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Princeton University (2002)

Soil moisture dynamics and vegetation structure in water-limited ecosystems

Fernandez-Illescas, Coral Pilar

Titre : Soil moisture dynamics and vegetation structure in water-limited ecosystems

Auteur : Fernandez-Illescas, Coral Pilar

Université de soutenance : Princeton University

Grade : Doctor of Philosophy (PhD) 2002

This dissertation seeks to clarify the ecological role of soil water hydrology within water-limited ecosystems. In particular, it examines the effect of temporal variations in soil moisture, as determined by climate, vegetation and soil characteristics, on plant overall condition and ecosystem structure. Soil texture has a key role in water-limited ecosystems since it affects the water balance and water stress processes. Chapter 2 shows the importance of soil texture in partitioning rainfall into the water balance loss components, and determining vegetation water stress and overall condition for the savanna in La Copita, Texas and the shortgrass steppe in Colorado. Dynamics similar to the inverse texture effect, are demonstrated at these two sites and soil texture is found to modulate the impact that interannual rainfall fluctuations have on the fitness of trees and grasses. Modeling water-limited ecosystems requires consideration of fluctuating levels of soil water availability and their impact of plant competition. Chapter 3 drives a hierarchical competition-colonization model by the stress conditions resulting from the annual fluctuations in rainfall. Ecosystem composition is shown to be very sensitive to the inclusion of interannual rainfall variability at the savannas at La Copita, Texas, and at Nylsvley, South Africa. The evolutionary dynamics of competing trees and grasses exhibit self-affine characteristics. Long term simulations reveal that information entropy of the temporal evolution of the densities of trees and grasses at both sites is a maximum at the historically observed rainfall characteristics. In chapter 4, the hydrologically driven hierarchical competition-colonization model developed in chapter 3 is applied in a spatially explicit manner to investigate the effect of interannual rainfall fluctuations and local seed dispersal on vegetation patterns. Results suggest that interannual rainfall fluctuations extend the range of dispersal distances that result in spatial organization (i.e. clustering, self-similarity) and proportional abundances of vegetation different from those expected for the globally dispersing case. Chapter 5 investigates the role of transient dynamics and climate heterogeneity on the growing season soil moisture dynamics in the Oklahoma pastures and in the shortgrass steppe in Colorado. An analytical representation of a simplified water balance including those two processes is obtained.

Mots clés : Ecology, Rainfall, Water-limited, Vegetation, Hydrology, Soil moisture Earth sciences, Biological sciences

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Page publiée le 24 février 2015, mise à jour le 19 novembre 2018