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Land Use

Wetlands supporting Scirpus maritimus are often grazed by livestock (Brehm 1979; Sykora et al. 1987; Westhoff 1979; Jerling 1983; Fulton et al. 1986). This bulrush usually replaces presumably more palatable emergents (Klavestad 1957; Britton and Podlejski 1981; Grillas and Duncan 1986). Podlejski (1981, 1982) found higher root-to-shoot ratios and lower underground biomass of S. maritimus in grazed, monotypic stands. Plants are most readily consumed by livestock in early summer when shoots are short and soft (Tyler 1969). Although mean stem densities usually decrease with heavy grazing, such grazing during the growing season usually results in stands of short, nonflowering plants; these stands may have greater stem densities than ungrazed stands (Bassett 1980; Duncan and D'Herbes 1982).

Grazing in northern European salt marshes favors the replacement of S. maritimus and Phragmites australis with Puccinellia maritima and Agrostis stolonifera (Beeftink 1977). Scirpus maritimus can temporarily increase in heavily grazed wetlands if grazing ceases (Coetzer 1987), but under such idle conditions, taller emergents such as Phragmites australis probably completely replace this bulrush in as little as 10 years (Pehrsson 1988). Submersed plants can replace S. maritimus in deeper wetlands that are intensively grazed (Grillas and Duncan 1986).

Natural herbivores, such as muskrats (Ondatra zibethicus), can consume competing emergents and increase the abundance of S. maritimus (McCabe and Wolfe 1988). However, grazing geese, ducks, and other waterbirds, especially along exposed shorelines, can greatly reduce the abundance of this bulrush (Fiala and Kvet 1971). Stands of S. maritimus can be destroyed if grazing by geese that forage on the corms is combined with long-term grazing by livestock (Olsen 1945; Pehrsson 1988).

Scirpus maritimus often inhabits cultivated areas (Visperas and Vergara 1976a; Bassett 1978). In Saskatchewan, plants flourish in wet meadows of moderate salinity that are occasionally rather than frequently cultivated (Walker and Coupland 1970).

Burning of dry stands of S. maritimus can significantly reduce the number of rhizomes in the upper 10 cm of the bottom substrate yet have little effect on vegetative reproduction (Smith, L. 1983). This bulrush occurs in areas formerly dominated by other emergents after draining, burning, and reflooding (Smith and Kadlec 1985b). Stands burned in fall attract avian and mammalian herbivores that reduce standing crops (Smith and Kadlec 1985c). Along the Texas gulf coast, fires in fall and winter expose corms and initiate new growth that is eagerly consumed by wintering geese (Stutzenbaker and Weller 1989). However, in more northerly areas, fires may destroy achenes that wintering waterfowl may otherwise obtain from inflorescences that protrude through the ice (Wetmore 1921). Palmisano (1967) placed S. robustus achenes in a wetland dominated by this species and burned the vegetation in the wetland a few days later. He found slight but probably nonsignificant increases in the speed with which achenes subject to fire germinate. However, he concluded that the results could have been much different had the moisture content of the wetland bottom been lower and the peat layer also burned. Smith et al. (1984) found no increases in protein content of S. maritimus after burning.

Mowing often increases dominance or frequency of S. maritimus (Walker and Coupland 1970; Britton and Podlejski 1981; Cowie et al. 1992) but may gradually decrease shoot length or weaken plants (Vestergaard 1985). Palmer (1986) found the frequency of occurrence and the cover percentage were greater for S. maritimus than for taller emergents in cleared ditches. Mowing with removal of vegetation before reflooding reduces S. maritimus biomass more than burning, probably because of the lack of a nutrient pulse from the ash (Smith and Kadlec 1985d). Culture experiments show that cutting of 110- to 140-day-old shoots of this bulrush induces the emergence of inflorescences, but earlier cutting and non-cutting of controls do not (Visperas and Vergara 1976c). The reasons for this phenomenon are unknown.

Less is known about the effects of common land use practices on S. robustus. Livestock are excluded from some tidal wetlands that support this bulrush because of large tidal amplitudes (Latham et al. 1994). Davison and Neely (1959) considered cattle grazing favorable to this bulrush in the southern United States. However, of the eight most common plants in a large California marsh, Mall (1969) found unsubmerged S. robustus the most vulnerable to damage by cattle grazing. Management to improve stands of S. robustus with cattle is difficult because the animals eat the seedheads and vegetative parts (George 1980). In a Florida wetland, S. robustus appeared after a dense stand of Juncus roemerianus was mowed, but the area was also grazed by cattle (Myers 1956). The percent cover of S. robustus increases after grazing by wintering geese in North Carolina and decreases when the birds are excluded (Smith, T. 1983). When Louisiana wetlands dominated by this bulrush are heavily grazed by wintering geese, the value of these wetlands for livestock grazing and muskrat trapping declines (Lynch et al. 1947).

Fire in stands of Spartina patens in Louisiana wetlands often increases Scirpus robustus or S. olneyi (Penfound and Hathaway 1938; Lay and O'Neil 1942; Wells 1942). With no further disturbances, other emergents largely replace these bulrushes within 1 to 2 years (Beter 1957). Whipple and White (1977) noted that although S. robustus appears after fires in these wetlands, the order of importance of the original dominant species remains unchanged. They attributed this resiliency to the long history of periodic fires in these wetlands. Louisiana landowners commonly burn wetlands to attract waterfowl, facilitate travel, and improve livestock grazing, but the resultant plant species composition depends on water depths, tides, and weather after burning (Hoffpauer 1968). In South Carolina, waterfowl increase their use of S. robustus when wetlands that support dense stands are drained, burned, and reflooded in late winter (Loesch et al. 1989). Wetlands burned in strip patterns during January and then flooded with 20-25 cm water seem to attract the most birds (R. K. Williams, Kinloch Plantation, Georgetown, South Carolina, personal communication). Established stands of S. robustus in California are mowed in August to reduce rankness and aid in control of Typha (Connelly 1979).