Introduction

I never saw saltcedar, Tamarisk, or any of the other common names that Tamarix species go by until I traveled south. So far, they have not ventured far into Canada and certainly haven’t been venturing there long. However, in the south, they thrive in hot, dry areas, particularly saline soils where few plants will grow, allowing them to take over. There are 50 – 60 species of Tamarix in the world, and not one is native to North America. In North America, we have Tamarix aralensis, Tamarix aphylla, Tamarix africana, Tamarix canariensis, Tamarix chinensis, Tamarix gallica, Tamarix parviflora, Tamarix ramosissima, and Tamarix tetragyna.

All Tamarix species should be considered invasive in North America. They have covered over a hundred million acres in the western US alone, and they frequently hybridize, making identification to the species level challenging. For the purpose of identifying them as an invasive species and for Tamarisk or Saltcedar removal or control, identification to the genus level is more than sufficient.

Description of Tamarix spp

Leaves & Stems of Tamarix spp

Tamarix spp are part of the Tamaricaceae family in the Caryophyllales Order of flowering dicot plants. They are either shrubs or small trees from 1- 10 m tall and are often multi-stemmed. They are a long-lived species living 100 years or more. Most species are deciduous. They are almost all very deep-rooted, with a tap root up to 30 m deep that also produces lateral roots up to 50 m long that can produce adventitious buds, especially when covered by shifting sand. Their deep taproots are meant to reach down into the groundwater, allowing them to survive in hot drought-prone climates as long as they are close to the water table.

Young branches are glabrous and are a variety of colors depending on the species. They may be reddish-brown, brown, blackish-brown, dark purple, grey, or black. Older branches have heavy bark that is frequently shredded and may be grey or brownish and reaches 10 – 15 (-30) cm in diameter.

The usually sessile (without leaf stalks) leaves of Saltcedars are much reduced and appear small and bract-like, somewhat resembling that of coniferous tree needles. Leaves are varying shades of dull, light, or dark green and turn golden-orange in the fall.

Flowers & Fruits of Tamarix spp

Tamarisk or Saltcedars produce a racemose inflorescence that is often paniculately branched. They are borne on the ends of current-year branches or in some species’ previous-year branches. In most species in North America, the flowers appear after the leaves have grown back. The flowers are very small, usually pink, and most have small petals only 1 – 2 mm long.

Fruits are multi-sided capsules with up to thousands of tiny seeds. The capsules usually have a tuft of hair that aids in wind dispersal. They can also be dispersed in water. Seed viability is very short, however, from around 20 to a maximum of 120 days, depending on the weather. However, Saltcedars can flower and produce seeds for extended periods of time, allowing them to reproduce prolifically even with their short seed life.

Similar Species Tamarix spp are Frequently Confused With

Other Genera

There are a few other genera that Tamarix species are occasionally confused with that also grow in similar habitats and ranges and have much-reduced leaves. However, all of those can easily be differentiated by their flowers.

Parkinsonia species are members of the Fabaceae family and have larger yellow, somewhat pea-like flowers and produce small legume fruits.

Prosopis glandulosa has sprays of yellow rather than pink flowers, and it is also a Fabaceae that produces long legume fruits.

Lepidospartum squamatum has a limited range native to the southwestern USA and northwestern Mexico and has small yellow Asteraceae-type disk flowers and typically Asteraceae cypsela fruits. Baccharis neglecta has a similar North American range, but it is a perennial plant, not a shrub, and produces individual whitish flowers more typical of the Asteraceae family it belongs to.

Polygonella robusta is an uncommon plant of the Polygonaceae family that is endemic to Florida and produces similar sprays of small pink flowers, but its leaves, while still small, are long and linear compared to all Tamarix species.

Juniperus virginiana smells strongly of Juniper and has characteristic powdery blue “berries” and no pink flowers.

Casuarina equisetifolia is widespread in Mexico and more limited in the southern USA. It has needle-like leaves, but they are longer, divided into septa, and grouped in fascicles, and it produces a globose cone-like fruit.

