Thesis (MScFor )--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Species-rich Renosterveld vegetation does not return to old agricultural fields even
after many years (10-20) of abandonment. In most cases the fields are slowly taken
over by non-indigenous species, particularly alien pasture grasses and African lawn
grass. While poor survival of indigenous seedlings due to competition, grazing or any
other establishment constraints, might explain the failure of natural vegetation to
colonise old fields, here I am testing the hypothesis that recolonisation by indigenous
plant species is limited by seed dispersal. I have quantified changes in seed density
with distance from the natural vegetation into old fields using seed traps and soil seed
bank assessment. I have also looked at seed dispersal in the dung of large herbivores.
Shrubs (with the exception of Eytropappus rhinocerotis) were poorly represented in
the seed rain indicating that they might be seed limited. Dicerothamnus rinocerotis (a
dominant shrub in Renosterveld) and certain geophytes (that were recovered in the
soil bank) have proven that seed dispersal is not the primary constraint to their return
to ploughed fields. Dicerothamnus rinocerotis produces a large number of seeds that
are dispersed long distances into the old field and a number of geophytes were well
represented in the soil bank. Large herbivores are dispersing a lot of herbaceous forbs
in their dung but make very little contribution to the dispersal of indigenous tussock
grass and shrubs. Seeds of indigenous Renosterveld tussock grasses (e.g Tribolium
hispidum) were restricted to the edge of the natural vegetation. My research has
shown that some indigenous seeds, particularly those dispersed in wind and through
large mammals, do reach the old ploughed field. I therefore conclude that seed
dispersal is not the primary constraint to the natural recovery of populations of some
indigenous plant species on old fields, but may limit recovery of certain indigenous
geophytes, grasses and shrubs. / AFRIKAANSE OPSOMMING: Spesie-ryke Renosterveld plantegroei hervestig nie op ou landerye nie, selfs ná baie
jare (l0-20) van verlating. Oor die algemeen word hierdie grond stadig oorgeneem
deur uitheemse spesies, veral uitheemse weidingsgrasse en kweekgras. Terwyl swak
oorlewing van inheemse saailinge as gevolg van kompetisie, weiding of enige ander
vestigingsbeperkinge, die mislukte vestiging van natuurlike plantegroei op ou benutte
grond kan verduidelik, toets ek hier die hipotese dat hervestiging deur inheemse
plantspesies deur saadverspreiding beperk word. Ek het veranderinge in saaddigtheid
oor afstand vanaf die natuurlike plantegroei na ou landerye gekwantifiseer,
deur gebruik te maak van saadopvangsvalle en sand saadbank beraminge. Ek het
ook gekyk na saadverspreiding in die mis van groot herbivore. Struike (behalwe
Eytropappus rhinocerotis) was swak verteenwoordig in die "saadreën", wat mag toon
dat struike saadbeperk is. Eytropappus rhinocerotis ('n dominante struik in
Renosterveld) en sekere geofiete (wat in die saadbank gevind is) het bewys dat
saadverspreiding nie die hoofbeperking is vir hulle terugkeer na geploegde lande nie.
Eytropappus rhinocerotis produseer 'n groot hoeveelheid saad wat oor groot afstande
oor die ou landerye versprei word en 'n aantal geofiete was goed verteenwoordig in
die saadbank. Groot herbivore versprei 'n groot hoeveelheid kruidagtige forbe in
hulle mis, maar maak 'n baie klein bydrae tot die verspreiding van inheemse polgras
en struike. Saad van inheemse Renosterveld polgrasse (bv. Tribolium hispidum) was
beperk tot die some van die natuurlike plantegroei. My navorsing het getoon dat
sommige inheemse saad, veral dié wat deur die wind en deur groot herbivore versprei
word, wel die ou geploegde landerye bereik. Ek maak dus die gevolgtrekking dat
saadverspreiding nie die hoofbeperking is vir die natuurlike herstel van populasies
van sommige inheemse plantspesies op ou landerye nie, maar mag die herstel van
sekere inheemse geofiete, grasse en struike beperk.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53396 |
| Date | 03 1900 |
| Creators | Shiponeni, Ndafuda Nangula |
| Contributors | Milton, J., Krug, M., Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science . |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 110 p. : ill. |
| Rights | Stellenbosch University |
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