Magister Scientiae (Biodiversity and Conservation Biology) / The aim of the study was to quantify the extent of inorganic chemical pollution of the Franschhoek River and draw relationships between contaminants in water, sediment and plants. The invasive Acacia mearnsii and Salix babylonica and indigenous Brabejum stellatifolium species were chosen as biomonitors due to their wide spread distribution along the river and their apparent ability to accumulate heavy metals. The sites chosen allowed for comparison of the river quality upstream with that of the river further down stream as it meandered through residential, agricultural and recreational areas, until it joined with the Berg River further downstream. The general aim of the study was to assess the degree of inorganic pollution in the Franschhoek River to evaluate its contribution to pollution of the Berg River, of which it is an important tributary. Also understanding the sources of the pollution would contribute to the ability to reduce pollution. / South Africa

Black wattle (Acacia mearnsii), which belongs to the genus Acacia, is one of the many species of trees or hardwoods grown commercially in South Africa. Black wattle is a species indigenous to Australia and was introduced into South Africa by the van der Plank brothers in 1864. These trees are grown in South Africa because of its tannin-rich bark, the extract of which is used by the leather tanning industry. Black wattle is also grown for its timber, timber products and pulp. The introduction and cultivation history of black wattle suggests that the South African plantations contain limited genetic variation with relatedness amongst groups estimated to be high, thus implying a narrow genetic base in the South African black wattle population. In this investigation, Random Amplified Polymorphic DNA (RAPD) was used to estimate the genetic variation between seven different black wattle groups. A total number of 34 individuals obtained from different areas in South Africa were examined; Piet Retief (group 47 and 50: half-sibs), Kumbula (group 85: unrelated individuals), Howick (group 400: unrelated individuals) and an unknown area (groups 88, 89, 91: full-sibs). As this investigation was the first of its kind, a DNA isolation method as well as a PCR-RAPD protocol had to be modified. Total genomic DNA was successfully extracted using the CTAB DNA extraction method. This method removed large amounts of tannin present in the cells of the black wattle leaves and extracted high quality DNA to conduct between 50-100 RAPD reactions. The DNA purities ranged from 0.1 to 1.8, with an average of 1.46. A total of fourteen 10-mer RAPD primer sequences were randomly selected from the Operon Technologies primer list A, and tested in this investigation. Of the 14 primers used, only nine primers produced clear, single and repeatable bands. Therefore nine primers were selected for subsequent analyses. Ninety one loci that generated bands ranging from 300-3050 base pairs were produced. Seven to 13 loci per primer were generated. A total of 95.6 % of the loci were polymorphic. The overall expected mean heterozygosity (H = 0.3) obtained in this study was high in comparison to other studies conducted on acacias. The high levels of genetic variation were attributed to mating systems, dissortative mating and geographic distribution. The statistical packages POPGENE and ARLEQUIN were used to analyse the RAPD fingerprints. The genetic measures, Nei's diversity and Shannon's Information Index, showed that there was greater diversity exhibited (Nei's gene diversity = 32.09 % and Shannon's = 48.31 %), in the whole population than in each of the groups (with average of Nei's gene diversity = 20.33 % and Shannon's = 34.64 %). With regards to individual group analyses, low levels of genetic variation was obtained in group 400 (unrelated), from the Howick region, and group 85 (unrelated), from the Kumbula region, (mean 0.14 and 0.17 respectively). The low genetic values were attributed to limited gene exchange occurring in these two areas, bottlenecks and selection pressures. Groups 88, 89 and 91, from the unknown region (full-sib groups), were the most variable in comparison to the other groups, with means of (0.27,0.24 and 0.18 respectively). These high genetic variation values could be due to the fact that gene migration could have occurred between these groups and others in the area. It is thought that most acacias are insect-pollinated and this could have lead to gene migration between groups or populations, thereby explaining the high mean values. The gene flow obtained for the seven groups (FST = 0.174) indicated that great genetic