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Accueil du site → Doctorat → Allemagne → 2007 → Plant survival in southern Mongolian desert steppes : ecology of communities, interactions and populations

Martin-Luther-Universität Halle-Wittenberg (2007)

Plant survival in southern Mongolian desert steppes : ecology of communities, interactions and populations

Wesche, Karsten

Titre : Plant survival in southern Mongolian desert steppes : ecology of communities, interactions and populations

Auteur : Wesche, Karsten

Université de soutenance : Martin-Luther-Universität Halle-Wittenberg

Grade : Doktorgrades der Naturwissenschaften (Dr. rer. nat.) 2007

Résumé
Grasslands are among the world’s most spatially extensive but also most threatened biomes. Mongolia alone has some 1.3 Mio. km2 of intensively grazed rangelands, and severe degradation has been described for the central and eastern parts of the country. The present thesis summarises new data from rangelands of southern Mongolia, where availability of water (mean annual precipitation a) Communities : A first comprehensive inventory of the flora and vegetation of the main nature reserves in southern Mongolia is given and a new vegetation map is presented. A paleoecological study indicates that forests were once more widespread even in the dry mountains of the Gobi. b) Interactions : Experiments demonstrate that the direct impact of livestock on plant community composition is limited. Livestock, however, triggers large-scale nutrient translocation from the steppes to some small high-impact points. Small mammals also translocate nutrients and concentrate them on their burrows thereby acting as ecosystem engineers. A fertilisation experiment shows that nutrient translocation is important because plant growth is apparently constrained by nutrient limitation even though the overall climate is arid and water should be the decisive factor. c) Populations : Perennial plants dominate in terms of richness and abundance. Unlike annuals, they show no evidence for seed dormancy and seeds apparently germinate whenever conditions happen to be suitable. Unfavourable periods are survived by clonal persistence which can last for hundreds of years as shown by the prostrate Juniperus sabina. The endemic plants of southern Mongolia show similarly mixed reproduction strategies with clonal and sexual recruitment occurring. Although there is no evidence of their populations actually shrinking, populations nonetheless show pronounced to very pronounced genetic structuring which is related to the strong isolation of suitable habitats.

Mots clés  : Central Asia germination grazing nature conservation population genetics small mammals semi-desert vegetation history

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