Study

Effects of seasonal flooding and grazing on the vegetation of former ricefields in the Rhône delta (southern France)

  • Published source details Mesléard F., Lepart J., Grillas P. & Mauchamp A. (1999) Effects of seasonal flooding and grazing on the vegetation of former ricefields in the Rhône delta (southern France). Plant Ecology (formerly Vegetatio 1948-1996), 145, 101-114.

Actions

This study is summarised as evidence for the following.

Action Category

Use grazing to maintain or restore disturbance: brackish/salt marshes

Action Link
Marsh and Swamp Conservation

Actively manage water level: brackish/salt marshes

Action Link
Marsh and Swamp Conservation

Exclude or remove livestock from historically grazed brackish/salt marshes

Action Link
Marsh and Swamp Conservation
  1. Use grazing to maintain or restore disturbance: brackish/salt marshes

    A replicated, paired, controlled, before-and-after study in 1989–1994 of eighteen brackish marshes in southern France (Mesléard et al. 1999) reported that the effects of continued grazing on plant community composition, abundance and species richness depended on the flooding regime. Unless specified, statistical significance was not assessed. Under all three flooding regimes, the overall plant community composition in grazed and ungrazed plots diverged over five years. However, the speed and direction of the changes depended on the flooding regime (data reported as graphical analyses). For example, under two artificial flooding regimes, grazing significantly reduced the final cover of sea club rush Bolboschoenus maritimus (grazed: 11–12%; ungrazed: 31–33%) and common reed Phragmites australis (grazed: <1%; ungrazed: 12–16%). Other species showed mixed responses to grazing depending on the season of artificial flooding (see original paper). After five years, total plant species richness was lower in grazed fields under artificial flooding regimes (grazed: 4 species/0.25 m2; ungrazed: 5–6 species/0.25 m2) but higher in grazed fields under an unmanaged flooding regime (grazed: 7 species/0.25 m2; ungrazed: 5 species/0.25 m2). Methods: The study used two sets of nine inland brackish marshes (former rice fields, but grazed since 1976 when cultivation stopped). In November 1989, one set was fenced to exclude livestock. The other set remained grazed (approximately 2 cattle and 1 horse/ha, April–November). Three of the nine 1-ha marshes within each set received each flooding regime: artificial winter flooding, artificial summer flooding, or year-round unmanaged flooding. Vegetation was surveyed every six months from early November 1989 to early November 1994 (nine 0.5 x 0.5 m quadrats/field/
    survey).

    (Summarised by: Nigel Taylor)

  2. Actively manage water level: brackish/salt marshes

    A replicated, paired, controlled, before-and-after study in 1989–1994 of 18 brackish marshes in southern France (Mesléard et al. 1999) reported that artificially flooded fields developed different plant communities with different species richness to fields with unmanaged flooding, but that the precise effects of artificial flooding depended on the flooding and/or grazing regime. Unless specified, statistical significance was not assessed. Over five years, the overall plant community composition changed in artificially flooded fields, becoming less like that of fields with unmanaged flooding (data reported as graphical analyses). Responses of individual plant species, and therefore the precise community that developed, depended on when fields were flooded and whether they were grazed. For example, final cover of common reed Phragmites australis was significantly greater in ungrazed, artificially flooded fields (12–16%) than in grazed, artificially flooded fields (<1%) or fields with unmanaged flooding (0%). In ungrazed fields, plant species richness was similar after five years of artificial flooding (5–6 species/0.25 m2) or unmanaged flooding (5 species/0.25 m2). In grazed fields, plant species richness was lower after five years of artificial flooding (4 species/0.25 m2) than unmanaged flooding (7 species/0.25 m2). Methods: The study used 18 adjacent former rice fields (1 ha; arranged in two sets of nine). From November 1989, six fields (three fields/set) received each flooding treatment: artificial winter flooding (10 cm depth November–April), artificial summer flooding (10 cm depth May–October) or year-round unmanaged flooding (inundated most of the winter most years). Half of the plots under each flooding treatment were also grazed. Vegetation was surveyed every six months from early November 1989 to early November 1994 (nine 0.5 x 0.5 m quadrats/field/survey).

    (Summarised by: Nigel Taylor)

  3. Exclude or remove livestock from historically grazed brackish/salt marshes

    A replicated, paired, controlled, before-and-after study in 1989–1994 of eighteen historically grazed brackish marshes in southern France (Mesléard et al. 1999) reported that the effects of excluding livestock on plant community composition, abundance and species richness depended on the flooding regime. Unless specified, statistical significance was not assessed. Under all three flooding regimes, the overall plant community composition in exclusion and grazed marshes diverged over five years. However, the speed and direction of the changes depended on the flooding regime (data reported as graphical analyses). For example, under two artificial flooding regimes, exclusion significantly increased the final cover of sea club rush Bolboschoenus maritimus (exclusion: 31–33%; grazed: 11–12%) and common reed Phragmites australis (exclusion: 12–16%; grazed: <1%). Under an unmanaged flooding regime, exclusion increased cover of the grass Aeluropus littoralis (exclusion: 16%; grazed: 0%). After five years, total plant species richness was higher in exclusion than grazed marshes under both artificial flooding regimes (exclusion: 4 species/0.25 m2; grazed: 5–6 species/0.25 m2) but lower in exclusion than grazed marshes under the unmanaged flooding regime (exclusion: 7 species/0.25 m2; grazed: 5 species/0.25 m2). Methods: The study used two sets of nine inland brackish marshes (former rice fields, but grazed since 1976 when cultivation stopped). In November 1989, one set was fenced to exclude livestock. The other set remained grazed (approximately 2 cattle and 1 horse/ha, April–November). Three of the nine 1-ha marshes within each set received each flooding regime: artificial winter flooding, artificial summer flooding, or year-round unmanaged flooding. Vegetation was surveyed every six months from early November 1989 to early November 1994 (nine 0.5 x 0.5 m quadrats/field/survey).

    (Summarised by: Nigel Taylor)

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