differentiation existed in this population of black wattle studied. This value is higher in comparison to other woody species; however it is similar to other acacia species. UPGMA cluster analysis using Nei's unbiased genetic distance, revealed four distinct clusters of groups corresponding to the distribution areas represented in this study. The Howick (group 400: unrelated) and Kumbula (group 85: unrelated) were more closely related to each other than to the other groups, since both these groups are from Natal. The Piet Retief groups (groups 47 and 50: half-sibs), branched-off together, indicating that they are distinct from the other groups. The pairwise analysis of identity showed that the relationship between the group from Howick (group 400: unrelated) and all the other groups from the other regions was the lowest, ranging from 64 % to 79 %. The relationship between all the groups beside the group from Howick (group 400: unrelated) was reasonably high, ranging from 78 % to 90 %. This distance displayed by group 400 (unrelated) from Howick in relation to the groups, is attributed to the fact that it is frost resistant and the other groups not. Genetic variation was also detected and partitioned, between and within groups, by Analysis of Molecular Variance (AMQVA). Majority of the variation existed within groups (82.65 %) but significant differentiation was recorded between groups (17.44 %). This high level of within group differentiation may be explained by many aspects, such as the species breeding system, genetic drift or genetic isolation of groups or populations. The application of RAPD fingerprinting in black wattle has provided a more in depth understanding of the genetic variation residing in the South African population. The results achieved implementing this technique has shown that significant genetic variation exists within the black wattle population in South Africa. The results obtained in this study are also important since it is contrary to the expectation that the black wattle population in South Africa has low genetic variation. This knowledge is of great value to genetically discriminate between individuals or groups, to improve the selection of superior genotypes and allowing improved quality control in breeding programmes and seed orchard management. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

The present work has objective to define wich is the distribution of probability that analysis of nutritional contents are adjusted, selecting a function that better explain its behavior and to estimate the limits values of nutrients contents for it classification on several vegetables tissues. It were used 176 datas et colected from 15,534 nutritional analysis of three forest species, Acacia mearnsii, Eucalyptus sp. and Pinus sp., determinated for 1999 to 2004 period, in Forest Ecological Laboratory, in UFSM. The analysis were separated by subgroups in macro and micronutrients, vegetables components (leaves, bark, wood, root), species and year of determination. The database determination trough it statistical describe with mean, standart-deveation, number of observations, maximum and dataset adjusts a Normal distribution, it was aplicated the Lilliofors Test. Where the dataset didn´t adjust the Normal, it was tested the functions Log-normal, Beta, Gamma and Weibull through Kolmogorov-Smirnov Test, with 5%. It was possible determinated that 70% of all dataset valued adjusts one of functions, being the Normal presented of 33.5% of settlings, the Log-normal 27.3%, the Gamma 3.4%, the Weibull 5.7% and the Beta function didn´t presented no one settling. Of all amount dataset valued, 30.1% didn´t adjust any one functions. The studied functions, exception Beta, can explain the results from chemical analysis of vegetables tissues and establis hed the control limits of nutrient contents in each species. / O presente trabalho teve como objetivo definir qual é a distribuição de probabilidade que os resultados de análises nutricionais se ajustam, selecionando uma função que melhor explica o comportamento dos teores e estimar os valores limites dos macro e micronutrientes para sua classificação nos diversos tecidos vegetais. Foram utilizados 176 conjuntos de dados coletados em 15.534 análises nutricionais de três espécies florestais, Acacia mearnsii, Eucalyptus sp. e Pinus sp., realizadas durante o período de 1999 a 2004 e determinadas no Laboratório de Ecologia florestal, da UFSM. As análises foram separadas em subgrupos por macro e micronutrientes, componente vegetal (folhas, galhos, casca, madeira, raiz, etc.), espécie e ano de determinação. O banco de dados passou pela determinação das estatísticas descritivas