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Universidad Nacional de Educación a Distancia (2014)

Patrones de vegetación en diferentes modelos discretos y continuos para regiones áridas y semiáridas

Alonso Palicio, Pedro

Titre : Patrones de vegetación en diferentes modelos discretos y continuos para regiones áridas y semiáridas

Auteur : Alonso Palicio, Pedro

Université de soutenance : Universidad Nacional de Educación a Distancia (España)

Grade : Máster Universitario en Física de Sistemas Complejos 2014

Présentation
In arid and semi-arid regions a wide range of patterns (like spots, labyrinths or holes) is observed. This pattern formation can be seen as a result of scale-dependent feedbacks between organisms and the environment. If the feedback is negative it leads to competition ; otherwise, organisms help others through facilitation, improving water storage or reducing stress. It is known that banded vegetation can develop on gentle hill slopes in water-limited regions ; for example, tiger bush is observed in semi-arid regions of Niger. Thiéry et al. (1995) explain such patterns in terms of surface water redistribution. Bare interband zones are covered by a biological crust that does not allow water infiltration. The excess of surface water ows downhill and is infilltrated in the first vegetation zone it found, because of the lack of biological crust under the canopy. In addition, termite activities related with plant growth increase soil porosity and destroy surface crusts. Runoff generated in bare soils favors upslope borders of banded pattern, and new plants tend to develop in these zones, so water consumption rises. Furthermore, down slope plants do not receive enough water to get alive and vegetated cover starts to disappear. As a consequence, upslope movement is expected. Several models have been proposed in order to explain band migration and other features. Whereas discrete models take into account interactions between neighboring plants, continuum models are based on coupled partial differential equations whose dynamical variables describe biomass or water densities. Tools of pattern formation theory can be used to study continuum models besides numerical solutions. As an introduction, we give a brief description of banded pattern features, and we discuss several field experiments about water redistribution and tiger bush vegetation. After that, we review both discrete and continuum models in order to establish correspondences with field observations. To conclude, our own results using the model of von Hardenberg et al. (2001) are presented. Advanced calculus is explained in final appendixes.

Présentation

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Page publiée le 12 septembre 2016, mise à jour le 20 juin 2018