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The Alkali (Scirpus Maritimus L.) and Saltmarsh (S. Robustus Pursh) Bulrushes: A Literature Review

Propagation and Management

Note: Some of the chemicals mentioned in this and the following section may be considered unsafe for application to aquatic environments, and no endorsement of the use of any particular chemical is implied or intended. Readers are hereby advised to strictly adhere to application instructions on pesticide labels formulated by the U.S. Environmental Protection Agency. Since the early 1930's, impounded coastal wetlands, where Scirpus robustus and other hydrophytes are grown for waterfowl food, have been reclaimed from colonial-age rice paddies in the southern and southeastern United States (Tiner 1977; Miglarese and Sandifer 1982; Tompkins 1986). The area of individual management units may exceed 4,000 ha (Sandifer et al. 1980). Similarly, during the late 1800's, cropland and pastures began to be reclaimed from tidally influenced wetlands in California; these efforts largely failed, and, during the 1930's, private hunting clubs began to acquire and manage most of these lands for waterfowl (Mall 1969). Additional interest in the management of S. robustus grew from its value to muskrats, especially in Louisiana (Lay and O'Neil 1942).

Common problems with the management of S. robustus in impoundments and natural wetlands include the plant's inconsistent achene germination, difficulties with maintenance of proper water levels and timing of annual salinity cycles, and competition from more and less salt-tolerant hydrophytes. Localized problems are acidification of bottom sediments caused by the oxidation of iron polysulfides and conflicts with attempts to control saltmarsh mosquitoes. Research findings and suggestions on how to produce and maintain S. robustus published before 1970 (Lay and O'Neil 1942; O'Neil 1949; Myers 1956; Beter 1957; Neely 1958, 1960, 1962; Davison and Neely 1959; Chabreck 1960; Miller 1962; George 1963; Palmisano 1967; Baldwin 1968; Hoffpauer 1968; Palmisano and Newsom 1968; Perkins 1968; Soileau 1968; Chandler 1969) indicate that the following factors are necessary to produce good stands: (1) flat- or nearly flat-bottomed wetlands; (2) achenes seeded in spring at adequate rates by aircraft (large areas) or corms planted 8-15 cm deep (small areas); (3) well-lit environments provided by dry bottoms irrigated with shallow water just prior to seeding, except where acidification of bottom sediments by oxidation of iron polysulfides is a problem; (4) water held 3-8 cm deep for 2-3 weeks during germination, followed by drainage to moist-soil conditions for 2-3 days to prevent wave-action damage to seedlings; (5) water-level management after stand establishment whereby levels are raised to depths of no more than 30 cm and then gradually lowered to moist-soil stage one or more times during the growing season; (6) soil extract or water salinities of about 7-10 g/L; and (7) an absence of introduced plants with similar ecological requirements. Managers attract wintering waterfowl by flooding these wetlands to prescribed depths at appropriate times and intervals.

These earlier studies showed that it is possible to maintain established stands for years with sustained management but that control of undesirable plants may be necessary. Irrigations with freshwater impede upward movement of salts to help reduce competition by halophytes. Further reductions in soil salinity and additional control of competing halophytes often are achieved when water tables are low if wetlands are drained for brief periods to take advantage of salt leaching by spring rainfall. Withdrawals of surface water or irrigations with seawater raise salinities and help control glycophytes. In some areas, two crops of achenes are produced with well-timed irrigations and drainages.

No experiments were conducted on the response of S. robustus to livestock grazing in managed impoundments during the pre-1970 period. However, general observations in the southern United States show a favorable response, whereas production in California stands is reduced, especially with summer grazing (Wendell Miller, U.S. Soil Conservation Service, California [retired], personal communication).

In brackish wetlands along the U.S. gulf coast, fire or combinations of fire and tillage in stands of competing emergents promote stands of S. robustus that can persist for 2 or 3 years. Such treatments in more saline wetlands may be totally unsuccessful. Managers sometimes reduce amounts of competing plants such as Spartina patens with properly timed fires, if climatic and tidal conditions after the burns are favorable. Application of some herbicides to competing emergents also favors this species.

In general, early studies revealed that effective management of Scirpus robustus for waterfowl must emphasize improvements to environmental conditions for the species during periods of the reproductive cycle when achene production can be stimulated. These studies also showed that freshening of irregularly flooded salt marshes encourages invasion by S. robustus and that tidal fluctuations can increase salinities to control many pest glycophytes.

