Use prescribed fire to control problematic plants: brackish/salt marshes
Overall effectiveness category Awaiting assessment
Number of studies: 4
Background information and definitions
Prescribed burns can be used to manage problematic plants that may overgrow and outcompete desirable vegetation. By removing above-ground vegetation, fire can also be used to manage the physical vegetation structure (Flores et al. 2011). Prescribed burns may have only temporary effects: many plants can regrow from remaining stumps, roots or rhizomes (underground horizontal stems).
Potential benefits of management by prescribed burning should be weighed up against potential risks. For example, it can be difficult to control the intensity, duration and area of a prescribed burn: burning when the ground is wet and/or cold might be safer (Hackney & de la Cruz 1981). Burning can damage seed banks, and might produce apparently desirable changes in vegetation over the short term followed by a rapid return to a degraded state. Burning can also damage the physical habitat (e.g. by exposing sediments, increasing erosion and reducing accumulation of organic matter; McKee & Grace 2012) and may be harmful to animals like amphibians (Smith & Sutherland 2014) and birds (Flores et al. 2011).
The timing and duration of monitoring might be particularly important when evaluating the effects of this action. Burning might produce apparently desirable changes in vegetation over the short term, followed by a rapid return to a degraded state.
For this action, “vegetation” refers to overall or non-target vegetation. Studies that only report responses of target problematic plants have not been summarized.
Flores C., Bounds D.L. & Ruby D.E. (2011) Does prescribed fire benefit wetland vegetation? Wetlands, 31, 35–44.
Hackney C.T. & de la Cruz A.A. (1981) Effects of fire on brackish marsh communities: management implications. Wetlands, 1, 75–86.
McKee K.L. & Grace J.B. (2012) Effects of Prescribed Burning on Marsh Elevation Change and the Risk of Wetland Loss. U.S. Geological Survey Open-File Report 2012-1031.
Smith R.K. & Sutherland W.J. (2014) Amphibian Conservation: Global Evidence for the Effects of Interventions. Pelagic Publishing, Exeter, UK.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled study in 1992–1993 in an ephemeral brackish marsh dominated by saltgrass Distichlis spicata in California, USA (De Szalay & Resh 1997) found that burned plots had greater plant species richness than unburned plots, and lower overall vegetation cover, but similar or greater cover of dominant species other than saltgrass. After 11 months, burned plots had greater overall plant species richness than unburned plots (burned: 6.3 species/m2; unburned: 3.1 species/m2) but lower overall vegetation cover (burned: 88%; unburned: >99%). Burned plots had lower saltgrass cover (burned: 65%; unburned: 99%) despite a statistically similar saltgrass density under both treatments (burned: 2,000; unburned: 1,770 stems/m2). Of six other dominant herb species, two had greater cover in burned plots (burned: 9–11%; unburned: 0%) whilst four had statistically similar cover under each treatment (burned 2–17%; unburned: <1–5%). Density of these species was not reported. Methods: Ten pairs of 100-m2 plots were established in an impounded brackish marsh, managed for waterfowl (autumn/winter flooding with spring/summer drawdown) but dominated by saltgrass. In September 1992, ten plots were burned (one plot/pair; 50 m2/plot). The other plots were not burned. In August 1993, vegetation was surveyed in two 1-m2 quadrats/plot. Cover estimates included live and dead standing plants.Study and other actions tested
A replicated, randomized, paired, controlled study in 1995–1997 in 14 brackish and salt marshes in Louisiana, USA (Gabrey et al. 1999) reported that prescribed winter burning had no significant effect on plant species richness, vegetation structure and overall vegetation cover in the following winter, but increased cover of the two dominant plant species and reduced cover of dead vegetation. Unless specified, statistical significance was not assessed. After one year, a total of 5–8 plant species were recorded across burned plots (vs 6–7 species across unburned plots). Burned and unburned plots created statistically similar visual obstruction (data reported as an index combining plant height and horizontal cover) and had statistically similar overall vegetation cover (burned: 72%; unburned: 76%). However, burned plots had greater live cover of the two dominant plant species (saltmeadow cordgrass Spartina patens: 28–59%; saltgrass Distichlis spicata: 2–11%) and less cover of standing dead vegetation (35–61%) than unburned plots (saltmeadow cordgrass: 19–23%; saltgrass: 1–5%; dead: 75–76%). Vegetation was also surveyed 1–2 months after burning. At this point, all metrics apart from species richness were lower in burned than unburned plots (see original paper for data). Methods: The experiment was carried out in 14 coastal marshes of varying salinity and tidal influence. In winter 1995/1996, when 5 cm of water covered the marshes, one random half of each marsh was burned. In January–February 1996 and 1997, vegetation was surveyed at 40 points in each half of each marsh. This study was based on the same experimental set-up as (3).Study and other actions tested
A replicated, randomized, paired, controlled study in 1995–1998 in 11 brackish and salt marshes in Louisiana, USA (Gabrey et al. 2001) found that prescribed winter burning typically had no significant effect on summer plant species richness but had mixed effects on the cover of two dominant plant species and caused only a temporary reduction in cover of dead vegetation. Averaged over the three summers following intervention, burned and unburned plots had statistically similar plant species richness in three of four marsh types (for which burned: 4.2–5.7 species/plot; unburned: 5.0–5.5 species/plot; other marsh type higher richness in burned plots). Cover of saltmeadow cordgrass Spartina patens was similar in burned and unburned plots in three of four marsh types, but greater in burned plots in the other marsh type. Cover of saltgrass Distichlis spicata was greater in burned plots in two of four marsh types, lower in burned plots in one marsh type and similar in burned and unburned plots in the other marsh type (see original paper for data). Averaged over all marsh types, cover of standing dead vegetation was lower in burned plots in the first summer (burned: 45%; unburned: 69%) but did not significantly differ between treatments in the following two summers (burned: 64–78%; unburned: 71–72%). Methods: The experiment was carried out in 11 coastal marshes (of four types based on salinity and tidal influence). In winter 1995/1996, one random half of each marsh was burned. The “unburned” half of one marsh experienced a lightning fire in summer 1997. In May–June 1996–1998, vegetation was surveyed at 40 points in each half of each marsh. This study was based on the same experimental set-up as (2).Study and other actions tested
A site comparison study in 2004 of three brackish marshes in an estuary in New Jersey, USA (Hagan et al. 2007) found that prescribed burning (along with applying herbicide) converted a marsh dominated by common reed Phragmites australis to one dominated by smooth cordgrass Spartina alterniflora, with similar cordgrass abundance and height to a natural marsh, but more plant species. After three years of burning and nine years of herbicide application, the treated marsh was statistically similar to a nearby natural marsh in terms of cordgrass dominance (treated: 78%; natural: 83% of stems were smooth cordgrass), density (treated: 286; natural: 360 stems/m2), above-ground biomass (treated: 457; natural: 802 g/m2) and height (treated: 78; natural: 94 cm). However, the treated marsh contained six plant species, including common reed, whilst the natural marsh contained only three. A third, untreated marsh was still dominated by common reed (100% of stems; density: 80 stems/m2; biomass: 2,124 g/m2; height: 317 cm; no other plant species). Methods: In August 2004, vegetation was surveyed in three tidal brackish marshes. One marsh was formerly dominated by common reed, but had been burned in 1996–1998 and sprayed with herbicide in 1996–2004. The study does not distinguish between the effects of these interventions. The second, natural marsh was dominated by smooth cordgrass. The third marsh was dominated by common reed and had not been treated. In each marsh, vegetation was clipped from six 0.25 x 0.25 m quadrats then identified, measured, dried and weighed.Study and other actions tested