Use prescribed fire to control problematic plants: brackish/salt marshes

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Four studies evaluated the effects, on vegetation, of using prescribed fire to control problematic plants in brackish/salt marshes. All four studies were in the USA. Two studies were based on the same experimental set-up.

VEGETATION COMMUNITY

  • Overall richness/diversity (4 studies): Two replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA reported that burned and unburned plots had similar plant species richness over the following 1–3 years. Two studies in saltgrass- or reed-dominated marshes in the USA reported that burned areas had greater plant species richness than unburned areas, after approximately 1–3 years. In one of the studies, burned areas had also been sprayed with herbicide for nine years – and contained more plant species than a nearby natural marsh.

VEGETATION ABUNDANCE

  • Overall abundance (3 studies): Three replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA evaluated the effect of prescribed burning on vegetation cover. One study found that autumn-burned plots had lower overall vegetation cover than unburned plots after 11 months, but one found that winter-burned plots had similar overall vegetation cover to unburned plots after one year. Two of the studies reported that winter-burned plots had less standing dead vegetation cover than unburned plots in the following summer or winter.
  • Individual species abundance (4 studies): All four studies quantified the effect of this action on the abundance of individual plant species, other than a species being controlled. For example, three replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA reported mixed effects of burning on cover of saltgrass Distichlis spicata: higher in burned than unburned plots in the following summer, lower in burned than unburned plots in the following winter, or mixed effects amongst marsh types. Two replicated, randomized, paired, controlled studies in brackish and salt marshes in the USA reported that burning did not reduce cover of saltmeadow cordgrass Spartina patens, compared to cover in unburned plots, over the following 1–3 years. One site comparison study of brackish marshes in the USA reported that a marsh that had been burned for three years (and sprayed with herbicide for nine) contained more smooth cordgrass Spartina alterniflora than an unburned and unsprayed marsh, and a similar amount of smooth cordgrass to a nearby natural marsh.

VEGETATION STRUCTURE

  • Visual obstruction (1 study): One replicated, randomized, paired, controlled study in brackish and salt marshes in the USA found that the visual obstruction caused by vegetation (combination of height and horizontal cover) was similar in burned and unburned plots, after 11 months.
  • Height (1 study): One site comparison study of brackish marshes in the USA found that in a marsh burned for two years (and sprayed with herbicide for nine), the dominant plant species (smooth cordgrass Spartina alterniflora) grew to a similar height as in a nearby natural marsh.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. 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
  2. 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
  3. 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
  4. 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
Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 18

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust