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University of Oxford (2005)

Lichen-dominated soil crusts in the hyper-arid Namib Desert : anthropogenic impacts and conservation implications

Lalley, Jennifer S.

Titre : Lichen-dominated soil crusts in the hyper-arid Namib Desert : anthropogenic impacts and conservation implications

Auteur : Lalley, Jennifer S.

Université de soutenance : University of Oxford

Grade : Doctor of Philosophy (Ph.D.) : 2005

Résumé
The first significant finding of this research is that soil crusts in the northern Namib share common species with the central and southern Namib Desert, but with considerably different distribution patterns. A total of 23 soil crust lichen species were recorded here, including several unclassified species and one newly recorded vagrant species. Distribution patterns were found to be most significantly associated with local scale variables (soil crust thickness, silt contents, and soil pH) rather than landscape scale variables such as fog. Secondary production, in the form of unique arthropod communities, was found to be encouraged by lichen-dominated soil crusts, especially where patchy lichen cover is found. Investigations of soil crust lichen recovery after vehicular disturbance showed total estimated recovery times of between 5 and 530 years, depending on the disturbance and the original community and soil crust types. Lichen community compositions in the disturbed sites were significantly different from their control communities, regardless of the recovery phase. The impacts of disturbance-induced microenvironmental changes (increased surface temperatures in tracks) on lichen productivity were assessed by measuring the photosynthesis activities of five common species. Desiccation rates of lichens in tracks were found to increase significantly, thus decreasing productivity. The results of this research highlight that largescale mechanical disturbances resulting in altered lichen community compositions, decreased overall lichen cover as a soil stabiliser and altered microenvironments, will most likely have negative cascading effects on the environment. The findings of this research lay the foundations for addressing the conservation issues surrounding vulnerable lichen communities forming biological soil crusts in hyper-arid coastal deserts.

Présentation : EThOS (UK)

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