Study

The interactive effects of fire and herbivory on a coastal marsh in Louisiana

  • Published source details Ford M.A. & Grace J.B. (1998) The interactive effects of fire and herbivory on a coastal marsh in Louisiana. Wetlands, 18, 1-8

Actions

This study is summarised as evidence for the following.

Action Category

Exclude wild vertebrates: freshwater marshes

Action Link
Marsh and Swamp Conservation

Use prescribed fire to maintain or restore disturbance: freshwater marshes

Action Link
Marsh and Swamp Conservation

Use prescribed fire to maintain or restore disturbance: brackish/salt marshes

Action Link
Marsh and Swamp Conservation

Exclude wild vertebrates: brackish/salt marshes

Action Link
Marsh and Swamp Conservation
  1. Exclude wild vertebrates: freshwater marshes

    A replicated, randomized, paired, controlled, before-and-after study in 1992–1994 in a freshwater marsh in Louisiana, USA (Ford & Grace 1998) found that fencing to exclude wild mammals increased overall vegetation biomass, but had mixed effects on the cover of dominant plant species and no significant effect on plant species richness. After two years, above-ground vegetation biomass was higher in fenced plots (960–2,080 g/m2) than in plots that remained open to grazing (780–920 g/m2). Fenced plots also had greater cover of switchgrass Panicum virgatum than open plots (fenced: 54–68%; open: 30–51%), but statistically similar cover of saltmeadow cordgrass Spartina patens (fenced: 31–78%; open: 56–71%). Fencing had no significant effect on plant species richness, with statistically similar changes in fenced plots (increase of 0–2.4 species/m2 over two years) and open plots (increase of 1.8 species/m2 over two years). Methods: In autumn 1992, ten pairs of 4-m2 plots were established in a freshwater marsh. Ten plots (one random plot/pair) were fenced (5 cm wire mesh with hooks to prevent burrowing) to exclude nutria Myocastor coypus and wild boar Sus scrofa (and other large mammals). The other 10 plots were not fenced. Half of the plots under each treatment were also burned in autumn 1992 and 1993. Plant species and cover were recorded in autumn 1992 (before intervention) and 1994. Vegetation was cut from one 0.25-m2 quadrat/plot, then dried and weighed, in autumn 1994. This study was in the same area as (2), but used a different experimental set-up.

    (Summarised by: Nigel Taylor)

  2. Use prescribed fire to maintain or restore disturbance: freshwater marshes

    A replicated, randomized, paired, controlled, before-and-after study in 1992–1994 in a freshwater marsh in Louisiana, USA (Ford & Grace 1998) found that burning reduced overall vegetation biomass, but had mixed effects on cover of the dominant plant species and no significant effect on plant species richness. One year after the latest burn, above-ground vegetation biomass was lower in burned areas (780–960 g/m2) than in unburned areas (920–2,080 g/m2). Burned and unburned areas had statistically similar cover of the dominant plant species in three of four comparisons. In the other comparison, amongst subplots fenced to exclude wild mammals, burned areas had lower cover of saltmeadow cordgrass Spartina patens (31%) than unburned areas (78%). Although plant species richness significantly increased in burned areas over two years of burning (by 1.8–2.4 species/m2), this change was not significantly different from the change in unburned areas (where species richness increased by 0–1.8 species/m2). Methods: Five pairs of 100-m2 plots were established in a freshwater marsh (regularly burned for at least 100 years). One random plot in each pair was burned in autumn 1992 and 1993. Each plot contained two 4-m2 subplots, one of which was fenced. Plant species and their cover were recorded in each subplot in autumn 1992 (before intervention) and 1994. Vegetation was cut from one 0.25-m2 quadrat/subplot, then dried and weighed, in autumn 1994.

    (Summarised by: Nigel Taylor)

  3. Use prescribed fire to maintain or restore disturbance: brackish/salt marshes

    A replicated, randomized, paired, controlled, before-and-after study in 1992–1994 in two brackish marshes in Louisiana, USA (Ford & Grace 1998) found that burning reduced vegetation biomass and affected the cover of dominant plant species, but had mixed effects on the cover of dominant plant species and plant species richness. One year after the latest burn, above-ground vegetation biomass was lower in burned areas (280–770 g/m2) than in unburned areas (450–1,200 g/m2). Burning significantly affected the cover of all three dominant plant species in one marsh (e.g. saltmeadow cordgrass Spartina patens cover was 27–35% in burned areas, vs 56–78% in unburned areas) but had no significant effect on cover of both dominant plant species in the other marsh (see original paper for data). Burning had no significant effect on plant species richness in three of four comparisons: there were statistically similar changes over two years in burned and unburned areas (see original paper for data). In the other comparison, involving subplots fenced to exclude wild mammals, plant species richness increased in burned areas (by 3.8 species/m2) but did not significantly change in unburned areas (non-significant decline of 0.4 species/m2). Methods: Ten pairs of 100-m2 plots were established across two brackish marshes (regularly burned for at least 100 years). One random plot in each pair was burned in autumn 1992 and 1993. The other plots were not burned. Each plot contained two 4-m2 subplots, one of which was fenced. Plant species and their cover were recorded in autumn 1992 (before intervention) and 1994. Vegetation was cut from one 0.25-m2 quadrat/subplot, then dried and weighed, in autumn 1994.

    (Summarised by: Nigel Taylor)

  4. Exclude wild vertebrates: brackish/salt marshes

    A replicated, randomized, paired, controlled, before-and-after study in 1992–1994 in two brackish marshes in Louisiana, USA (Ford & Grace 1998) found that fencing to exclude wild mammals increased overall vegetation biomass, but had mixed effects on the cover of dominant plant species and plant species richness. After two years, above-ground vegetation biomass was higher in fenced plots (600–1,200 g/m2) than in plots that remained open to grazing (280–450 g/m2). Fenced and open plots had similar cover of the dominant plant species in 7 of 10 comparisons. In two of the other comparisons, fenced plots had greater cover of American bulrush Scirpus americanus (54–57%) than open plots (18–19%). Fencing had no significant effect on plant species richness in three of four comparisons: there were statistically similar changes over two years in fenced and open plots (see original paper for data). In the other comparison, in burned areas, plant species richness increased in fenced plots (by 3.8 species/m2) but did not significantly change in open plots (non-significant increase of 0.2 species/m2). Methods: In autumn 1992, twenty pairs of 4-m2 plots were established across two brackish marshes. Twenty plots (one random plot/pair) were fenced (5 cm wire mesh with hooks to prevent burrowing) to exclude nutria Myocastor coypus and wild boar Sus scrofa (and other large mammals). The other 20 plots were not fenced. Half of the plots under each treatment were also burned in autumn 1992 and 1993. Plant species and cover were recorded in autumn 1992 (before intervention) and 1994. Vegetation was cut from one 0.25-m2 quadrat/plot, then dried and weighed, in autumn 1994. This study was in the same area as (4), but used a different experimental set-up.

    (Summarised by: Nigel Taylor)

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