Plant Assessment Form

Tamarix aphylla

Synonyms: T. articulata Vahl., T. orientalis Forssk., Thuja aphylla L.

Common Names: athel; athel pine; tamarisk; evergreen saltcedar

Evaluated on: 8/12/04

List committee review date: 11/03/2005

Re-evaluation date:


T. Dudley, Assoc. Research Prof.
Univ. of Nevada
Dept. of Natural Resource & Environmental Science, MS 186; 1000 Valley Rd.; University of Nevada Reno, NV, 89512-0013

List committee members

Joe DiTomaso
John Randall
Carla Bossard

General Comments

There is a basic problem with assessing individual species within the Tamarix complex - there exist many species and hybrid forms of these that are invasive across the west, and in fact hybrids are more common than any true species. Thus, this assessment may miss an important aspect of the situation in the field, esp. if hybrids consititue greater threats than the indentified species. In addition, the impacts of T. aphylla are minor in California and Arizona so far, so responses rely in large part on a real problem situation with this species in other continents so impacts would be listed as more severe than we are likely to experience here (but potential may exist).

Table 2. Criteria, Section, and Overall Scores

Overall Score? Limited
Alert Status? No Alert
Documentation? 3.5 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes C. Minor Other Published Material
Four-part score CCBD Total Score
1.2 ?Impact on plant community C. Minor Reviewed Scientific Publication
1.3 ?Impact on higher trophic levels B. Moderate Reviewed Scientific Publication
1.4 ?Impact on genetic integrity D. None Reviewed Scientific Publication
2.1 ?Role of anthropogenic and natural disturbance in establishment B. Moderate Reviewed Scientific Publication
Total Points
11 Total Score B
2.2 ?Local rate of spread with no management C. Stable Reviewed Scientific Publication
2.3 ?Recent trend in total area infested within state D. Declining Observational
2.4 ?Innate reproductive potential
(see Worksheet A)
B. Moderate Reviewed Scientific Publication
2.5 ?Potential for human-caused dispersal B. Moderate Other Published Material
2.6 ? Potential for natural long-distance dispersal B. Occasional Other Published Material
2.7 ?Other regions invaded B. Invades 1 or 2 ecological types Reviewed Scientific Publication
3.1 ?Ecological amplitude/Range
(see Worksheet C)
A. Widespread Reviewed Scientific Publication
Total Score B
3.2 ?Distribution/Peak frequency
(see Worksheet C)
D. Very low Other Published Material

Table 3. Documentation

Scores are explained in the "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands".

Section 1: Impact
Question 1.1 Impact on abiotic ecosystem processes? C Other Published Material
Identify ecosystem processes impacted:

groundwater/soil water availability, soil chemistry, hydrological resistance (flow regimes and flooding). Populations do not grow dense in western US and have only been found to escape in a couple of area so it is unlikely that abiotic processes are affected to the extent of other Tamarix species. takes up salts through roots and salinates surface soils by both salty litterfall and salt drip, probably depletes water table based on congeners, interferes with waterflow and therefore can exacerbate over-bank flooding; unlike other saltcedar species; light transmission is very low through athel canopy; T. aphylla is not known to increase fire risks and presumably is substantially less flammable than the deciduous species

Sources of information:

Griffin, G. F., D. M. Stafford Smith, S. R. Morton, G. E. Allan, K. A. Masters, and N. Preece. 1989. Status and implications of the invasions of tamarisk (Tamaris aphylla) on the Finke River, Northern Territory, Australia. Journal of Environmental Management. 29:297-315
Berry, W. L. 1970. Characteristics of salts secreted by Tamarix aphylla. American Journal of Botany. 57:1226-1230 (salt uptake)
Waisel, Y. 1960. Ecological studies on Tamarix aphylla (L.) Karst. Distribution and reproduction. Phyton 15:7-17.
Waisel, Y. 1960. Ecological studies on Tamarix aphylla (L.) Karst. The water economy. Phyton 15: 19-29.
Litwak, M. 1957. The influence of T. aphylla on soil composition in the northern Negev of Israel. Bulletin of Resources Council of Israel 6D:38-45
Hagemeyer, J. and Y. Waisel 1988. Excretion of ions (Cd2+, Li+, Na+, and Cl-) by Tamarix aphylla. Physiologia Plantarum. 73:541-546.

Question 1.2 Impact on plant community composition,
structure, and interactions?
C Reviewed Scientific Publication
Identify type of impact or alteration:

reduction in native plant diversity and inhibition of native trees, promotion of non-native plants where it is common, but not found in high densities anywhere in western US. lower species diversity and greater proportion of non-native plants are found in association with T. aphylla in Australia, although it is not clear whether it displaces natives or just occupies sites that have been opened by natural disturbance and possibly made saltier by salt inputs from nearby sites; in U.S. it may be associated with higher diversity than adjoining habitats because seeding of all plants may be higher in more favorable sites

Sources of information:

Griffin, G., D. Smith, S. Morton, G. Allan and K. Masters. 1989. Status and implications of the invasion of tamarisk (T. aphylla) on the Finke River, Northern Territory, Australia. Journal of Environmental Management 29:297-315.
Barnes, P.L., L.R. Walker and E.A. Power. Tamarix aphylla: A newly invasive tree in southern Nevada. Wetlands (in review).

Question 1.3 Impact on higher trophic levels? B Reviewed Scientific Publication
Identify type of impact or alteration:

reduction in native wildlife abundance, and reduced harbivore abundance in Australia there are fewer birds associated with T. aphylla vs. native riparian eucalypt forest, presumably related to lower insect numbers; does contain high phenol levels which can inhibit herbivores, and also salts and other chemicals (e.g. cadmium) that are taken up through roots can further reduce suitability for herbivores; repitles are also reduced in numbers, as litter is denser under tamarix which reduces invertebrate numbers and habitat diversity

Sources of information:

Griffin et al. 1989, Hagemeyer and Waisel 1988

Question 1.4 Impact on genetic integrity? D Reviewed Scientific Publication

none, but does hybridize with other Tamarix hybrids between T. aphylla and T. ramosissima are present on lower Colorado River systems (esp. Lake Mead), and these are less suitable for herbivores (including biocontrol agents) than normal T. ramosissima type so may cause control problems in future

Sources of information:

Barnes et al. in review
Gaskin, J.F. and P.B. Shafroth. Hybridization of invasive saltcedars (Tamarix ramosissima, T. chinensis) and athel (T. aphylla) in the southwestern USA, determined from morphology and DNA sequence data. Madro_o (in review).
Caires and Dudley, unpublished data

Section 2: Invasiveness
Question 2.1 Role of anthropogenic and natural disturbance
in establishment?
C Reviewed Scientific Publication
Describe role of disturbance:

natural high flows and anthopogenic reduced flows can both facilitate invasion in Australia, natural flooding (removes native competitors and opens substrate for colonization) promoted seed dispersal and widespread establishment, but reduced natural flooding (Salt and Colorado Rivers) or river regulation and then water level declines (Lake Mead shoreline) provide substrate and conditions for colonization without removal that would occur during natural floods (this is the case for all Tamarix spp.)

Sources of information:

Barnes et al. in review, Griffin et al. 1989, D'Antonio et al. 1999

Question 2.2 Local rate of spread with no management? C Reviewed Scientific Publication
Describe rate of spread:

potentially explosive, but typically incremental in U.S. Does not appear to be expanding much, probably stable. flood conditions promoted infestation of hundreds of kilometers of a river in Australia; In lower Coloardo watershed relatively few new recruits occur but regularly along the Lake Mead shoreline, leading to a more gradual infestation rate - this is increasing as densities increase

Sources of information:

Griffin et al. 1989, Barnes et al. in review

Question 2.3 Recent trend in total area infested within state? D Observational
Describe trend:

increasing at Lake Mead, being controlled near Coalinga, not known elsewhere, as densities along shoreline increase there are more seeds produced leading to exponential increase in potential recruits

Sources of information:

Barnes et al. in review

Question 2.4 Innate reproductive potential? B Reviewed Scientific Publication
Describe key reproductive characteristics:

relatively low because seed viability is moderate (ca. 22% under best conditions) and seed production period fairly restricted (ca. 50 days, as opposed to many months for some other Tamarix species), but because millions of seeds CAN be produced, under the right conditions the potential for invasion is theoretically very high see above