média, desvio padrão, número de observações, valores máximo e mínimo. Para verificar se os dados seguiam a distribuição Normal, foi aplicado o teste de Lilliofors. Nos casos onde o teste não foi normal, foram testadas as funções Log-normal, Beta, Gamma e Weibull, via teste de Kolmogorov-Smirnov, com alfa 5%. Foi possível determinar que 70% do total avaliado seguiam alguma das funções, sendo que a Normal apresentou 33,5% de ajustes, a Log-normal 27,3%, a Gamma 3,4%, a Weibull 5,7% e a função Beta não apresentou nenhum ajuste. Do total de conjunto de dados avaliados, 30,1% não se aderiu a nenhuma das funções. As funções estudadas, com exceção da Beta, podem explicar a distribuição dos resultados das análises químicas de tecidos vegetais e estabelecer limites de controle dos teores de elementos químicos em cada espécie.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Invasive alien plant species have devastating effects on the environments that they invade. Australian Acacias, a group of plants that has been planted globally for a range of uses, but has escape plantation areas and became invasive in many countries, are particularly problematic. Acacia mearnsii is one of these invasive alien plant species and in South Africa it is also an important forestry species. It is currently the fifth most widespread invasive alien plant in South Africa, only restricted by the very arid Karoo, thus it is important to assess the different habitats that it enters. The Afromontane forest complex in South Africa is highly fragmented and is one of the most threatened Biomes in the country. The widespread forest margin tree Virgilia divaricata occurs within these forest margins. It is ecologically similar to A. mearnsii as these two species share many characteristics (nodulating legumes, forest pioneer species, fast growing and fire adapted). These species occur sympatrically within invaded forest margins and within these sites, there is a potential for biological exchanges of associated pests and pathogens in the form of arthropods and fungal species. We hypothesize that these two species have different interactions with their pests and pathogens in accordance with the Enemy Release Hypothesis (ERH) and the Biotic Resistance Hypothesis (BRH), respectively. We first compared arthropod associates between these two tree species and found that they share many arthropod species. The native tree did, however, have much higher abundances of herbivores and overall arthropod associates than the invasive tree species, which supports the predictions of the ERH. The distribution of these two species also had an effect on their arthropod assemblages. We assessed their ophiostomatoid fungal associates and herbivore loads and then determined how these pests and pathogens were influenced by environmental conditions along a water gradient. We also compared the effect of plant nutrient content of the two tree species on pest and pathogen loads. A. mearnsii was unaffected by water limitation along this gradient, while δ12C/ δ13C analyses showed that V. divaricata trees experienced drought within drier sites. V. divaricata also had higher herbivore loads in drier sites. A. mearnsii had higher herbivore loads on nutrient deficient trees and higher disease development in trees with sufficient nutrient levels. Comparisons of the nutrient economies of the two legume trees showed that they had similar leaf nutrient contents and resorption efficiencies, but they differed in the use of Biological Nitrogen Fixation (BNF). The native tree utilized BNF more than the invasive. We also tested the physiological effects of a native fungal species on the two tree species. We found the infection elicited more response from the invasive, while the native plant was almost non-responsive. Both plants had significantly longer lesions on infected seedlings than on control plants after inoculation with this pathogen. This difference in response offers a measure of support to the BRH, as the invasive may be more vulnerable to infection. The importance of using related, ecologically similar species in the assessment of the impacts of invasive alien plants is highlighted here. This may provide more information on the actual ecological interaction between native and invasive species within invaded ranges. Forest margins are very vulnerable and dynamic habitats. The influx of a new species into this habitat in the form of an invasive alien plant may therefore have much negative effects. We found support for the exchange of pest and pathogens where these two tree species co-occur. The two host species were very similar in their nutrient economies, creating a potential for competition