Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Species’ seasonal behaviour is of paramount importance in understanding community functioning
and dynamics. Recently, plant phenology has further gained significance as a reliable indicator of
climate change impacts. Despite the importance of understanding plant dynamics, there are
relatively few plant phenological records for the sub-Antarctic region, and where records exist they
are often not extensive. Sub-Antarctic Marion Island, typical of Southern Ocean Islands, offers a
useful setting for addressing these knowledge gaps. This study documented the vegetative and
reproductive phenologies (or aggregate phenological patterns) of twelve indigenous and three alien
vascular plant species on the island. The phenological differences among the species and distinct
seasonal groupings (e.g. early, intermediate and late species) were examined. I also investigated the
phenological differences among the indigenous and alien plant species. Furthermore, the onset of
selected reproductive phenophases from the current records was compared with historical records
for determining the extent of climate change-related alterations in phenology. Phenological data
were collected fortnightly on five, 5 m x 5 m permanent plots per species (except for a few species)
for a full growing season. Thus the sample size is n = 5 for all plant species except for Crassula
moschata (n = 4), Juncus effusus (n=4) and Rumex acetosella (n=1). Sites of the same species were
separated by at least 500 m except for the alien plant, Juncus effusus, where all four known
populations were selected despite two of these populations being < 500 m apart. This study
indicated that Marion Island plants grow throughout the year with no major peaks except in
Azorella selago and Acaena magellanica which showed winter dormancy. However, reproduction
in most plant species predominately occurred in spring and summer months. Pringlea
antiscorbutica and Poa cookii were the first two species to set flower buds in September while most
species dispersed their seeds in summer except for Agrostis magellanica and Crassula moschata
which dispersed in early autumn. Distinct from most temperate systems, the reproductive
seasonality displayed by Marion Island plant species is explained more by daylength than by
temperature, perhaps due to the region’s typical thermal aseasonality. Interestingly, many cooccurring
species and/or clades across the Falkland, Kerguelen, Macquarie and South Georgia
Islands also showed similar flowering onset date to the Marion Island plants, further confirming
their daylength sensitivity. However, other external factors seem to come into play at later events of
reproduction. Consequently, fruit maturation time of similar species across the sub-Antarctic islands
varied substantially despite the plants having flowered in the same month. Although plant species
showed similar reproductive seasonality, there were significant differences among species phenologies i.e. phenophase timing, duration and peak occurrence dates. However, using 95%
confidence intervals of Generalized Linear Models weighted means, and/or one-way ANOVA
(Tukey post hoc test), three homogenous sets of species (early, late, or intermediate onsets) were
identified based on flower bud, flowering and seed dispersal phenophase onset dates. The
homogenous species groupings observed for flower buds also remained unchanged during flowering
onset except for Cotula plumosa and Callitriche antarctica which switched groups. As for the seed
dispersal timing, the pattern was not consistent with that of the flower bud and flowering onset
homogenous groupings, except for Acaena magellanica and Agrostis magellanica which remained
in the early and late groups, respectively. Conversely, in the case of the timing of other phenophases
(pollen release, fruit set and fruit ripening), entire phenophase durations, and peak occurrence dates,
species overlapped greatly, resulting in an unbroken progression or continuum of phenology among
species. Similarly, the three alien plant species investigated here (Cerastium fontanum, Juncus
effusus and Rumex acetosella) showed no consistent phenological differences from the rest of the
species. However, a widespread alien plant species on Marion Island, C. fontanum, reproduced for
most of the year, although its reproduction peak was in summer months as was the case for the rest
of the species. This study also indicated that indigenous plant species have altered their reproductive
phenologies since 1965. Although the response was species-specific, the majority of plant species
significantly delayed the onset of reproductive activities in 2007 by comparison with 1965.
However, it is not clear if the observed species response was caused by the now drier and warmer
Marion Island climate or by discrepancies in reporting in the earlier studies and/or sampling
differences between the recent and historical records. Therefore, these results should be taken with
caution. In conclusion, this research provided a detailed phenological dynamics record for vascular
plant species on the island. Over time these records may be used as a basis for monitoring and
modelling the impact of climate on plant phenology on the island. / AFRIKAANSE OPSOMMING: Spesies se seisoenale gedrag is van die allergrootste belang in die begrip van
gemeenskapsfunksionering en dinamika. Meer onlangs het plant fenologie verdere betekenis
verwerf as ‘n betroubare indikator vir die impakte van klimaatsverandering. Ondanks die
belangrikheid om plant dinamika te verstaan, is daar relatief min plant fenologiese rekords vir die
sub-Antarktiese streek en waar rekords wel bestaan is dit dikwels nie omvangryk nie. Sub-
Antarktiese Marion Eiland, tipies van Suidelike Oseaan Eilande, bied ‘n nuttige ligging om hierdie
kennis gapings aan te spreek. Hierdie studie het die vegetatiewe en voorplantingsfenologieë (of
gesamentlike fenologiese patrone) van elf inheemse en drie uitheemse vaatplantspesies op die
eiland gedokumenteer. Die fenologiese verskille tussen die spesies en duidelike seisoenale
groeperings (bv. vroeë, intermediêre en laat spesies) is ondersoek. Ek het ook die betekenisvolle
fenologiese verskille tussen die inheemse en uitheemse plantspesies ondersoek. Voorts, die aanvang
van gekose voortplanting feno-fases van huidige rekords is vergelyk met historiese rekords om die
mate van klimaatsverandering verbandhoudende veranderings in die fenologie te bepaal.
