Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The passive recovery of old fields in the Karoo is a slow process, hampered by low
and erratic rainfall, poor seed germination due to limited availability of suitable micro
sites for seedling establishment, competition from existing vegetation, altered soil
properties and the reduction of key soil biotic processes. The objectives of the study
were to investigate the role of seed banks in the recovery of old fields, and to identify
possible plant species and methods of establishing these species with the primary
aim of initiating the process of succession / recovery of old fields in the Little Karoo.
The investigation of the seed bank addressed the following issues: the resemblance
of the seed bank to the above-ground vegetation in an old field and the effect of
disturbance on the seed bank. Furthermore, the role of propaguie migration was
investigated to establish possible propaguie movement from undisturbed to disturbed
areas was investigated. The study indicated that the perennial seed bank had a 31 %
similarity to the above ground vegetation in the old field. The seed bank was
dominated by annual species. In the above-ground vegetation perennial canopy
cover was higher compared to annual cover. The perennials with the highest
densities in the soil seed bank were disturbance-adapted species with little
importance for grazing animals except perhaps in the short-term. Disturbance caused
annual densities to increase and perennial densities to decrease. The investigation of
propaguie migration compared adult canopy cover and seedling densities. The
results show that perennial distribution was patchy and that propaguie migration is
low to non-existent. This led to the conclusion that old fields require supplemental
seed additions.
A total of seven species were assessed for their restoration potential. The species
used in the investigation were Tripteris sinuata, Ruschia spinose, Drosanthemum
speciosum, Indigofera sessifolia, Pteronia incana, Ehrharfa calycina and
Chaetobromus dregeanus. Seed viability was examined using one of two techniques
ie. tetrazolium or a standard germination technique. The optimal temperature for
germination was determined using the following temperature regimes: 15°C day /
1DoC night, 20°C day /1 DoC night and 30°C day / 15°C night. The temperature range
with the best performance was 20°C day / 1DoC night indicating that species should
be sown in autumn or early winter. This timing coincides with the onset of rains in this
region. The field trial investigated the influence that various mechanical cultivation
techniques (ploughing, disking, tilling and clearing) and soil amendments (seed,
seed+aquasorb and seed+straw+branches) have on the establishment of the
selected species. Seed germination and seedling survival was monitored. The
influence of treatments on water infiltration and soil moisture was investigated. Only
four of the seven species germinated (Tripteris sinuata, Ehrharta calycina,
Chaetobromus dregeanus and Pteronia incana). As far as species performance was
concerned, T. sinuata performed best followed by E. calycina and C. dregeanus,
while P. incana failed to persist. The cultivation treatments that yielded the best
results were tilling, disking and ploughing. Emergence success in cleared and
untreated plots was relatively low. As far as seedling emergence was concerned the
most appropriate soil amendments were seed+aquasorb, seed and
seed+straw+branches. Although soil moisture was higher on-heuweltjies than offheuweltjies
there was no significant difference in seedling emergence and survival
between these localities. Even though soil moisture was higher in
seed+straw+branches treatment than in seed+aquasorb and seed treatments,
seedling emergence in this treatment were lower than in the two latter treatments.
This clearly indicates that soil moisture is not the only factor that influences the
establishment of species.
In the trial a mixture of late successional and pioneer species were sown, primarily
with the aim of initiating the process of succession! recovery of old fields. Contrary to
what was expected the late successional species germinated first. This has led to the
conclusion that these late successional species have no innate dormancy, further
proved by the inability of species to germinate after the second season. It could thus
be that these late successional species have a short live span, and that they
germinate when conditions are favourable. It must also be kept in mind that the seed
sown were freshly harvested, and it could be that the pioneer species needed an
after-ripening period before they germinated. / AFRIKAANSE OPSOMMING: Die passiewe herstel van oulande in die Karoo is 'n tydrowende proses, wat vertraag
word deur wisselvallige reënval, swak ontkieming as gevolg van 'n tekort aan
geskikte mikro-habitatte vir saailingvestiging, kompetisie van bestaande plantegroei,
veranderende grondeienskappe en die afname in sleutel biotiese prosesse. Die doel
van hierdie studie was, om die rol van saadbank in die herstel van oulande te bepaal,
sowel as om moontlike plantspesies te identifiseer en metodes van vestiging van
hierdie spesies te bepaal met die primêre doelom die proses van suksessie / herstel
van oulande in die Klein Karoo te inisieër.
Met die saadbankstudie is die volgende punte aangespreek: die ooreenkoms tussen
die meerjarige spesies in die saadbank en bogrondse plantegroei op ou lande, en die
effek van versteuring op die saadbank. Verder is gekyk na die rol van voortplantingsmeganisme
verspreiding om moontlike beweging vanaf onversteurde na versteurde
areas te ondersoek.
