The regeneration potential of Themeda triandra in the Middelburg district of the Eastern Cape

Hendricks, Noel Colin (2003-03)

Thesis (MSc)--University of Stellenbosch, 2003.

Thesis

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/53669
This item appears in the following collections: