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Master Thesis

Contribution à l'étude phytosociologique du massif des Eaux-Chaudes (Pyrénées Atlantiques)

Abstract : This Master dissertation analyses the supra-forest vegetation communities, mainly grasslands and low-shrub vegetation, but also rocks and screes, of a western Pyrenean limestone massif, the Eaux-Bonnes / Eaux-Chaudes massif. A set of 96 phytosociological records, containing 378 taxa, is analysed by factorial correspondence analysis. Partial analyses, based on our own samples, but also including a selection of bibliographic relevés, complete the overall analysis. These analyses identified six main sets of relevés:
- limestone rocks of the order Potentilletalia caulescentis Br.-Bl. 1926 (Asplenietea rupestria (H. Meier) Br.-Bl. 1934);
- calcareous screes of Thlaspietalia rotundifolii Br.-Bl. 1926 (Thlaspietea rotundifolii Br.-Bl. 1948);
- snowfields of Salicetea herbaceae Br.-Bl. 1947;
- flayed lawns of the class of Festuco-Seslerietea Barbero and Bonin 1969;
- mesophilic lawns of Elyno-Seslerietea Br.-Bl. 1948;
- acidophilic vegetation of the Juncetea trifidi Hadac 1944 (or Caricetea curvulae Br.-Bl. 1948) and Vaccinio-Piceetea Br.-Bl. 1939. There are also some records of the Festuco-Brometea Br.-Bl. and Tx. 1943.
Vegetation communities are structured according to two edaphic gradients, moisture and pH. The different recognized syntaxons are presented, with their characteristic or differential species. Their syntactical place is discussed. The importance of mesophilic communities in the Primulion intricatae Br.-Bl. 1948. The massif des Eaux-Chaudes is, in our opinion, the eastern limit of a well-marked biogeographic element. The flora contains indeed many taxa that disappear beyond the Ger Peak: Armeria pubinervis, Euphorbia chamaebuxus, Koeleria vallesiana subsp. abbreviata should be added to lberis bernardiana, Buglossoides gastonis, Androsace hirtella and Ranunculus parnassifolius subsp. favargeri. There is also a clear climate difference between central and western Pyrenees, which are very open to Atlantic influences, those much less watered. Some species, limited by competition to very particular environments in the central and eastern Pyrenees, are able to colonize other environments in the Western Pyrenees (this is the "coenotic spray"). Plant groups, often well differentiated elsewhere, then lose their individuality: the Ononidion striatae merges into the Festucion scopariae, Elyno-Seslerietea and Salicetea intricate themselves closely. It would therefore require a very precise knowledge of the biogeography of species throughout the chain to understand the synsystematic relationships between plant groups in the Western Pyrenees. Another interest of the massif is the opposition, over a short distance, between a highly developed southern slope, refuge of an abundant Mediterranean or Oromediterranean flora, and a northern slope of medio-european and boreal-alpine type. The concept of vegetation stage then becomes not very applicable and we did not use it in this work. It is regrettable that at the level of this very rich massif, the limit of the Western Pyrenees National Park goes to spend a few kilometers to the South. The complete plant records are given in the appendix.
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Master Thesis
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Jean-Luc Dupouey. Contribution à l'étude phytosociologique du massif des Eaux-Chaudes (Pyrénées Atlantiques). Biologie végétale. 1981. ⟨dumas-02445105⟩



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