Die studie het aangedui dat daar 'n 31% ooreenkoms is tussen meerjarige spesies in
die saadbank en die bogrondse plantegroei op ou lande areas. In die bogrondse
plantegroei van die ou land was die kroonbedekking van meerjarige spesies hoër as
die van eenjarige spesies. Die dominante meerjarige spesies in die saadbank was
spesies wat aangepas is by versteurings, met min weidingswaarde, behalwe
moontlik oor die kort termyn. Versteuring het In verhoging in eenjarige en In afname
in meerjarige saailingdigthede veroorsaak. Resultate dui daarop dat meerjarige
verspreiding onreëlmatig is in die versteurde area en dat die teenwoordigheid van
voortplantingsmeganismes, baie laag is. Dit lei tot die gevolgtrekking dat oulande
addisionele saad benodig vir hervestiging.
'n Totaal van sewe spesies is ge-evalueer vir hulle moontlike restorasie potensiaal.
Die spesies wat in die ondersoek gebruik was, is Tripteris sinuata, Ruschia spinose,
Orosanthemum speciosum, Indigofera sessitolie. Pteronia incana, Ehrharta calycina
en Chaetobromus dregeanus. Die kiemkragtigheid van die spesies is bepaal deur
gebruik te maak van een van twee tegnieke nl. die tetrazolium of 'n standaard
ontkiemings tegniek. Die optimale temperature vir ontkieming is bepaal deur gebruik
te maak van die volgende temperatuurreekse: 15°e dag / 1Qoe nag, 200e dag /10oe
nag and 300e dag / 15°e nag. Die temperatuur reeks waarop spesies die beste presteer het, was 2DOC dag /1DOC nag. Dit dui daarop dat spesies tydens herfs en
vroeë winter gesaai moet word. Dit is dan ook die tydperk vir die aanvangs van die
reënseisoen in hierdie streek.
In die veldproef is gekyk na die invloed van verskeie meganiese bewerkings -
tegnieke (ploeg, dis, ghrop en plant verwydering) en grondverbeterings behandelings
(saad, saad+aquasorb en saad+strooi+takke), op die vestiging van geselekteerde
spesies. Saadontkieming en saailingoorlewing is gemonitor. Die invloed van die
behandelings op waterinfiltrasie en grondvog is ook ondersoek. Slegs vier van die
sewe spesies het ontkiem naamlik: Tripteris sinuata, Ehrharfa calycina,
Chaetobromus dregeanus en Pteronia incana. Spesies wat die beste presteer het,
was T. sinuata die gevolg deur E. calycina en C. dregeanus, terwyl P. incana nie
oorleef het nie. Die bewerkingsbehandelings wat die beste vestiging van plante
gegee het, was die ghrop en disbewerkings gevolg deur ploegbewerking.
Ontkiemings sukses in areas waar plante verwyder is en onbehandelde persele was
relatief laag. Die grondverbeterings behandeling wat die beste ontkieming gelewer
het was saad+aquasorb gevolg deur saad en saad+strooi+takke. Alhoewel grondvog
hoër was op heuweltjies as weg van heuweltjies, was daar geen betekenisvolle
verskil in ontkieming en oorlewing tussen hierdie lokaliteite nie. Alhoewel grondvog
hoër was in saad+strooi+takke behandelings as in saad+aquasorb en saad
behandelings was ontkieming laer in hierdie behandeling as in die saad+aquasorb en
saad behandelings. Dit dui dus daarop dat grondvog nie die enigste faktor is wat die
vestiging van spesies beinvloed nie.
In die veldproef is 'n mengsel van pionier en klimaks spesies gesaai, met die primêre
doelom die proses van suksessie/herstel van oulande te inisieër. In teenstelling met
wat verwag is het die meer klimaks spesies eerste ontkiem. Dit het gelei tot die
gevolgtrekking dat hierdie spesies geen dormansie het nie, en dit is verder bewys
deur 'n onvermoë om te ontkiem in die tweede seisoen. Dit mag wees dat die meer
klimaks spesies 'n kort lewensduur het, en dat hulle ontkiem wanneer toestande
gunstig is. Dit moet ingedagte gehou word dat die saad vars geoes was, en dit kon
dus wees dat die pionier spesies 'n na-rypwordings periode benodig voordat hulle
ontkiem.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53012 |
| Date | 12 1900 |
| Creators | Witbooi, Bernadette M. (Bernadette Mary) |
| 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 | Unknown |
| Type | Thesis |
| Format | 104 p. : ill. |
| Rights | Stellenbosch University |
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