Northern Prairie Wildlife Research Center
Vogl (1967) used fire to control woody plants in Wisconsin wetlands, and Truax and Gunther (1951) used fall and winter burns to control undesirable vegetation in Horicon Marsh, Wisconsin. Uhler (1944) stated that several wetland plant species were controlled in Minnesota marshes by burning when the substrate soils were dry.
Fire has been used extensively to open up dense stands of vegetation in marshes (Ward 1942; Uhler 1944; Schlichtemeier 1967; Ward 1968; van der Toorn and Mook 1982; Ball 1984). Burning has also been used to control plant succession and to promote the aquatic plants that produce seeds and roots for waterfowl foods (Grange 1949; Yancey 1964) and to improve the use of wetlands by breeding waterfowl (Evans and Black 1956).
Phragmites is an aggressive perennial of little value to waterfowl (Ward 1942), often forming dense stands in northern marshes.
Pratt and Andrews (1981) estimated the dry weight of an above-ground standing crop of phragmites to be as much as 0.23 lb/sq ft (1,118 gm/sq m). Stem densities up to 19 stems/sq ft (200 stems/sq m) have been recorded in a Utah marsh (Cross 1983). Weller (1981) stated that phragmites communities are very productive, having an estimated 9.4 T/A (21 metric tons per hectare) of emergent plant material produced per growing season.
Spring fires are effective in removing stem litter and creating openings in dense stands of phragmites (Ward 1942). Schlichtemeier (1967) observed an 85% decrease in accumulated dead stems after burning over the ice in February.
Fires conducted in early spring can initiate an earlier emergence of overwintering buds (Cross 1983) and increase the opportunity for frost to damage new growth (Mook and van der Toorn 1982; Thompson and Shay 1984).
Generally, the thicker shoots emerge first (van der Toorn and Mook 1982; Cross 1983). When these shoots are damaged by fire or frost, plants respond by forming one or more thinner regrowth shoots (Mook and van der Toorn 1982; van der Toorn and Mook 1982; Thompson and Shay 1984).
Higher values for shoot densities, flowering shoot densities, aerial biomass, and carbohydrate reserves were observed after a mid-May burn at the Delta Marsh in Manitoba (Thompson and Shay 1984). These observations support Ward's (1968) statement that spring burns maintain the climax status of mature stands of phragmites.
After a July fire in the Delta Marsh, regrowth attained only half of its normal height and stem densities were reduced (Ward 1968). Thompson and Shay (1984) found that an August burn resulted in lower values for aerial biomass, standing crop of overwinter buds, shoot biomass, and flowering shoot densities the following summer.
The movement of nutrients from shoots to rhizomes for deposition in winter buds begins in mid-June (Mook and van der Toorn 1982). This is also the time when rhizome carbohydrate levels are at a minimum, suggesting that a fire in mid-June could have a more deleterious effect on stands than a burn conducted earlier in the growing season (Thompson and Shay 1984).
These observations suggest that summer burns have potential for thinning dense stands of phragmites.
October burns may enhance vegetative spread during the following growing season through higher below ground biomass and higher carbohydrate reserves (Thompson and Shay 1984). Higher aerial biomass and lower flowering shoot densities were also noted in these burns.
Burning of phragmites stands when the substrate is dry and the humidity of litter and stem bases is low can damage rhizomes. The effects of these intense burns vary from retarding emergence for 1 to 2 months (van der Toorn and Mook 1982) to burning deep into peat layers and destroying the rhizomes, thereby permanently eliminating stands (Ward 1942; Uhler 1944; Cross 1983).
In summary, phragmites can be maintained and even encouraged by using spring and fall burns. It also can be reduced and eliminated by using summer burns. Fire in stands of phragmites with dry substrates in late summer (June through August) combines the effect of burning when carbohydrate reserves are low with the potential of burning deep into organic soils. Such a burn could have a significant impact on the rhizome network of a dense stand of phragmites.
Whitetop is a common hydrophyte in the shallow marsh zone of wetlands throughout the prairie pothole region (Stewart and Kantrud 1971).
Seasonal wetlands with flooded stands of whitetop were the preferred brood-rearing habitat of mallards (Talent et al 1982).
Whitetop growing on drier ground is used as nesting cover by waterfowl (Ward 1968). Shallow seasonal wetlands containing stands of whitetop frequently dry up by late summer and are mowed for hay (Diiro 1982; Neckles et al 1985).
Burning and mowing can increase the yield of whitetop (Smith 1973). Herbage production ranged from 2,744 to 13,436 lb/A (3,080 to 15,080 kg/hectare), with a production estimate of 10,246 lb/A (11,500 kg/ha) for burned areas.
Millar (1973) found that burned stands of whitetop apparently suffered no damage. Kantrud (1986) has suggested that whitetop is a fire-tolerant species. Shallow basins subjected to repeated burning and mowing will form pure stands of whitetop; grazing will eventually eliminate whitetop (Smith 1973).
