Thesis (M.Sc. Agriculture (Pasture Science)) -- University of Limpopo, 2021 / Savanna rangelands are ecosystems which are characterized by the co-existence of scattered trees and shrubs with a continuous grass layer. However, the grass and tree balance has been highly altered as a result of disturbances caused by bush encroachment. Encroaching woody species have been shown to decrease species richness and abundance of the seed bank and ground‐layer diversity. So far little is known on the effect of bush encroachment and soil depth on the soil seed bank diversity in savanna rangelands. The objectives of this mini-dissertation were to (1) determine the influence of soil depth on soil seed bank diversity in bush encroached savanna rangelands, and (2) determine the relationships between soil seed bank herbaceous vegetation and physicochemical properties in encroached rangeland. In order to address these objectives, a savanna rangeland was demarcated into two encroachment gradients spanning from open to encroached rangeland. Within each encroachment gradient, six plots of 10 m x 10 m were randomly selected, whereby soil sampling and herbaceous vegetation were carried out and determined. In each replicate plot per encroachment level, five soil samples were randomly collected at 0-10 and 10-20 cm depths. The number of seedlings of different species emerging from the soil samples was used as a measure of the number of viable seeds in the soil and the composition of the seed bank using the seedling emergence method. The total seed densities showed significant differences (P<0.05) in the 0-10 cm depth layer in the open rangeland and encroached rangeland. Bush encroachment significantly (P<0.05) decreased the seed density of perennial grasses, specifically in 0-10 cm depth layer. Further, species diversity increased with bush encroachment in the 10-20 cm depth layer. Menhinick’s richness index showed no significant difference in the open and encroached rangeland, while species evenness decreased in the 0-10 cm depth layer and increased at 10-20 cm depth.The study also revealed negative correlations between organic carbon, calcium, clay, silt and forbs while mean weight diameter (MWD), a measure of soil aggregate stability was positively correlated with forbs. The canonical correspondence analysis (CCA) showed that pH, phosphorus, potassium and calcium were positively correlated to Eragrostis curvula and magnesium was negatively correlated to Panicum maximum. In open rangeland, CCA revealed that clay content was negatively correlated with species evenness while xii magnesium was negatively correlated to the Shannon Weiner index. Further, silt content was positively correlated with species richness and evenness. In the encroached rangeland, the CCA showed a negative correlation between magnesium and the Shannon Weiner index. The Sørensen’s index between soil seed banks and aboveground vegetation was low with index values of 0.22 and 0.24 in open and encroached rangeland, respectively. / AgriSeta

The effect of shared enemies between invasive and native species has been argued to facilitate biological invasions (i.e., the apparent competition hypothesis or ACH). This study investigated a previously untested possibility: whether granivorous small mammals facilitate cheatgrass (Bromus tectorum) invasion by driving food-mediated apparent competition between cheatgrass and native grasses. Specifically, we tested three predictions that must be true if such apparent competition occurs. First, cheatgrass invasion augments total seeds available to granivorous small mammals. Second, density of granivorous small mammals increases in response to increased seed availability (simulated with experimental additions of cheatgrass seeds). Third, granivorous small mammals prefer seeds from native grasses over cheatgrass seeds. We tested these predictions in the Great Basin Desert of Utah, USA. Cheatgrass invasion augmented total yearly seed production. Granivorous small mammals preferred native seeds over cheatgrass seeds. However, neither abundance, richness, nor diversity of granivorous small mammals increased in response to experimental additions of cheatgrass seed. We therefore conclude that granivorous small mammals did not drive food-mediated apparent competition during the study period. The lack of support for the ACH in this study may suggest that the role of small mammal-driven apparent competition is either unimportant in the Great Basin, or that the appropriate indirect interactions between small mammals, cheatgrass, and native grasses have yet to be evaluated. Testing the third prediction required the separation of seeds from the soil matrix. We employed a chemical flotation methodology to recover target seeds from soil, and developed a novel method of decanting target material from the flotation solution. We compared the utility of the novel method to that of a traditional decantation method. Specifically, we compared effectiveness (the proportion of seeds recovered from a known sample), rapidity (the time required to decant that sample), efficiency (the number of seeds decanted per second), and recovery bias (the effect of relative density on seed recovery) between methods. Our proposed method was more effective, more rapid, more efficient, and less biased than the traditional method. Therefore, any future work relying on flotation to analyze seed banks should clearly describe how samples are decanted and should consider the proposed method as a potential means of enhancing the efficiency of chemical flotation.

