The following description of giant reed provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g., [40,53,56,57,62,63,69,77,103,105,107]). Giant reed and common reed, a native grass distributed across most of the United States, can be difficult to distinguish. Proper identification of giant reed is essential before implementing control measures [24].
Giant reed is a tall, erect, perennial graminoid. It is the largest member of the genus and among the largest of grasses, growing 6 to 30 feet (2-8 m) tall [11,28,74]. The culms reach a diameter of 0.4 to 1.6 inches (1-4 cm) and commonly branch during the second year of growth. Culms are hollow, with walls 2 to 7 mm thick and divided by partitions at the nodes. The nodes vary in length from 5 to 12 inches (12-30 cm). Leaves are conspicuously 2-ranked, 2 to 3.2 inches (5-8 cm) broad at the base and tapering to a fine point. Bases of the leaves are cordate and more-or-less hairy-tufted, persisting long after the blades have fallen [74]. Giant reed has large plume-like panicles. Spikelets are several-flowered with upper florets successively smaller [33].
Giant reed has thick, knotty rhizomes [103] and deeply penetrating roots [74]. Once established, it tends to form large, continuous, clonal root masses, sometimes covering several acres. These root masses can be more than 3 feet (1 m) thick (review by [11]).
Although giant reed has been widely cultivated for centuries, little information on its biology and ecology has been published. As of this writing (2004), more research is needed to understand the biology and ecology of giant reed.
Though accounts in the literature vary, a review by Bell [11] indicates giant reed is thought to be native in eastern Asia, and it has been cultivated throughout Asia, southern Europe, northern Africa and the Middle East for thousands of years. In North America, it was intentionally introduced from the Mediterranean to the Los Angeles area in California in the early 1800s (Robbins and others 1951, as cited in [49])[28], and has been widely planted throughout the warmer states as an ornamental and for erosion control along drainage canals [49,74]. It has escaped cultivation as far north as Virginia and Missouri, and abundant wild populations occur along the Rio Grande River [74] and along ditches, streams, and seeps in arid and cis montane regions of California (Robbins and others 1951, as cited in [49]).
According to Bell [11], giant reed is invasive throughout the warmer coastal freshwaters of the United States from Maryland westward to northern California. Wunderlin [107] recognizes the variety versicolor as occurring in Florida, and Jones and others [53] describe that variety as a cultivar. The literature contains specific references to the occurrence of giant reed in the 4 provinces of Mexico listed below [2,61,82,98]. Giant reed is likely present in other areas of Mexico.
Plants database provides a state distribution map of giant reed in the United States.
The following lists include North American ecosystems, habitat types, and forest and range cover types in which giant reed is known or thought to be invasive, as well as some that may be invaded by giant reed following disturbances in which vegetation is killed and/or removed and/or soil is disturbed (e.g. cultivation, fire, grazing, herbicide application, flooding). Giant reed is a hydrophyte and riparian areas or wetlands within these habitats could be subject to invasion by giant reed even if the habitat itself is not considered a wetland. For example, Nixon and Willett [71] list giant reed as a plant found within the Trinity River Basin in Texas. Habitats within the basin include cross timbers and prairies, blackland prairies, post oak (Quercus stellata) savannah, pineywoods, and Gulf prairies and marshes.
These lists are not necessarily exhaustive. More information is needed regarding incidents and examples of particular ecosystems and plant communities where giant reed is invasive.
Fire adaptations: As of this writing (2004), information on fire adaptations of giant reed are limited to anecdotal accounts and assertions based on known biological attributes. Giant reed's extensive rhizomes are likely to survive and sprout after fire removes top growth. Reviews (e.g., [11,28,95]) provide anecdotal evidence that indicates that sprouts emerge from rhizomes of giant reed soon after fire and grow quickly. Rieger and Kreager [80] observed rapid sprouting and growth of giant reed after removing top-growth by cutting (see Growth).
FIRE REGIMES: With the exception of California, almost no published information is available that describes the types of plant communities in which giant reed is invasive, although giant reed generally occurs in riparian and wetland areas throughout its wide distribution. Characteristics of riparian zones and wetlands vary substantially throughout this range, and FIRE REGIMES are not well described for many of these communities. A review by Dwire and Kauffman [30] discusses how differences in topography, microclimate, geomorphology, and vegetation may lead to differences in fire behavior and fire effects between riparian areas and surrounding uplands. Riparian areas may act as a fire barrier or a fire corridor, depending on topography, weather, and fuel characteristics [30]. Recovery of riparian vegetation depends on fire severity and postfire hydrology [22].
Dwire and Kauffman [30] indicate that riparian microclimates are generally characterized by cooler air temperature, lower daily maximum air temperature, and higher relative humidity than the adjacent uplands, contributing to higher fuel moisture content and presumably lowering the intensity, severity, and frequency of fire in riparian areas compared to adjacent uplands. Similarly, Bell [11] suggests that fire is uncommon in riparian areas in southern California, and that native riparian species are not well adapted to frequent or severe fire. In this area, lightning-ignited wildfires usually occur in late fall, winter, and early spring when riparian vegetation is typically moist and green and would act as a fire break [11]. In southern California, riparian areas invaded by giant reed often occur within grasslands or chaparral shrublands. The limited available research from such ecosystems suggests longer fire return intervals and lower-severity burns in riparian areas relative to adjacent upland vegetation [30]. Human-caused wildfires often occur during the dry months of the year (July through October) in southern California, when drier conditions make riparian vegetation more vulnerable to fire damage [11].
Information regarding the effects of giant reed on fuels and fire regime characteristics in plant communities in which it is invasive in North America is limited to accounts from southern California. Although evidence is entirely anecdotal, several accounts (e.g., [11,20,29,84,95]) describe changes in fuels, fire characteristics, and/or postfire plant community response in southern California riparian areas invaded by giant reed that are suggestive of an invasive grass/fire cycle. Because giant reed grows quickly and produces large amounts of biomass [74] in dense stands described as having "large quantities of dry material" [95], it is conceivable that its invasion introduces novel fuel properties to the invaded ecosystem. It thus has the potential to alter fire behavior and the fire regime (sensu [14,19]). Giant reed is among the most productive of plant communities and can produce over 20 tons of aboveground biomass per hectare under some conditions [74]. Scott [84] observes that in the Santa Ana Basin in southern California, the invasion of giant reed into riparian corridors has doubled and in some areas tripled the amount of fuels available for wildfire.
According to Bell [9,11] giant reed is "extremely flammable" throughout most of the year, and once established increases the probability of wildfire occurrence and the intensity of fires that do occur. This observation is upheld by manager and newspaper accounts of intense wildfires fueled by giant reed in Riverside County (as cited in [95]), the Santa Ana River drainage (J. Wright, personal communication in [87]), and the Russian River further north [29]. For example, a fire in Soledad Canyon in January 1991 was said to have "burned aggressively through the riparian vegetation" due to dry conditions from a prolonged drought coupled with the presence of dried stands of giant reed (Joyce, personal observation cited in [95]). Dudley [29] describes destructive fires fueled by continuous, 15-foot-high colonies of giant reed along the Santa Ana River, noting that "such flammable vegetation is now changing riparian corridors from barriers to the spread of fires into wicks that carry fire up and downstream, into highway bridges or crowns of native, fire-sensitive trees". See Fire hazard potential for more information on this topic.
As of this writing (2004) no research is available on postfire response of giant reed; however, observations indicate that in most circumstances fire cannot kill the underground rhizomes and probably favors giant reed regeneration over native riparian species (e.g., Gaffney and Cushman 1998, cited in [28]). One week after a fire in Soledad Canyon in January 1991, for example, burned giant reed colonies were sprouting from their extensive rhizomes. Many sprouts were over 2 feet (0.6 m) tall within 2 weeks after the fire, even though January is normally the dormant period for giant reed. Most willow, mulefat, and aquatic plants were also burned, and many cottonwoods were scorched. The aquatic plants in the stream were the only plants other than giant reed that were recovering within the first few weeks of burning. In this way, fire gives giant reed an advantage over native riparian plants, and its dominance in the area has increased dramatically (Joyce, personal observation in [95]). In this sense, Bell [11] suggests that riparian communities invaded by giant reed can change from "flood-defined" to "fire-defined" communities, as has occurred on the Santa Ana River. This grass/fire cycle would thus result in river corridors dominated by stands of giant reed with little biological diversity [11].