Tamarix Genera

Tamarix species can be challenging to identify at the species level. For the most part, genus-level identification in North America is sufficient for treating the plants as invasive species, as none are native to North America. However, with a bit of patience and a small amount of skill, they can be identified to the species level as follows:

• Tamarix aralensis Russian Tamarisk has a limited range in North America. It is similar to T. chinensis and T. ramosissima but has a much more limited range. It can be differentiated by its petals that fall off at the time of seed maturation.
• Tamarix aphylla Athel Tamarisk is more widespread in Mexico than in the southern USA. It is the only evergreen species, and its leaves are sheathing on the stems rather than sessile or amplexicaul like all other Tamarix species in our area. It also produces white instead of pink flowers.
• Tamarix africana African Tamarisk has a very limited range in the southern USA. It has the largest flowers (though still small) with petals that are 2 – 3 mm long and racemes that are 5 – 9 mm wide.
• Tamarix canariensis Canary Island Tamarisk has a limited range in the southern USA. It is similar to T. chinensis and T. ramosissima, but its sepal margins are denticulate, and it has obovate petals that are 1.2 – 1.5 mm long.
• Tamarix chinensis Five-Stamen Tamarisk is widespread in Mexico and the USA. It also is the most similar to T. ramosissima, and the two often hybridize, leading some to believe they should be considered the same species. They have five petals and five stamens. They can only be differentiated by this one’s sepal margins that are entire and that some or all of the stamens’ filaments originate from below the nectar disc. Filament inspection requires patience, a hand lens, and some skill. Furthermore, its petals persist at seed maturation, unlike T. aralensis.
• Tamarix gallica French Tamarisk has a limited west and south range in the USA and northern Mexico. It is also similar to T. chinensis and T. ramosissima, but its sepal margins are entire or almost entire, and it has elliptic to ovate petals that are 1.5 – 2 mm long.
• Tamarix parviflora is very widespread in the USA and is limited to the northern parts of Mexico. Its flowers are produced before it gets its leaves, and it usually only has four petals, unlike all other species in North America, whose flowers are five-petaled and arrive after the appearance of leaves.
• Tamarix ramosissima is fairly widespread in both USA and Mexico. It is the most similar to T. chinensis, and the two often hybridize, leading some to believe they should be considered the same species. They have five petals and five stamens. However, this species’ sepal margins are denticulate rather than entire, and all the stamens’ filaments originate from the edge of the nectar disc rather than below it in T. chinensis. Filament inspection requires patience, a hand lens, and some skill. Furthermore, its petals persist at seed maturation, unlike T. aralensis.
• Tamarix tetragyna Four-Stamen Tamarisk is found only in Georgia. It can be differentiated by its flowers that have only four stamens as opposed to the five that all other species in North America have.

Native Distribution of Tamarix spp

There are approximately 100 species of Tamarix, and all are native to Eurasia and Africa. None are native to the Americas.

Habitat Types Where Saltcedar is Found

Saltcedar, with its long taproots, is usually found only near groundwater and is, therefore, particularly common in riparian habitats, including floodplains, permanent or ephemeral stream banks, and around lakes and water reservoirs. They can also grow in upland habitats out of contact with groundwater, but they are less common there and grow less vigorously there. They can grow from 0 – 2000 m above sea level.

There is a common misconception that they are saline-loving plants, but in fact, they tolerate a wide range of soils, including those fairly high in salinity. This gives them a significant competitive advantage in saline areas where most other plants cannot survive. In those conditions, they typically rapidly produce monocultures displacing the few native halophytes found there.

Human Uses of Tamarisk

Tamarisk is used as an ornamental, especially in marginal habitats or saline soils. It was also widely planted as a stream and dune stabilizer in some areas. It is being used in China to fight the expansion of deserts.

Tamarisk wood is sometimes used for firewood, carpentry, and the making of bows and other tools.

In Africa and Asia, Tamarix species are used medicinally to treat wounds and infections as well as liver and spleen disorders. It is seldom currently used in North America medicinally.

Distribution of Tamarix spp in North America

The species was first brought to North America in the 1800s as an ornamental species. There are no species of Tamarix native to North America.

In Canada, Tamarix ramosissima has been recorded but ephemeral in British Columbia. It has been seen but not lasted long enough to confirm in Ontario, Manitoba, Quebec, and Nova Scotia.

In the USA, nine Tamarix spp are found. They are distributed as follows:

• Tamarix aralensis Russian Tamarisk is found in California and North Carolina.
• Tamarix aphylla Athel Tamarisk is found in California, Nevada, Utah, Arizona, and Texas.
• Tamarix africana African Tamarisk is found in California, Arizona, Texas, Louisiana, and South Carolina.
• Tamarix canariensis Canary Island Tamarisk is found in Arizona, Louisiana, Georgia, South Carolina, and North Carolina.
• Tamarix chinensis Five-Stamen Tamarisk is more widespread and is found in Washington, California, Nevada, Utah, Arizona, Montana, Wyoming, Colorado, New Mexico, Oklahoma, Texas, Arkansas, Ohio, and North Carolina.
• Tamarix gallica French Tamarisk is found in Washington, California, New Mexico, Texas, Louisiana, Georgia, South Carolina, and North Carolina.
• Tamarix parviflora is the most widespread species in the USA, being found in Washington, Oregon, California, Idaho, Nevada, Utah, Arizona, Montana, Colorado, New Mexico, Kansas, Oklahoma, Texas, Missouri, Louisiana, Illinois, Mississippi, Kentucky, Tennessee, Florida, North Carolina, Virginia, Michigan, Pennsylvania, Delaware, New Jersey, Connecticut, and Massachusetts.
• Tamarix ramosissima is also fairly widespread, being found in California, Nevada, Utah, Arizona, Colorado, New Mexico, North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Texas, Arkansas, Louisiana, Mississippi, Georgia, South Carolina, North Carolina and Virginia.
• Tamarix tetragyna Four-Stamen Tamarisk is found in Georgia.

In Mexico, there are five species of Tamarix found as follows:

• Tamarix aphylla is the most widespread found in Baja California, Baja California Sur, Sonora, Sinaloa, Chihuahua, Durango, Jalisco, Michoacan, Coahuila, Nuevo León, Tamaulipas, San Luis Potosi, Guanajuato, and Mexico City.
• Tamarix chinensis is found in northern Mexico in Baja California, Baja California Sur, Sonora, Sinaloa, Chihuahua, Coahuila and Nuevo León. It is possibly found in Mexico City, Mexico State, and Tamaulipas, but this is unconfirmed.
• Tamarix gallica is much less widespread and also only found in the northern states of Baja California, Coahuila, and Nuevo León. There is also an unconfirmed location in Chihuahua.
• Tamarix parviflora is the least widespread in Mexico and is only found on the northern border of Baja California. It is not far from the border in New Mexico, so it may likely spread to Chihuahua from there soon.
• Tamarix ramosissima is the second most widespread in Mexico, with populations found in Baja California, Baja California Sur, Sonora, Sinaloa, Chihuahua, Coahuila, Nuevo León, Guanajuato, Queretaro, Mexico State, Mexico City, and Guerrero.

How Tamarisk Spreads

It is primarily spread long-distance by deliberate human introductions into gardens or as a landscape plant.

Short-distance dispersal occurs through the abundant tiny seeds spread by wind, water, humans or animals. Seeds have a very short viability period; however, if they are not germinated during the summer that they are dispersed, almost none germinate the following year. However, Saltcedar produces seeds over a very long period enabling its rapid spread. Mature tamarisk plants also spread vegetatively by adventitious roots producing colonies of clones. 

Habitats at Risk of Invasion in North America

All riparian areas are at risk of invasion, particularly in the semi-arid and arid southern areas of our continent. More northern areas are less at risk, but we have seen invasion into North and South Dakota, Washington State, and New York, as well as the so-far ephemeral invasion into southern Canada. Tamarisk or Saltcedar has expanded its riparian dominance significantly since the 1800s and now covers huge geographical areas. Its rapid spread does not seem to be slowing, and its range continually grows.

In California desert areas, Saltcedars have now even become established in remote mountain springs, streams, and washes. These areas show no sign of human disturbance and are long distances away from any source of infestation. This means that wild riparian areas far from humans are not safe from Saltcedar invasion.

Impacts of Invasion

Tamarisk thrives in riparian habitats where it quickly displaces native vegetation due to rapid growth, tolerance of a wide range of environmental conditions, and long periods of abundant seed production. Tamarisk also accumulates salt in its leaf glands and excretes it onto the leaf surface. These salts accumulate in the soil when the plants drop their salty leaves. As surface soils become more saline over time, they further exclude native vegetation, producing monocultures. Native herbivores’ preference for native plants gives Tamarix species yet another competitive advantage.

