LONG-TERM VEGETATION CHANGE derived from palaeoecological techniques in West-Coast

211 Pages·2014·5.11 MB·English

by  Forbes, Cherie

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BENCHMARKS FOR THE FUTURE: LONG-TERM VEGETATION CHANGE
DERIVED FROM PALAEOECOLOGICAL TECHNIQUES IN WEST-COAST
RENOSTERVELD, SOUTH AFRICA

CHERIE JANINE FORBES

Supervisor:
A/Prof. Lindsey Gillson
Plant Conservation Unit, Department of Biological Sciences
University of Cape Town

Co-supervisor:
Prof. Timm Hoffman
Plant Conservation Unit, Department of Biological Sciences
University of Cape Town

A thesis submitted in partial fulfilment of the requirements for the degree of Master of
Science in the Department of Biological Sciences, University of Cape Town

February 2014
BENCHMARKS FOR THE FUTURE: LONG-TERM VEGETATION CHANGE
DERIVED FROM PALAEOECOLOGICAL TECHNIQUES IN WEST-COAST
RENOSTERVELD, SOUTH AFRICA

CHERIE JANINE FORBES

Keywords: Palaeoecology, resilience, climate, land-use, fire history, herbivory,
restoration, Renosterveld, Elytropappus

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ABSTRACT
This study focuses on long-term vegetation changes in West-Coast Renosterveld in the winter
rainfall zone of the Cape Floristic Region (CFR), Western Cape, South Africa. Renosterveld
is an evergreen, fire-prone Mediterranean-type shrubland consisting of asteraceous elements,
grasses and geophytes. It is restricted to fertile, fine-grained soils and more than 90% of this
vegetation type has been transformed by agriculture. High richness of endemic geophytes in
particular gives remaining fragments an irreplaceable conservation value. Future climate
projections for the region suggest a general warming of 1.5-3.5 °C, a 30-50% decrease in
precipitation, an increase in drought periods and shorter rainy seasons with important
consequences for the vegetation of the CFR. There is limited information regarding the
response of Renosterveld to past climate change and land-use disturbance and there is much
debate about the pristine composition of Renosterveld vegetation. The lack of Renosterveld
environmental history with appropriate pre-colonial or pre-Iron age benchmarks makes it
difficult to build evidence-based arguments for conservation management and restoration.
Studying the history of Renosterveld in the late Holocene may provide information on
responses to past warmer climates, and the more recent effects of anthropogenic disturbance.

The aim of the present study was to reconstruct vegetation change, fire regime and changes in
herbivory over the past ca. 1300 years at a West-Coast Renosterveld site in the Western Cape
and to interpret these findings in light of known climate history and land-use change with a
specific focus on the effects of disturbance by fire and herbivory. Findings were explored in
relation to resilience theory, and the implications for conservation management and
restoration. The following research questions were investigated, (1) How has vegetation, fire
and herbivory changed over time in West-Coast Renosterveld vegetation? (2) How do
changes in vegetation relate to climate and land-use disturbance and what are the main
drivers of change? (3) What are the links to theoretical frameworks such as resilience theory?
Are recent changes unprecedented and is there evidence of a threshold response to climate
and disturbance? (4) What are the implications of these findings for conservation
management and restoration such as present day management of fire and herbivores?

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The study was carried out on Elandsberg Private Nature Reserve, which is one of the largest
West-Coast Renosterveld conservation areas (ca.<1000 ha) in the region. A sediment core
was retrieved from Vangkraal Spring wetland which occurs on an ecotone between Swartland
Shale Renosterveld and Swartland Alluvium Fynbos. The small wetland is particularly
sensitive to changes in local disturbance such as fire and herbivory. The methodology
included palaeoecological techniques such as the analysis of fossil pollen, macro- and micro-
charcoal, coprophilous spores, AMS radio-carbon and 10Pb dating.

The sediment sequence is ca. 1300 years old ranging from ca. AD 750-2012. Stratigraphy
results were not related to pollen, spore and charcoal data. The fossil pollen data show that
prior to ca. AD 1943 vegetation remained relatively stable, with asteraceous elements
(Asteraceae long-spine type-1 pollen) dominant and Elytropappus rhinocerotis and Poaceae
less dominant. Over the same time period, macro-charcoal was low in abundance with little
fluctuation over time while coprophilous spores were either low in abundance or absent.
Micro-charcoal data showed that regional fires were frequent and highly variable from ca.
AD 750-1400. Post ca. AD 1943, vegetation changed noticeably with a significant increase in
Elytropappus rhinocerotis associated with an increase in macro-charcoal abundance and
coprophilous spores, suggesting increased local fires and increased herbivory. Micro-charcoal
abundance was lower and less variable, suggesting less regional fire.