As mentioned above, there is little research regarding FIRE REGIMES and fire return intervals in riparian areas. However, riparian communities may be influenced by the FIRE REGIMES of adjacent and surrounding plant communities. The following table provides fire return intervals for plant communities and ecosystems where riparian vegetation may include giant reed, though its invasiveness in many of these communities has not yet been demonstrated. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Although giant reed has a wide distribution in North America, details about site characteristics where it is invasive are limited. Most available information on its biology and ecology in North America comes from reviews and studies in California.
Giant reed is a hydrophyte, and grows best where water tables are near or at the soil surface [79]. Giant reed growth may be retarded by lack of moisture during its first year, but drought causes no serious damage in patches 2 to 3 years old [74]. In California, it typically grows along lakes, streams, drains and other wet sites [11]. It is well adapted for establishment and spread in riparian areas with regular flood cycles (see Asexual regeneration). In California, it is most commonly associated with waterways with altered hydrologic regimes (e.g., dams) and/or disturbed riparian vegetation, but can also establish in the understory of native riparian vegetation [28]. In southern California giant reed reaches peak abundance downstream along major rivers in coastal basins, and has generally not spread up the steep, narrow canyons that characterize lower montane areas [87]. It establishes primarily on streamside microsites, but can spread beyond the zone occupied by native riparian vegetation [24,28,102], and can occur on dry riverbanks far from permanent water [28]. A study along the San Luis Rey River in San Diego County found the highest concentration of giant reed colonies within 24 feet (7.3 m) of the river. The authors suggest frequency and magnitude of river flow contribute to this pattern of distribution [80].
Giant reed tolerates excessive salinity and periods of excessive moisture [74]. In South Carolina, it has invaded abandoned rice fields and grows in brackish water [86]. In a greenhouse experiment designed to test the tolerance of giant reed to salt stress, Peck [73] determined giant reed can grow in saline conditions and may be able to invade and persist in salt marshes.
Reviews (e.g., [24,28,49,74]) report that giant reed grows on a variety of soil types including coarse sands, gravelly soil, heavy clays, and river sediments; however, the sources and context of this information are unclear. Stephenson and Calcarone [87] suggest that it requires "well-developed" soils to become established, while DiTomaso [24] indicates that giant reed is "best developed in poor, sandy soil and in sunny situations," and survives in areas with pH values between 5 and 8.7. Purdue [74] states that its growth is most vigorous in well-drained soils where moisture is abundant.
Giant reed occurs in areas with annual precipitation ranging from 12 to 158 inches (300-4,000 mm) [24]. According to Purdue [74], it is a warm-temperate or subtropical species, and is able to survive very low temperatures when dormant, but is subject to serious damage by frosts that occur after initiation of spring growth.
In California, giant reed is apparently restricted to elevations below 1,640 feet (500 m) [47]. However, Perdue [74] reports it grows at altitudes to 8,000 feet (2,438 m) in the Himalayas.
Elevation ranges reported for giant reed in other areas include:
Nevada: 2,500 to 4,000 feet (760-1,220 m) [56]
New Mexico: 4,000 to 4,500 feet (1,220-1,370 m) [62]
Utah: 2,790 to 4,100 feet (850-1,250 m) [103]
Impacts: Bell [11] considers giant reed to be the greatest threat to southern California's remaining riparian corridors. It is so widespread and problematic in this area that more than 20 public and private organizations came together to form the Santa Ana River Arundo Management Task Force, also known as Team Arundo [54].
Once established, giant reed often forms monocultural stands that physically inhibit growth of other plant species [11,80]. For example, Douthit [26] describes a 1993 preliminary riparian assessment of the Santa Ana River basin where in the Riverside West Quad, 762 acres (308 ha) of 1,116 acres (470 ha) of riparian vegetation are impacted by giant reed. Of the impacted acres, 535 acres (217 ha) are monospecific stands of giant reed.
Although evidence is entirely anecdotal, several accounts (e.g., [11,20,29,84,95]) describe changes in fuels, fire characteristics, and/or postfire plant community response in southern California riparian areas invaded by giant reed that are suggestive of an invasive grass/fire cycle. The result of such cycle is loss of native riparian species, and continued dominance and spread of giant reed. See Fire ecology for more details.
Canopy structure of giant reed colonies differs from that of native vegetation, resulting in changes in water quality and wildlife habitat. The lack of stream-side canopy structure may result in increased pH in the shallower sections of rivers due to high algal photosynthetic activity [9,17]. In turn, high pH facilitates conversion of ammonium (NH4+) to toxic ammonia (NH3), which further degrades water quality for aquatic species and for downstream users [9]. Several species listed as endangered are further threatened by giant reed invasion and control efforts in San Francisquito Canyon including least Bell's vireo, unarmored threespine stickleback, and Nevin's barberry (Mahonia nevinii) [95].
Giant reed is becoming a major biological pollutant of river estuaries and beaches. It is often ripped out of the soft bottoms of rivers during storms and washed downstream into flood control channels [25]. Giant reed growing in flood control channels necessitates constant removal. It can form debris dams against flood control and transportation structures such as bridges and culverts [29,37]. Because the rhizomes of giant reed grow close to the surface, they break off during floods. When the root mass breaks away during these floods the riverbanks are destabilized. Destabilization of riverbanks is the leading cause of flooding in southern California [99].
Iverson [50] provides insight into the economics of giant reed's impact on water use. He estimates giant reed transpires 56,200 acre-feet of water per year on the Santa Ana River, compared to an estimated 18,700 acre-feet that would be consumed by native vegetation - the difference being enough water to serve a population of about 190,000 people. If that amount of untreated water (37,500 acre-feet) was purchased from the Metropolitan Water Association it would cost approximately $12,000,000 in 1993 dollars [50].
Control: A suite of methods is needed to control giant reed depending on presence or absence of native plants, size of the stand, amount of biomass involved, terrain, and season. The key to effective treatment of established giant reed is killing or removing the rhizomes [11].
To be successful, a program to eliminate a riparian invasive plant like giant reed must start at the uppermost reaches of the watershed and work down stream. This means there must be coordination with all of the landowners and land managers, top to bottom, in a watershed. Regulatory agencies must provide technical assistance and required permits, and private landowners must provide work crews access to land [99].
To adequately coordinate removal of giant reed in a watershed, 3 programs need to be operating: 1) create a functional mapped database that contains hydrology, land ownership/use, infestations, project sites, etc.; 2) coordination with regulatory agencies to plan mitigation project sites to fit within other current projects; 3) regular meetings of stakeholders to share information regarding threats from giant reed, control techniques, funding opportunities, and each stakeholder's direct role and responsibility [99].
Prevention: Grading and construction can spread giant reed [80]. Care must therefore be taken in areas where it occurs such that soil disturbance and movement of plant parts is minimized.
Integrated management: A popular approach to treating giant reed has been to cut the stalks and remove the biomass, wait 3 to 6 weeks for the plants to grow about 3.3 feet (1 m) tall, then apply a foliar spray of herbicide solution. The chief advantage to this approach is less herbicide is needed to treat fresh growth compared with tall, established plants, and coverage is often better because of the shorter and uniform-height plants. However, cutting the stems may result in plants returning to growth-phase, drawing nutrients from the root mass. As a result there is less translocation of herbicide to the roots and less root-kill. Additionally, cut-stem treatment requires more time and personnel than foliar spraying and requires careful timing. Cut stems must be treated with concentrated herbicide within 1 to 2 minutes of cutting to ensure tissue uptake. This treatment is most effective after flowering. The advantage of this treatment is that it requires less herbicide and the herbicide can be applied more precisely. It is rarely less expensive than foliar spraying except on very small, isolated patches or individual plants [11].
An investigation to test the effectiveness of glyphosate for control of giant reed was conducted in southern California by Caltrans, the state transportation agency. Results indicate cut-stem treatments, regardless of time of application (May, July, or September), provided 100% control with no resprouting. In contrast, virtually all plants that were left untreated following cutting resprouted vigorously. Foliar treatments produced highly variable results with top die-back varying from 10 to 90% and resprouting ranging from 0 to 100% at various sites. The authors conclude treatment of cut stems appears more effective than foliar spraying in controlling giant reed with glyphosate [34].
In 1995, a full-scale project for control of giant reed was initiated in San Francisquito Canyon in the Angeles National Forest. The standing giant reed was mulched in place, using a hammer flail mower attached to a tractor, and then glyphosate was applied to the resprouts. Initial mulching occurred in October and November, 1995. Resprouts in spring, 1996, were treated with a solution of glyphosate in April, May, July, and August. Resprouts were treated again in June and September, 1997. In 1998, giant reed continued to resprout in the treatment area, but comprised only 1% of vegetative cover, as compared to 30% to 80% prior to treatment [8]. No information is provided about the composition of the plant community posttreatment.
Physical/mechanical: Minor infestations of giant reed can be eradicated by manual methods, especially where sensitive native plants and wildlife might be damaged by other methods. Hand pulling works with new plants less than 6.6 feet (2 m) in height, but care must be taken that all rhizomes are removed [49]. This may be most effective in loose soils and after rains have loosened the substrate. Giant reed can be dug using hand tools and in combination with cutting plants near the base. Stems and roots should be removed and burned on site to prevent rerooting. The fibrous nature of giant reed makes using a chipper difficult (R. Dale personal communication in [28]). For larger infestations on accessible terrain, heavier tools (rotary brush cutter, chainsaw, or tractor-mounted mower) may facilitate biomass removal followed by rhizome removal or chemical treatment. Such methods may be of limited value on complex or sensitive terrain or on slopes over 30%. These methods may also interfere with re-establishment of native plants [49]. Mechanical eradication of giant reed is extremely difficult, even with the use of a backhoe, as rhizomes buried under 3 to 10 feet (1-3 m) of alluvium readily resprout (R. Dale personal communication in [28]).
Cut material is often burned on site, subject to local fire regulations, because of the difficulty and expense involved in collecting and removing or chipping all material. Stems and roots must be removed, chipped, or burned on site to avoid re-rooting (Dale, personal communication in [28]).
Fire: See Fire Management Considerations.
Biological: Tracy and DeLoach [93] provide an exhaustive summary of the search for biological control agents for giant reed in the United States. Areas dominated by giant reed in North America are essentially devoid of wildlife. This means native flora and fauna do not offer any significant control potential [11]. It is uncertain what natural controlling mechanisms for giant reed are in its countries of origin, although corn borers (Eizaguirre and others 1990 in [11]), spider mites [31], and aphids [65] have been reported in the Mediterranean. A sugar cane moth-borer in Barbados is reported to attack giant reed, but it is also a major pest of sugar cane and is already found in the United States in Texas, Louisiana, Mississippi, and Florida [94]. A leafhopper in Pakistan utilizes giant reed as an alternate host but attacks corn and wheat [1].
In the United States a number of diseases have been reported on giant reed, including root rot, lesions, crown rust, and stem speckle, but none seem to have seriously impacted advance of this weed [11].
Giant reed is not very palatable to cattle, but during the drier seasons they will graze the young shoots, followed by the upper parts of the older plants [108]. In many areas of California the use of Angora and Spanish goats is showing promise for controlling giant reed [21].
Chemical: Application of herbicides on giant reed is most effective after flowering and before dormancy. During this period, usually mid-August to early November in southern California, the plants are actively translocating nutrients to the root mass in preparation for winter dormancy. This may result in effective translocation of herbicide to the roots [11]. Comparison trials on the Santa Margarita River in southern California indicate foliar application during the appropriate season results in almost 100% control, compared with only 5 to 50% control using cut-stem treatment. Two to 3 weeks after foliar treatment the leaves and stalks brown and soften creating an additional advantage in dealing with the biomass. Cut green stems might take root if left on damp soil and are very difficult to cut and chip. Treated stems have little or no potential to root and are brittle (Omori 1996 in Bell [11]). Bell [11], Hoshovsky [49], and Jackson [52] provide detailed information on specific herbicides and concentrations used to treat giant reed.
In the proceedings from a workshop on giant reed control published online, Bell [11] asserts pure stands of giant reed (>80% canopy cover) are most efficiently and effectively treated by aerial application of an herbicide concentrate, usually by helicopter. Helicopter application can treat at least 124 acres (50 ha) per day. In areas where helicopter access is impossible and giant reed makes up the understory, where patches are too small to make aerial application financially efficient, or where giant reed is mixed with native plants (<80% canopy coverage), herbicides must be applied by hand.