Significant loss of biodiversity occurs in the stands of Saltcedar. Plant diversity is dramatically reduced, resulting in a loss of riparian bird, insect, invertebrate, aquatic and animal diversity.

Potential Benefits of Invasion

Saltcedar provides a habitat for a number of bird species. However, many of these are introduced from the Old World, where Tamarix evolved; though some of our native birds do use it, they still prefer native plants.

Methods to Remove Tamarix spp

As always, prevention is the preferred method of control. It, like most invasive species, is still widely sold online and in many local garden stores. Do not buy or transport any Saltcedar. Do not plant it in your yard. There are so many Native Plant Species that would make suitable garden specimens that are noninvasive and provide additional wildlife and biodiversity values.

If you see Tamarisks being sold online or in your local garden stores, please inform them of their invasive status and ask them to do their part and cease selling them. Ask them to instead sell more native species as ecologically friendly garden alternatives to invasive species.

Physical Control of Saltcedar Tamarisk

Once already established, however, physical control is a labor-intensive but effective means to remove Saltcedar. Physical control is time-consuming and costly, but it usually causes the least amount of environmental damage and leaves the area the most biodiverse afterward.

The best time to remove Saltcedar or Tamarisk is before it has gone to seed. Because it flowers and seeds for an extended period of time, this must be done in the late fall, winter, or early spring. If the plants are in seed upon removal, they can be burned or solarized as the seeds are sensitive and should die easily.

Physical methods to remove Saltcedar generally involve pulling young plants by hand, if very small, or with a weed puller or digging them out with a hoe or shovel.

Mature specimens are generally cut down, but the rootstock must be either dug out with a machine or chemically treated for a period of time to prevent re-sprouting. Isolated larger specimens can be solarized to prevent re-sprouting, but the tarp must remain for 2 growing seasons. Another method is to simply keep returning to the area a few times each growing season for several years in a row to keep cutting any new sprouts. This will eventually starve out the roots and kill the plant.

Along controlled rivers scheduling 5 – 10 year floods which wash out the Saltcedars removing them and leaching salts from the soil. This allows the native vegetation adapted to periodic flooding to grow back and displace the Saltcedar. The seedlings can be easily killed by keeping an area flooded for one month. The flooding method can also be used in low-lying areas that are isolated. Cut down all mature plants to the ground and keep the area flooded for an extended period of time. It will kill or prevent any new seedlings or sprouting and will eventually start rotting out and starving the roots. After the water is allowed to drain, the short seed viability period makes it unlikely that many new seedlings will emerge. Ongoing monitoring and hand-pulling of the few that do grow can be effective at preventing the population from becoming re-established.

Methods Not Recommend

Neither mowing nor burning will effectively control mature Saltcedar. Plants will quickly regrow from their basal stem buds and be supported by their extensive and deep root systems. Seedlings can be controlled by physical removal as mowing is generally ineffective on them as well due to their roots.

Disposal of the Shrubs Once Removed

If you have plants that have seeds on them, they must either be burned or solarized. Though mature plants are fire-adapted and will regrow, their sensitive seeds are vulnerable to fire, so the burning of shrubs is desirable in areas where burning is allowed.

If burning is not allowed, you should solarize the shrubs under a thick black tarp or in thick black garbage bags and leave them in the full sun for 6-8 weeks to be sure that all seeds are no longer viable. Since seed viability is poor, solarizing is also an effective method to destroy seeds.

Chemical Control of Saltcedar Tamarisk

Chemical applications are almost never an ideal method of control for any invasive species. That is because chemical alteration of the environment often makes the environment more suitable for invasive species than native species. Furthermore, it is often difficult to keep the chemical control method contained so that it does not directly affect any native species that are there during the application process itself. As a result, plots where chemical control is used usually show a decrease in species richness. On the other hand, in plots where only physical control is used, species riches significantly increase.

Saltcedar is somewhat resistant to chemical control methods, with up to 30% of plants resprouting up to three years after treatment. This means multiple applications will be needed. Furthermore, there are no chemical control methods that effectively target only the control of Saltcedar. Finally, due to their preference for riparian habitats, the use of herbicides is often not allowed due to proximity to water.

However, professionals and government officials may determine where and when chemical applications can be safely carried out to deal with vast areas of infestation. Chemical control by individuals is generally not recommended.

