Thesis (MSc)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The composition and state of soil-stored seed banks on- and off the mesa Tafelberg, in the
Nama Karoo rangelands of the Eastem Cape, South Africa, were investigated within the
context of a broader restoration ecology project "Restoration of degraded Nama Karoo
rangelands: the role of conservation islands'".
The premise for this seed bank study was that restoration of degraded semi-arid
rangelands is possible through applied management programs based on the methodology
and practice of ecological restoration. Broadly acknowledged properties of non-equilibrium
environments (e.g. unpredictable climates and varying degrees of disturbance) and soilstored
seed banks (e.g. spatial and temporal distributions) formed the basis for
investigating. the general environment and the properties.. of existing seed, banks, in the
Tafelberg locality. The potential role of hills as refugia for palatable plant species was an
under-lying element of the investigation.
Following a brief investigation, of historical and contemporary research and policy on
rangeland degradation in semi-arid regions of the world, the fundamental need for
comprehensive and applied seed bank research in the Nama Karoo is emphasised.
Within the framework of the umbrella project, the seed bank study examined local
environmental criteria commencing with an investigation into seed bank- and vegetation
habitats. Chemical and physical properties of soils from twenty two sites on- and off Tafelberg
were described. Substantial soil habitat variation, between the top, the north west slopes and
plains and the south east slopes and plains of Tafelberg, was identified. Micro-site variation
between open-canopy (interplant spaces) and closed-canopy (under plant cover) microhabitats
was found to be significant Primary soil habitat differences were linked to soil organic
matter content which was found to be low on the plains relative to the top and slopes; and, low
in open-canopy micro-sites relative to closed-canopy sites. Soil texture and nutrient composition
on- and off Tafelberg was found to be highly variable with significant differences between the
top and the plains as well as between the north west and south east plains. The slopes were
found to be intermediate (showing some level of gradient) between the top and the plains.
Soil nutrient variation was interpreted as a function of textural and parent-material properties
of soils. Anthropogenic factors for accelerated erosion, deposition, leaching and salt-crust
formation were also considered. It was concluded that while properties of soils on- and off
Tafelberg are inherently related to parent soils, changes to textural and nutrient properties
may be occurring and these changes may have been exacerbated by high levels of grazing.
An investigation (focusing on small shrubs) of plant phenological response, in relation to
rainfall and grazing gradients, identified trends of peak budding- and flowering seasons
following rainfall during summer and autumn respectively. A continuum of seeding activity, with peaks in late autumn and early winter, was construed from quarterly data. Flush
vegetative growth was noted for most small shrubs during spring, autumn and summer
surveys. Since some form of activity related to reproductive output (flush growth, budding,
flowering or seeding) was apparent at almost all times of the year, it is argued that high
intensity disturbance (including grazing) might impact negatively on plant survival, leading
to reduced reproductive input (i.e. seeds) into future generations.
Plant communities on the top and plains are described noting significant differences between
vegetation on top of Tafelberg (comprising primarily high production, palatable grass and
shrub species) and that on the plains (comprising mainly spinescent, ephemeral, toxic and
low production species). Given the high grazing pressure on the plains (relative to the less
utilised slopes and top of Tafelberg), differences in vegetation composition are discussed in
relation to studies elsewhere that describe degraded rangelands. It is concluded firstly that
the plains surrounding Tafelberg are degraded, secondty that long term over-utilisation has
altered vegetation composition and finally that inter-grazing rest periods of three- or six
months alone may not restore vegetation diversity nor desirable plant species to the plains.
Results of germination trials (investigating soil-stored seed banks) from two sampling episodes
(spring and autumn 1998) revealed that seed banks in soils removed from the plains, slopes
and top of Tafelberg followed distribution patterns observed in above-ground vegetation.
Species-specific data was not finalised for this thesis since not all seedlings matured and
flowered within given time constraints. In order to compare seedling emergence data, plant
categories were developed that distinguished ephemerals versus persistent (perennial)
species and dicotyledonous species versus grasses and other monocotyledonous plants.