for similar resources between A. mearnsii and V. divaricata. The environment had an influence on how these plants responded to pest and pathogens and this may be important under the predicted scenario of future climate change. / AFRIKAANSE OPSOMMING: Uitheemse indringer plant spesies het vernietigende effekte op die omgewings waarbinne hulle indring. Australiese Acacias, ‗n groep plante wat reg oor die wêreld aangeplant is vir ‗n reeks gebruike, maar wat uit plantasie areas ontsnap het en indringers geword het in baie lande, is besonder problematies. Acacia mearnsii is een van hierdie indringer uitheemse plant spesies, en in Suid Afrika is ook ‗n belangrike bosbou spesie. Dit is tans die vyfde mees wydverspreide uitheemse indringer plant in Suid Afrika, en word slegs beperk deur die baie droë Karoo, so dit is belangrik om die verskillende habitatte wat dit binnedring te ondersoek. Woudrandte, the grense van die Afromontane woudkompleks in Suid Afrika, is hoogs gefragmenteerd en is dus een van die mees bedreigde Biome in die land. Die wydverspreide woudrand boom Virgilia divaricata kom in hierdie woudrandte voor. Dit is ekologies eenders aan A. mearnsii, aangesien hierdie twee spesies baie kenmerke deel (wortelknop-vormende peulplante, woudpionier spesies, vining groeiend, aangepas tot brande). Hierdie spesies kom simpatries voor binne woudrandte wat deur A. mearnsii ingedring is, en in hierdie lokaliteite bestaan daar die potensiaal vir biologiese uitruiling van geassosieerde peste en patogene in die vorm van geleedpotiges en fungi spesies. Ons stel die hipotese dat hierdie twee spesies verkillende interaksies met hulle peste en patogene het, in ooreenstemming met die Vyand-Vrystellingshipotese (VVH) en die Biologiese-Weerstandshipotese (BWH), onderskeidelik. Ons het eers die geleedpotige assosieasie tussen hierdie twee boom spesies vergelyk en het bevind dat hulle baie geleedpotige spesies deel. Die inheemse boom het egter baie hoër getalle herbivore en algehele geleedpotige-assosiasies gehad as die indringer boom spesie, wat die voorspellings van die VVH ondersteun. Die verspreiding van hierdie twee spesies het ook ‗n effek gehad op hulle geleedpotige samestellings. Ons het ook hulle geassosieerde ophiostomatiede fungus assosiate en hulle herbivoor ladings bestudeer, en het bepaal hoe hierdie peste en patogene deur omgewingstoestande beinvloed is langs ‗n water gradient. Ons het ook die effek van hierdie peste en patogene op die voedingstof-inhoud van hierdie twee spesies vergelyk. A. meansii is nie geaffekteer deur waterbeperkings langs hierdie gradient nie, terwyl δ12C/ δ13C analises aangedui het dat V. divaricata bome droogte stres in droër lokaliteite ervaar het. V. divaricata het ook hoër herbivoorladings gehad in die droër lokaliteite. A. meanrsii het hoër herbivoorladings gehad op voedingstof-beperkte bome, en daar was verhoogde siekte-ontwikkeling in bome met genoegsame voiding. Vergelykings van die voedingstof-ekonomië van die twee peulplant bome het aangedui dat hulle eenderse blaarvoedingstof-inhoude en resorpsie effektiwiteite het, maar het verskil in die gebruik van Biologiese Stikstof Fiksasie (BSF). Die inheemse boom het meer van BSF gebruik gemaak as die indringer. Ons het ook die fisiologiese effekte van ‗n inheemse fungus spesie op die twee boomspesies getoets. Ons het bevind dat infeksie ‗n sterker reaksie in die indringer ontlok het, terwyl die inheemse plant feitlik glad nie op infeksie gereageer het nie. Beide plante het beduidend langer wondmerke in geinfekteerde saailinge ontwikkel as in kontrole plante na innokulasie met die patogeen. Hierdie verskil in reaksie verleen ‗n mate van ondersteuning aan die BWH, aangesien die indringer meer vatbaar mag wees teen infeksie. Die belang daarvan om verwante, ekologies soortgelyke spesies te gebruik in die bepaling van die effekte van uitheemse indringer spesies word hier beklemtoon. Dit mag meer inligting verskaf oor die werklike ekologiese interaksie tussen inheemse en indringer spesies binne verspreidings wat binnegedring is. Woudrandte is baie weerlose en dinamiese habitatte. Die invoer van nuwe spesies in hierdie habitat in die vorm van ‗n uitheemse indringer plant mag daarom baie negatiewe effekte hê. Ons het ondersteuning gevind vir die uitruiling van peste en patogene waar hierdie twee spesies saam voorkom. Hierdie spesies was baie eenders in terme van hulle voedingstof-ekonomië, wat die potensiaal skep vir kompetisie tussen A. mearnsii en V. divaricata. Die omgewing het ‗n effek gehad op hoe hierdie plante gereageer het op peste en patogene, en dit mag belangrik wees onder die huidig voorspelde senarios van toekomstige klimaatsverandering.

