Potential of selected Karoo plant species for rehabilitation of old fields

Witbooi, Bernadette M. (Bernadette Mary) (2002-12)

Thesis (MSc)--University of Stellenbosch, 2002.

Thesis

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.

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