Samples from the top and the middle to upper slopes showed a high percentage of palatable
and persistent grass and shrub species present in soil-stored seed banks while over twothirds
of plants germinating from plains' soil samples were ephemeral species and most of
these were both tiny «Scm) and short-lived «3 months). Most of the perennial species
germinating from plains' samples were seedlings of Pentzia incana, Chrysocoma ciliata and
succulents (mostly Mesembryanthemaceae) but few perennial grasses were present. On
the other hand, roughly 94% of seedlings germinating from samples from the top and 63%
of seedlings germinating from two slopes of Tafelberg respectively were persistent- grass
or shrubby species. Roughly 89% of ephemeral species recorded from slopes' samples
germinated from the lowest footslope sites.
Seed densities were closely linked to micro-habitats with roughly three-fold differences between
open- (lower seed density) and closed-canopy (higher seed density) micro-sites. Multivariate
analysis of variance (MANOVA) indicated that most of the variation in seed density data was
explained at the micro-habitat level. Seasonality played a secondary role with significant twoway
interaction between the two effects. It is concluded that both factors must be considered
when developing restoration programmes that aim to improve both overall plant cover and
improved plant species diversity. While the original or "pristine" state of vegetation composition and seed banks on the plains
is unknown, concems were raised regarding the apparently degraded state of total above- and
below-ground plant diversity on these plains. A likely consequence of habitat degradation is
that species with specific soil-, nutrient ratio-, aspect- and altitudinal requirements from the top
and slopes of Tafelberg (as well as from nearby plains' refugia) may not be able to establish in
degraded habitats on the plains. The identification of pioneer plant species (tolerant of habitat
degradation) that allow increased vegetation cover and safe-sites for seedling germination of
desirable plant species is recommended. Restoration programmes will need to be coupled
with strict grazing management principles that allow seedling germination. establishment
and successful reproductive output of desirable plants for future rangeland regeneration.
Common and salient features of the soil habitat, plant pbenological response and germination
trial studies are brought together in an examination of habitats and related seed bank diversity
on- and off Tafelberg. Acknowledging the brevity of this research study, but utilising case
studies from elsewhere and integrating both lines of questioning, the conclusion is again
reached that the plains surrounding Tafelberg are degraded through decades and probably
centuries of grazing by domestic livestock. It is considered crucial that restoration through
improvement (or rehabilitation) of habitats and increased seedling safe-sites be considered.
Both climate and grazing management appear to play an irrevocably linked role in shaping
vegetation composition in rangelands. While rangelands are intrinsiCalfy adapted to surviving
extremes of climatic variability found in non-equilibrium regions it is argued that the impacts
of grazing, particularly during times of drought and climate change, are slowly reducing the
intrinsic "buffer-capacity" of rangelands to withstand these changes and extremes.
It seems apparent from research elsewhere that restoration through passive management is
slow and probably not economically achievable within a viable time frame. The instifution and
promotion of integrated and strategic programmes that identify and address issues of land
degradation and land use change in semi-arid rangelands is recommended. The input and
endeavours of different authorities, ministries and a broad public participation incentive are
encouraged in these proposed programmes in order to ensure broadly-based input into long
term sustainability and conservation of the considerable biological diversity of these regions.
Seed bank assessment is considered to be a valuable means of indicating restoration potential
and ranqeland condition with potential for the identification of both degraded and conservationworthy
areas.
Finally, some limitations and challenges of this study are examined through a process of
firstly identifying alternative approaches to research methodologies and secondly through
proposing recommendations for future research projects. While alternative methods could
have been applied for the purposes of accomplishing this study it is concluded that, within
the given time- and other constraints, the appropriate methods were applied. / AFRIKAANSE OPSOMMING: Die samestelling entoestand van groncbbewaarde saadbanke.op en van die mesa Tafelberg af,
in die Nama Karoo weiveld van die Oos-Kaap, Suid-Afrika, is ondersoek binne die konteks van
'n wyer herstelekologieprojek: "Restourasie van oorbeweide Nama Karoo weiveld: die rol van
bewannqseilande'".
