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Species
Tamarix chinensis Lour. (1790)
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NCBI
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More info for the terms: fuel, natural, shrub
The family Tamaricaceae consists of 4 genera and about 100 species, none of which are native to North America [171]. The genus Tamarix occurs naturally from western Europe and the Mediterranean to North Africa, northeastern China, India, and Japan [21], generally within dry, saline habitats in the subtropical and temperate zones [171]. Tamarix is the only genus that occurs in North America [138], with 8 or 9 species, depending on the author.
The history of the introduction and spread of tamarisk into North America is well documented [52,83,195]. Some have suggested that tamarisk was first introduced by the Spaniards although there is little evidence to support this [239], and it was not identified in the western U.S. until the 1800s when it was introduced for sale as an ornamental shrub and a windbreak species. It was available in New York City in 1823, in Philadelphia in 1828, and in several nurseries along the eastern seaboard during the 1930s. Tamarisk was listed for sale by nurseries in California as early as 1856 [124]. The U.S. Department of Agriculture began growing several species of tamarisk in the Department Arboretum around 1868, and released saltcedar for cultivation in 1870 [124,239]. French tamarisk became well established on Galveston Island, Texas, by 1877. In the early 1900s, tamarisk was recommended for ornamental purposes, windbreaks, shade for poultry and small stock, and for fuel. According to Horton [124] early herbarium specimens indicate that 3 species of deciduous tamarisk were introduced to North America prior to 1920, the descriptions of which correspond to small-flowered tamarisk, saltcedar, and French tamarisk. By 1903 French tamarisk was common along roadsides and in waste places in the southern states, and was well established in much of the area by 1916. Another species, probably saltcedar, was "common in river bottoms" in Arizona by 1901 [124].
From the 1920s to the 1960s tamarisk spread rapidly, from an estimated 10,000 acres (4000 ha) in 1920 to over 1.2 million acres (500,000 ha) in the mid-1960s [195]. This rapid increase was due primarily to regulation of streamflows following construction of large dams and water diversion projects in the western U.S. [83,84]. Once established along the major drainages, tamarisk successfully invaded outlying ephemeral water courses, isolated marshes, and springs via its windblown seeds and possibly due to occasional plantings [83,102,212]. As recently as 1964 tamarisk was recommended as a windbreak species for the central Great Plains [191].
Since its escape from cultivation, saltcedar has spread primarily in the southwestern U.S., Texas and Mexico, although its distribution extends to many other parts of North America. It is especially pervasive in Arizona, New Mexico, western Texas, Nevada, and Utah but is also widespread in southern California, the Rocky Mountain states, the western Plains states, and parts of Oregon and Idaho. It occurs throughout broad regions of northwestern Mexico [260,266], and is spreading along the Gulf of Mexico into the coastal prairie [101]. Tamarisk is a problem in many natural areas and state and national parks and monuments in the western U.S. [19,143,153].
Small-flowered tamarisk originates in southern Europe and Asia Minor from Yugoslavia to Turkey [21,171]. Small-flowered tamarisk is now common in California and Arizona, and occurs sporadically in Nevada, Utah, Colorado, Missouri, North Carolina, British Columbia, Ontario, and Nova Scotia [20]. Small-flowered tamarisk is rarely encountered in New Mexico. It is of limited occurrence in the Albuquerque and Las Cruces areas, mostly in ornamental situations, and while it may escape, it is hardly invasive [3,20]. Small-flowered tamarisk is found on beaches in Florida, but it is rare [263]. It is also found in Massachusetts, Connecticut [202], and Oregon [112,138]. In the Great Plains, small-flowered tamarisk sometimes escapes from cultivation to waste places and along river flood plains. It is widely scattered in Texas, Oklahoma and Kansas [20,103]. Gleason and Cronquist [96] recognize small-flowered tamarisk in the northeastern U.S. where it occasionally escapes cultivation, although it is uncommon in this area.
French tamarisk is not common in New Mexico [3]. In California, French tamarisk occurs in the Central Valley, the Bay Area, and along the central and south coasts [156].
T. ramosissima is native to the Ukraine and Iraq east through China and Tibet to Korea [21,171]. It is now commonly cultivated and invasive in Arizona and California, with specimens also found in Nevada, Utah, Colorado, New Mexico, Oklahoma, Texas, Kansas, Arkansas, New York, and Manitoba [20].
T. chinensis is native to Mongolia and China to Japan. It is now common in Arizona, New Mexico, Oklahoma, and Texas, with specimens from California, Nevada, Colorado, Arkansas, North Carolina, British Columbia, Manitoba, Ontario, and Quebec [20].