Student Number : 9202137P - MSc Dissertation - School of Animal, Plant and Environmental Studies - Faculty of Science / The Reconstruction and Development Programme’s Mpumalanga Working for Water Programme (WWP) has cleared exotic and commercial weed species from the riverine environment since 1994. This study serves as an assessment of the impact and modification caused as a result of invasion and the subsequent clearing of the exotic vegetation on flora in the riverine zone of the Sabie River Catchment. The experimental design compares the before and after clearing effects and includes altitude and invasion intensity variables. The investigations included: in situ soil seed banks, environmental modification, vegetation structure, species diversity and effectiveness of clearing. Clearing and invasion by exotic species altered soil chemical, physical and ground cover parameters. The extent of these modifications was dependent on the extent of invasion and clearing done within the community. Clearing of exotic species however, acted as an additional disturbance to that caused by invasion. Environmental modifications that occurred with clearing and invasion within the study were positively related to percentage soil organic matter, and ground cover (soil, litter, vegetation). Invasion by exotic species alters the vegetation structure, the extent of which was directly related to the invasion intensity. The main source of vegetation structure modification is attributed to tall growing exotic species such as Eucalyptus grandis and Solanum mauritianum. Both of these species dominated the indigenous vegetation, E. grandis by expanding the upper canopy and S. mauritianum by dominating the mid canopy. Clearing of invasive vegetation resulted in an additional disturbance proportional to the extent of invasion intensity. Invasion did not result in any large changes to the vegetation at low intensity but clearing at this intensity increased the disturbance and altered the vegetation structure. Soil seed banks were limited in the number of species and dominated by two exotic species. The soil seed bank of woody species related positively to the community species richness. The total soil seed bank density did not relate to invasion intensity or clearing thereof but propagules of individual species within the soil seed banks did. The seeds of the exotic species, Acacia mearnsii and S. mauritianum, illustrated burial as prerequisite for persistence in the soil seed bank. A. mearnsii and S. mauritianum seeds were found to have half-life’s of up to 25 years and 13 months respectively. The species richness and diversity varied only marginally because of invasion and clearing. Species alpha diversity increased with clearing due to weedy and pioneer species establishment. Beta diversity effectively highlights the species turnover with clearing and invasion. Success in eradication of exotic species had mixed results. Clearing of high invasion sites was effective but in lower invasion categories a number of exotic individuals were missed. Clearing effectiveness was good for certain species such as E. grandis and Pinus patula, but poor for others such as S. mauritianum. Coppicing is a significant issue for E. grandis and S. mauritianum. The persistence of individuals (coppicing & missed individuals) coupled with very large persistent seed banks has repercussions for the clearing programme, as it may prevent effective eradication. Initially the WWP has been successful in removing exotic vegetation, however there is a failure to address the regenerative properties of some exotic species. Unless a rigid schedule of follow up clearing treatments occurs, an even larger invasion problem could exist.

Plants that can self-fertilise should, on average, be more invasive than plants that can not self-fertilise because they can reproduce regardless of the availability of mates and pollinators. Self-fertilisation should have a strong effect on invasiveness because, to become invasive, introduced plants have to pass through bottlenecks of low plant abundance when mates and pollinators are likely to be scarce. Under these conditions, reproduction of plants that can not self-fertilise is often limited by pollen receipt. Selfing may thus contribute to invasiveness by alleviating pollen limitation Allee effects (pollen limitation caused by low abundance) especially as theoretical work indicates that ability to invade and rate of invasion are highly sensitive to fecundity of small and isolated populations and single individuals. Recently, a correlation between ability to self-fertilise and invasiveness has been observed in several invasive floras, consistent with the hypothesis that species that can self-fertilise should be more invasive. However, it has not yet been demonstrated that this relationship arises from reproductive assurance. To establish the causal basis of a correlation between a plant trait and invasiveness, a mechanism linking that trait to invasiveness must be demonstrated. For this it is necessary to show firstly that the trait actually affects performance in the introduced range and secondly that plant performance affects invasiveness. Self-fertilisation is hypothesised to increase invasiveness by enhancing reproductive performance. The first step in testing this hypothesis is therefore to show that being able to self-fertilise increases fecundity, i.e. that it provides reproductive assurance. However, progeny from self-fertilisation often suffer from inbreeding depression – they perform worse than those from cross-fertilisation – so it is also necessary to show that this cost does not outweigh the reproductive assurance benefit of selfing. So far, reproductive assurance has been assessed in only a few invasive plant species. These studies did not assess inbreeding depression and only one investigated reproductive assurance in relation to abundance, finding no relationship. In this thesis I have sought to understand the importance of self-fertilisation for reproduction of invasive plants in the introduced range through case studies. In particular, I assessed whether reproductive assurance from self-fertilization alleviates Allee effects via pollen limitation. To do this I tested whether pollen limitation and reproductive assurance were greater at low plant abundance. Further, I conducted progeny trials to assess inbreeding depression, as this cost of selfing potentially negates reproductive assurance benefits. I also conducted observations and experiments to identify the principle pollinators of my study species as reproductive assurance and its relationship to plant abundance depend on pollinator visitation, The Australian trees Acacia mearnsii and A. dealbata are highly invasive in the study region of KwaZulu-Natal, South Africa. Through controlled pollination experiments I established that A. dealbata was self-compatible