Die uitqanqspunt van hierdie saadbankondersoek was dat dit moontlik is om beskadigde semidroë
weiveld te herstel deur middel van toegepaste bestuursprogramme wat gebaseer is op die
metodologie en praktyk van ekologiese herstel. Algemeen erkende eienskappe van nieekwilibrium-
omgewings (byvoorbeeld onvoorspelbare klimate en wisselende mates van
versteuring) en grond-bewaarde saadbanke (byvoorbeeld ruimtelike en temporale
verspreidings), het die basis gevorm vir die ondersoek van die algemene omgewing en die
eienskappe van bestaande saadbanke in die Tafelberg omgewing. Die potensiële rol van
heuwels as skuilplek vir aanvaarbare plantspesies was 'n onder1iggende element van die
ondersoek.
Na 'n kort ondersoek van historiese ~n kontemporêre navorsing en beleid oor weiveldbeskadiging
in semi-droë streke van die wêreld, is die fundamentele behoefte aan omvattende
en toegepaste saadbanknavorsing in die Nama Karoo beklemtoon.
Binne die raamwerk van die oorkoepelende projek het die saadbankondersoek plaaslike
omgewingskriteria bestudeer, beginnende met 'n ondersoek na saadbank- en
plantegroeihabitats. Chemiese en fisiese eienskappe van grond vanaf twee en twintig terreine
op en van Tafelberg af is beskryf. Omvattende grondhabitatwisseling tussen die kruin, die
noordwestelike hange en die vlaktes en die suidoostelike hange en vlaktes van Tafelberg is
geïdentifiseer. Mikroterreinwisseling tussen die oop-dak (tussenplantruimtes) en toe-dak
(onderplantdekking) -mikrohabitats is as beduidend bevind. Primêre grondhabitatverskille is
gekoppel aan die inhoud van die grond se organiese materiaal, wat op die vlaktes as laag
bevind is vergeleke met die kruin en hange; en laag bevind is in oop-dak-mikroterreine
vergeleke met toe-dak-terreine, Daar is gevind dat die grondtekstuur en voedingstofsamestelling
op en van Tafelberg af aansienlik varieer, met beduidende verskille tussen die kruin en die
vlaktes, en ook tussen die noordwestelike en suidoostelike vlaktes. Daar is gevind dat die hange
intermediêr is (toon 'n mate van gradiënt) tussen die kruin en die vlaktes.
Die wisseling in grondvoedingstowwe is vertolk as 'n funksie van teksturele en ouermateriaaleienskappe
van grond. Antropogeniese faktore vir versnelde erosie, neerslag, loging
en soutkorsvorming is ook oorweeg. Die gevolgtrekking is gemaak dat terwyl die eienskappe
van grond op en van Tafelberg af inherent aan ouergrond verwant is, kan veranderinge aan
tekstuur en voedingstofeienskappe voorkom, en hierdie veranderinge kon deur hoë vlakke van
weiding vererger gewees het.
'n Ondersoek (wat op klein struike gefokus het) van plantfenologiese reaksie met betrekking tot
reënval en weidingsgradiënte het tendense van piekbot- en blomseisoene na reënval gedurende
die somer en herfs onderskeidelik geïdentifiseer. 'n Kontinuum van saadskietaktiwiteit, met
piektye in laat herfs en vroeë winter, is van kwartaallikse data saamgestel. Groeistuwing is vir
die meeste klein struike waargeneem gedurende lente-, herfs- en someropnames. Aangesien die een of ander vorm van aktiwiteit met betrekking tot voortplantingsgroei (groeistuwing, bot,
blom of saadskiet) op feitlik al die tye van die jaar sigbaar was, word daar geredeneer dat hoëintensiteitversteuring
(ook weiding) 'n negatiewe impak op plantoorlewing kan hê, wat sal lei tot
verminderde voortplantingsinset (m.a.w. sade) in toekomstige geslagte.
