Plant species and functional diversity along altitudinal gradients, Southwest Ethiopian highlands [Elektronische Ressource] / von Desalegn Wana Dalacho

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• Publié par: universitat_bayreuth
• Publié le: 01 janvier 2009
• Nombre de lectures: 30
• Langue: English
• Poids de l'ouvrage: 2 Mo

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Plant Species and Functional Diversity along Altitudinal
Gradients, Southwest Ethiopian Highlands


Dissertation
Zur Erlangung des akademischen Grades
Dr. rer. nat.

Vorgelegt der Fakultät für Biologie, Chemie und Geowissenschaften der Universität
Bayreuth



von
Herrn Desalegn Wana Dalacho
geb. am 08. 08. 1973, Äthiopien














Bayreuth, den 27. October 2009
Die vorliegende Arbeit wurde in dem Zeitraum von April 2006 bis October 2009 an der
Universität Bayreuth unter der Leitung von Professor Dr. Carl Beierkuhnlein erstellt.


Vollständiger Abdruck der von der Fakultät für Biologie, Chemie und Geowissenschaften der
Universität Bayreuth zur Erlangung des akademischen Grades eines Doktors der
Naturwissenschaften genehmigten Dissertation.









Prüfungsausschuss

1. Prof. Dr. Carl Beierkuhnlein (1. Gutachter)
2. Prof. Dr. Sigrid Liede-Schumann (2. Gutachter)
3. PD. Dr. Gregor Aas (Vorsitz)
4. Prof. Dr. Ludwig Zöller
5. Prof. Dr. Björn Reineking



Datum der Einreichung der Dissertation: 27. 10. 2009
Datum des wissenschaftlichen Kolloquiums: 21. 12. 2009
Contents
Summary 1
Zusammenfassung 3
Introduction 5
Drivers of Diversity Patterns 5
Deconstruction of Diversity Patterns 9
Threats of Biodiversity Loss in the Ttropics 10
Objectives, Research Questions and Hypotheses 12
Synopsis 15
Thesis Outline 15
Synthesis and Conclusions 17
References 21
Acknowledgments 27
List of Manuscripts and Specification of Own Contribution 30
Manuscript 1
Plant Species and Growth Form Richness along Altitudinal Gradients in the Southwest
Ethiopian Highlands 32
Manuscript 2
The Relative Abundance of Plant Functional Types along Environmental Gradients in the
Southwest Ethiopian highlands 54
Manuscript 3
Land Use/Land Cover Change in the Southwestern Ethiopian Highlands 84
Manuscript 4
Climate Warming and Tropical Plant Species – Consequences of a Potential Upslope Shift
of Isotherms in Southern Ethiopia 102
List of Publications 135
Declaration/Erklärung 136
Summary
Summary

Understanding how biodiversity is organized across space and time has long been a central
focus of ecologists and biogeographers. Altitudinal patterns of richness gradients are one of
such striking patterns in the landscape. Despite its historical and ecological importance as a
heuristic natural experimental site for development of ecological theories, the emergent
patterns and mechanisms that structure them are poorly understood. This is partly because of
the complex relationships of species to the environment and the choice of the response
variable itself, i.e. using taxonomic richness as a metrics of diversity. This thesis, therefore,
applies plant functional types (hereafter PFTs) approach to study the response of vegetation to
environmental factors in the southwest Ethiopian highlands. It focuses on the classification of
the vegetation into a few main plant functional response categories and relate them to
environmental variables. For pattern identification and mechanistic explanations, a
deconstructive approach of the taxonomic richness into its constituent components was used.
Furthermore, the potential effects of land use/land cover change and global warming on the
biodiversity of the study area was investigated.

The results reveal that the application of plant functional types is a promising tool to
understand vegetation-environment relationships. Local topographic attributes (altitude and
slope) and soil properties found to structure the variance in the relative abundance of PFTs
along environmental gradients. Moreover, specific response to drought favours the abundance
of species with thorns/spines and tussocks in the lowlands as opposed to chilling which
favours rosettes and rhizomes PFTs in the highlands. Concerning patterns of richness along
altitudinal gradients, various structures of richness appear for total vascular plant species and
growth forms. Woody plants, graminoids and climbers showed a uni-modal structure while
ferns and herbs revealed an increasing pattern of richness along the altitudinal gradient. By
contrast, total vascular plants species richness did not show any strong response to altitudinal
gradients. Climate related water-energy dynamics, species area relationships due to the
physical shape of the mountain, local topographic and soil conditions were found to be
predominant factors structuring the observed richness in the study area.

