Using a plant functional trait approach to determine dynamics of plant community assembly on granite outcrops of southwest Western Australia

Gianluigi Ottaviani

    Research output: ThesisDoctoral Thesis

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    Abstract

    The main target of my research was to infer ecological and evolutionary processes shaping plant communities on granite outcrops of the SW Australia, using plant functional traits and dominant species. Granite outcrops are insular habitats, different from the surrounding landscape matrix. Because of their unique characteristics, it has been suggested that granite outcrop shave repeatedly served as refugia for biota during past climatic oscillations. A trait-based study focusing on refugia is considered relevant, although still missing.
    The core of this Thesis is formed by a series of standing-alone scientific papers, submitted or close to submission to peer-reviewed journals; the core chapters are flanked by the General Introduction, and General Summary and Outlook.

    Chapter 1 (General Introduction) depicts the state of the knowledge of the research topic of the Thesis, defining the research context and objectives. The relevance of refugia, combined with the need to use trait-based approach in refugia-oriented research is exposed.
    Chapter 2 introduces a novel concept of ‘functional signature’ of refugia. Using established knowledge (vegetation-environment axiom, plant functional trait approach, mass ratio hypothesis), a new framework to characterise putative refugia from a functional-trait perspective is presented. This framework is implemented using data from the studied granite-outcrop system.
    Chapter 3 deals with a specific aspect of granitic outcrops -the function of the outcrops as fire refugia. It has been suggested granite outcrops, showing sparse vegetation cover, abundant bare-soil patches, and low litter accumulation, can serve as refugia in otherwise extremely fire-prone landscape. In this paper, we studied intra-specific trait variability of three target species. Data partially supported the expectation of the granite outcrops may function as fire refugia, i.e. promoting the persistence of older and less flammable individuals than outside the putative refugia. This finding invokes a necessity to include other main environmental drivers in the region supposed to drive trait patterns in combination with fire, namely water and nutrients stress.
    Chapter 4 looks into functional diversity of dominant species on the outcrops in relation to soil depth and aridity gradients. We found that soil depth positively influenced
    functional diversity patterns for some traits. I conclude that more benign environments characterized by deep soils can support large functional diversity for some traits than more stressed habitats (those having shallow soils). This finding might point upon increased role of limiting similarity in deep-soil habitats. Additionally, patches of deep soils on the granite outcrops may serve as ecological repositories, promoting the persistence of diversified functional strategies, acting as micro-refugia.
    Chapter 5 is a methodological piece expanding on Trait Gradient Analysis by introducing three new parameters allowing quantifying ecological constraining (a combination of both biotic and abiotic filtering). These tools have been preliminary implemented using two data sets (Californian chaparral, and granite outcrops vegetation of the SW Australia).
    Chapter 6 (General Summary and Outlook) places the key findings of the core research chapters forming the Thesis into a general context, and outlines avenues of future research in using trait-based approach in studies of biotic communities in refugia.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - Dec 2015

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