Plantgemeenskappe op die kruin en vlaktes word beskryf met beduidende verskille tussen
plantegroei op die kruin van Tafelberg (wat hoofsaaklik bestaan uit hoëproduksie, smaaklike
gras- en struikspesies) en dié ap die vlaktes (wat bestaan uit hoofsaaklik doringagtige, efemere,
toksiese en laeproduksie-spesies). Gegee die hoë weidingsdruk op die vlaktes (vergeleke met
die minder benutte hange en kruin van Tafelberg), word verskille in die samestelling van
plantegroei bespreek met betrekking tot studies elders wat beskadigde weiveld beskryf. Die
gevolgtrekking word eerstens gemaak dat die vlaktes om Tafelberg beskadig is, tweedens dat
langtermyn-oorbenutting die samestelling van die plantegroei verander het, en laastens dat
interweiding-rusperiodes van drie tot ses maande alleen dalk nie die diversiteit van plantegroei
of die verlangde plantspesies op die vlaktes kan herstel nie.
Die uitslae van kiemingstoetse (wat ondersoek ingestel het na grond-bewaarde saadbanke) van
twee steekproefepisodes (lente en herfs 1'998)het getoon dat saadbanke in grond wat van die
vlaktes, hange en kruin van Tafelberg verwyder is, die verspreidingspatrone volg wat in
bogrondse plantegroei waargeneem is. Spesie-spesifieke data is nie vir hierdie tesis gefinaliseer
nie, aangesien nie alle saailinge binne die gegewe tydsbeperkinge gegroei en geblom het nie.
Ten einde saailing-verskyningsdata te vergelyk, is plantkategorieë ontwikkel wat efemere en
langdurige (meerjarige) spesies en dikotiele spesies en grassoorte en ander monokotiele plante
onderskei.
Steekproewe van die kruin en teen die middelste en boonste hange het 'n hoë persentasie van
aanvaarbare en standhoudende gras- en struikspesies getoon wat in grond-bewaarde
saadbanke teenwoordig is, terwyl meer as twee derdes van plante wat in die vlaktes se
grondmonsters ontkiem het, efemere spesies was, en die meeste daarvan was klein «5cm) en
met 'n kort leeftyd «3 maande). Die meeste van die meerjarige spesies wat van die vlaktes se
steekproewe kom, was saailinge van Pentzia incana, Chrysocoma ciliata en vetplante
(hoofsaaklik Mesembryanthemaceae), maar min meerjarige grasse was teenwoordig.
Daarenteen was onderskeidelik ongeveer 94% van saailinge wat van monsters van die kruin en
63% van saailinge wat van twee van die hange van Tafelberg ontkiem het, langdurige gras- of
struikspesies. Ongeveer 89% van die efemere spesies wat van die hange se steekproewe
aangeteken is, het op die laagste voethang-terreine ontkiem.
