Use prescribed fire to maintain or restore disturbance: freshwater swamps

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

Study locations

Key messages

  • Two studies evaluated the effects, on vegetation, of using prescribed fire to maintain or restore disturbance in freshwater swamps. Both studies were in the USA.

VEGETATION COMMUNITY

  • Tree/shrub richness/diversity (1 study): One replicated, site comparison study in the USA found that shrub-dominated wetlands burned every three years contained fewer species of mature tree than unburned wetlands, but a similar number of shrub and sapling species.

VEGETATION ABUNDANCE

  • Overall abundance (1 study): One replicated, site comparison study of bottomland swamps in the USA found that swamps burned every 2–3 years had a similar overall density of midstory and understory vegetation to unburned swamps.
  • Herb abundance (2 studies): One replicated, site comparison study of shrub-dominated wetlands in the USA found that wetlands burned every three years had greater cover of grasses than unburned wetlands, but statistically similar cover of forbs and ferns. Another replicated, site comparison study of bottomland swamps in the USA found that swamps burned every 2–3 years had a similar density of understory grasses to unburned swamps.
  • Tree/shrub abundance (2 studies): One replicated, site comparison study of shrub-dominated wetlands in the USA found that wetlands burned every three years had greater cover of shrubs than unburned wetlands. Another replicated, site comparison study of bottomland swamps in the USA found that swamps burned every 2–3 years had a similar density of shrubs, vines and other woody plants to unburned swamps.

VEGETATION STRUCTURE

  • Height (2 studies): One replicated, site comparison study of bottomland swamps in the USA found that swamps burned every 2–3 years had a shorter tree canopy than unburned swamps – but a similar-height midstory and understory. Another replicated, site comparison study of shrub-dominated wetlands in the USA found that the tree canopy was a similar height in wetlands burned every three years and unburned wetlands.
  • Basal area (1 study): One replicated, site comparison study of bottomland swamps in the USA found that swamps burned every 2–3 years had a similar basal area of trees to unburned swamps.
  • Canopy cover (1 study): One replicated, site comparison study of shrub-dominated wetlands in the USA found that wetlands burned every three years had less canopy cover than unburned wetlands.

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, site comparison study in 2001 of six bottomland swamp stands in Georgia, USA (Moseley et al. 2003) found that burned stands had a shorter tree canopy than unburned stands, but there were no other significant differences in vegetation structure or abundance. Burned stands had a shorter canopy (21 m) than unburned stands (24 m), but a statistically similar midstory height (burned: 13 m; unburned: 12 m) and understory height (burned: 26 cm; unburned: 26 cm). The treatments also had a statistically similar basal area (burned: 31.6; unburned: 30.3 m2/ha), midstory density (burned: 1,342; unburned: 2,370 stems/ha), understory density (burned: 170; unburned: 98 stems/6 m2). The same was true separately for understory grasses (37 vs 1 stems/6 m2), vines (30 vs 38 stems/6 m2), shrubs (75 vs 26 stems/6 m2) and other woody plants (26 vs 32 stems/6 m2). Methods: In summer 2001, vegetation was surveyed in six stands of poorly drained, bottomland hardwood forest. Three stands had been burned every 2–3 years for the past nine years (final burn January 2001). The other three stands had not been burned for at least nine years. Canopy and midstory vegetation were surveyed in two 0.04-ha plots/stand. Understory vegetation was surveyed in six 1-m2 quadrats/plot.

    Study and other actions tested
  2. A replicated, site comparison study in 1996 of 48 pocosins (shrub-dominated, freshwater wetlands) within pine forest in North Carolina, USA (Allen et al. 2006) found that triennial prescribed burning increased shrub and grass cover, but reduced canopy cover and tree species richness, and had no significant effect on fern cover, forb cover, canopy height or shrub/sapling species richness. Compared to pocosins that had not burned during any growing season, pocosins burned every three growing seasons had greater shrub cover (burned: 50%; unburned: 40%) and greater grass cover (burned: 14%; unburned: 6%). However, burned pocosins had lower canopy cover (burned: 75%; unburned: 89%) and contained fewer mature tree species (burned: 6 species/site; unburned: 10 species/site). Burned and unburned pocosins had statistically similar fern cover (10% vs 6%), forb cover (3% vs 2%), tree canopy height (22 vs 19 m), shrub species richness (13 vs 12 species/site) and sapling species richness (12 species/site). Methods: In 2006, vegetation was surveyed at 19 sites within pocosins burned every three growing seasons since 1989, and at 29 sites within pocosins that had not burned during the growing season in this period. The pocosins were historically disturbed by fire, but this was suppressed after European settlement. Mature trees were surveyed in four 11-m-radius plots/site. Other vegetation was surveyed in four 5-m-radius plots/site.

    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.

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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

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