaskin and Schaal (2003) also refer to differences in raceme width (3-4 mm in T. ramosissima and 5-7 mm in T. chinensis) and in the insertion of the filaments (below the sinuses of the disc in T. ramosissima and in the sinuses of the disc in T. chinensis). This paper incidentally includes excellent drawings of the leaves and nectary discs of several of the species/species complexes. Unfortunately, while these differences may be seen under the microscope, they are not readily observable in the field.

Prevention and Control

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Control

Cultural control

Saltcedars rapidly invade disturbed areas, especially after floods or fires, and maintaining vigorous stands of native riparian plants would probably impede establishment of saltcedar seedlings. Along controlled rivers, the most effective method would be to programme periodic floods every 5-10 years (equivalent to the timing of El Niño years under which the native plants evolved) by releasing water from reservoirs that would wash out saltcedars, leach out salts, and allow revegetation by native plants. If floods occur during the period of poplar/cottonwood (Populus spp.) or willow (Salix spp.) seeding (which precedes saltcedar seeding), then natural revegetation will consist of almost pure stands of those, with very little saltcedar. Young seedlings can be controlled by flooding for 1 month.

Mechanical control

Neither mowing nor burning effectively control Tamarix because the plants soon resprout from basel stem buds and regrow very rapidly, sometimes to 3 m during the first year after control. Root ploughing, discing or bulldozing kill more plants but remaining severed roots and severed stem pieces are able to resprout. All these methods are expensive and also kill much of the native vegetation, whose preservation is often the reason for control. Hand removal by pulling seedlings effectively kills the plants and causes little damage to native plants but is highly labour intensive and too expensive except in small patches or with volunteer labour.

Chemical control

Sisneros (1991) reviewed the chemical herbicides used for Tamarix control, and a few herbicides provide a high degree of whole-plant kill and are sufficiently inexpensive for practical use. In the USA along the Pecos River in New Mexico and Texas, Duncan and McDaniel (1998) and Hart (2003a,b), respectively, have developed an extensive herbicidal control programme that uses aerial applications of imazapyr or imazapyr plus glyphosate. These treatments produce 29-75% mortality of plants larger than 1.5 m tall and 50-100% mortality of smaller plants. The project also includes revegetation experiments using willows, poplar/cottonwoods and other shrubs and herbs. It is the least expensive of all non-biological control methods but the confinement of the area treated is insufficient for use along winding streams or lakeshores where drift of herbicides into the water is prohibited. Application by helicopters can be controlled more exactly; however, it still cannot kill all streamside saltcedar plants without drift into the water and application costs are much greater than with fixed-wing aircraft. Both methods will kill much native vegetation in areas of mixed saltcedar-native plant stands.

Imazapyr is very toxic to poplar/cottonwoods and willows (the premier native plants for wildlife habitat) and is labelled for their control. It also kills other native plants although some groups of plants such as legumes are little damaged. During the last 5 years, thousands of hectares of nearly monotypic saltcedar along the saline Pecos River of New Mexico and Texas have been treated with helicopter-applied herbicides, at a cost of several million dollars, for the purpose of salvaging water for agricultural irrigation and municipal use (Hart (2003a,b), however, by 2004, no increase in available stream flow was measured, partly due to the on-going drought.

Chopping, raking and burning the dead trees and ploughing the soil adds greatly to the cost of control. Such treatments are necessary for some methods of revegetation, or for cosmetic appearance, but may not be needed if the objective is the recovery of wildlife habitat or increased stream flow.

Hand-spraying of chemical herbicides with a back-pack sprayer on the basal stems of saltcedar also provides good control. The combination of hand-cutting with chainsaws or hand clippers, followed immediately by painting triclopyr on the cut stump, also provides good control. Both of these methods cause much less damage to non-target plants (the latter essentially no damage) but both are highly labour-intensive and costly.

None of these methods kill 100% of the saltcedar plants, allowing some amount of resprouting and then the rapid production of more seeds from the regrowth. These methods also leave the treated area vulnerable to re-invasion by windblown or waterborne seeds from remaining plants outside the treated area. Therefore, repeated application of control measures every few years are necessary to maintain control.

Biological control

A biological control programme, primarily on T. ramosissima, was begun in the western USA by the USDA-ARS at Temple, Texas in 1986 (joined by ARS, Albany, California in 1998) and progressed to the stage of releasing control insects into the open environment in May 2001. The first agent released was a leaf beetle, Diorhabda elongata deserticola from western China and eastern Kazakhstan (DeLoach et al., 2003), at ten sites in the six western states of Texas, Colorado, Wyoming, Utah, Nevada and California. It established quickly at five sites in the more northern areas (all north of the 38°Nl), at Lovelock and Schurz (Nevada), Delta (Utah), Pueblo (Colorado) and Lovell (Wyoming), but did not establish at any of the three more southerly sites in California and Texas. At the five successful sites, by the end of the third growing season after release (late August 2003), the beetles had defoliated 95-98% of the foliage over continuous areas of Tamarix covering 194 ha at Lovelock, Nevada; 12 ha at Schurz, Nevada; 40 ha at Delta, Utah and Pueblo, Colorado; and 6 ha at Lovell, Wyoming (DeLoach et al., 2004). During 2004, the area defoliated at these sites increased by three- to five-fold over that in 2003. The Lovelock site was unique in having very little other vegetation and essentially no predators present; the beetles at the other sites sustained some losses from ants, birds, lady beetles (ladybirds), spiders, predaceous bugs and other predators. The degree and rapidity of control at Lovelock would indicate that releases of beetles at the intersections of a 1-km grid would control all the saltcedar in whatever area applied within 3 years. Sites with predators would require somewhat longer. The degree of whole-plant kill is not yet known; however, in large field cages, severe defoliation by the beetles for 2 years completely killed quite large plants.

Establishment of these beetles south of the 37°N was unsuccessful because the short summer day length stimulated the beetles to enter diapause in early summer and they never successfully overwintered (Lewis et al., 2003). Laboratory experiments showed that the beetles require 14 h 45 min of daylight to avoid diapause and the maximum reached in the southern release sites is only 14 h 20 min (DW Bean, University of California, Davis, USA, unpublished data, 2003). Additional biotypes (or possibly different subspecies or even species) of D. elongata have now been obtained from Turpan, China, from lower latitudes in Crete and at Posidi (near Thessaloniki), Greece, from Sfax, Tunisia, and from Karshi, Uzbekistan and tested at Temple and Albany. Some results are promising, but no firm conclusions can yet be drawn.

Integrated control

The integration of conventional control methods such as fire followed by herbicides, or fire and/or herbicides followed by root-ploughing and raking provide increased control (Hart, 2003b). However, these methods greatly increase the costs and still do not eliminate the need for repeated application to control regrowth or re-invasion unless dense stands of native plants can be re-established that can exclude or suppress the saltcedar. All these efforts are then erased with the next flood or wildfire that kills the native vegetation and allows the re-establishment of saltcedars. Integration of any of the other controls with cultural controls, such as increasing herbaceous ground cover, would appear to improve both control and riparian ecosystem health, but as yet has not been developed.

Integration of biological and chemical/mechanical controls would appear to have some advantages, with the herbicides producing rapid control to increase stream flow and with biological control to maintain control thereafter. A large-scale experiment is underway on the upper Colorado River and its tributaries of northwestern Texas, USA, to integrate biological and chemical control methods (McGinty and Thornton, 2003; DeLoach and Knutson, USDA-ARS, Temple, USA, unpublished data). However, the herbicidal component greatly increases the cost, damages non-target vegetation, and so far has not demonstrated increased stream flow. Biological control alone so far has been shown to be rather rapid (3-4 years after releases of the beetles), and to provide a high level of defoliation and possibly of whole-plant kill, and with the expectation of very low costs from the present time and into the future, of permanent and self-sustaining control, and with no harm to non-target plants (DeLoach et al., 2004). The more expensive conventional controls or integrated controls may be unnecessary and even may be harmful to the environment.

References

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30/11/2007 Updated by:

Nick Pasiecznik, Consultant, France

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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Please click OK to ACCEPT or Cancel to REJECT