Saaddigthede toon 'n noue verband met mikrohabitats, met ongeveer drievoudige verskille
tussen oop- (laer saaddigtheid) en toe-dak (hoër saaddigtheid) -mikroterreine. 'n Multivariaatontleding
van variansie (MANOVA) het aangedui dat die meeste van die variasie in
saaddigtheidsdata op die mikrohabitat-vlak verduidelik is. Seisoenaliteit het 'n sekondêre rol
gespeel, met beduidende tweerigting-interaksie tussen die twee uitwerkings. Die gevolgtrekking
word gemaak dat albei faktore oorweeg moet word wanneer herstelprogramme ontwikkel word
wat ten doel het om algehele plantbedekking en die diversiteit van verbeterde plantspesies te
verhoog. Terwyl die oorspronklike of "ongerepte" toestand van die plantegroei se samestelling en
saadbanke op die vlaktes onbekend is, is kommer uitgespreek oor die klaarblyklik beskadigde
toestand van die totale bo- en ondergrondse plantdiversiteit op hierdie vlaktes. 'n Waarskynlike
gevolg van habitatbeskadiging is dat spesies met spesifieke grond-, voedingstofverhouding-,
aspek- en seevlak-vereistes van die kruin en hange van Tafelberg (asook van nabygeleë
vlakteskuilings) nie in staat sal wees om in beskadigde habitats op die vlaktes te vestig nie. Die
identifikasie van pionierplantspesies (verdraagsaam vir habitatbeskadiging) wat verhoogde
plantegroeidekking en veilige terreine vir saailingontkieming van verlangde plantspesies toelaat,
word aanbeveel. Herstelprogramme sal gekoppel moet word aan streng weidingsbeginsels wat
saailingontkieming, die vestiging en suksesvolle voortplantingsproduksie van gewenste plante
vir toekomstige weiveldherstel moontlik maak.
Algemene en belangrike eienskappe van die grondhabitat, plantfenologiereaksie en
kiemingsproefondersoeke word saamgevoeg in 'n ondersoek van habitats en verwante
saadbankdiversiteit op en van Tafelberg af. Met erkenning van die kortstondigheid van hierdie
navorsingsondersoek, maar met benutting van gevallestudies van elders en die integrasie van
albei vraaglyne, word daarweertot die slotsom gekom dat die vlaktes om Tafelberg beskadig is
deur dekades en waarskynlik eeue se beweiding deur mak lewende hawe. Dit word as uiters
belangrik beskou dat herstel deur verbetering (of rehabilitasie) van habitats en 'n groter aantal
saailing beveiligingsterreine oorweeg moet word.
Dit lyk asof klimaat sowel as weidingsbestuur 'n onherroeplik gekoppelde rol speel in die
vorming van die samestelling van plantegroei op weiveld. Terwyl weiveld intrinsiek aangepas is
by die oorlewing van uiterste klimaatswisseling wat in nie-ekwilibriese streke aangetref word,
word daar geredeneer dat die impak van beweiding, veral gedurende droogtetye en
klimaatsverandering, stadigaan die intrinsieke "buffervermoë" van weiveld verminder om hierdie
veranderinge en uiterstes te weerstaan.
Dit blyk uit navorsing elders dat herstel deur passiewe bestuur stadig en waarskynlik nie
ekonomies haalbaar is binne 'n lewensvatbare tydsraamwerk nie. Die instelling en bevordering
van geïntegreerde en strategiese programme wat kwessies van grondbeskadiging en
verandering van grondgebruik in semi-droë gebiede identifiseer en oplos, word aanbeveel. Die
insette en pogings van verskillende owerhede en ministeries en deelname deur die breë publiek
word aangemoedig in hierdie voorgestelde programme ten einde insette met 'n breë basis in die
langtermyn~volhoubaarheid en bewaring van die aansienlike biologiese diversiteit van hierdie
streke te verseker.
Saadbankbeoordeling word beskou as 'n waardevolle manier om die herstelpotensiaal en
weiveldtoestande met die potensiaal vir die identifisering van beskadigde sowel as
bewaringswaardige gebiede aan te dui.
Laastens word 'n paar beperkings en uitdagings van hierdie studie ondersoek deur 'n proses
van eerstens die identifisering van alternatiewe benaderings tot navorsingsmetodologieë, en
tweedens deur die voorstel van aanbevelings vir toekomstige navorsingsprojekte. Terwyl
alternatiewe metodes toegepas kon gewees het ten einde hierdie studie af te handel, is die
gevolgtrekking dat die toepaslike metodes binne die gegewe tyd5- en ander beperkings
toegepas is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51592 |
| Date | 12 1900 |
| Creators | Jones, F. Elizabeth (Freda Elizabeth) |
| Contributors | Esler, K. J., 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 | 185 p. : ill. |
| Rights | Stellenbosch University |
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