Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: A common topographical feature of the Nama-Karoo are mesas, commonly known as
"platkoppies" , that provide an interesting source of landscape heterogeneity to an
otherwise flat landscape. Although these isolated mesas are geologically and
edaphically distinct from the surrounding flats, many species are shared between these
habitats. These include palatable species such as Themeda triandra. A question asked
by the broad umbrella project under which this project falls was: to what extent do mesas
provide refuges for palatable species that are under pressure from heavy overstocking
on the surrounding flats?
A study on the regeneration potential of T triandra on and off the Tafelberg Mesa in the
Middelburg district of the Eastern Cape, South Africa, was undertaken within the context
of a broader umbrella project "Restoration of degraded Nama-Karoo: role of
conservation islands". The Nama-Karoo has had centuries of heavy commercial
livestock production and it is considered to have been transformed from a relatively (by
arid ecosystems) productive system to one dominated by shrubs and somewhat less
productive species. Themeda triandra is one of the preferred grass species for livestock
production. Although T. triandra is a preferred grass species, relatively, little is known
about its ability to produce viable seed and the establishment of seedlings particularly in
restoration and rehabilitation programmes. This study examines the pattern of seed
production and seedling survival, seed dispersal, seed germination, and the
morphological and ecophysiological variability of T. triandra, a species with great
potential for restoration of degraded Nama-Karoo sites, particularly those in the Eastern
Cape.
Themeda triandra was found to be one of the dominant species on summit of the
Tafelberg Mesa. In comparison, it occurred in small isolated populations on the flats
surrounding the mesa. The flats and slopes are grazed more intensely by domestic
livestock than the summit of the mesa. This is due to the inaccessibility to livestock due
to a steeper topography and the lack of water at the higher altitudes.
Annual seed production of T. triandra per plant and per m2 was highest for the
populations on the flats despite these populations being grazed most intensively. Rainfall had an effect on annual seed production, which was monitored over two years. Rainfall
increased from less than 20mm in November 1999 to 125, 110, 50 and 135mm in
December 1999, January 2000, February 2000 and March 2000 respectively. With the
increased rainfall prior to the May 2000 sampling period, more seeds were produced per
plant and per m2 for the flats and slopes habitats of the Tafelberg Mesa. The opposite
trend occurred on the summit of the mesa, where seed production actually decreased.
This could be attributed to increased competition or to lower grazing intensities. Increase
in rainfall also had a positive effect on the cover of other grasses (excluding T. triandra)
and T. triandra itself. Despite higher levels of seed production in populations of T.
triandra on the flats, seedling survival was clearly low whereas seedlings on the slopes
and summit had significantly higher seedling survivorship. This negative impact could be
explained due to the trampling effect of domestic herbivores.
The results of a seed dispersal experiment clearly suggest that the seed dispersal
distance of T. triandra to "safe" microsites is short distance (majority of seeds disperse
up to 60cm) and that the dispersal agent is wind. Microsites for re-establishment was
found to be open or rocky sites.
In a controlled experiment, seed emergence of T. triandra indicated that optimal sowing
depths varied with soil type. Maximum germination was achieved at sowing depth 2cm
and 3cm in soil collected from the flats surrounding the Tafelberg Mesa. The soil texture
of the flats was found to be more sandy loam clay. The flats had slightly higher content
(%) of stone, clay, silt and sand compared to the soils collected from the summit and
slopes. Themeda triandra is clearly not limited in its expansion onto the flats in the
Middelburg district due to soil conditions at the germination/recruitment phase. This
study also revealed that T. triandra germinates best under summer conditions when the
probability of rainfall is at its highest. Results with T. triandra seed did not convincingly
suggest that smoke water is of adaptive significance to boost germination in restoration
attempts in the Middelburg district of the Eastern Cape.
In a controlled greenhouse experiment, individuals of T. triandra taken from the summit
of Tafelberg Mesa showed no differences in photosynthesis, stomatal conductance or
transpiration rates to individuals occurring on the flatland areas surrounding the mesa.
Themeda triandra appears to be relatively adaptable to a range of temperature conditions. These findings suggest that there should be no problem using seed from
mesa summits in restoration programmes on the surrounding flats.
This study revealed no conclusive evidence, indicating that the populations on the
summit of the mesa were a source of T. triandra seed for the flats surrounding the
Tafelberg Mesa. However, this two year long investigation found that T. triandra has the
potential to be used in restoration and rehabilitation programmes. If released from
grazing pressures, and assuming favourable climatic conditions, the density of T.
triandra on the flats can be increased and can be used as a suitable species for the
restoration of heavily degraded patches in the Nama-Karoo Region. / AFRIKAANSE OPSOMMING: OnAlgemene topografiese kenmerk van die Nama-Karoo is mesas, plaaslik bekend as
"platkoppies", wat Oninteressante bron van landskap ongelyksoortigheid voorsien aan On
andersins vlakte landskap. Alhoewel hierdie geisoleerde mesas geologies en biofisies
verskillend is van die omliggende vlaktes, word baie plant spesies gedeel tussen hierdie
habitats. Hierdie sluit in smaaklike spesies soos Themeda triandra. OnVraag gevra deur
die groter restorasieekologieprojek waaronder hierdie navorsingsprojek resorteer was:
tot watter mate dien mesas as ° n hawe aan vreetbare spesies wat onder druk is van
swaar oorbeweiding in die omliggende vlaktes?
