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Dryland ecosystems of the Sudano-Sahel : a vegetation model perspective

Wim Verbruggen (UGent)
(2021)
Author
Promoter
(UGent) , Guy Schurgers, Stéphanie Horion and (UGent)
Organization
Project
Abstract
Drylands form a major component of our Earth’s land surface. These ecosystems encompass several biomes, such as dry forests, savannas, grasslands, shrublands and deserts. More than 30% of the global human population lives in dryland ecosystems and depends on the ecosystem services that drylands provide. However, these ecosystems are subject to climate extremes that are projected to increase in frequency and severity under most future climate scenarios. Such extremes can have a devastating impact on the ecosystems and livelihoods of global drylands. Drylands account for a large fraction of the total land carbon sink, and have been shown to dominate its trend and year-to-year variability. Despite their global importance, drylands remain severely understudied and especially a detailed optimization of vegetation models is lacking. In this thesis I contributed to resolve this problem. Based on data from our own field work, I parameterized two dynamic vegetation models (LPJ-GUESS and ED2.2) to dryland conditions, specifically the Sudano-Sahel region. My optimized parameterization enables these models to realistically simulate carbon and water fluxes that were measured at several fluxtower sites across the Sahel. Using the LPJ-GUESS model I then studied how the distribution of rainfall over the rainy season can impact dryland ecosystems at the site level. Using the ED2.2 model I studied how access to the perennial soil moisture layer can influence dry season water use by deep rooted trees. In a next step I upscaled the LPJ-GUESS model to the regional level and I evaluated its simulations of the Sudano-Sahel vegetation against satellite data. Using this regional model I then studied how soil texture can influence dryland leaf cover and ecosystem composition. While soil texture had almost no impact at the ecosystem scale, at the plant level soil texture strongly shifted the competitive balance between evergreen and deciduous woody species. In another chapter I studied the impact of rainfall variability and found that an increased year-to-year rainfall variability can decrease dryland ecosystem productivity, offseting the gains by CO2 fertilization, especially for southern regions. By using and tuning dynamic vegetation models for simulating dryland vegetation, this thesis provides a unique insight into dryland ecosystem functioning.
Keywords
Sahel, Sudano-Sahel, drylands, vegetation modelling, savanna, grassland, climate change, ecology

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Citation

Please use this url to cite or link to this publication:

MLA
Verbruggen, Wim. Dryland Ecosystems of the Sudano-Sahel : A Vegetation Model Perspective. Ghent University. Faculty of Bioscience Engineering ; University of Copenhagen. Faculty of Science, 2021.
APA
Verbruggen, W. (2021). Dryland ecosystems of the Sudano-Sahel : a vegetation model perspective. Ghent University. Faculty of Bioscience Engineering ; University of Copenhagen. Faculty of Science, Ghent, Belgium ; Copenhagen, Denmark.
Chicago author-date
Verbruggen, Wim. 2021. “Dryland Ecosystems of the Sudano-Sahel : A Vegetation Model Perspective.” Ghent, Belgium ; Copenhagen, Denmark: Ghent University. Faculty of Bioscience Engineering ; University of Copenhagen. Faculty of Science.
Chicago author-date (all authors)
Verbruggen, Wim. 2021. “Dryland Ecosystems of the Sudano-Sahel : A Vegetation Model Perspective.” Ghent, Belgium ; Copenhagen, Denmark: Ghent University. Faculty of Bioscience Engineering ; University of Copenhagen. Faculty of Science.
Vancouver
1.
Verbruggen W. Dryland ecosystems of the Sudano-Sahel : a vegetation model perspective. [Ghent, Belgium ; Copenhagen, Denmark]: Ghent University. Faculty of Bioscience Engineering ; University of Copenhagen. Faculty of Science; 2021.
IEEE
[1]
W. Verbruggen, “Dryland ecosystems of the Sudano-Sahel : a vegetation model perspective,” Ghent University. Faculty of Bioscience Engineering ; University of Copenhagen. Faculty of Science, Ghent, Belgium ; Copenhagen, Denmark, 2021.
@phdthesis{8729935,
  abstract     = {{Drylands form a major component of our Earth’s land surface. These ecosystems encompass
several biomes, such as dry forests, savannas, grasslands, shrublands and deserts. More than
30% of the global human population lives in dryland ecosystems and depends on the ecosystem
services that drylands provide. However, these ecosystems are subject to climate extremes
that are projected to increase in frequency and severity under most future climate scenarios.
Such extremes can have a devastating impact on the ecosystems and livelihoods of global
drylands. Drylands account for a large fraction of the total land carbon sink, and have been
shown to dominate its trend and year-to-year variability. Despite their global importance,
drylands remain severely understudied and especially a detailed optimization of vegetation
models is lacking.
In this thesis I contributed to resolve this problem. Based on data from our own field work, I
parameterized two dynamic vegetation models (LPJ-GUESS and ED2.2) to dryland conditions,
specifically the Sudano-Sahel region. My optimized parameterization enables these models to
realistically simulate carbon and water fluxes that were measured at several fluxtower sites
across the Sahel. Using the LPJ-GUESS model I then studied how the distribution of rainfall
over the rainy season can impact dryland ecosystems at the site level. Using the ED2.2 model
I studied how access to the perennial soil moisture layer can influence dry season water use
by deep rooted trees.
In a next step I upscaled the LPJ-GUESS model to the regional level and I evaluated its
simulations of the Sudano-Sahel vegetation against satellite data. Using this regional model I
then studied how soil texture can influence dryland leaf cover and ecosystem composition.
While soil texture had almost no impact at the ecosystem scale, at the plant level soil texture
strongly shifted the competitive balance between evergreen and deciduous woody species.
In another chapter I studied the impact of rainfall variability and found that an increased
year-to-year rainfall variability can decrease dryland ecosystem productivity, offseting the
gains by CO2 fertilization, especially for southern regions. By using and tuning dynamic
vegetation models for simulating dryland vegetation, this thesis provides a unique insight into
dryland ecosystem functioning.}},
  author       = {{Verbruggen, Wim}},
  isbn         = {{9789463574600}},
  keywords     = {{Sahel,Sudano-Sahel,drylands,vegetation modelling,savanna,grassland,climate change,ecology}},
  language     = {{eng}},
  pages        = {{X, 227}},
  publisher    = {{Ghent University. Faculty of Bioscience Engineering ; University of Copenhagen. Faculty of Science}},
  school       = {{Ghent University}},
  title        = {{Dryland ecosystems of the Sudano-Sahel : a vegetation model perspective}},
  year         = {{2021}},
}