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Ben-Gurion University of the Negev (2014)

Spatial and Temporal Dynamics of Biological Soil Crust in Arid Environments

Kinast Shai

Titre : Spatial and Temporal Dynamics of Biological Soil Crust in Arid Environments

Auteur : Kinast Shai

Université de soutenance : Ben-Gurion University of the Negev

Grade : DOCTOR OF PHILOSOPHY (PhD) 2014

Résumé partiel
Desert soils throughout the world are often covered with biological crusts. Until a few decades ago, little was known about the structure and functions of these crusts. Recent research has improved our understanding, and now it is widely agreed that biological soil crusts have crucial impacts on the ecosystems in which they reside. Moreover, such crusts can play a key role in possible future global changes such as climatic changes or desertification. In this dissertation we study the spatial and temporal dynamics of biological soil crust and their ecological influence on ecosystems. Most of the research was carried out within the framework of nonlinear mathematical models which are based on the physical properties of soil crust, its relation with desert vegetation and the impact of climatic factors such as precipitation and evaporation on the crust dynamics. The thesis includes both theoretical and numerical analysis of the models. In addition, we study general phenomena related to the field of nonlinear dynamics and pattern formation of nonequilibrium physics. The first part of the study is dedicated to the dynamics of biogenic crust on sand dunes and its influences on vegetation and thus on sand dune stabilization. Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in dune stabilization, biogenic crusts have rarely been considered in continuous models of dune dynamics. Using a mathematical model, we studied the existence and stability ranges of different dunecover states along gradients of rainfall and wind power. We identified two ranges of alternative stable states : fixed crusted dunes and fixed vegetated dunes at low wind power, and fixed vegetated dunes and active dunes at high wind power. These results suggest a crossover between two different forms of climate shifts. In the second part of this dissertation we focus on the special role that biological soil crusts play in the self-emergence of patterned vegetation in arid ecosystems, and we introduce a new model for patchy landscapes indrylands. The model captures the dynamics of biogenic soil crusts and their mutual interactions with vegetation growth. The model was used to identify spatially uniform and spatially periodic solutions that represent different vegetation-crust states, and to map them along the rainfall gradient. The results are consistent extensions of the vegetation states found in earlier models. A significant difference between the current and earlier models of patchy landscapes is found in the bistability range of vegetated and unvegetated states. When crust dynamics is taken into account, there is a shift in the fold-bifurcation point at which stable vegetation patterns appear, to higher precipitation and biomass values. These results shed new light on the roles that biogenic crusts play in desertification processes involving permanent loss of vegetation.

Mots clés :  : biological soil crust, desertification, ecosystem rehabilitation, pattern formation, self-organization, sand dunes, Turing instability vegetation patterns,.

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Page publiée le 1er avril 2015, mise à jour le 11 septembre 2017