Fenologiese data is twee weekliks ingesamel op vyf, 5 m x 5 m permanente plotte per spesie
(behalwe vir ‘n paar spesies) vir ‘n volle groei seisoen. Dus, die insamelings grootte is n = 5 vir al
die plantspesies behalwe vir C. moschata (n = 4), Juncus effusus (n=4) en Rumex acetosella (n=1).
Persele vir dieselfde spesies is geskei deur ten minste 500 m, behalwe vir die uitheemse plant,
Juncus effusus, waar al vier populasies wat bekend is gekies is, ten spyte daarvan dat twee van
hierdie populasies < 500 m uitmekaar is. Hierdie studie het aangedui dat Marion Eiland plante
regdeur die jaar groei, met geen belangrike spitstye nie, behalwe in Azorella selago en Acaena
magellanica wat ‘n winter rusperiode wys. Hoe ookal, voortplanting in meeste van die plantspesies
het hoofsaaklik voorgekom tussen die lente en somermaande. Pringlea antiscorbutica en Poa cookii
was die eerste twee spesies om blomknoppe uit te stoot in September, terwyl die meeste spesies
hulle sade versprei het gedurende die somer, behalwe vir Agrostis magellanica en Crassula
moschata wat versprei het in vroeg herfs. Duidelik van meeste gematigde sisteme, word die
voortplanting seisoenaliteit, getoon deur die Marion Eiland plantspesies, verduidelik meer deur daglengte
as deur temperatuur, moontlik weens die streek se tipiese termiese a-seisoenaliteit.
Interessant, baie spesies en/of afstameling-groeperings wat saam aangtref word dwarsoor die
Falkland, Kerguelen, Macquarie en Suid Georgia Eilande wys ook soortgelyke bloei
aanvangsdatums as die Marion Eiland plante, nog meer bevestigend van hulle dag-lengte
sensitieweteit. Hoe ookal, ander eksterne faktore blyk betrokke te raak by latere gebeure van voortplanting. Gevolglik het vrug rypwordingstyd van dieselfde spesies oor die sub-Antarktiek
noemenswaardig verskil, ten spyte daarvan dat die plante in dieselfde maand geblom het. Alhoewel
plantspesies dieselfde voortplanting seisoenaliteit gewys het, was daar ‘n noemenswaardige veskil
tussen spesie fenologieë, m. a. w. feno-fase tydsberekenning, tydsduur en spits voorkomsdatums.
Hoe ookal, deur gebruik te maak van 95% betroubaarheid intervalle van Algemene Lineêre Modelle
gewigte gemiddelde en/of een rigting ANOVA (Turkey post hoc toets), is drie homogene stelle van
spesies (vroeë, laat en intermediêre aanvang) geïdentifiseer gebasseer op blomknop, bloei en saad
verspreiding feno-fase aanvangsdatums. Die homogene spesie groeperings waargeneem op
blomknoppe het ook onveranderd gebly gedurende bloei aanvang behalwe vir Cotula plumosa en
Crassula antarctica wat groepe geruil het. Vir die saadverspreiding tydsberekenning was die
patroon nie konstant met die van die blomknop en bloei aanvang homogene groepe nie, behalwe vir
Acaena magellanica en Agrostis magellanica wat in die vroeë en laat groepe respektiewelik gebly
het. Omgekeerd, in die geval van tydsberekenning van ander feno-fases (stuifmeel vrysetelling,
vrugwerp, vrugrypwording), volledige feno-fase tydsduur en spits voorkomsdatums het spesies
grootliks oorvleuel, wat ‘n ongebroke vordering of deurlopendheid van fenologie tussen die spesies
tot gevolg het. Ooreenkomstig het die drie uitheemse spesies wat hier ondersoek is (Cerastium
fontanum, Juncus effusus en Rumex acetosella) geen bestendige fenologiese verskille van die res
van die spesies gewys nie. Hoe ookal, ‘n wydverspreide uitheemse spesie op Marion Eiland,
Cerastium fontanum, het deur die meeste van die jaar voortgeplant, hoewel met ‘n voorplanting
spits in die somer maande soos die res van die spesies. Hierdie studie dui ook aan dat inheemse
plantspesies hulle voortplanting fenologieë verander het sedert 1965. Alhoewel die reaksie spesiespesifiek
was, het die meerderheid van die plantspesies hulle voortplanting aanvang aansienlik
vertraag gedurende 2007 in vergelyking met 1965. Hoe ookal, dis nie duidelik of die waargeneemde
spesie reaksie was as gevolg van die nou droër en warmer Marion Eiland klimaat of deur
teenstrydighede in verslagewing gedurende die vroëre studies en/of insameling verskille tussen die
onlangse en historiese rekords. Daarom moet hierdie resultate met versigtigheid hanteer word. In
samevatting, hierdie navorsing voorsien ‘n gedetaileerde fenologiese dinamieka rekord vir
vaatplantspesies op die eiland. Oor tyd kan hierdie rekords gebruik word as basis vir monitering en
modellering van die impak van klimaat.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6890 |
| Date | 03 1900 |
| Creators | Mukhadi, Fulufhelo Licken |
| Contributors | Chown, Steven L., Shaw, Justine D., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 126 p. : ill. |
| Rights | Stellenbosch University |
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