Thesis (MScConEcol)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Acacia saligna, or Port Jackson, is an Australian Acacia which has spread throughout the Western
and Eastern Cape provinces of South Africa where it has become invasive and a prominent feature
of the vegetation. In areas where A. saligna establishes it replaces natural vegetation, alters
ecosystem processes and interferes with agricultural practices. Consequently large management
efforts have been made to eradicate this invasive alien tree. However, its large and persistent soil
stored seed bank, even in the presence of management and biological control agents, poses a
serious obstacle to its successful removal. Furthermore the reproductive output and the size of the
seed bank of A. saligna over its whole distribution as well as the variation of seed production and
the seed bank with environmental conditions in time and space is poorly known. Understanding the
seed bank dynamics of A. saligna in time and space is essential for reducing invasive success and
achieving management objectives. This study has filled this knowledge gap through studying the
seed production and seed bank of A. saligna over its invaded range in South Africa, including how
environmental factors influence these factors in time and space. The seed rain of A. saligna was
assessed at 10 sites across its distribution in South Africa. The seed rain of A. saligna at the sites
was determined through the use of seed rain traps. Twenty five traps were placed out at every site
during November 2010 (pre-dehiscence) which was collected again during April 2011 (postdehiscence).
The seed bank of A. saligna was estimated through sampling at 25 sites across its
distribution range in South Africa. The seed bank was sampled during April 2010 (postdehiscence),
November 2010 (pre-dehiscence) and April 2011 (post-dehiscence) through taking 50
litter and soil samples at every site which gave a total sampling size of 3 750 for both the seed in
the soil and litter over its distribution in South Africa. In addition the average tree diameter, tree
density, average number of Uromycladium tepperianum induced galls per tree, the summer aridity
index, De Martonne aridity index, winter concentration of precipitation, temperature of coldest
month and the soil texture for every site was determined. The damage done by the seed feeding
weevil, Melanterius compactus, was also estimated for the seed rain study sites. Water availability
during the hot summer months was assessed as the most important factor governing seed
production and seed bank size. Riparian and non-riparian water regimes were shown to be
important in understanding the seed bank dynamics of A. saligna over its distribution range in the
Cape Floristic Region. In non-riparian A. saligna populations the seed production and consequently
the size of the seed bank and its rate of accumulation is limited by both water and temperature and
in riparian A. saligna populations, only by temperature. Therefore, two environmental gradients
influence the seed bank dynamics of Port Jackson in South Africa. In non-riparian A. saligna
populations the number of seed produced and the accumulation of seed in the seed bank generally
increases along the west coast of South Africa from Clanwilliam towards Cape Town and along the
south coast from Cape Town towards Port Elizabeth. Seed banks are larger closer to the coast,
when A. saligna populations of similar age are compared. In riparian A. saligna populations, the number of seed produced generally increases from Port Elizabeth towards Cape Town and from
Cape Town towards Clanwilliam, again, with larger seed banks being accumulated closer to the
coast, when populations of similar age are compared. This study provides managers with a useful
tool for prioritising management efforts. / AFRIKAANSE OPSOMMING: Acacia saligna of Port Jackson is ‘n indringerplant in Suid-Afrika wat afkomstig is uit Suid-Wes
Australië. Acacia saligna is ‘n onmisbare kenmerk van die plantegroei in die Wes en Oos-Kaap.
Waar Port Jackson vestig, verplaas dit natuurlike plantegroei, verander dit ekosisteem prossesse
en verhinder dit landbou praktyke. Gevolglik is groot bestuurspogings aangewend om hierdie
indringer plant uit te roei. In die teenwoordigheid van bestuursprogramme en biologiese beheer bly
A. saligna lewensvatbaar as ‘n gevolg van die plant se groot blywende grond saadreserwes.
Verder is die saad produksie en saadbank grootte van A. saligna oor sy verspreiding bereike
asook hoe dit met omgewingstoestande in tyd en ruimte interreageer en varieer grootendeels
onbekend. ‘n Goeie en omvattende begrip van die saadbankdinamika is belangrik om die
indringings vermoë van die plant te verlaag en om bestuursdoelwitte te bereik. Hierdie studie vul
die bestaande gaping in die kennis aangaande die saadbank dinamika van A. saligna aan deur die
saadproduksie en die saadreserves van die indringerplant oor sy verspreiding in Suid-Afrika te
bestudeer, insluitend hoe omgewingstoestande die saadbankdinamika beïnvloed in tyd en ruimte.
Die saadreën vir 10 A. saligna populasies was bepaal deur die gebruik van saadlokvalle. Vyf-entwintig
lokvalle was uitgeplaas in elke bestudeerde Port Jackson perseel gedurende November
2010 (voor-saadval) wat weer gaan haal is gedurende April 2011 (na-saadval). Die saadbank van
A. saligna was bepaal in 25 populasies van die boom gedurende April 2010 (na-saadval),
November 2010 (voor-saadval) en April 2011 (na-saadval) deur die neem van 50 blaar- en
grondmonsters by elke perseel wat ‘n totaal van 3 750 blaar- en grondmonster gee oor die hele
verspreiding van A. saligna in Suid-Afrika. Verder is die gemiddelde boomdeursnee, boomdigtheid,
gemiddelde Uromycladium tepperianum geinduseerde galle per boom, die somers droogtheids
indeks, De Martonnes droogtheids indeks, die winter konsentrasie van presipitasie, die
temperatuur van die koudste maand en die grond tekstuur van elke Port Jackson stand bepaal. Die
skade wat die saad voedende kewer, Melanterius compactus, aanrig aan die sade van A. saligna
is ook vir die persele waar die saadreën eksperiment uitgevoer is, bepaal. Die beskikbaarheid van
water vir A. saligna in die droë somermaande is bepaal as die belangrikste faktor wat die grootte
van die saadproduksie en saadbank beïnvloed. Oewer en nie-oewer water omgewings is bevind as
noodsaaklik om die saadbank dinamika van A. saligna oor die indringerplant se verspreidingareas
in die Kaap Floristiese Streek te verstaan. In nie-oewer A. saligna populasies word saadproduksie
en gevolglik die grootte en tempo van akkumulasie van die saadbank deur beide water en
temperatuur omstandighede beperk, terwyl in oewer A. saligna populasies word die indringerplant
slegs deur temperatuur omstandighede beperk. Gevolglik blyk dit dat twee water beskikbaarheids
gradiënte bestaan waarop die plant reageer wat dan uitgedruk word in die plant se saad produksie
en gevolglik ook die plant se saadbank. In nie-oewer Port Jackson populasies neem die
saadproduksie en die tempo waarteen die saadbank akkumuleer algemeen toe langs die weskus
van Clanwilliam na Kaapstad en van Kaapstad na Port Elizabeth, met grootter saadproduksie en saadbank akkumulasie nader aan die kusgebiede, wanneer A. saligna populasies van dieselfde
ouderdom vergelyk word. In oewer Port Jackson populasies neem die saadproduksie en die tempo
waarteen die saadbank akkumuleer algemeen toe van Port Elizabeth na Kaapstad en van
Kaapstad na Clanwilliam, met grootter saadproduksie en saadbank akkumulasie nader aan die
kusgebiede, wanneer A. saligna populasies van dieselfde ouderdom vergelyk word. Hierdie studie
verskaf bestuursplanne met ‘n nuttige raamwerk waarvolgens uitroeiing en beheer programme vir
A. saligna beplan kan word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20389 |
| Date | 03 1900 |
| Creators | Strydom, Matthys |
| Contributors | Esler, Karen J., Wood, Alan R., 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 | Unknown |
| Type | Thesis |
| Format | 170 p. : ill., maps |
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