Later research and reviews of existing programs refined management of S. robustus in coastal impoundments in the eastern and southern United States (McNease and Glasgow 1970; Palmisano 1970, 1972; Wilkinson 1970; Morgan 1974; Landers et al. 1976; Morgan et al. 1976; Barko et al. 1977; Heitzman 1978; Prevost and Gresham 1981; Epstein and Baughman 1986; Loesch et al. 1989). Brief summaries of current management practices in these areas are available (Prevost 1987; Gordon et al. 1989; Hindman and Stotts 1989; Payne 1992). Falco and Cali (1977) and Kadlec and Smith (1984) reviewed general establishment techniques for hydrophytes. The South Carolina Sea Grant Consortium (1986, 1987) provided additional management and maintenance recommendations for impoundments that support S. robustus communities.

Recent techniques for managing S. robustus include complex water-level management and salinity control measures to take advantage of daily tides and discharges over pre-set spillways for better water circulation. Salinities are carefully and frequently monitored and water tables are maintained below bottom surfaces, especially during critical rainfall periods, to prevent proliferation of undesirable emergents. Modern managers of impoundments also consider the needs of animal species other than waterfowl (e.g., penaeid shrimp and transient marine fish) and try to minimize mosquito production (DeVoe et al. 1986).

Currently, a typical management cycle for established stands of S. robustus includes: (1) a partial spring drainage for 2-8 weeks to create moist-soil conditions, allowing sprouting of belowground parts and minimizing acidification of bottom substrates; (2) a complete drainage in late spring or early summer to water table depths of 25-46 cm below the bottom surface for 1-2 weeks; (3) an early or midsummer irrigation with 15-20 cm of water; and (4) a slow increase in water depths while maintaining water circulation to maturate achenes for use by waterfowl. Above- or below-normal rainfall during late spring or early summer frequently necessitates salinity management. Water salinity in wetlands managed for S. robustus is usually about 1-20 g/L, whereas wetlands of higher salinity are usually managed for submersed species. Salinity stress caused by summer drought may require that managers switch to production of other plants. Impoundments at the lower end of the salinity range (1-5 g/L) are usually managed without a complete drainage in late spring or early summer. New plantings of S. robustus from achenes are made in March on moist bottoms where soluble salts do not exceed 9 ppt. Water levels are raised to no more than 5 cm after seedlings appear. Whole-plant transplants are sometimes used in small areas such as dredge spoils. Transplanting in fall is not recommended because of dormancy in winter.

The later studies of Scirpus robustus showed that burning in winter of dense, established stands can greatly increase use of this species by dabbling ducks, especially when managers quickly reflood stands to optimum foraging depths of 10-15 cm. Burning is usually done every 3 years, during mid-November to mid-March, after hard frosts terminate photosynthesis. Burns in November or December encourage feeding by geese and ducks, whereas burns in February or March facilitate trapping of rodents to reduce their damage to dikes. Managers recommend not burning during drought when the salinity of tidal waters is greater than 15 g/L to avoid creating areas devoid of vegetation. Burning of brackish marshes should be combined with water level and salinity management. Burning and tilling established stands of less desirable perennial emergents generally does not result in great increases in the abundance of S. robustus. Control of undesirable plants with herbicides is costly and the effects are poorly understood, although Jones and Lehman (1987) noted a great increase in S. robustus 2 years after a stand of Phragmites australis was fall-treated with glyphosate.

Techniques for managing S. robustus were also refined in valley and coastal wetlands of California, where stands are subject to high salinities and large seasonal changes in salinities (Ustin et al. 1982). In these wetlands, rapid growth of S. robustus in the spring may increase its competitive advantage over certain halophytes (e.g., Salicornia) during summer periods of high salinity. Although growth of the bulrush may cease completely during these periods, corms survive. Maintenance of the normal cycle of low salinity in spring and high salinity in summer may also prevent the encroachment of less salt-tolerant but highly competitive glycophytes such as Scirpus acutus and Typha latifolia. Studies on natural and impounded wetlands (Rollins 1973; George 1980; Pearcy et al 1982; Ustin et al. 1982; Pearcy and Ustin 1984; [all summarized by Heitmeyer et al. 1989]) show the importance of spring leaching cycles with low-salinity water that is followed by circulation at constant water depths during the growing season. These practices help reduce soil salinity and enhance growing conditions. In other areas, fall flooding may be followed by spring drainage, or a series of spring drainages may be followed by short irrigations in spring or summer or in spring and summer. For established stands in the San Joaquin Valley, Connelly (1979) recommended drainage in March to achieve a 19-21° C bottom substrate temperature for germination of achenes and to stimulate rhizome growth. This is followed by irrigation in May, when flowers are in the pollen stage, to aid achene production. A second irrigation in June helps mature the achenes. Flooding from about October to late March reduces disease potential and plant regrowth and maximizes waterfowl consumption of the achene crop. In summary, management of S. robustus in these wetlands must involve maintenance of annual salinity cycles as well as reductions in yearly average salinities.