Biological Control of Saltcedar

Biological control involves the use of a predator, herbivore, disease, or some other agent to control an invasive species once it is established in the environment. The problem with biological control is that the agent used must be entirely specific to only the target organism before releasing it into the environment. This is often difficult to determine since the agent of control is also not native to the environment and could behave differently when released there. Take the example of the mongoose and the rat. The mongoose was released in Hawaii in the late 1800s to help control the rat. To this day, there are still rats in Hawaii, but the mongoose has helped to decimate many native bird populations.

Biological control methods are extremely risky and should only be carried out by professionals after years of rigorous study. The use of biological control methods can never be used alone. They must be part of an integrated pest management approach. This is because the control agent would need to effectively destroy over 99% of seeds to actually control the Saltcedar on their own. Results this high have never been achieved in the field. However, using biological control in conjunction with physical control and ongoing monitoring can be very effective.

So far, in North America, only one biological control agent has been released to control Tamarisk. Diorhabda elongata deserticola is a leaf beetle from western China and eastern Kazakhstan that was released in the USA in 1986. The beetles established well in the more northern areas and, after the third season, were seen to defoliate over 95% of the plants in the area. The populations have been spreading and are successfully helping to control Saltcedar in larger and larger areas. The introduced leaf beetle has also shown to be highly selective for Tamarisk and so far has not been observed eating any native vegetation. This makes it highly suitable for the biological control of Saltcedar.

The leaf beetles, however, did not establish in the southern areas due to increased predation and climatic differences. Additional subspecies of D. elongata have now been obtained from lower latitudes in Europe and Asia to be tested in more southern locations. It is too early for conclusive results.

Goats and cattle will graze on Saltcedar, but cattle, in particular, will selectively graze on native vegetation where it is present. Goats are less selective and will generally eat anything. Grazing would need to be done on a continual basis for at least 4 – 5 years so that they eat all sprouts that try to grow back up from the rootstock. Eventually, this would starve out the rootstock, and the plants would die.

Integrated Pest Management & Ongoing Monitoring

Integrated management is always the best approach. In its simplest and least impactful form, this involves physical removal methods, possibly biological control methods, replanting, and ongoing monitoring. Integrated management is required because the area needs to be monitored for returning sprouts or seedlings; otherwise, all the hard work done in removal could be wasted if the invasive species is allowed to regrow.

Replanting With Native Species is Crucial

In all cases of removal, the site should be replanted once the area has been cleared of Saltcedar and the soil has been leached of excess salts. Leaching the soil involves manually flooding the area with fresh water if there is insufficient rain in the region. Otherwise, waiting until after the rainy season may be sufficient as long as there are no more Saltcedars there.

Bare soil invites more infestations, and high salinity prevents biodiversity from improving. A replanting program should be planned and ready to implement the following year after the removal of Saltcedar. Then ongoing monitoring will be necessary to ensure no sprouts survive and no new seeds are accidentally brought into the area.

Ongoing Monitoring is Essential

In all cases of invasive Saltcedar removal, ongoing monitoring is absolutely essential. Yearly monitoring programs should be put in place to ensure that any surviving sprouting individuals are removed so that the population is not able to recover. Due to the short viability of seeds, new seedlings will stop emerging after a single season, provided no new seeds are accidentally transported to the site. Monitoring is required whether the area is replanted or not. Saltcedar has very deep and widespread roots that will easily regrow and start a new infestation if left unchecked. Yearly monitoring will prevent this and will allow the site to recover so that native plants will return.

References and Resources

CABI on Tamarix ramosissima https://www.cabi.org/isc/datasheet/52503

Canadensys Plant Search https://data.canadensys.net/vascan/search

Dictionary of Botanical Terms – Lyrae’s Nature Blog Dictionary of Botanical Terms

Eflora Plants of North America http://www.efloras.org/browse.aspx?flora_id=1

Fire Effects Information System on Tamarix spp https://www.fs.fed.us/database/feis/plants/tree/tamspp/all.html

iNaturalist Plant Search https://www.inaturalist.org/home

USDA Plants Database https://plants.sc.egov.usda.gov/home

Wikipedia Tamarix https://en.wikipedia.org/wiki/Tamarix

Willis, Lyrae (Unpublished).  Plant Families of North America.

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