The threats to biodiversity loss due to land use/land cover change and global warming is
eminent in the study area. Land conversion for agricultural purposes was a pervasive process
that had a deleterious effect on the biodiversity of the study area. Population growth, socio-
1
Summary
economic challenges (poverty) and government policy regimes drive land cover change
processes. In addition, recent climate change poses a serious challenge to the biodiversity of
the study area. The results of model predictions indicated that biodiversity of the study area
will suffer severe consequences of lowland biotic attrition (i.e. the net loss of species richness
in the tropical lowlands caused by altitudinal range shifts in the absence of new species
arriving), range gap shifts and contraction, and extinction due to expected warming at the end
of this century. The model also predicted that endangered and endemic species with restricted
elevational ranges will disproportionately suffer from range contraction and extinction due to
warming.

In conclusion, the plant functional types approach was found to be an essential tool to reduce
complexity of the vegetation of the study system and to elucidate vegetation-environment
relationships. Moreover, the identification of emergent patterns and attributing them to
mechanistic explanations are pre-requisites for conservation planning to save biodiversity of
the study area. The study also evidenced that land use/land cover change and global warming
will present strong threats to the loss of biodiversity in the study area. Salvaging biodiversity
in the future requires the consideration of the effect of land use and climate change on
vegetation responses. Consequently, nature conservation strategies and future reserve designs
should take into account options of human assisted migration across fragmented landscapes
and creating dispersal routes for species to track to new thermal niches.
2
Zusammenfassung
Zusammenfassung

Seit längerem streben Biogeographen und Ökologen nach dem Verständnis, wie Biodiversität
in Zeit und Raum organisiert ist. Die höhenbedingte Abnahme der Vielfalt ist hierbei eines
der prägenden Landschaftsbilder. Trotz der historisch gewachsenen ökologischen Bedeutung
als heuristisches, natürliches Studiengebiet sind die zugrundeliegenden Muster und
Mechanismen noch weitgehend unklar. Dies liegt nicht zuletzt an der komplexen Beziehung
zwischen Arten zu ihrer Umwelt und auch in der Wahl der Untersuchungsmethodik an sich.
Als Beispiel sei der häufige Gebrauch der taxonomischen Vielfalt als ausschließliches
Biodiversitätsmaß genannt.

Diese Arbeit wendet insofern den erweiterten Ansatz der Pflanzenfunktionstypen an (im
Folgenden: PFTs) um die Reaktion der Vegetation auf diverse Umweltfaktoren im Südwesten
des äthiopischen Hochlandes zu erforschen. Ziel der Studie ist es, die Vegetation in einige
wenige Hauptkategorien von Pflanzenfunktionstypen zu klassifizieren und diese in Bezug zu
ihrer Reaktion auf Umweltvariablen zu setzen. Der Ansatz der taxonomischen Vielfalt wurde
somit und ergänzt, um sowohl räumliche Muster zu identifizieren, als auch die dahinter
befindlichen Mechanismen erklären zu können. Darüber hinaus wurden sowohl potentielle
Einflüsse von Landnutzungs- und Landbedeckungswandel, als auch die Auswirkungen der
globalen Erwärmung auf die Biodiversität des Untersuchungsgebietes analysiert.

Die Ergebnisse verdeutlichen, dass der Ansatz von Pflanzenfunktionstypen vielversprechend
ist, um Vegetation-Umwelt-Beziehungen zu verstehen. Lokale topographische Parameter
(z.B. Höhe und Hangneigung) scheinen die Varianz in der relativen Häufigkeit der PFTs
entlang eines Umweltgradienten zu beeinflussen. Des Weiteren erklärt die spezifische
Adaption an Hitzeereignisse die hohe Abundanz von Arten mit Dornen/Stacheln und
Tussock-Gras in den niederen Lagen.

Hinsichtlich der Vielzahl vo