Call number: LD2668 .T4 1956 B76 / Master of Science

Sustainable rehabilitation can be compromised by the inability of vegetation to survive in hostile mine wastes on a long-term basis. The adverse chemical and physical properties of mine wastes, together with extreme pH conditions and lack of nutrients, provide poor growth conditions for vegetation during seed development and germination. This raises concern for the long-term survival of vegetation through means of seed production when under stress from the punitive properties of mine wastes. Seed vigour is a function of a variety of factors to which the parent plant is subjected during seed formation and maturation. Environmental conditions experienced by the maternal plant during the growth season plays a significant role in determining subsequent germination rates in seeds. Traits of offspring seed depend on the abiotic environment attributed by the growth medium during seed development and maturation The general aim of this study was to determine the viability of seed produced by a previous generation of grass species established in eight different mine wastes and two soils (namely: gypsum wastes; gold tailings with low pyrite content; gold tailings with high pyrite content; platinum tailings; kimberlite mine waste; fluorspar mine waste; andalusite mine waste; coal discard; red soil; and vertic soil) in order to identify suitable species for specific mine wastes to ensure long-term survival through means of seed production. The species selected included: Eragrostis curvula; Eragrostis tef; Cenchrus ciliaris; Eragrostis curvula; Digitaria eriantha; Cynodon dactylon; Chloris gayana; Hyparrhenia hirta; and Sorghum bicolor. The progeny seed‟s viability and ability to germinate were determined through a pot trial study and additional germination testing at the laboratory of Advance Seed (Pty) Ltd. (AS). The germination results were correlated with the growth media analyses by statistical non-parametric correlations which indicated several significant correlations among the growth media properties themselves, and with the germination of the progeny seed. C. gayana (Rhodes grass) seed had poor germination percentages, especially seed harvested from Rhodes grass grown in acidic wastes. Seed harvested from each of the E. curvula grasses grown in various mine wastes, had excellent germination percentages. According to the Repeated Measures ANOVA statistical analysis, there was a significant influence of the growth media in which the parent grass were grown as a variable on the germination of the progeny seed batches from S. bicolor, C. ciliaris, C. gayana, and D. eriantha, indicating that the environmental factors as attributed by the growth media, i.e. the eight different mine waste materials and two soils, and experienced by the maternal plant, did indeed influence the germination of progeny seed. However, it was found that significant correlations between the properties of the growth media and the germination of the progeny seed, was species dependent. The second general aim for this study was to evaluate above-ground re-growth of parent plants after cutting in the mine waste materials and soil types mentioned above. The ability of established grasses to re-grow after a cutting event was determined by cutting the above-ground biomass of the parent grasses, after which it was scored according observable above-ground growth in the following growth season. The measurement of re-growth was subjectively done by scoring the grasses according to observable above-ground biomass. Re-growth was observed for all the perennial grass species. This can be ascribed to the grasses showing resilience to stress factors attributed by the growth media; or new grasses which emerged from seed that collected in the pots, being mistaken for re-growth; or new emerging grasses from the nodes of stolons and/or rhizomes being mistaken for re-growth. However, the emergence of new grasses was an indicator of good health, as biomass allocation to rhizomes and stolons is reduced under low nutrient availability and stress conditions. Therefore the emergence of new grasses is indicative that the plant is either tolerant to stress conditions or that the plant adapted to the restriction of growth due to the roots being bound to the size of the pot. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Sustainable rehabilitation can be compromised by the inability of vegetation to survive in hostile mine wastes on a long-term basis. The adverse chemical and physical properties of mine wastes, together with extreme pH conditions and lack of nutrients, provide poor growth conditions for vegetation during seed development and germination. This raises concern for the long-term survival of vegetation through means of seed production when under stress from the punitive properties of mine wastes. Seed vigour is a function of a variety of factors to which the parent plant is subjected during seed formation and maturation. Environmental conditions experienced by the maternal plant during the growth season plays a significant role in determining subsequent germination rates in seeds. Traits of offspring seed depend on the abiotic environment attributed by the growth medium during seed development and maturation The general aim of this study was to determine the viability of seed produced by a previous generation of grass species established in eight different mine wastes and two soils (namely: gypsum wastes; gold tailings with low pyrite content; gold tailings with high pyrite content; platinum tailings; kimberlite mine waste; fluorspar mine waste; andalusite mine waste; coal discard; red soil; and vertic soil) in order to identify suitable species for specific mine wastes to ensure long-term survival through means of seed production. The species selected included: Eragrostis curvula; Eragrostis tef; Cenchrus ciliaris; Eragrostis curvula; Digitaria eriantha; Cynodon dactylon; Chloris gayana; Hyparrhenia hirta; and Sorghum bicolor. The progeny seed‟s viability and ability to germinate were determined through a pot trial study and additional germination testing at the laboratory of Advance Seed (Pty) Ltd. (AS). The germination results were correlated with the growth media analyses by statistical non-parametric correlations which indicated several significant correlations among the growth media properties themselves, and with the germination of the progeny seed. C. gayana (Rhodes grass) seed had poor germination percentages, especially seed harvested from Rhodes grass grown in acidic wastes. Seed harvested from each of the E. curvula grasses grown in various mine wastes, had excellent germination percentages. According to the Repeated Measures ANOVA statistical analysis, there was a significant influence of the growth media in which the parent grass were grown as a variable on the germination of the progeny seed batches from S. bicolor, C. ciliaris, C. gayana, and D. eriantha, indicating that the environmental factors as attributed by the growth media, i.e. the eight different mine waste materials and two soils, and experienced by the maternal plant, did indeed influence the germination of progeny seed. However, it was found that significant correlations between the properties of the growth media and the germination of the progeny seed, was species dependent. The second general aim for this study was to evaluate above-ground re-growth of parent plants after cutting in the mine waste materials and soil types mentioned above. The ability of established grasses to re-grow after a cutting event was determined by cutting the above-ground biomass of the parent grasses, after which it was scored according observable above-ground growth in the following growth season. The measurement of re-growth was subjectively done by scoring the grasses according to observable above-ground biomass. Re-growth was observed for all the perennial grass species. This can be ascribed to the grasses showing resilience to stress factors attributed by the growth media; or new grasses which emerged from seed that collected in the pots, being mistaken for re-growth; or new emerging grasses from the nodes of stolons and/or rhizomes being mistaken for re-growth. However, the emergence of new grasses was an indicator of good health, as biomass allocation to rhizomes and stolons is reduced under low nutrient availability and stress conditions. Therefore the emergence of new grasses is indicative that the plant is either tolerant to stress conditions or that the plant adapted to the restriction of growth due to the roots being bound to the size of the pot. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Invasive alien plants have had diverse ecological and social impacts on recipient ecosystems and are a major problem for land managers. Successful management demands an understanding of the ecology of invading taxa. The invasive status and impacts are documented for Prosopis populations in South Africa. However, unresolved taxonomic issues, the extent of hybridization, the applicability of morphology as a species identification approach, and the role that some traits plays in the invasion success have not been studied. This creates a gap that hinders implementation of effective management policies. In this thesis I use a phylogenetic approach to determine the taxonomic make-up of invasive Prosopis populations in South Africa (Chapter 2) and compare the results to morphological identification (Chapter 3). I also look at seedling growth rates in the context of variation in genome size and seed size (Chapter 4). Almost all regions invaded by Prosopis are characterized by taxonomic uncertainty exacerbated by the ease of inter-specific hybridization. In Chapter 2 I aim to resolve taxonomic issues of invasive Prosopis populations in South Africa using a phylogenetic approach. In addition, I aim to unravel the extent of hybridization and the species involved in South Africa. Here, I found that Prosopis populations in South Africa comprise both reported and previously unreported species, indicating a need for a reassessment of the identity of invasive taxa. Hybridization is prevalent and all confirmed species are involved. These findings call for a rethink of legislation and management approaches, e.g. the selection of classical biological control agents. Overall