and autonomously self-fertilising, while previous studies reported A. mearnsii as self-incompatible. I identified the native honeybee Apis mellifera scutellata as the principal pollinator of A. mearnsii, A. dealbata and a co-occuring related invasive species, Acacia decurrens, in the study region. I conducted pollen supplementation experiments in two of these species, aiming to indirectly assess reproductive assurance from selfing in the self-compatible A. dealbata by comparing pollen limitation between this species and the self-incompatible A. mearnsii. In both species, I conducted pollen supplementation in single isolated trees and trees in continuous populations, to test whether pollen limitation was more severe in isolation. These pollen supplementation experiments were inconclusive with respect to pollen limitation but indicated that if there was pollen limitation in A. mearnsii, it was not related to isolation. Progeny trials in A. dealbata revealed relatively strong inbreeding depression in progeny growth and survival. This suggests that selfed progeny may not reach reproduction, so even if self-fertilisation provides reproductive assurance, it may not contribute to invasion in this species. As floral morphology of Acacia species prohibits the use of emasculation experiments to directly measure reproductive assurance, I conducted further investigations on Lilium formosanum, a large-flowered, autonomously self-pollinating invasive geophyte native to Taiwan. I identified the long tongued hawkmoth Agrius convolvuli as its primary pollinator in its introduced range in KwaZulu-Natal, South Africa. Trials of progeny from self- and crosspollination in the field (to 31 months) and in a controlled shade-house environment (to 26 months) showed no evidence of inbreeding depression in germination, growth or survival. Flowering was assessed in the shade-house as most plants did not flower in the field. Only one of five populations showed inbreeding depression in probability of flowering in the second year of growth but none showed inbreeding depression in the third year. Inbreeding depression was thus generally undetectable in L. formosanum. I tested for reproductive assurance and pollen limitation in L. formosanum by conducting floral emasculations and pollen supplementations in multiple populations across a range of population size and isolation in three different years. These experiments demonstrated that reproductive assurance was substantial and that pollen limitation was low or absent. Contrary to expectations, reproductive assurance was not greater in smaller populations and was greater for more isolated populations in only one of three years. However, that study did not include many very small populations. To assess reproductive assurance at very low abundance, I created arrays of emasculated and intact plants within and around naturally occurring populations at two sites. Isolated plants had higher reproductive assurance than did plants placed inside the continuous population at one site, supporting the hypothesis that selfing provides reproductive assurance against pollen-limitation Allee effects. However, in these studies, generally inadequate pollinator visitation was the main reason that L. formosanum exhibited reproductive assurance through selfing. The substantial reproductive assurance and minimal inbreeding depression displayed by L. formosanum makes a compelling case for the hypothesis that self-pollination promotes invasion. Nevertheless, demographic modelling will be necessary to assess whether increased fecundity through reproductive assurance results in increased rates of population growth and spread, and hence invasion, in this species. To assess whether reproductive assurance accounts for the relationship between ability to self-fertilise and invasiveness in plants generally, the contribution of self-fertilisation to invasiveness will have to be evaluated for a larger sample of invasive and non-invasive introduced species, using the approaches taken in this thesis, followed up by demographic modelling. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: This project consists of two botanical investigations in an agricultural area of the Western Cape Province. A farm known as De Rust, in the Elgin Valley, was used to sample the geographic location, density, height and life stage of six prominent invasive plant species in various land-use categories. In the first investigation, the density, height and age structures of the six invasive species populations were analyzed. The density distribution of the six species was also displayed cartographically. Species were then ranked according to the potential threat that they pose to the conservation of the remaining natural areas on the farm. Results indicated that Acacia mearnsii and Acacia saligna are the major invaders at De Rust and that Hakea sericea can be considered as an emerging invader. The second investigation explores the statistical relationship between the various land-use categories and density, height and age of the six prominent invaders identified in the first investigation. The loglikelihood ratio analysis of observed frequencies resulted in statistically significant (P<0.01; P-values range between 1.35 x 10-3 and 2.7 x 10-224) relationships between certain land-use types and certain invasive species. A conclusion was reached that it could be useful to include land-use categories in simulation models of invasive plant species distribution and spread. / AFRIKAANSE OPSOMMING: Hierdie projek behels twee botaniese ondersoeke in ‘n landbou gebied van die Weskaap. Die plaas bekend as De Rust, in die Elgin Vallei, was gebruik vir die versameling van data te doen met die geografiese ligging, plant digtheid, lengte en lewens stadium van ses prominente indringer plant spesies in verskeie landgebruik kategorieë. Die digtheid, lengte en ouderdomstruktuur van ses indringerspesies was in die eerste ondersoek geanaliseer. Die verspreiding van digtheid was ook in kaarte uitgelê. Spesies was daarna volgens hulle potentiële dreiging teen die bewaring van oorblywende natuurlike dele van die plaas in ‘n rangorde geplaas. Resiltate dui aan dat Acacia mearnsii en Acacia saligna die belangrikste indringer plante op De Rust is en dat Hakea sericea as ‘n opkomende indringer beskou kan word. Die tweede ondersoek kyk na die verhouding tussen verskeie grondgebruik kategorië en die digtheid, lengte en ouderdom van die ses prominente indringer spesies wat in die eerste ondersoek identifiseër is. ‘n Log tipe ratios ontleding van bewaarde frekwensies het ‘n statisties belangrike uitkoms gehad (P<0.01; P-waardes tussen 1.35 x 10-3 en 2.7 x 10-224) vir die verhoudings tussen sekere grondgebruik tipes en sekere indringer spesies. Die gevolgtrekking was dat dit handig mag wees om grondgebruik kategorieë in simulasies van indringer plant verspreiding te gebruik.

