The Vegetation of a Camargue Pasture

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Abstract
A vegetation and soil survey of a 400 ha pasture in the Camargue (southern France) was conducted as part of a program on the ecology of grazing animals and their impact on the vegetation. A classification of the vegetation by indicator-species analysis gave 8 groups. One of these was a closed grassland dominated by Brachypodium phoenicoides. Two others typically contained rich swards with abundant Limonium vulgare, Halimione portulacoides and annual grasses. The 4th group was very species-poor, containing sparse clumps of Arthrocnemum glaucum separated by large expanses of bare ground, while the 5th was similar but richer in species. Two groups were characteristic of marshes; one group, dominated by Scirpus maritimus or Phragmites communis, was typical of the wetter parts, while the other, with abundant S. maritimus and Aeluropus littoralis, was found at the edges. There was a group restricted to disused rice-fields, rich in ruderal species. An ordination of the stands by correspondence analysis (reciprocal averaging) separated the main marsh sites from the remainder on the 1st axis. Stands in the old rice-fields and in small temporary marshes were separated out on the 2nd axis, while the remainder of the stands (the majority) were spread fairly evenly along the 3rd axis, showing a gradation from completely glycophytic sites to extremely halophytic ones. Of the 11 soil factors measured in each stand, 4 (pH, depth of the water table, percentage of the organic matter and amount of extractable K) were significantly correlated with the 1st axis of the ordination. These were related to soil hydrology. Four more (extractable Na and Mg, the total amount of extractable bases, and the depth of the mottled horizon) were significantly correlated with the 2nd and the 3rd axes. These factors were connected with soil salinity. The remaining 3 (extractable Ca and the percentages of P and N) were significantly correlated with all 3 axes. The vegetation and soil show parallel responses to variations in the hydrology and salinity of the area. A number of normally glycophytic species were found in saline soils; some hypotheses are put forward to explain this occurrence. Comparisons with previous phytosociological work in southern France suggests that the vegetation in the pasture shows affinities with 4 Zurich-Montpellier orders: Thero-Brachypodietalia, Salicornietalia, Juncetalia maritimi and Phragmitetalia.

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