OnStudie van die regenerasie potensiaal van T. triandra op-en-vanaf die Tafelberg Mesa
in die Middelburg distrik van die Oos-Kaap, Suid-Afrika, was onderneem binne die
verband van die wyer herstelekologieprojek "Herstel van oorbeweide Nama-Karoo
weiveld: die rol van bewaringseilande". Die Nama-Karoo was vir honderde jare al
blootgestel aan swaar kommersiële lewende hawe produksie en is klaarblyklik verander
van ° n relatiewe produktiewe sisteem na 'n ekosisteem gedomineerd deur struike en
enigsins minder produktiewe spesies. Alhoewel dit ° n verkiesde grasspesie is bo ander
inheemse grasse as weigras, is min bekend oor die fertiliteit van T. triandra sade of oor
die vestiging van saailinge, veral in veldrehabilitasie programme. Hierdie studie
ondersoek die patrone van saadproduksie, saadverspreiding, saadontkieming, en die
morfologiese en ekofisiologiese veranderlikheid van T. triandra, ° n spesie met groot
potensiaal vir die herstel van oorbeweide Nama-Karoo terriene van veral die Oos-Kaap.
Themeda triandra was een van die dominante spesies op die kruin van die Tafelberg
Mesa. Dit kom voor in klein geïsoleerde populasies op die uitgestrekte vlaktes rondom
die mesa. Die vlaktes en hange van die mesa word op groot skaaloorbewei deur
lewende hawe in vergelyking met op die kruin van die mesa. Dit is te wyte aan die
onbereikbaarheid van die mesa vanweë Onsteiler topografie, asook die gebrek aan
standhoudende water op die mesa's self.
Jaarlikse saad produksie van T. triandra per plant en per m2 was die hoogste vir die
populasies op die vlaktes, ten spyte daarvan dat hierdie populasies intensief bewei word. Reënval het 'n effek op jaarlikse saad produksie gehad wat oor twee jaar
gekontroleer was. Met die vermeerdering van reënval voor die Mei 2000 proeftydperk,
was meer sade geproduseer per plant en per m2 op die vlaktes en hange van die
Tafelberg Mesa. Die teenoorgestelde patroon het voor gekom op die kruin van die mesa,
waar saadproduksie afgeneem het. Laasgenoemde kan toegeskryf word aan die
toename in kompetisie. Toename in reënval het ook 'n positiewe effek gehad op die
bedekking van T. triandra self sowel as van ander grasse. Ten spyte van hoër vlakke
van saadproduksie, is saailing oorlewing in T. triandra populasies op die vlaktes duidelik
negatief terwyl saailinge op die hange en kruin 'n betekenisvolle hoër saailing
oorlewingsskap gehad het. Die negatiewe impak kan verduidelik word deur die
vertrappings-effek van lewende hawe.
Die resultate van die saadvespreidingeksperiment toon dat die saadverspreiding afstand
van T. triandra na 'veilige' mikroterreine kort is (die meerderheid van die sade is tot
minder as 60cm versprei). Wind is die verspreidingsagent. Dit is gevind dat oop of
klipperige terreine gunstige mikroterreine vir hervestiging van T. triandra is.
In die gekontroleerde-eksperiment het saadverskyning van T. triandra aangedui dat die
optimale saai-diepte wissel met grondsoort. Maksimum ontkieming is behaal by saaidiepte
van 2cm en 3cm in die grond versamel in die vlaktes rondom die Tafelberg Mesa.
Die grondtekstuur op die vlaktes is 'n sanderige leem-klei. Die vlaktes het effens hoër
persentasies klip, klei, slik en sand vergelyke met die grond versamelop die kruin en
hange. Themeda triandra is duidelik nie as gevolg van grondtoestande beperk in sy
uitbreiding op vlaktes in die Middelburg distrik by die ontkieming/werwing fase.
Gondtoestande tydens die ontkiemingsfase is duidelik niw beperkend op die gigthede
van T. triandra op die vlaktes nie. Hierdie studie maak bekend dat T. triandra die beste
ontkiem onder somer toestande wanneer die waarskynlikheid van reënval op sy hoogste
is. Rookwater het geen effect op die ontkiemingspotensiaal van T. triandra in die
Middelburg streek van die Oos-Kaap nie. Pogings om T. triandra saad se ontkieming
met rookwaterekstrak te bevorder was onsuksesvol.
In die gekontroleerde eksperiment het individue van T. triandra op die kruin van
Tafelberg Mesa geen verskil getoon in fotosintese, huidmondjie begeleiding en
transpirasie tempo nie in vergelyking met individue wat voorkom op die vlaktes rondom
die mesa. Themeda triandra blyk relatief aanpasbaar te wees aan 'n wye reeks van temperatuur toestande. Hierdie bevindings dui aan dat daar geen probleem hoef te wees
om sade van die kruin van die mesa te gebruik in hervestigig-programme in die
omliggende vlaktes nie.
Hierdie studie verskaf geen bewyse wat aandui dat die T. triandra bevolkings op die
kruin van die mesa as Onbron van saad vir die vlaktes rondom die Tafelberg Mesa dien
nie. Hierdie twee-jaar ondersoek vind dat T. triandra 'n potensiaal het om gebruik te
word in herstel en rehabilitasie programme. As dit aan ligter weidingsruk onderwerp is
en gunstige klimaatstoestande heers, kan T. triandra hervestig word op die vlaktes en
gebruik word as Onplantspesie om erg beskadigde areas in die Nama-Karoo streek te
herstel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53669 |
| Date | 03 1900 |
| Creators | Hendricks, Noel Colin |
| Contributors | Esler, K. J., Knight, R., 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 | 117 p. : ill. |
| Rights | Stellenbosch University |
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