Phenology of indigenous and alien vascular flowering plants on sub-Antarctic Marion Island

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Date
2014-04-24Author
Mukhadi, Fulufhelo Licken
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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...