Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Riparian ecosystems of the Mediterranean south-western Cape region are projected to experience
significant decreases in streamflow due to climate change and increased demands for water associated
with human demographic trends and increasing living standards. Aggravating this problem are woody
invasive alien plants, such as Acacia mearnsii, whose impacts, including those on catchment water
yields, have justified extensive eradication programmes such as Working for Water (WfW). WfW has
been highly successful in managing invasive alien species in some areas, while at the same time
enhancing the quality of life of poor South Africans. Unfortunately, the managers of these eradication
initiatives often experience a lack of information on the species- and site-specific ecological properties
that may aid in prioritising sites more prone to invasion, essentially inhibiting accurate management
output. Knowledge, such as that associated with the possible future distribution of invasive species in
a changing environment, may help to optimise eradication initiatives. I therefore determined whether
woody plants portray different physiological (vulnerability to cavitation) and wood anatomical traits
(wood density, vessel resistance to implosion, vessel lumen and wall diameters) across three
prominent riparian zones in the south-western Cape that each differ in streamflow quantity – to gain a
mechanistic understanding of how woody species, especially invasive species, adapt their hydraulic
strategy across this proxy for water availability. Using factorial ANOVA’s, to distinguish any
differences in plant physiological and wood anatomical responses to water availability within and
between species, showed Acacia mearnsii having consistently higher drought-tolerance (lower P50
values and denser wood) compared to native species under reduced water availability. These results
supported the significant variation in drought-tolerance strategies that exist within and between
taxonomically different species across different environments. Water availability thus has a strong
selective effect on functional traits of species; however, minimum water potentials were more useful
in describing in situ hydrological conditions than streamflow. Additionally, a non-causal relationship
between wood anatomical traits and drought-induced cavitation was observed. Therefore, using only
wood anatomical measurements to assess drought-tolerance of species might not be accurate across all
species. This mechanistic approach to assess the invasive potential of species under projected drier
conditions has great practical value. It can be used to improve species selection for restoration
initiatives, and is of great value for future use in prioritizing eradication programmes. / AFRIKAANSE OPSOMMING: Rivieroewer ekosisteme in die Mediterreense Suidwes-Kaap streek kan groot afnames in stroomvloei
verwag, wat meestal toegeskryf kan word aan klimaatsverandering en die verhoogde aanvraag na
water geassosieerd met stygende populasiegrootte. Uitheemse indringerplante soos Acacia mearnsii
vererger hierdie probleem. Laasgenoemde spesies plaas groot druk op opvanggebiede se water
opbrengs, en vorm grootliks die rede waarom uitroeiing programme soos Werk vir Water (WfW)
gestig is. WfW het al groot suksesse behaal in die bestuur van uitheemse indringerplante, en
terselfdertyd die lewenskwaliteit van arm Suid-Afrikaners verhoog. Ongelukkig sukkel hierdie
indringer uitroeiing inisiatiewe telkens met ongenoegsame bewyse wat kan help om leiding te verskaf
by die prioritisering van areas meer geneig tot indringing. Die gevolg is dat onvoldoende bestuurs
besluite gemaak kan word. Gevolglik sal kennis geassosieerd met die moontlike toekomstige
verspreiding van hierdie indringerplant in ʼn veranderlike omgewing help om uitroeiing programme
meer akkuraat te stel en gevolglik waardevol wees t.o.v. prioritisering van kwesbare areas. Die doel
van hierdie studie was om die kwesbaarheid van sleutel inheemse houtagtige rivier spesies en veral die
dreigende indringerplant Acacia mearnsii, te bestudeer in terme van verlaagde stroomvloei soos
voorspel vir die Wes-Kaap fynbos ekosisteem. Deur te bepaal of houtagtige plante verskillende
fisiologiese (kwesbaarheid teen xileem blokkasie) en anatomiese (hout digtheid, vat
weerstandbiedendheid teen inmekaarkolking, vat holte en wand deursnee) hidrologiese eienskappe
tentoonstel gemeet tussen drie prominente rivieroewer sones in die suidwes Kaap wat variëer in
stroomvloei kwantiteit, verskaf ʼn meganistiese begrip van hoe spesies, veral die indringerplante, hul
hidrologiese strategieë ten opsigte van droogtes kan aanpas. Faktoriële ANOVAS’s tussen spesies en
liggings het getoon dat beide plant fisiologiese en hout anatomiese data beduidend variëer tussen
taksonomies verskillende spesies. Veral Acacia mearnsii het deurgaans laer P50 waardes asook hoër
houtdigtheid getoon, ‘n teken van hierdie spesies se verhoogde droogte toleransie in vergelyking met
die inheemse spesies. Wat beduidend is is dat spesies-spesifieke lewensstrategieë ten opsigte van
droogte toleransie in hierdie rivieroewer sones voorkom. Resultate het bevestig dat water
beskikbaarheid ʼn groot rol speel in die seleksie van funksionele karaktereienskappe in plante, maar,
dat minimum water potensiaal meer akkuraat was om in situ hidrologiese toestande te beskryf as wat
stroomvloei kon. Die verhouding tussen plant fisiologiese en hout anatomiese karaktereienskappe was
indirek as gevolg van spesies-spesifieke lewensstrategieë. Gevolglik sal die allenige gebruik van hout
anatomiese eienskappe om droogte toleransie in plante te assesseer onakkuraat wees omdat daar ʼn
swak verhouding tussen hout anatomie en droogte-geïnduseerde xileem blokkasie bestaan. ʼn
Meganistiese benadering om die indringing potensiaal van spesies onder voorspelde droër kondisies te
assesseer, asook om spesies seleksie vir restourasie doeleindes op te skerp, is prakties uitvoerbaar, en
van groot waarde vir toekomstige gebruik in uitroeiing en restourasie inisiatiewe.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4203 |
| Date | 03 1900 |
| Creators | Crous, Casparus Johannes |
| Contributors | Jacobs, Shayne M., Esler, Karen J., University of Stellenbosch. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 102 p. : ill., maps |
| Rights | University of Stellenbosch |
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