Comparison with known climate history shows that vegetation composition changed little in
response to the warmer and drier conditions of the Medieval Climate Anomaly (ca. AD 900-
1400) and cooler and wetter conditions of the Little Ice Age (ca. AD 1400-1800). Land-use
by the Khoi-San hunter/herders (ca. AD 750-1650) and early European settlers (ca. AD 1650-
1943) appear not to have had a significant effect on the vegetation of the region though
changes observed in regional fire frequency and intensity (AD ca.750-1400) were probably
due to either climate change or anthropogenic disturbance. Macro-charcoal and coprophilous
spore data show that recent land-use, specifically increasing fire and herbivory associated
with agricultural intensification, resulted in unprecedented changes in vegetation post ca. AD
1943. There was a notable increase in Elytropappus rhinocerotis, an unpalatable shrub, over
this period. Statistical analysis of the data suggests that no ecological threshold has been
crossed. However, land-use change and recent climate variation interact, and the results
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cannot rule out a threshold being crossed if further warming and intensive fire and herbivory
continues, resulting in a transition to “Degraded Renosterveld” in the future Elytropappus
rhinocerotis.

The study provides insight into interacting changes in climate and land-use, providing a guide
to the restoration and management of West-Coast Renosterveld at Elandsberg Private Nature
Reserve. In order to preserve the resilience of the system and prevent an alternative stable
state being reached, a pre-AD 1943 benchmark is optimal. Managers are recommended to
decrease the abundance of Elytropappus rhinocerotis through intermediate levels of fire and
herbivory creating patchiness of varying post-fire ages and densities of Elytropappus
rhinocerotis at the local-landscape level. Climate and land-use impacts (and feedbacks
between them) on biodiversity hotspots are of international conservation concern. More high
temporal resolution palaeoecological studies are needed to understand the variability of
ecosystems over time, in order to design management plans that restore and enhance
resilience of highly threatened environments.

February 2014

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DECLARATION
I know the meaning of plagiarism and declare that all of the work in ‘Benchmarks for the
future: Long-term vegetation change derived from palaeoecological techniques in West-Coast
Renosterveld, South Africa’, save for that which is properly acknowledged, is my own and
has not been submitted for any degree or examination in any other university, and that all the
sources I have used or quoted have been indicated and acknowledged by complete references.

....................................... ........................................
Name Date

This thesis is dedicated to my mother, Sharon Ann Peters.
“I am a rose of Sharon, a lily of the valleys.” (Song of Solomon 2:1)

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ACKNOWLEDGEMENTS
I would like to thank the fine institution, the University of Cape Town, for giving me the
opportunity to complete my Master of Science degree. The NRF which provided financial
support through the Masters Scarce Skills Scholarship, special thanks to Bongiwe Ndyama
for her administration assistance. I would also like to thank NRF and ACCESS for providing
generous funding for field work, lab work and equipment. Thanks to the Plant Conservation
Unit for welcoming me into the family of bright and friendly Postgraduate students and
Academics within the Department of Biological Sciences. A special mention to my co-
supervisor, Prof Timm Hoffman, for his time and valuable input. Also to my awesome
supervisor, A/Prof Lindsey Gillson, who openly provided a great deal of advice, time and
effort. A huge heart-warming thank you for her encouragement, dedication and friendship.

So many people have played a part in making the past few years a success for me: from past
lecturers, supervisors, field work assistants, assistance with statistical analysis, to those that
attended Monday PCU presentations, administrative staff and support staff who never failed
to put a smile on my face. I would like to single out the following people: Awot
Gebregziabher, James MacPherson, Abraham Dabengwa (my awesome friend and helpful
colleague) , Robyn Powell, Zoe Poulsen, Leonard Masubelele, Sam Jack (a special thank you
for his assistance with creating the GIS maps), Rob Skelton, Sandy-Lynn Steenhuizen, Carina
Becker, A/Prof Muthama Muasya, Dr Samson Chimphango, Oudette Curtis, Anneli Ekblom,
Laura Blamey, Sandy Smuts, Anthea Stain, Tamara Nozewu, Tosh Williams, Rupert
Koopman, Mireille Lewarne, Sayed Hess, Ullrich Mutzeck, Dawood Hattas, Gonzalo
Aguilar, Desmond Barnes, Nazli Davids, Francois Majola, Lynne Quick, Matthew Britton,
Keith Bennett and Maarten Blaauw. Many thanks to the helpful and friendly team at
Elandsberg PNR: Bernard wooding (reserve manager), Nicola Wooding, Mike Gregor,
Edward Julius and Johann Ungerer. Thank you to Sandeep Singh from Core Scientific
International and Leizl Brand from SIAL.

To my dearest friends and family (they know who they are) for all their love and
encouragement. Thanks to my parents, Nigel Forbes and Sharon Peters. A special mention to
my incredible mom, for her unconditional love and support through laughter and tears, for
being patient with me during exhausting and stressful days, for putting a roof over my head
and for making the most awesome packed lunches UCT has ever seen. I would like to thank
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my love and best friend, Heinrich Dirk, for being such an inspiration, for supporting me
through late nights counting pollen and intense lab work sessions, and for the encouragement
to see this project through with positivity and a smile. Last but not least I would like to thank
my God: because of You I study, I learn, I love, I breathe. You created something as tiny,
intricate, beautiful and perfect as a pollen grain and I thank you Daddy God for the great
privilege of witnessing your creation and serving you through my Masters project.

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