the extent of hybridization indicates that Prosopis species in South Africa comprise a freely inter-breeding population typical of a syngameon. Proper morphological identification of invasive species is crucial for ecological studies and management of invasions. In Chapter 3, I use the total evidence approach to assess whether morphological approaches for identification are adequate for identifying Prosopis species in South Africa. I found that Prosopis taxa in South Africa cannot be reliably distinguished using existing morphological keys. This is likely due mainly to the proliferation of hybrids with a diverse morphology. Therefore, molecular tools are crucial for confirming any morphological identities and for determining the presence of any unreported species. Genome size and seed size have been reported to be associated with invasiveness in a number of plant groups, but not often in a system with multiple hybrids like Prosopis. In Chapter 4, I first investigate the relationship between genome size and seed size in invasive populations of Prosopis spp. in South Africa and secondly I investigate how genome and seed sizes influence germination and early growth. Here I found that genome size loses its distinctness, being diluted in hybridizing populations, but can still be used to assess hybridization events themselves. Large seed size seems to be important for invasiveness as it positively influences germination and early growth. This thesis confirms the taxonomic conundrum of Prosopis species in invasive ranges. This coupled with inadequacy of morphological identification calls for a global study involving native and invasive range taxa to clarify the existing confusions. In view of the presence of unreported Prosopis species in South Africa and extensive hybridization, a rethink of the current legislation and control is needed. / AFRIKAANSE OPSOMMING: Uitheemse indringer plante het grootskaalse ekologiese en sosiale impakte op die ekosisteme wat hulle indring en stel 'n groot uitdaging vir bestuurders van natuurlike hulpbronne. Suksesvolle bestuur en bestryding van indringer plante verg deeglike kennis oor hulle ekologie. Die indringer status en impakte van Prosopis populasies in Suid Afrika is reeds voorheen beskryf. Nieteenstaande, die problematiese taksonomie, die omvang van hibridisasie, die waarde van morfologiese identifikasie, en die rol wat sekere eienskappe speel in die sukses van hierdie groep is nog nie bestudeer nie. Daar is dus 'n gaping in kennis wat die effektiewe beheer van die groep in Suid Afrika belemmer. In hierdie tesis pas ek 'n filogenetiese benadering toe om die taksonomiese verwantskappe van Prosopis populasies in Suid Afrika te bepaal (Hoofstuk 2) en vergelyk my resultate met morfologiese identifikasie sleutels (Hoofstuk 3). Ek ondersoek ook saailing groei tempos in die konteks van variasie in genoom en saad groote in die groep (Hoofstuk 4). Bykans alle areas in Suid Afrika waar Prosopis voorkom word gekenmerk deur taksonomiese onsekerheid, verder bemoeilik deur die gemak waarmee spesies vrylik hibridiseer. Ek vind dat beide bekende en voorheen-onbeskryfde Prosopis spesies in Suid Afrika aangetref word en beklemtoon die behoefte om die identiteit van spesies in die land te hersien. Hibridisasie kom algemeen voor tussen alle spesies teenwoordig in Suid Afrika. Hierdie bevindinge beklemtoon dat wetgewing en beheermaatreêls hersiening benodig, byvoorbeeld in die toepassing van biologiese beheer. In samevatting kom dit voor asof hibridisasie gelei het tot 'n vrytelende Prosopis groep in Suid Afrika, tipies van 'n singameon. Ordentlike morfologiese identifikasie van indringer spesies is belangrik in enige ekologiese studie en die implementering van doeltreffende beheermaatreëls. In Hoofstuk 3 gebruik ek ʼn ‘totale bewys’ benadering om vas te stel of morfologiese eienskappe alleenlik genoegsaam is om Prosopis spesies in Suid Afrika korrek te kan identifiseer. Ek vind dat spesies nie geloofwaardig geïdentifiseer kan word nie, heel moontlik as gevolg van wydverspreide hibridisasie tussen alle spesies teenwoordig in die land. Genoom en saad groote is voorheen geassosieer met die indringer aard van verskeie plant groepe. In Hoofstuk 4 ondersoek ek die verwantskap tussen genoom en saad groote. Tweedens bepaal ek die invloed van genoom en saad groote op ontkieming en vroeë groei eienskappe van Prosopis. My bevindinge toon dat, terwyl die kenmerklikheid van genoom groote verloor word as gevolg van hibridisasie, dit steeds hibridisasie gebeurtenisse per se kan identifiseer. Groot sade het ook ʼn positiewe invloed op die ontkieming en vroeë groei eienskappe van Prosopis. Die tesis bevestig die taksonomiese onduidelikheid van indringer Prosopis taksa in Suid Afrika. Tesame met die onakkuraatheid van morfologiese sleutels beklemtoon my bevindinge die behoefte vir ʼn dringende wêreldwye studie op indringer en inheemse populasies van Prosopis om taksonomiese onsekerhede op te klaar. Die identifikasie van nuwe spesies in Suid Afrika beklemtoon ook die behoefte om huidige wetgewing en beheer van die groep in die land te hersien.

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Revised / 2 pp.