The removal of litter enhances growth and increases shoot densities of whitetop on burned areas (Diiro 1982). Ward (1968) found that after a spring fire had opened dense stands of phragmites, whitetop growth was stimulated, stem densities increased, and whitetop invaded areas formerly dominated by phragmites. Diiro (1982) observed that whitetop plants grew most rapidly in seasonal wetlands that were burned on June 1.
Spring burns in wetlands that are not flooded after the fire have no significant increase in whitetop production (Diiro 1982). Therefore, spring burning is recommended to manage whitetop stands only in wetlands which will be flooded following a burn (Neckles et al 1985).
Fall burning removes litter and darkens the substrate, causing the soils to warm rapidly the following spring. This enhances shoot growth and increases stem densities (Diiro 1982; Neckles et al 1985). Diiro (1982) found that whitetop plants in fall-burned ponds were taller than plants in control ponds during early spring.
Production of whitetop was greater on fall-burned ponds than in any other burn treatment used (Diiro 1982). Smith (1973) stated that fall burning can increase production up to 55% if the area is flooded the following spring.
Because residual vegetation is removed during a fall burn, the amount of snow trapped in a burned wetland may be reduced. But, as with spring burns, those wetlands that are burned in the fall and receive sufficient runoff the following spring will have the highest production increase (Smith 1973; Diiro 1982; Neckles et al 1985).
Cattail has become a problem in many prairie wetlands because it often forms dominant monotypic stands (Linde et al 1976). These tall, dense monotypic stands are less attractive to wildlife (Kantrud 1986). Fire is often used to increase interspersion in cattail stands (Uhler 1944; Beule 1979; Ball 1984).
Some studies have shown that fire is not an effective means of controlling cattail (Beule 1979; Gorenzel et al 1981). In a Utah marsh burned in September, cattail growth the following summer had higher shoot weights (Smith and Kadlec 1985) and higher protein content (Smith and Kadlec 1984) than cattail from control areas. This would suggest that cattail stands may even be enhanced by fire, depending on the conditions.
Nevertheless, under proper conditions, fire can control cattail. Interspersion will improve by burning over the ice. Stem densities were reduced by 70% and no fruiting heads were formed on areas burned over the ice and flooded the following spring (Ball 1984).
Burning or mowing cattail over the ice is less effective in eliminating cattails when the remaining stubble is not flooded the following spring.
Cattail rhizomes are supplied with oxygen during the dormant season by old stems extending above the water surface (Linde et al 1976). Removal of these stems by burning and subsequent flooding of the stubble the following spring will cause anaerobic conditions to develop in the rapidly growing shoots (Ball 1984), causing many shoots to die before emerging above the water surface.
Ball (1984) also concluded that burning over the ice is a practical technique for improving interspersion when water levels are adequate to submerge stubble the following spring. He also noted that backing fires left shorter stubble above the ice, requiring a smaller increase in water levels to flood stubble the following growing season.
Like phragmites, cattail can also be killed by burning when the substrate is dry. Uhler (1944) stated that "root burns," which occurred when the soil was dry 3 to 6 inches (8 to 15 cm) below the surface, provided long-term control of cattail. Beule (1979) noted that occasionally a fire that had burned into the peat layer of a dry marsh would kill cattails.
Linde et al (1976) found that the total non-structural carbohydrate levels in cattail stands at the Horicon Marsh reached a minimum in late June. Therefore, burning in late June or early July in wetlands with dry substrates could be a potentially effective technique for killing cattail. The use and effectiveness of such a burn would depend on the ability to draw the water levels down enough to dry the substrate surface.
A February burn over the ice in Nebraska reduced stem densities of bulrush (Scirpus spp) by 60% (Schlichtemeier 1967).
The annual production of bulrush species in a Utah marsh was not affected by a burn conducted in September (Smith and Kadlec 1985). However protein levels were higher in hardstem bulrush (S. acutus) (Smith and Kadlec 1984) and shoot weights lower in bulrush (S. lacustris) (Smith and Kadlec 1985) following the same burn.
Sedge communities were maintained with annual burning in Wisconsin wetlands (Thompson 1959). Millar (1973) found no change in sedge stands after repeated burning, suggesting fire tolerance.
Stands of spikerush (Eleocharis palustris) also appeared to change little after repeated burns (Millar 1973).
In summary, wetland grasses and sedges can be enhanced with properly timed, less intense burns. In contrast, a slow moving fire which would burn deep into the organic soil or peat of wetland substrates will have an impact on all hydrophytes (Uhler 1944; Yancey 1964; Millar 1969). Uhler (1944) noted that such a fire (called a "root burn") provided a control of phragmites, cordgrass (Spartina spp), cattail, river bulrush (Scirpus fluviatilis), sedges, and other hydrophytes.
The use of a "root burn" fire is limited to marshes that can be completely drawn down or those marshes experiencing severe or periodic drought.