Cultural: Giant reed appears to be insensitive to flood regime. It survives and spreads through vegetative propagation during long periods without flooding but spreads during flood events as well. Because it does not reproduce sexually, giant reed is not affected by the timing of spring flows, but can establish any time that flood flows carry and deposit stem fragments or rhizomes. It thrives along edges of reservoirs, irrigation canals, and other structures where timing of drawdowns is incompatible with maintenance of native species [97].Conversely, native riparian species and communities depend on natural flood regimes for maintenance and reproduction. If natural flood dynamics are maintained as part of an integrated management approach, native species may have a better chance of competing with giant reed in the long term [11].
Available evidence indicates giant reed provides neither food nor habitat for native species of wildlife [11]. Bell [11] speculates that insects are sparse in sites dominated by giant reed because of abundant chemical defense compounds produced by the plant.
Palatability/nutritional value: Giant reed stems and leaves contain a wide array of chemicals that probably protect it from most native insects and grazers. These chemicals include silica [51,74], triterpines, sterols [18], cardiac glycosides, curare-mimicking indoles [39], hydroxamic acid, and numerous other alkaloids (Bell [11] and references therein).
Giant reed is not very palatable to cattle, but they will eat it during dry seasons [49,108]. Domestic goats will also eat it [21,49].
Giant reed is low in protein but has a comparatively high concentration of phosphorus in the upper portions even when grown on soils with an extremely low concentration of this mineral [74,108].
Nutritional content of giant reed. Results are an average of 2 samples for each category and are presented as percentages of oven-dry weight [108]:
Old plant Young plant Lower half Upper half Lower half Upper half Total nitrogen 0.63 1.10 0.50 1.96 Protein (total N x 6.25) 3.94 6.88 3.13 12.25 Phosphorus 0.082 0.114 0.105 0.152 Calcium 0.52 0.67 0.30 0.43 Magnesium 0.25 0.32 0.12 0.19 Potassium 2.04 2.42 3.09 3.19 Carbohydrate 23.2 21.7 20.0 20.7Cover value: Areas dominated by giant reed are largely depauperate of wildlife [9,11,54]. Additionally, a study by Chadwick and Associates [17] suggests giant reed also lacks the canopy structure to provide shading of bank-edge river habitats, resulting in warmer water than would be found with a native gallery of willows and cottonwoods. In the Santa Ana River system in California, this lack of streambank structure and shading has been implicated in the decline of native stream fishes including the arroyo chub, three-spined stickleback, speckled dace, and the Santa Ana sucker [9,17].
Giant reed has no structural similarity to any dominant riparian plant it replaces and offers little useful cover or nest placement opportunities for birds. Main stems are vertical with no horizontal structure strong enough to support birds [110]. For example, the southwestern willow flycatcher, an endangered species, has not been reported nesting in any vegetation patches dominated by giant reed [97]. Only a few of bird species have been observed using giant reed for nest sites. Dramatic reductions (50% or more) in abundance and diversity of invertebrates were also documented in giant reed thickets in southern California compared with those found in native willow/cottonwood vegetation [29]. Giant reed's most observed use as cover has been by feral pigs [110].
Giant reed has been planted extensively for erosion control along drainage canals [49]. Wynd and others [108] report it can also be used to stabilize sand dunes. It is also used for thatching roofs of sheds, barns and other buildings [49]. Mexican campesinos use new tillers of giant reed for roofing and construction materials. It is the most important construction material in the Juamave region of Mexico [2]. Giant reed makes a good quality paper, and in Italy it is used in the manufacture of rayon [24].
Giant reed is used to make reeds for a variety of musical instruments including bagpipes [11,74]. Reeds for woodwind musical instruments are still made from the culms of giant reed, and no satisfactory substitutes have been developed. The basis for the origin of the most primitive pipe organ, the Pan pipe or syrinx, was made from giant reed [74].