Sources of information:

Barnes et al. in review, Griffin et al., Waisel 1960a, b, Usher 1986,

Question 2.5 Potential for human-caused dispersal? B Other Published Material
Identify dispersal mechanisms:

water- and wind-dispersed seeds from planted populations, cuttings are planted or can be dispersed by water. Still sold commercially in some areas. humans are important factors because T. aphylla is widely used as a horticultural plant, often near natural resource areas, where seeds are then available for recruitment; flood management creates better conditions for seed dispersal to suitable sites and subsequent establishment

Sources of information:

same as above

Question 2.6 Potential for natural long-distance dispersal? B Other Published Material
Identify dispersal mechanisms:

wind- and water-dispersed seed, water-dispersed vegetative propagules. Generally does not produce viable seed. seeds can be carried long distances by rivers, as was observed in Australia

Sources of information:

Healy and DiTomaso

Question 2.7 Other regions invaded? B Reviewed Scientific Publication
Identify other regions:

Austalia, Hawaii, Texas and New Mexico, probably northern Mexico, global distribution not clear. Found in dry and riparian areas in other regions.

Sources of information:

Lyon 1924, Weber 2003

Section 3: Distribution
Question 3.1 Ecological amplitude/Range? A Reviewed Scientific Publication

although athel is widespread as a horticultural plant under many growth conditions in California and adjacent regions (ARizona, Mexico), it is only functioning as an invader in a small subset of systems, primarily along the lower Colorado River and associated reservoirs and possibly in the Salton Sea Basin; it has presumably been used ornamentally/culturally since the the 1800's - documentation of its invasive potential was only determined in the last 5 years or so based on studies at Lake Mead (in Nevada) see above

Sources of information:

Barnes et al., Shafroth and Gaskin

Question 3.2 Distribution/Peak frequency? D Other Published Material
Describe distribution:

Not common in western US. same as for 3.2

Sources of information:

Healy and DiTomaso. 2003

Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less No
Dense infestations produce >1,000 viable seed per square meter Yes
Populations of this species produce seeds every year. Yes
Seed production sustained over 3 or more months within a population annually Yes
Seeds remain viable in soil for three or more years No
Viable seed produced with both self-pollination and cross-pollination No
Has quickly spreading vegetative structures (rhizomes, roots, etc.) that may root at nodes No
Fragments easily and fragments can become established elsewhere No
Resprouts readily when cut, grazed, or burned Yes
Total points: 5
Total unknowns: 0
Total score: B?

Related traits:

documented to form hybrids with a more invasive congener, tolerates physiologically stressful conditions such as extreme drought and high salinity soils

Worksheet B - Arizona Ecological Types is not included here

Worksheet C - California Ecological Types

(sensu Holland 1986)
Major Ecological Types Minor Ecological Types Code?
Marine Systemsmarine systems
Freshwater and Estuarine lakes, ponds, reservoirsD, < 5%
Aquatic Systemsrivers, streams, canalsD, < 5%
desertD, < 5%
Scrub and Chaparralcoastal bluff scrub
coastal scrub
Sonoran desert scrub
Mojavean desert scrub (incl. Joshua tree woodland)
Great Basin scrub
chenopod scrub
montane dwarf scrub
Upper Sonoran subshrub scrub
Grasslands, Vernal Pools, Meadows, and other Herb Communitiescoastal prairie
valley and foothill grassland
Great Basin grassland
vernal pool
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forest
riparian woodland
riparian scrub (incl.desert washes)D, < 5%
Woodlandcismontane woodland
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forest
North Coast coniferous forest
closed cone coniferous forest
lower montane coniferous forest
upper montane coniferous forest
subalpine coniferous forest
Alpine Habitatsalpine boulder and rock field
alpine dwarf scrub
Amplitude (breadth): B
Distribution (highest score): D

Infested Jepson Regions

Click here for a map of Jepson regions

  • Central West
  • Great Valley
  • Northwest
  • Southwest
  • Sierra Nevada East
  • Desert Province
  • Mojave Desert
  • Sonoran Desert