Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Woody plant diversity in tropical savannas of Africa and Australia

Auteur Trotter, Felix

Université de soutenance : University of Edinburgh

Grade : PhD Doctor of Philosophy 2023

Résumé partiel
Tropical savannas are a dominant biome on Earth characterised by co-dominance of woody plants (trees and shrubs) and grasses that is fundamental to understanding of the global carbon cycle. Tropical savannas display a high level of biogeographic contingency, where both the constituent flora and ecosystem dynamics vary widely among regions, and woody plant composition is dissimilar between continents. To date, there remains a limited understanding of patterns of woody diversity related to climate, fire and drought. Although a new understanding of patterns of diversity and composition will help inform ecosystem models of these regions alongside informing land use policies and highlighting vulnerabilities to climate change. My thesis aims to : 1) quantify patterns of woody diversity in tropical savannas of Africa and Australia in relation to climate and fire ; 2) explore use of woody diversity to map the limits of savanna distributions in Africa and Australia ; and 3) examine the impacts of drought and fire on community composition in juvenile and adult woody species in a semi-arid savanna in South Africa. To address these aims, I used a combination of data synthesis, experimental field data and statistical modelling. In Chapter one, I introduce the topic and field of research to highlight data gaps related to understanding history, composition and patterns of woody diversity across African and Australian savannas. In Chapter two, using a compilation of 314 plot inventories from Australian and African savannas I quantified the relationship between site level taxonomic richness (alpha diversity) with climate and fire. I found that alpha diversity is higher in African than Australian savannas at any given location. In Africa, patterns of woody diversity have a non-linear relationship with water availability, while in Australia diversity is linearly related to water availability. This chapter is written as a research manuscript to be submitted to the Journal of Biogeography. In Chapter three, I use the same inventory plot data as in Chapter two to quantify woody taxonomic turnover (beta diversity) across gradients of climate and fire. Species turnover is higher over shorter distances in Australia, but decreases for genera and disappears for families, likely due to the dominance of the Eucalyptus and Corymbia genera, and the Myrtaceae family, respectively.

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