Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Climate has shown some remarkable changes over the past century, especially at the
polar and sub-polar regions. Southern Ocean Islands provide good models for studies
related to climate change effects, since effects may be evident in the short term and may
also be clearer. Marion Island is an example of such a system with a harsh abiotic
environment, and low species richness often vulnerable to change. Climate change is
predicted, and also reported, to have biological consequences on plant communities,
affecting the phenology, morphology, and the interaction between individuals and
species. This study examines the association between the keystone plant species, Azorella
selago Hook. (Apiaceace), and its dominant epiphyte Agrostis magellanica Lam.
(Poaceae). Two complimentary approaches were used, one observational and the other
experimental. The main objective for the observational study was to quantify bioticallyrelevant
microclimate temperature, as well as the morphology, epiphyte load and
phenology of A. selago at three different altitude sites on Marion Island. This provided
information on baseline variation for understanding specific variability in plant response
to the experimental part of this study, against which future patterns arising from
biological monitoring can be compared. Studying plants at different altitudes provides a
possible analogue for temperature-related climate change consequences for the ecology
of A. selago, and its interaction with A. magellanica. The microclimate temperature
associated with A. selago differed between the three sites examined. This difference was
related to local topographic conditions and altitude differences. Cushion size differed
distinctively between the three altitude sites, with this difference related to environmental
heterogeneity such as differences in age and substrate structure. Azorella selago annual
growth rate was estimated through stem length and the number of leaves on both exposed
and shaded stems. Within-site variability, as well as epiphyte cover were found to be the
contributing factors on A. selago annual growth rate. This highlights the importance of
site-specificity when estimating growth rate within and between different altitude sites.
Leaf characteristics differed between the sites, with this attributed to local habitat
conditions, such as topography, as well as epiphyte cover. As expected, the difference in
leaf size between exposed and shaded leaves demonstrated a larger specific leaf area on leaves shaded by A. magellanica. Agrostis magellanica abundance and density were
altitudinally related, with A. selago demonstrating facilitation effects on A. magellanica.
The trend shown in this study suggests that in spite of general facilitative effect of A.
selago on A. magellanica towards higher altitudes, the abiotic environmental threshold
for A. magellanica occurs at lower altitudes than it does for A. selago. Phenological
differences were also apparent between the three sites. The objectives of the experimental
part of this study were to quantify the effect of the dominant epiphyte, A. magellanica on
biotically-relevant microclimatic temperatures, as well as on the phenology and physical
condition of A. selago. Different treatments were applied to cushions at the three altitude
sites to examine the shading effect of epiphytic A. magellanica on cushion plants, as well
as the effect of treatment-related disturbance. Azorella selago microclimate temperature
showed no significant difference between treatments, suggesting that on average
epiphytic A. magellanica cover has no effect on cushion microclimate temperature. The
percentage of flower budding and flowering of A. selago was negatively related to
epiphyte cover. Cushion vitality was also responsive to epiphyte cover, with higher
vitality scores on low grass covered cushions than on high grass cushions. This shows
that A. magellanica competes with A. selago, while A. selago facilitates A. magellanica.