Much less is known about management of S. maritimus than of S. robustus, although successful programs to increase populations of the former on Great Plains waterfowl refuges began during the mid-1930's (Steenis 1939). Some S. maritimus is managed for waterfowl as far north as Montana, where irrigation return flows provide a water source (Ball et al. 1989). Plantings of this bulrush can revegetate stripmine ponds in the northern Great Plains (Fulton et al. 1983).

Most information on the management of S. maritimus is from studies in the Great Basin, northern Europe, and the Camargue, France. Work by Wetmore (1921), Jensen (1940), and Nelson (1954) on impoundments in Utah led to studies by Kaushik (1963), Teeter (1963, 1965), Bolen (1964), Craner (1964), and Nelson and Dietz (1966), who outlined the effects of salinity and other factors on the germination, growth requirements, production, ecology, and waterfowl use of several salt-tolerant plants of known importance as waterfowl foods. Methods to control Typha, a serious competitor of S. maritimus in these impoundments, were also investigated. Results of these earlier studies are summarized in Christiansen and Low (1970). More recent investigations improved techniques for the management of S. maritimus. O'Neill (1972) developed methods to increase achene germination of California populations and to seed and manage established stands. Currently, many California wetlands are managed for waterfowl plant foods other than S. maritimus (Mushet et al. 1992). (Note that plants in these California studies may have been S. robustus or S. glaucus or S. maritimus glaucus hybrids; see the taxonomy and distribution sections).

In Utah, L. Smith (1983), Smith and Kadlec (1983), Kadlec and Smith (1984), Smith et al. (1984), Smith and Kadlec (1985a,b,c,d), and Foote (1988) studied the effects of wetland drainage in combination with burning and haying, how composition of seed banks relates to existing vegetation, and the natural movements of achenes among various vegetation types (findings summarized in Smith and Kadlec [1986] and Kadlec and Smith [1989]).

Investigations in northern European salt marshes and in the Camargue wetlands reveal various aspects of the results of livestock grazing on S. maritimus (Pehrsson et al. 1973; Bassett 1980; Britton and Podlejski 1981; Podlejski 1981, 1982; Duncan and D'Herbes 1982; Pehrsson 1988).

A summary of the aforementioned studies indicates that S. maritimus readily pioneers on saline bottoms of managed wetlands if water is applied and depths do not exceed 18 cm. Established stands withstand occasional exposure of bottom substrates. Invasion of glycophytes such as Typha spp. is probable where conductivities of bottom substrates (1:5 soil suspension) fall below about 6 mS/cm. Drainage of the impoundments for at least 2 years increases salinities and allows S. maritimus achenes to germinate and replace the Typha. More S. maritimus achenes germinate under 4-5 cm of water than on moist soil. Plants that germinate under increased salinity compete with S. maritimus in many wetlands. For example, control of the woody halophyte Tamarix pentandra, which is common in the western United States, is difficult after stands enter their second growing season. Fortunately, flooded conditions do not allow T. pentandra to germinate. Therefore, the most practical water-level management scheme for S. maritimus in many areas is alternating drying and reflooding several times during a growing season to keep salinities high enough to discourage glycophytes, while maintaining shallow water during periods when certain competing halophytes are most likely to germinate. Flooding during fall and winter of established stands followed by gradual drainage by midsummer produces good yields of achenes where competition by halophytes is not a problem. In these areas, prolonged flooding in summer results in poor achene production and stands are usually rapidly invaded by Typha and other undesirable freshwater plants. In addition, high water levels can increase wave action and decrease survival rates of corms (Foote 1988).

Burning in spring of stands of S. maritimus after removal of surface water seems to have little influence on achene production and on the number of germinable achenes in the seed bank. Nevertheless, such fires probably are beneficial because the frequency of plants increases while vegetative reproduction continues. In wetlands of coastal Texas, prescribed burning of S. maritimus (probably S. robustus, see taxonomy and distribution sections) increases its use by wintering geese (Stutzenbaker and Weller 1989). Mowing with removal of plants (haying) reduces productivity significantly more than burning, probably because of the lack of a nutrient pulse from the ash. Nevertheless, stands may benefit from occasional haying to remove excess vegetation. In northern Europe, mowing of achene-producing stands of S. maritimus in September should be followed by an increase in water level (Pehrsson 1988). This practice allows ducks to feed on newly mature achenes and discourages the problem plant Phragmites australis.