The following biogeographic classification systems are presented to demonstrate where tamarisk might be found or is likely to be invasive, based on reported occurrence and biological tolerance to factors likely to limit its distribution. Precise distribution information is limited, especially for small-flowered tamarisk and French tamarisk. Therefore, these lists are speculative and not exhaustive, as some tamarisk species may be invasive in other types.
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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):
BLM PHYSIOGRAPHIC REGIONS [22]:
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands
More info for the terms: density, fire frequency, fire regime, fire severity, frequency, fuel, litter, natural, presence, root crown, severity, shrub, shrubs, top-kill, tree, wildfire, wildland fire
Fire adaptations: Evidence for specialized adaptation to fire in tamarisk remains unclear, despite its efficient postfire recovery [43]. An abundance of anecdotal and observational evidence indicates that tamarisk can sprout and rapidly form new plants after top-kill from fire [35,90,107,178,211,220] (see Asexual regeneration). After a wildfire in a Rio Grande riparian forest, Ellis [80] found that "root suckering was nearly absent" in tamarisk but that 53% to 55% of tamarisk individuals sprouted from existing root crowns. Repeated disturbances may lead to the development of dense thickets of tamarisk [62,81,178].
Saltcedar leaves are not highly flammable due to high moisture content, even though they contain volatile oils. Saltcedar flammability increases with the build-up of dead and senescent woody material within the plant, and dense stands of tamarisk can be highly flammable [43,116,185,231]. When plants burn under conditions of high fuel loads, fire tends to be more severe, top-killing more tamarisk plants in a stand and increasing the likelihood of killing the root crown of some individuals (e.g., [80,116]).
FIRE REGIMES: Information on FIRE REGIMES in which tamarisk evolved is lacking. Busch and Smith [44] cite research that suggests that halophytic tamarisk species increase in abundance in burned areas previously dominated by common reed (Phragmites australis), whereas successional pathways suggested for T. dioica in southwestern Nepal indicate replacement by other taxa after fire [72].
There is little quantitative information on prehistoric frequency, seasonality, severity and spatial extent of fire in North American riparian ecosystems. According to a review by the U.S. Fish and Wildlife Service [244], fire frequency probably varied with drought cycles, prevalence of lightning strikes, prevalence of burning by Native Americans, and fires in surrounding uplands. Fire was probably more frequent along rivers in grassland and savanna biomes than those in deserts, chaparral shrublands, and conifer forests [244] (see fire regime Table below).
Fires in low- to mid-elevation southwestern riparian plant communities dominated by cottonwood, willow and/or mesquite are thought to have been infrequent [44]. Evidence used to support this supposition includes the high water content of most riparian forests; low fire frequency in much of the surrounding uplands (Sonoran and Mojave desert, and drier portions of Chihuahuan desert and Great Basin desert scrub); and suggestions that the dominant trees in these communities, notably Fremont and Rio Grande cottonwood, are not well-adapted to fire [43,81,244]. There remains, however, considerable uncertainty as to the effects of fire on cottonwood [80], with limited and mixed experimental evidence (e.g. [1,16,80,230]).
Increases in fire size or frequency have been reported for the lower Colorado and Bill Williams [42], Gila [242], Rio Grande [230,231], and Owens [32] rivers in recent decades [244]. While tamarisk may promote more frequent and severe wildfires in these areas, the role of fire in these ecosystems is still not well understood [80,231]. Fire appears to be less common in riparian ecosystems where tamarisk has not invaded [42,44,107,242]. Increases in fire size and frequency are attributed to a number of factors including an increase in ignition sources, increased fire frequency in surrounding uplands, and increased abundance of fuels.
Ignition sources, including intentional burning by farmers and ranchers, and accidental ignition from campfires, children, cigarettes, equipment, railroads, and fireworks, have increased as population densities have increased in riparian areas [32,231,242].
Fire frequency has increased in surrounding Sonoran and Mojave desert communities during the past century, primarily as a result of increases in fine fuels from nonnative annual grasses [31].
Several interrelated factors have contributed to increased fuel loads in many riparian communities. Disturbance regimes in many southwestern riparian communities have been altered by factors including dams and diversions, groundwater pumping, agriculture, and urban development, all of which have contributed to reduced base flows, lowered water tables, less frequent inundation, and changes in the frequency, timing and severity of flooding [9,84]. The result is a drier floodplain environment where much of the native broad-leaved vegetation becomes senescent or dies, and is replaced by more drought-tolerant vegetation such as tamarisk [9,84,212]. Natural flood regimes that once served to clear away live and dead vegetation and redistribute it in a patchy nature on the floodplain are suppressed, thus leading to increased build-up and continuity of fuels [44,80,81,178]. Typical stand conditions on the Middle Rio Grande, for example, are now characterized by mature and over-mature Rio Grande cottonwood trees, with accumulation of dead wood and litter on the forest floor [231]. The organic matter that has accumulated on the floor of riparian forests along the middle Rio Grande now averages over 50,000 kg/ha in some areas [169].
The structure of saltcedar stands may be more conducive to repeated fire [116,185,231] than that of native vegetation. Saltcedar and Russian-olive can contribute to increased vertical canopy density, creating volatile fuel ladders, thereby increasing the likelihood and impacts of wildfire [231]. Tamarisk plants can have many stems and high rates of stem mortality, resulting in a dense accumulation of dead, dry branches. Large quantities of dead branches and leaf litter are caught in tamarisk branches above the ground surface, enhancing the crowns' flammability [43,185,244]. Authors have suggested that fire hazard peaks in tamarisk stands at 10 to 20 years of age [178,244]. Anderson and others [5] observed that 21 of 25 tamarisk stands along the lower Colorado River had burned in the prior 15 years. This implies a disturbance interval that is insufficient for full maturation of cottonwood, willow and mesquite [42], or for tamarisk to mature and senesce.
The spread of highly flammable, nonnative vegetation such as tamarisk, giant reed (Arundo donax), red brome (Bromus madritensis), and cheatgrass (Bromus tectorum) in these communities, "is due partly to the same changes in flow regimes that render riparian areas more flammable, making it difficult to disentangle the effects of the nonnative species from the effects of the management factors that have enhanced their spread." Tamarisk is, nonetheless, a key factor in the flood-to-fire regime shift (review by [244]).
With the combination of flood suppression, water stress, and invasion by tamarisk and other flammable, nonnative plants, fires have replaced floods as the primary disturbance factor in many southwestern riparian ecosystems. Many of the tree and shrub species in these biotic communities can resprout following top-kill that may result from flooding. They may have more resilience to floods than to fire because fires, especially those of high severity, may cause more damage to perennating tissues than floods. More research is needed in this area. Additionally, fires do not necessarily create opportunities for regeneration by seed. Cottonwood and willow are adapted to release seed at a particular time that corresponds to annual flood pulses - a time that does not necessarily correspond to a high likelihood of fire (review by [244]). Tamarisk may be better adapted to persist in an environment of frequent fires than native riparian trees [43].
While cottonwood and willow species can resprout following fire (see FEIS summaries of individual species for more information), tamarisk may be better adapted to the postfire environment than native species, especially on dammed rivers. For example, stomatal conductance was greater in burned versus unburned tamarisk, and it had higher postfire water use efficiency relative to cottonwood and willow. The ability of tamarisk to tolerate high levels of soil salinity may also favor it in the postfire environment, as soil salinity tends to increase after fire. Tamarisk is likely to persist following fire and expand its dominance with repeated burning of low-elevation riparian plant communities [44]. Many sites along southwestern river systems are characterized by saltcedar communities with halophytic, fire-tolerant shrubs (e.g. big saltbrush and arrowweed) as codominants, with only senescent individuals of the historically dominant cottonwood and willow remaining. It has been suggested that cottonwood is nearing localized extinction on many riverine systems of the desert Southwest [45,81,212,231].
Busch [43] observed that cottonwood was virtually absent, willow persisted, and tamarisk was abundant in all communities of burned riparian vegetation studied along the lower Colorado River. Arrowweed had even larger increases in all communities and can be considered to share dominance of the study area's burned riparian vegetation with tamarisk [43]. Stuever and others [231] agree that fire may be an important contributor to cottonwood decline along the middle Rio Grande, but that further research on the response of Rio Grande cottonwood to wildland fire would provide important insight into the role of fire in stand structure and species composition. For example, after a mixed-severity wildfire at the Bosque del Apache National Wildlife Refuge, Ellis [80] found that fire severity was related to flood history (i.e. the site that had been regularly flooded had low severity fire), and was important in determining postfire plant communities. Sprouting of native plants was higher at the site with lower fire severity [80].
In summary, the likelihood of fire in southwestern riparian ecosystems is greatest with the combination of flood suppression, water stress, and tamarisk presence. The presence of tamarisk in southwestern riparian ecosystems may favor its own propagation by further altering the natural disturbance regime, thereby further decreasing the already limited extent of native cottonwoods [81]. Additionally, in the absence of flooding, regeneration of native trees is impeded, and organic matter accumulates, thus increasing chances for future fires that may further alter the species composition and structure of southwestern riparian forests and promote the spread of saltcedar and other fire tolerant species [80,81].
The cottonwood-willow habitats (now cottonwood-willow-tamarisk habitats) have undergone serious changes in disturbance regimes (review by [244]). Tamarisk may or may not affect FIRE REGIMES in other communities in which it occurs. More research is needed in this area.
The following table provides information on fire return intervals for several communities or ecosystems in which tamarisk may be found. If you are interested in the fire regime of a plant community that is not listed here, please consult the complete FEIS fire regime table.
Community or Ecosystem | Dominant Species | Fire Return Interval Range (years) |
saltbush-greasewood | Atriplex confertifolia-Sarcobatus vermiculatus | < 35 to < 100 |
desert grasslands | Bouteloua eriopoda and/or Pleuraphis mutica | 5-100 [180] |
plains grasslands | Bouteloua spp. | 180,262] |
paloverde-cactus shrub | Cercidium microphyllum/Opuntia spp. | 180] |
curlleaf mountain-mahogany* | Cercocarpus ledifolius | 13-1000 [12,199] |
mountain-mahogany-Gambel oak scrub | C. l.-Quercus gambelii | < 35 to < 100 |
Arizona cypress | Cupressus arizonica | 180] |
California steppe | Festuca-Danthonia spp. | 180,229] |
western juniper | Juniperus occidentalis | 20-70 |
Rocky Mountain juniper | J. scopulorum | < 35 |
creosotebush | Larrea tridentata | < 35 to < 100 |
Ceniza shrub | L. tridentata-Leucophyllum frutescens-Prosopis glandulosa | 180] |
wheatgrass plains grasslands | Pascopyrum smithii | 180,183] |
pinyon-juniper | Pinus-Juniperus spp. | 180] |
Mexican pinyon | P. cembroides | 20-70 [168,233] |
Colorado pinyon | P. edulis | 10-400+ [88,100,140,180] |
sycamore-sweetgum-American elm | Platanus occidentalis-Liquidambar styraciflua-Ulmus americana | 250] |
galleta-threeawn shrubsteppe | Pleuraphis jamesii-Aristida purpurea | < 35 to < 100 |
eastern cottonwood | Populus deltoides | 180] |
mesquite | Prosopis glandulosa | 163,180] |
mesquite-buffalo grass | P. g.-Buchloe dactyloides | < 35 |
Texas savanna | P. g. var. glandulosa | 180] |
California oakwoods | Quercus spp. | 11] |
oak-juniper woodland (Southwest) | Quercus-Juniperus spp. | 180] |
shinnery | Q. mohriana | < 35 |
elm-ash-cottonwood | Ulmus-Fraxinus-Populus spp. | 73,250] |
*fire return interval varies widely; trends in variation are noted in the species summary
STATES [138]:
saltcedar
AZ | AR | CA | CO | GA | ID | KS | LA | MS | MT |
NE | NV | NM | NC | ND | OH | OK | OR | SC | SD |
TX | UT | VA | WY |
BC | MB | ON | PQ |
MEXICO |
French tamarisk
CA | GA | LA | NM | NC | SC | TX | WA |
small-flowered tamarisk
AZ | CA | CO | CT | DE | FL | ID | IL | KS | LA |
MA | MI | MS | MO | MT | NV | NJ | NM | NC | OK |
OR | PA | TN | TX | UT | VA | WA |
BC | NS | ON |
MEXICO |
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More info for the terms: cover, density, litter, natural, relative dominance, succession
Tamarisk is an early to late seral species. Seedlings establish as flood waters recede leaving moist deposits of bare soil along riparian corridors. Its small, wind- and water-dispersed seeds make it ideally suited as a pioneer species on these sites. Tamarisk is also early successional after fire [44,231]. Its role in mid- to late seral communities is site specific and may depend on climate as well as the composition of the plant community in which it occurs, and on disturbances subsequent to its establishment (including management practices, grazing, fire, and flooding). Under certain conditions (e.g. altered flow regimes, drought, lowered water table, grazing, fire) tamarisk has a competitive advantage and is likely to be a late successional dominant.
Once a dense stand of tamarisk is established, there tends to be little regeneration of other species in the absence of disturbance, resulting in late-successional dominance by tamarisk [121]. In much of the Southwest, tamarisk stands have been maintained in a "youthful thicket" stage by burning, chemical treatment, or mechanical disturbance, and other seral species are not able to occupy these sites. Stands that have been allowed to age naturally are rare. If tamarisk is allowed to complete its life cycle it may provide an understanding of its role in the natural succession of riverbank vegetation [84].
Preliminary results and field observations indicate that mature tamarisk is highly susceptible to shading, with shaded plants having greatly altered leaf morphology and reduced reproductive effort [121,220]. Tamarisk has the advantage of producing seed over a longer portion of the growing season than native species and is able to establish later in the season when seeds of other species are not present. However, if cottonwood is present in the seedling establishment stage, there can be a gradual increase of cottonwood dominance [121]. When present and not grazed, cottonwood grows faster than tamarisk, eventually shading it and causing its decline [149]. This relationship can be observed along the Rio Grande south of Albuquerque, and along the San Pedro River in Arizona [115,121]. In central and northern New Mexico, Campbell and Dick-Peddie [47] observed that Fremont cottonwood assumes dominance over saltcedar if the cottonwood is left to mature without disturbance. Measurement of canopy cover, density, height and age of tamarisk and plains cottonwood in 50 plots at 25 sites along rivers in southeastern Montana indicated that tamarisk commonly formed thickets on open, low terraces and along overflow channels but was less dense under cottonwood. Even when tamarisk occupied a site before cottonwood, it appeared unable to suppress cottonwood dominance. At 6 study sites, the authors observed vigorous cottonwood plants 3 to 5 years old growing up in dense stands of tamarisk 10 to 23 years old [149]. Willow and seepwillow can also be competitive with tamarisk [115,121].
Tamarisk is competitively superior to natives under dry, saline conditions [23,30,127,151,211,226,248]. In the southwestern states, saltcedar has interrupted normal successional pathways and is not only maintaining its land area, but is continuing to increase in dominance [54,107], often forming essentially monotypic stands [54,108]. Tamarisk is more drought tolerant and less palatable to grazing animals than the native species [121] and is expected to exhibit greatest differential success during drought years and in late successional communities [54]. On the lower Virgin River in southern Nevada, postfire stands <10 years old are characterized by a mixture of tamarisk, arrowweed, sandbar willow, and screwbean mesquite. As stands age, the natives tend to decrease in relative dominance. Arrowweed maintains co-dominance with tamarisk the longest, but after 50 to 60 years stands are characterized by 100% cover of tamarisk. Stands become increasingly desiccated and saline with age and with increasing cover of tamarisk [54,211]. As floodplains in the Mojave Desert region become more desiccated with age, saltcedar assumes greater dominance over native phreatophytes. Saltcedar further desiccates floodplains and lowers water tables through its ability to produce high density stands and high leaf area and its ability to maintain sap flows at high canopy level transpiration rates [198]. Additionally, because tamarisk foliage concentrates salts and creates saline litter, it has a further competitive advantage over most native species [66,171].
A review by Simberloff and VanHolle [209] indicates that in the Southwest, among the few species that thrive in a saltcedar subcanopy are 3 nonnative brome grasses (Bromus spp.). To further exacerbate saline conditions, a nonnative, honeydew-producing leafhopper found on tamarisk interacts with a fungus to change soil characteristics so that plant recruitment is virtually eliminated under a tamarisk canopy [209].
Akashi [2] notes that herbaceous growth is poor in saltcedar-currant shrublands and relatively rich in saltcedar-sandbar willow shrublands. In shrublands associated with saltcedar, nonnative plants, particularly hairy whitetop (Cardaria pubescens), Russian knapweed (Acroptilon repens), and Canada thistle (Cirsium arvense) are more common than in native shrublands and often dominate herbaceous cover. With reduced flooding and increasing aridity, saltcedar associated shrublands could give way to black greasewood [2].
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License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
Rights holder/Author | Pablo Gutierrez, IABIN |
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More info for the terms: adventitious, bisexual, breeding system, density, hypocotyl, natural, pappus, radicle, root crown, tree, wildfire
Mature tamarisk plants reproduce vegetatively by adventitious roots, or by seed. Stevens [220] states that assertions concerning the pollination strategy, out-crossing requirements, and genetic variability of saltcedar are untested.
Breeding system: Tamarisk flowers are bisexual [3,171]. It has been stated by some that saltcedar has a self-compatible breeding system [36,201], but preliminary tests suggest this is unlikely [220].
Pollination: Brotherson and von Winkel [36] suggest that tamarisk is cross-pollinated by wind. However, experiments by Stevens [220] in which tamarisk racemes were bagged to prevent insects from reaching the flowers demonstrated conclusively that virtually no seed development occurred without insect visitation. Wind pollination and selfing are under investigation; however, preliminary tests suggest that wind-pollination is unlikely [220].
Seed production: Tamarisk plants may flower in their 1st year of growth [254] but most begin to reproduce in their 3rd year or later [220]. Saltcedar flowers occur in dense panicles on young tissues at or near the end of vegetative stems. Studies of tamarisk by Merkel and Hopkins [165] in Kansas found racemes to average 1.5 to 2 inches (3.8-5 cm) long and contain about 20 flowers per inch (2.5 cm) of raceme. The average number of ovules in the ovaries examined was 22, all of which were often fertilized and developed into seeds. Stevens [220] found each flower capable of producing about 8 to 20+ minute seeds. Because saltcedar reproduces sexually throughout most of the growing season, a small plant can produce a substantial seed crop, and a large plant may bear several hundred thousand seeds in a single growing season [165]. Stevens [219] states that mature saltcedar plants are capable of producing 2.5 x 108 seeds per year [219]. Warren and Turner [254] used seed traps to estimate the number of viable seeds reaching the soil surface in stands of varying density. They found that about 100 seeds per square inch (17/cm2) reached the soil surface in a dense saltcedar stand over 1 growing season; and that more than 4 seeds per square inch per day (0.64 seeds/cm2/day) might settle on the soil surface during the peak of seed production [254]. Saltcedar can produce seed throughout the growing season. High stress induced by fire, drought, herbicides, or cutting can increase flowering and seed production in saltcedar [107].
Seed dispersal: Saltcedar seeds have small hairs on the apex of the seed coat and are readily dispersed by wind (mean fall rate in still air = 0.187 m/sec), and can also be dispersed by water [165,220].
Seed banking: Tamarisk seeds are short-lived and do not form a persistent seed bank [219]. Saltcedar seeds produced during the summer remain viable for up to 45 days under ideal field conditions (ambient humidity and full shade), or for as few as 24 days when exposed to full sunlight and dry conditions. Winter field longevity under ideal conditions is approximately 130 days. Seed mortality is generally due to desiccation [220]. If seeds are not germinated during the summer that they are dispersed, almost none germinate the following spring [107].
Viability of tamarisk seed collected in Kansas decreased with storage, especially 12 to 16 weeks after collection [165]. Saltcedar seed collected along the Salt River in Arizona in spring and early summer and stored in the laboratory lost its viability in 6 to 17 weeks. Longevity differed by collection date, with seed collected in the late summer and fall remaining viable over the winter. Viability of saltcedar seeds was prolonged by cold storage at 40 degrees Fahrenheit (4 °C). Saltcedar seed stored in the greenhouse, where daily temperatures rose almost daily to 100 degrees Fahrenheit (38 °C), lost its viability much sooner than seed stored in the laboratory, suggesting that seeds do not remain viable for long under field conditions characteristic of Arizona deserts [120]. Saltcedar seeds went from 65% viability 2 days after dispersal, to 40% viability 14 days after dispersal [252].
Germination: Tamarisk seeds have no dormancy or after-ripening requirements [220]. Germination requires direct contact with water or extremely high humidity, and is very rapid (<24 hours) [120,165,220]. Seeds require a moist, fine-grained (silt or smaller particle size) substrate for germination, such as is found in southwestern riparian habitats after flood waters subside [220]. Tamarisk seeds germinate equally well in light or dark [120,220]. Those germinating in dark were etiolated; when placed in light, they became green in several hours [120]. Seed produced in August had the highest germination percentage (51.4%) and in those produced in June had the lowest (19.0%) [165]. Germination is not greatly affected by high salinity under experimental conditions [204], and was not reduced in a strong solution of soil leachates from tamarisk or sandbar willow [220].
Stevens [220] describes the germination process as follows: At 68 degrees Fahrenheit (20 °C), imbibition lasts for about 2 hours, during which time the seed swells to about twice its normal size. The hypocotyl may begin to emerge at 2 hours, and the seed becomes photosynthetic within 5 to 10 hours. Germination "root hairs" emerge by hour 10 and the seed coat (with the pappus still attached) is shed between hours 10 and 20. Tap root emergence begins after hour 20. Thus tamarisk germination is usually completed in less than a day [220]. Horton and others [120] describe it as follows: in 5 to 8 hours after moistening, the embryo has usually swollen enough to break the seed coat. By 24 hours the seedling is free from the seed coat, the hypocotyl has turned downward, and a corona of root hairs has developed around the radicle to anchor the seedling. As the stem straightens, the cotyledons separate [120].
Seedling establishment/growth: Receding spring and summer flows leave saturated soils that are ideal for tamarisk, cottonwood, and willow germination and seedling establishment. However, saltcedar produces seeds over a much longer period and can establish throughout the summer during low flow regimes when seeds of the other species are not present [59,107,120,225]. Saltcedar seedling establishment and survival in these low landscape positions is facilitated by 3 or 4 sequential low flow years, after which they appear able to survive very large floods [59].
Tamarisk seedlings are sensitive to drying, and survival is dependent upon saturated soils during the first 2 to 4 weeks of growth [120]. However, even as seedlings, tamarisk is more desiccation tolerant than sandbar willow seedlings [220]. Tamarisk seedlings can be submerged for several days (most survived even after 24 days), but 4-6 weeks of submergence killed the majority of tamarisk seedlings in one study. Also, when seedlings are small they are easily detached from soil and float away if there is any appreciable current [120].
Tamarisk seedlings grow more slowly than many associated riparian species [54,120,220]. At 8 weeks old, tamarisk seedling shoot length averaged 4.6 inches (11.7 cm) and root length averaged 6 inches (15.6 cm) [120]. In controlled growth rate experiments, total biomass accumulation rate was 0.25 mg/day, and stem elongation rate was 2 to 5 mm/day during the 1st month of growth. Nutrient and water addition experiments demonstrated that water availability regulated biomass accumulation rate, while nutrient availability regulated root:shoot allocation patterns [220]. While often grazed, tamarisk seedling are less sought after than cottonwood and willow seedlings [107], and selective browsing by livestock at 1 site in the Sonoran Desert reduced the natural height advantage of the native tree species and favored saltcedar [225].
Self-thinning occurs rapidly among young tamarisk, with densities of more than 8,000 seedlings/m2 immediately following germination, to several hundred plants/m2 by the 3rd year, to "several" plants/m2 by year 15, to less than 1 plant/m2 by year 30. Tamarisk seedlings grown in equal density with sandbar willow seedlings had reduced growth of more than 80% compared to tamarisk grown separately [220].
Mature plants grow apically and may also produce numerous lateral shoots [220]. Under favorable growing conditions, saltcedar shoots reportedly grow to heights of 10 to 13 feet (3-4 m) in 1 growing season [69]. Growth rates vary between sites. Saltcedar required 7.68 years for a 0.39 inch (1 cm) increase in stem diameter in Utah, and 2.36 years for a similar increase in Arizona [34].
Asexual regeneration: According to Brotherson and Field [35], mature tamarisk plants reproduce vegetatively by adventitious roots, although the source of this information is not given. Several authors indicate that tamarisk sprouts following fire [35,80,107,178,211,220] or other disturbances that kill or injure aboveground portions of the plant [17,107,175,211]. Some of these accounts specify sprouting from the root crown [178,211], and others suggest sprouting from roots [35,214] (see Plant Response to Fire). After a wildfire in a Rio Grande riparian forest, Ellis [80] found that "root suckering was nearly absent" in tamarisk but that 53% to 55% of tamarisk individuals sprouted from existing root crowns. Sala [197] noted that "underground lateral roots" are actually rhizomes in saltcedar. If that is the case, tamarisk likely sprouts from rhizomes. However, Gary and Horton [93] found that root cuttings taken at varying distances from the root crown failed to sprout under laboratory conditions.
All of the aboveground portions of saltcedar develop adventitious roots and form new plants if kept in warm, moist soil [93,165]. This allows tamarisk to produce new plants vegetatively from stems torn from the parent plants and buried by sediment during floods. If stem cuttings are allowed to dry, even for as little as 1 day, their sprouting capability is reduced [107]. With 15% moisture loss, sprouting success drops rapidly, and no sprouting occurs after 45% moisture loss. Sprouting is delayed in winter. One cutting planted in November sprouted after 6 months of dormancy. Root cuttings did not sprout [93].
More info for the terms: adventitious, capsule, formation, genotype, perfect, phenotypic plasticity, resistance, shrubs
The following description of tamarisk provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available in these sources: [3,111].
Allred [3] distinguishes 4 species of tamarisk in New Mexico: athel tamarisk (T. aphylla), small-flowered tamarisk, saltcedar, and French tamarisk. Of these, only athel tamarisk can be separated by traits readily observable in the field (i.e. leaves conspicuously sheathing the stems and not scale-like, branchlets drooping, and foliage not deciduous). Athel tamarisk is not included in this review. The other species are similar in most traits, differing slightly in floral and leaf morphology [3,156].
Tamarisk are shrubs or shrub-like trees with numerous large basal branches, reaching 13 to 26 feet (4-8 m) in height, but usually less than 20 feet (6 m). Leaves are scale-like, 1.5 to 3.5 mm long, with salt-secreting glands. The foliage is deciduous. Flowering branches are racemes and are mostly primary or secondary branches. The inflorescence is a panicle of several small, perfect flowers, subtended by a small bract. Panicle branches of small-flowered tamarisk are 0.4 to 0.8 inches (1-2 cm) long and 3 to 5 mm wide and flowers have 4 sepals and 4 petals. Panicle branches of French tamarisk and saltcedar are 0.8 to 3 inches (2-8 cm) long and 3 to 5 mm wide, and flowers have 5 sepals and 5 petals. Petals of all species may be persistent or deciduous after anthesis. French tamarisk differs from saltcedar primarily in nectary disk morphology [3]. Tamarisk fruit is a capsule, bearing many tiny seeds (<0.5 mm in diameter and <0.5 mm long) with apical pappi [3,165,171]. The weight of a mature tamarisk seed is about 0.00001 gram [165].
Tamarisk has a deep, extensive root system that extends to the water table, and is also capable of extracting water from unsaturated soil layers (a facultative phreatophyte). Tamarisk has a primary root that grows with little branching until it reaches the water table, at which point secondary root branching is profuse ([36] and references therein). For example, a plant that was 15 inches (38 cm) tall had a well-developed primary root about 30 inches (76 cm) deep, and a branch root that extended laterally 96 inches (244 cm). In areas where mature plants are spaced 25 feet (7.6 m) or more apart, their roots may be intermixed and occupy the entire area. The location of the water table during root formation influences the morphology of the root system. In areas with shallow water tables, more extensive lateral development was observed. When the water table rose above the surface, adventitious roots appeared along the stem [165]. Mature tamarisk plants are able to reproduce from adventitious roots, even after the aboveground portion of the plant has been removed [35,93]. Sala [197] noted that "underground lateral roots" are actually rhizomes in saltcedar.
As a facultative phreatophyte and halophyte, tamarisk has a competitive advantage over native, obligate phreatophytes (e.g. cottonwood and willow) in areas where salinities are elevated or water tables depressed, conditions characteristic of disturbed riparian environments [44,115,165,170,181,211,212]. Saltcedar can obtain water at lower plant water potential and has higher water use efficiency than native riparian trees in both mature and postfire communities [44,45,54]. When tamarisk has contact with groundwater, stomatal control of water loss may be slight, but under droughty conditions, tamarisk can exert effective stomatal control of water loss [212,213]. Even when the water supply is interrupted or reduced, tamarisk maintains relatively high transpiration rates, greater resistance to cavitation, and lower turgor loss thresholds than other riparian species [181]. The ability of tamarisk to closely regulate photosynthesis and leaf conductance during drought increases its survivability and competitive ability in arid and semiarid rangelands [170].
Tamarisk accumulates salt in special glands in its leaves, and then excretes it onto the leaf surface. Foliage of saltcedar is often covered with a bloom of salt [66,171]. These salts accumulate in the surface layer of soil when plants drop their leaves [171]. As surface soils become more saline over time, particularly along regulated rivers that are no longer subjected to annual flooding and scouring, germination and establishment of many native species become impaired [45,212].
Tamarisk can tolerate an extreme range of environmental conditions, and Brotherson and von Winkel [36] suggest a general purpose genotype in saltcedar that gives it the capability to "exploit a wide spectrum of habitats." Phenotypic plasticity, ecotypic differentiation and high genetic variation suggest a high invasive potential. Sexton and others [201] found no genetic differences between regions for most functional traits sampled in saltcedar. An exception was a regional genetic divergence (likely a result of multiple introductions) for root biomass investment in cold environments, indicating ecotypic differentiation and perhaps local adaptation in seedlings. In general, seedlings from the northern edge of tamarisk's range were shorter regardless of temperature and invested more in roots when grown at low temperature. A relative increase in root investment in cold climates allows increased belowground storage of reserves while minimizing heat transfer to the environment. Gas exchange in saltcedar seedlings also decreased in response to decreasing temperatures; however no genetic variation was detected. Their results show plasticity for all morphological and gas exchange traits sampled in saltcedar [201].
Saltcedar can be long lived. In New Mexico, individual shrubs 75 to 100 years old have not yet shown signs of deteriorating due to age [121].
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More info for the terms: geophyte, phanerophyte
RAUNKIAER [189] LIFE FORM:
Phanerophyte
Geophyte