Biology and Identification

There are no known native North American species in the four total genera, including Tamarix, belonging to the Tamaricaceae family. The name Tamarix is derived from the Tamaris River in Spain. Tamarix ramosissima, T. chinensis, and their hybrids are the most common saltcedar shrubs invading Montana riverways and lakeshores of the 8 to 12 Tamarix species known to have established in the United States. These species and hybrids originated in cold deserts from eastern Turkey to Korea, where winters are severe and frost-free growing seasons range from 60 to 120 days. Saltcedar’s tolerance of climatic extremes suggests that its expansion throughout Montana will not be limited by our characteristic cold winters, short growing seasons, and periodic droughts. Other Tamarix species used for horticultural planting may not be invasive. A recent DNA study of 32 ornamental specimens and 182 saltcedar plants that had escaped cultivation (or ‘wild’ plants/populations) in Montana found that wild saltcedar populations originated from other wild plants and not from ornamentals. The results also suggest that ornamental plants can contribute genetic material to an invasion or re-establishment of wild populations after wild plants are removed.

• Seeds
• Stems
• Leaves
• Flowers
• Roots
• Habitat
• Economic Importance
• Spread

Seeds

Saltcedar will produce seeds throughout the growing season when soil moisture is sufficient to maintain active plant metabolism. Plants generally reach reproductive maturity in three years; large saltcedars produce several hundred thousand seeds annually. The extremely small seeds (0.17 mm diameter, 0.45 mm long) are contained within capsules. Each seed has an apical pappus, a tuft of hairs on the tip of the seed coat, which aids in wind and water dispersal (see Figure 2). Saltcedar seeds typically germinate at very high rates (up to 100%), but due to their extreme susceptibility to desiccation, remain viable only up to 45 days under ideal summer conditions and 130 days under ideal winter seedbank conditions. Seeds have been kept viable in laboratory storage for over 40 weeks. Once they come into contact with sufficient moisture, the seeds quickly germinate and where abundant produce extensive seedling carpets of over 800 seedlings per square meter. Seedling survival of the first year is less than 10 percent. Seedlings can withstand total inundation by water for up to four weeks.

Stems

Saltcedar stems are slender and often recurved or arching (see Figure 3). The bark of young branches is smooth, reddish-brown, and after leaves fall, is distinctively marked with light-colored leaf scars. Older branches and stems become brownish-purple, ridged, and furrowed. Stems can grow up to 20 feet (4.5 m) tall. In Montana, stems often die back to the ground over winter and re-sprout from root crowns forming multiple stemmed plants that are generally less than 10 feet (3 m) tall. Saltcedar stems are capable of rapid growth and can grow up to 10 to 13 feet (3 to 4 m) in one season. Mature plants and root crowns can survive 70 and 98 days of flooding, respectively. Plants are short-lived relative to other shrubs and trees, and are said to have a total life expectancy of 20 years.

Leaves

The leaves of saltcedar are scale-like, small (about 1/16-inch or 1.5 mm long) and overlap each other along the stem, with an appearance similar to cedar or juniper leaves. They are grey-green in the summer and turn golden in the fall (see Figure 3). Buds break in early spring. Saltcedar species in Montana are deciduous, dropping their leaves in October. Salt-secreting glands are located on the underside of the leaves. On saline sites, leaves can become glazed with salt crystals secreted by the plant from water taken up through the roots to compensate for salty growing conditions. Salt that leaches from leaf liter can build up in the upper 2 inches (5 cm) of the soil profile and prevent the establishment of other plant species. Saltcedar prefers full sun and does not tolerate shade from overtopping cottonwood and willow species.

Flowers

The flowers of saltcedar are pink to white, small (3 to 5 mm across), with five distinct sepals and five distinct petals. They are clustered in showy compound catkin-like racemes (see Figure 4). Saltcedar typically blooms from May to September, although flowers have been observed blooming into October. Plants can flower in the first year after establishment, although viable seed is not produced until the third year of growth. Fruits mature to form capsules that contain thousands of seeds.

Roots

Saltcedar grows an extensive root system with a strong, deep taproot that enables access to groundwater. Root morphology is adaptable depending on water table and soil conditions. Adventitious roots that grow from near the vascular cambium of stems and branches allow severed stems to sprout and form separate plants. Stems can grow from roots and root crowns. Root growth is rapid. In one year, lateral roots can grow up to 20 feet (6 m) and the primary root can grow 11 feet (3.5 m) long.

Habitat

Saltcedar is an early seral species with specific adaptations to flood and drought conditions. Although it requires moist, barren soil for germination, mature plants are facultative phreatopytes capable of drawing adequate water supplies, as circumstances demand, from either surface soil moisture or groundwater. Mature stands of saltcedar consume vast amounts of groundwater; neighboring obligate phreatopyte species such as cottonwoods and willows cannot survive when the groundwater level drops below that of their roots for any sustained period. These adaptations allow saltcedar to successfully colonize, establish and dominate along rivers; streams, lakes, irrigation ditches and reservoirs (see Figure 1 on the Abstract page). Also, in mixed stands of native willow and saltcedar or cottonwood and saltcedar, beaver select native species over saltceder by a ratio of 10:1, giving saltcedar a further competitive advantage over the native species. Older plants are generally found along the high water mark (see Figure 5) while flooding zones are more likely to be populated by seedling plants (see Figure 6). This distribution reflects seasonal extremes in surface water levels, and is likely due to saltcedar’s inability to survive inundation for a period of three months or longer. Mechanical disturbances such as riverbank scouring that accompany natural river flooding cycles are thought to inhibit the buildup of saltcedar populations (see Figure 5 and Figure 6). Saltcedar has also been reported in roadside borrow pits where bare soil and standing water from roadbed drainage provides suitable conditions for establishment.

Although saltcedar ecology is similar to that of cottonwood, it has a longer seed production and dispersal period. This allows it to take advantage of floods or flow releases of dammed river systems that occur throughout the summer. Saltcedar is also more deeply rooted than native species and more tolerant of salinity.

Economic Importance

Impacts associated with saltcedar include reduced native plant and small mammal diversity, altered avian composition in riparian communities, increased evapo-transpiration-mediated water loss from riparian systems (although research suggests losses similar to native species use), and altered stream hydrology. Nationwide, millions of dollars are spent each year to control saltcedar and restore native plants to riparian areas where large scale saltcedar populations have been removed.

Spread

The highly invasive nature of saltcedar is thought to be due to its high regenerative capability through crown and root sprouts, profuse seed production, and high rates of seedling establishment. Short- and long-distance dispersal mechanisms include wind and waterways. It is believed that seeds from horticultural plantings in yards can be carried by wind to nearby waterways. On the Musselshell River, saltcedar has spread at estimated rates of 12 and 1.25 miles per year downstream and upstream, respectively. Saltcedar is also spread when seeds on boats, in water ballast, on boat trailers, and on fishermen’s waders are transported from one body of water to another.

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Last Modified: 07/12/2007