Heavy epiphyte numbers impose negative effects on A. selago vegetative and
reproductive performance, as well as cushion vitality. Therefore, the results of this
research show that the vegetative and reproductive performance of A. selago and cushion
vitality are likely to be negatively affected under ongoing climate change on Marion
Island if this brings about heavier epiphyte loads on this keystone cushion plant species. / AFRIKAANSE OPSOMMING: In die afgelope eeu het die klimaat in die Antarktiese en sub-Antarktiese gebiede
merkwaardige verandering getoon. Die Suidelike See Eilande dien as goeie modelle vir
studies verwant aan die gevolge van klimaatsverandering, aangesien die kort termyn
effekte in die gebiede duideliker mag wees in die toekoms. Marion Eiland is ‘n voorbeeld
van so ‘n sisteem, met ‘n ruwe abiotiese omgewing en lae spesies rykheid, wat vatbaar is
vir verandering. Daar word voorspel, en is reeds bevind dat klimaatsverandering
biologiese gevolge op plant gemeenskappe het, in terme van morfologie, fenologie en die
interaksie tussen individue en spesies. Hierdie studie ondersoek die assosiasie tussen die
hoeksteen plant spesie, Azorella selago (Apiaceace), en sy dominante epifietiese gras,
Agrostis magellanica Lam. (Poaceae). Die studie is op twee komplimentêre maniere
benader, naamlik deur waarneming en eksperiment. Die hoof doel van die studie was om
die biotiese belang van mikroklimaat temperatuur te kwantifiseer, en die hoeveelheid
epifiete, die morfologie en die fenologie van A. selago te bepaal by drie verskillende
hoogtes op Marion Eiland. Laasgenoemde het inligting verskaf oor die variasie in die
reaksie van plante tot die eksperimentele aspek van die studie, waarteen patrone vanaf
toekomstige biologiese beheer vergelyk kon word. Deur plante te bestudeer by
verskillende hoogtes bo seespieël word ‘n moontlike analoog vir die gevolge van
temperatuur-verwante klimaatverandering in terme van die ekologie van A. selago, en
laasgenoemde se interaksie met A. magellanica verskaf. Die mikroklimaat temperatuur
geassosieer met A. selago verskil tussen dié drie liggings. Die versil was verwant aan die
plaaslike topografiese toestande en die verskillende hoogtes bo seespieël. Die grootte van
die kussingplante het duidelik versil tussen die drie liggings, met die verskille verwant
aan die omgewing se heterogeneïteit, byvoorbeeld die verskille in ouderdom en substraat
struktuur. Azorella selago se jaarlikse groeitempo was bepaal deur die stingel lengte en
die aantal blare, op beide die wat oorskadu is deur die gras, en die was nie oorskadu is
nie. Daar is gevind dat die faktore wat bygedra het tot die jaarlikse groeitempo van A.
selago, varieër binne die verskillende liggings, en bedekking deur epifiete. Dit
beklemtoon die belang van spesifisiteit van ligging wanneer groeitempo in en tussen die
liggings van verskillende hoogtes bepaal word. Die blaar eienskappe het verskil tussen verskillende liggings, as gevolg van plaaslike habitat toestande, soos topografie en
bedekking deur epifiete. Soos verwag, het die blare wat oorskadu was deur A.
magellanica ‘n groter spesifieke blaar area getoon as blare wat blootgestel was. Die
hoeveelheid en digtheid van Agrosits magellanica was verwant aan hoogte bo seespieël,
met A. selago wat fasiliterende effekte toon op A. magellanica. Die tendens waargeneem
in hierdie studie is dat ten spyte van die algemene fasiliterende effek van A. selago op A.
magellanica, die abiotiese omgewingsdrempel op ‘n laer hoogte is vir A. magellanica as
vir A. selago. Fenologiese verskille was ook duidelik tussen die drie liggings. Die doel
van die eksperimentele deel van die studie was om die effek van die dominante epifiet, A.
magellanica, te bepaal op bioties relevante mikroklimaat temperature, asook op die
fenologie en fiesiese toestand van A. selago. Verskeie behandelings is aangewend op die
kussingplante by die drie liggings om die effek van skaduwee van die epifietiese A.
magellanica op die plante te bepaal, asook die effek van versteurings versoorsaak deur
die behandelings. Azorella selago se mikroklimaat temperatuur het geen betekenisvolle
verskille tussen behandelings getoon nie, wat voorstel dat epifitiese A. magellanica oor
die algemeen geen effek op die kussingplante se mikroklimaat temperatuur het nie. Daar
was ‘n negatiewe verwantskap tussen die hoeveelheid epifiete op A. selago en die
persentasie blomme en blomknoppe op die kussingplante. Die plante se vitaliteit was ook
afhanklik van epifiet bedekking, met ‘n hoër vitaliteit telling vir kussingplante bedek met
lae gras as die bedek met hoë gras. Dit toon dat A. magellanica met A. selago wedywer,
terwyl A. selago vir A. magellanica fasiliteer. Hoë epifiet getalle het negatiewe effekte op
A. selago se vegetatiewe en reproproduktiewe nakoming, asook die kussingplante se
vitaliteit. Die resultate van hierdie studie toon dus dat die vegetatiewe en reproduktiewe
nakoming van A. selago en kussingplant vitaliteit heel moontlik negatief geaffekteer sal
word indien klimaatsverandering op Marion Eiland hoër epifiet getalle op die sleutel
kussingplant spesie tot gevolg sal hê.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17743 |
| Date | 12 1900 |
| Creators | Buwa, Ziphokazi Siyasanga |
| Contributors | McGeoch, M.A., Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | vi, 153 leaves : ill. |
| Rights | Stellenbosch University |
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