Cattle and horses readily graze S. maritimus, especially young plants. Cattle often consume only the reproductive buds and inflorescences, even at high stocking rates. Heavy grazing can increase corm consumption by geese because these birds are reluctant to enter dense, ungrazed vegetation. However, severe grazing by livestock can greatly reduce the value of affected wetlands to waterfowl that consume achenes. In the French Camargue, S. maritimus often remains dominant in wetlands regularly grazed by horses during the growing season; without horses, Phragmites australis becomes dominant. Because maximal production of achenes, corms, and herbage of S. maritimus cannot be obtained simultaneously in the same area, Pehrsson (1988) proposed alternating cattle grazing and nongrazing on an interval of several years as the best option for wildlife managers in northern Europe. He noted the need, however, for the development of better methods to control Phragmites australis where S. maritimus may attain high achene production. In some Great Basin wetlands, cattle grazing of stands of S. maritimus after mid-July helps maintain the semiopen aspect preferred by feeding or resting waterfowl. In the northern Great Plains, stands of S. maritimus may benefit from moderate to heavy grazing and tillage (Pederson et al. 1989). In England, herbicides that kill aboveground but not belowground parts of S. maritimus can temporarily control competing emergents (Axell 1982). Regrowth occurs and the bulrush colonizes bare areas formerly occupied by less herbicide-tolerant competitors.

Early attempts by Fischer (1907, cited in Isely 1944) and Martin and Uhler (1939) to obtain high germination rates in S. maritimus and S. robustus were generally unsatisfactory. Isely (1944) showed that the two species are similar because germination of achenes is extremely poor unless they are after-ripened (stratified) and then exposed to relatively high temperatures (30-32° C) and light during the germination period. Thus, best conditions for good germination in the field probably are shallow, clear, warm water. Achenes of S. robustus are highly resistant to deterioration. When submerged, weight loss is only about 1% in 90 days (Neely 1956, 1960, 1962; George 1963). Germinability declines with age of achenes (George and Young 1977) and is highly variable geographically (George 1980). Fresh achenes of both bulrushes require scarification, stratification, fermentation, and extended periods of soaking or other treatments to assure high germination rates and to prevent achenes from drifting away (Steenis 1939; Christensen et al. 1947; Salyer 1949; Clevering 1995).

Salyer (1949) noted that dry-stored achenes of both bulrushes are prone to weevil infestations and require frequent inspection. He recommended planting rootstocks (rhizomes) to establish stands in relatively stable water. Rootstock removal is easier if stands established from seed are first thinned, mowed, and plowed. To prevent the spread of noxious weeds, Salyer (1949) recommended washing rootstocks to free them of soil and extraneous plant material. Rootstocks are resistant to dry, cold conditions and can be stored under heavy layers of straw or other mulch (Steenis 1939). Managers can also plant substrate cores that contain rhizomes to establish stands of S. maritimus (Moody 1978). Transplant sites should not have excessive wave action (Pomeroy et al. 1981). Hoag and Sellers (1994) noted better survival of wild S. maritimus plants than of those grown in a greenhouse.

For both bulrushes, germinability of dry achenes can be improved by soaking them in a dilute (1-4%) solution of sodium hypochlorite (common laundry bleach; George 1963; Clevering 1995). However, the treatment may yield inconsistent germination if posttreatment drying is excessive (George and Young 1977; George 1980). O'Neill (1972) successfully seeded S. maritimus (possibly including S. robustus or "S. tuberosus" = S. glaucus or various hybrids; see taxonomy and distribution section) after such treatment in combination with a regime of high illumination and temperature. He achieved the regime by holding achenes in an outdoor pit lined with plastic sheeting and covered with transparent film. Achene dormancy is broken in about 12-15 days, after which sowing can begin immediately at 3.4-5.6 kg wet weight/ha on shallowly flooded areas. The most effective procedure is probably moist overwinter storage followed by air-drying in spring just before sowing. Moist achenes stratified for 2-3 months at constant 2° C may yield germination rates as high as 97%. Stratification periods should not exceed 2 years (Clevering 1995). Prevost and Gresham (1981) recommended submersing achenes in polyester bags in brackish impoundments for 45 days. Achenes mixed with clean sand and refrigerated in darkness at 4.5° C for 45 days show even better germination but require more material and equipment. The germination rate of achenes dry-stored for 4 months can reach 80% if the achenes are scarified by immersion in concentrated sulfuric acid for 2 minutes (Dietert and Shontz 1978).

Achenes of both bulrushes can also be pre-germinated (incubated until roots or epicotyls emerge from the achenes) and held in outdoor peat pots until used (Garbisch 1993; Clevering 1995). Clevering (1995) noted higher rates of plant establishment by S. maritimus when pre-germinated achenes were buried at 0.5 cm in sediment than when raw achenes were similarly buried or merely sown on the sediment surface. Gloves should be worn when handling these achenes because the awns on their scales frequently penetrate the skin.

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