Five thousand years ago Egyptians used giant reed to line underground grain storage bins, and mummies from the 4th century A.D. were wrapped in giant reed leaves. Additional uses include basket-making, fishing rods, arrows, and ornamental plants. Medicinally, giant reed's rhizome has been used as a sudorific, a diuretic, an antilactant, and in the treatment of dropsy [74].
State
Time of flowering California (southern) late summer [11] Carolina, North and South September-October [77] Florida all year [107] New Mexico June to September [62]The reproductive biology of giant reed is not well studied. As of this writing (2004), information on the importance of sexual reproduction, seed viability, dormancy, germination and seedling establishment is not available.
Giant reed reproduces vegetatively by sprouting from rhizomes and stem nodes (reviews by [11,28,49]).
Breeding system: No information is available on this topic.
Pollination: No information is available on this topic.
Seed production: Although giant reed is well adapted in many parts of North America, it rarely, if ever, produces viable seed here (reviews by [11,74])[47].
Seed dispersal: The hairy, light-weight disseminules (individual florets with the enclosed grain) are dispersed by wind [33].
Seed banking: No information is available on this topic.
Germination: No information is available on this topic.
Seedling establishment/growth: Seedlings of giant reed have not been observed in the field [28]. Establishment of giant reed is from fragmented rhizomes or stem nodes that take root (see Asexual regeneration, below).
Giant reed grows very rapidly. In a southern California study, Rieger and Kreager [80] cut an established giant reed community and measured its growth after cutting. Growth rates from established rhizomes averaged 2.5 inches (6.25 cm) per day in the first 40 days and 1 inch (2.67 cm) per day in the first 150 days. Under optimal conditions (i.e., cultivation) giant reed is reported to grow 1.5 to 4 inches (4-10 cm) per day (review by [74]).
Asexual regeneration: Population expansion of giant reed in North America is through vegetative reproduction. This occurs either via underground rhizome extension or from plant fragments carried downstream (review by [28]). Giant reed is well adapted to the high disturbance dynamics of riparian systems, as floods break up clumps of giant reed and spread pieces downstream where they can take root and establish new clones [11,28]. Anecdotal accounts suggest that rhizomes buried under as much as 3 to 10 feet (1-3 m) of alluvium can "readily resprout" (R. Dale, personal communication in [28]).
Much of the cultivation of giant reed throughout the world is initiated by planting rhizomes which root and sprout easily [48,49]. A 1949 joint publication by the U.S. Forest Service and the California Department of Natural Resources, Division of Forestry, describing recommended plants for erosion control [48] states pieces of giant reed rhizomes can be buried to establish the plant. A 1988 paper describes giant reed as a planted rhizome which "performs well" as an understory plant in riparian zones in New Mexico [91]. In a greenhouse experiment, Motamed [68] determined that giant reed stem fragments rooted throughout the growing season.
Giant reed can establish and spread in communities of various successional stages, acting as an early-successional pioneer species, and a late-successional dominant.
According to reviews by Bell [11] and Dudley [28], giant reed is well adapted to the high disturbance dynamics of riparian systems, as floods break up clumps of giant reed and spread pieces downstream where they can take root and establish new clones. In California, it is most common along waterways with altered hydrologic regimes (e.g., dams) and/or disturbed riparian vegetation, but can also establish in the understory of native riparian vegetation [28]. However, establishment of giant reed in dense, mature riparian vegetation may be limited [80].
Once established, giant reed grows quickly [74,80] and spreads vegetatively, often forming monocultural stands that physically inhibit growth of other plant species [11,26,80]. Invaded habitats may thus become pure stands of giant reed [10,80,95].
Although evidence is limited and anecdotal, some authors (e.g., [9,84]) note changes in fuels, fire characteristics, and postfire plant community response that are suggestive of an invasive grass/fire cycle perpetuated by giant reed invasion in southern California riparian areas. Because giant reed produces abundant biomass (i.e., fuel), is "extremely flammable", and responds with rapid growth from sprouting rhizomes after top-kill, it may alter fire regime characteristics and successional processes of invaded riparian ecosystems (see FIRE REGIMES).
The currently accepted scientific name of giant reed is Arundo donax L.
(Poaceae) [13,40,53,56,57,62,63,69,77,103,105,107]. One variety of giant reed
is recognized in the literature:
