Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Riparian vegetation communities that occur along perennial rivers are structured in lateral
zones that run parallel to river flow. This dissertation investigated the structure of South
African riparian vegetation communities along perennial, single-thread headwater streams.
The central assumption was that lateral zones result from differential species’ responses to
changing abiotic factors along a lateral gradient up the river bank. It was first necessary to
establish the pattern of zones and whether this pattern occurs repetitively and predictably on
different rivers in different biomes. Since the flow regime is considered to be the master
variable that controls the occurrence of lateral zones, the link between flow as the major
abiotic driver and the distribution of plants in zones was determined. Predictions were made
with respect to how variable flow may influence phenological traits, particularly with respect
to seed dispersal, and physiological tolerances to drying out and were tested.
The existence of lateral zones at reference sites in the Western Cape of South Africa was
explored and their vegetation characteristics were described. Plant distribution was related
to bank slope, as defined by elevation and distance from the wetted channel edge during
summer (dry season) low flow, indicating a direct link to river bank hydraulics. Whether or
not the same zonation patterns occur in riparian communities in other parts of South Africa
was explored next. The four zones described for Fynbos Riparian Vegetation were evident
at all of the other rivers tested, despite major differences in geographic location, vegetation
community type, climate and patterns of seasonal flow. The four lateral zones could be
separated from each other using a combination of flood recurrence and inundation duration.
Functional differences were investigated between three tree species that occur in Fynbos
Riparian Vegetation. Functional differences were apparent with respect to timing of seed
dispersal, growth in branch length versus girth and three physiological measures of tolerance
to drying out; specific leaf area (cm2.g-1), wood density (g.cm-3) and levels of carbon isotopes
(δ13C). In order to determine the impact of invasive alien plants and to monitor recovery after
clearing, the physical rules devised to help delineate zones were used to locate lateral zones
that had been obliterated after invasion and subsequent clearing. At the sites invaded by A.
mearnsii plants, the zone delineations showed that invasion started in the lower dynamic
zone, where adult and sapling A. mearnsii were most abundant. In un-invaded systems, this
zone was the least densely vegetated of the four zones, the most varied in terms of
inundation duration and the frequency of inter- and intra-annual floods, and was an area of
active recruitment comprised mainly of recruiting seedlings and saplings.
An understanding of the functional differences between lateral zones was a common thread
at each riparian community that was linked to the annual frequency of inundation and the
period, when inundated. / AFRIKAANSE OPSOMMING: Oewer plantegroei gemeenskappe wat langs standhoudende riviere voorkom is gestruktureer
in laterale sones parallel met die rivier vloei. Hierdie verhandeling ondersoek die struktuur
van Suid-Afrikaanse oewer plantegroei gemeenskappe langs standhoudende, enkelloop hoof
strome. Die sentrale aanname was dat laterale sones vorm as gevolg van verskillende
spesies se reaksie teenoor die verandering van abiotiese faktore teen 'n laterale gradiënt met
die rivierbank op. Dit was eers nodig om die patroon van die gebiede vas te stel en uit te
vind of hierdie patroon herhaaldelik en voorspelbaar binne verskillende riviere in verskillende
biome voorkom. Aangesien die vloeiwyse beskou word as die hoof veranderlike wat die
teenwoordigheid van laterale sones beheer, is die skakel tussen die vloei, as die belangrikste
abiotiese bestuurder, en die verspreiding van plante in sones bepaal. Voorspellings is
gemaak met betrekking tot hoe veranderlike vloei fenologiese eienskappe kan beïnvloed,
veral met betrekking tot die saad verspreiding, en fisiologiese toleransie teen uitdroog, en is
getoets.
Die bestaan van laterale sones binne verwysings studie terreine in die Wes-Kaap van Suid-
Afrika is ondersoek en hul plantegroei eienskappe is beskryf. Plant verspreiding was
verwant aan bank helling, soos gedefinieer deur hoogte en afstand vanaf die nat kanaal rand
gedurende somer (droë seisoen) lae vloei, en dui dus op 'n direkte skakel met die rivier bank
hidroulika. Of dieselfde sonering patrone voorkom in oewer gemeenskappe in ander dele
van Suid-Afrika is volgende verken. Die vier sones beskryf vir fynbos oewer plantegroei was
duidelik by al die ander riviere wat ondersoek is, ten spyte van groot verskille in geografiese
ligging, plantegroei gemeenskap tipe, klimaat en patrone van seisoenale vloei. Die vier
laterale sones kan onderskei word van mekaar deur middel van 'n kombinasie van vloed
herhaling en oorstroomde toestand duur. Funksionele verskille is ondersoek tussen drie
boom spesies wat voorkom in Fynbos Oewer Plantegroei. Funksionele verskille was duidelik
met betrekking tot tydsberekening van saad verspreiding, groei in tak lengte tenoor omtrek,
en drie fisiologiese maatstawwe van verdraagsaamheid teenoor uitdroging; spesifieke blaar
area (cm2.g-1), hout digtheid (g.cm-3) en vlakke van koolstof isotope (δ13C). Ten einde die
impak van indringerplante te bepaal en die herstel na ontbossing te monitor is die fisiese
reëls voorheen vasgestel om sones te help baken gebruik om laterale sones, wat vernietig is
na indringing en die daaropvolgende ontbossing, te vind. Op die terreine wat deur A.
mearnsii indringerplante binnegeval is, het die indeling van sones getoon dat die indringing
begin het in die laer dinamiese sone, waar volwasse en klein A. mearnsii bome die volopste
was. In stelsels wat nie binnegeval is deur indringerplante was hierdie sone die minste dig
begroei van die vier sones, die mees verskillend in terme van oorstroomde toestand duur en
die frekwensie van inter-en intra-jaarlikse vloede, en was 'n gebied van aktiewe werwing
hoofsaaklik bestaande uit rekruut saailinge en boompies.
'n Begrip van die funksionele verskille tussen laterale sones was 'n algemene verskynsel by
elke oewer gemeenskap wat gekoppel was aan die jaarlikse frekwensie van oorstroming en
die oorstroomde toestand duur.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95482 |
| Date | 12 1900 |
| Creators | Reinecke, Michiel Karl |
| Contributors | Esler, Karen, Brown, Cate, King, Jackie, Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xiv, 148 p. : ill. |
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