Mixed-species plantations of eucalypts and acacias have the potential to improve stand productivity over that of respective monocultures through the facilitative effect of nitrogen-fixation by acacias, and increased resource capture through above- and belowground stratification. However, growth in mixed-species plantations may not be improved compared to that of monocultures when competitive interactions outweigh the effects of improved nutrient availability and resource capture. Careful selection of sites and species is therefore critical to successfully improving stand productivity using mixed-species plantations. This study set out to examine some of the processes and interactions that occur in mixed-species plantations, and the effect nutrient and water availability can have on the growth of mixtures. In three out of four mixed-species field trials examined in this study, growth was not increased in mixtures compared to monocultures. However, in the fourth field trial, heights, diameters, stand volume and aboveground biomass were higher in mixtures of E. globulus and A. mearnsii from 3-4 years after planting. The range in outcomes from mixing species in these four trials shows that a fundamental understanding of the underlying processes is required to enable a greater predictive capacity for the circumstances under which mixtures will be successful. Therefore the growth dynamics, processes and interactions were examined in the mixtures of E. globulus and A. mearnsii. The difference in productivity between mixtures and monocultures in this trial increased with time up to age 11 years, when 1:1 mixtures contained twice the aboveground biomass of E. globulus monocultures. The positive growth response of trees in mixture compared to monocultures was the result of accelerated rates of nutrient cycling, a shift in C allocation and reductions in light competition through canopy stratification. Nitrogen contents of foliage and soil clearly showed that A. mearnsii influenced the N dynamics in this trial. If these changes in N contents were due to N fixation by A. mearnsii, then about 51 and 86 kg N ha-1 yr-1 was fixed in the 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation was also examined using the natural abundance method. The delta15N values of foliage collected at 10 years were grouped according to the mycorrhizal status of the host plant. Therefore the discrimination of 15N during transfer from mycorrhizae to the host plant appeared to vary with mycorrhizal status, and the natural abundance of 15N was not used to quantify N fixation. Rates of N and P cycling in litterfall were significantly higher in stands containing at least 25% A. mearnsii (more than 31 kg N ha-1 yr-1 and more than 0.68 kg P ha-1 yr-1) compared to E. globulus monocultures (24 kg N ha-1 yr-1 and 0.45 kg P ha-1 yr-1). Rates of litter decomposition and N and P release were about twice as high in 1:1 mixtures compared to E. globulus monocultures and were even higher in A. mearnsii monocultures. It is therefore important to select N-fixing species that are capable of cycling nutrients quickly between the plant and soil, and that have readily decomposable litter. The total belowground C allocation was not significantly different between mixtures and monocultures (14 to 16 Mg C ha-1 yr-1). However, since aboveground net primary production was greater in 1:1 mixtures, the changes in nutrient availability appears to have increased total productivity (both above- and belowground), and reduced the proportion of C allocated belowground in mixtures compared to E. globulus monocultures. In a pot trial containing mixtures of E. globulus and A. mearnsii both species grew larger in mixture than in monoculture at low N levels, and mixtures were more productive than monocultures. However, at high N levels, E. globulus suppressed A. mearnsii and mixtures were less productive than E. globulus monocultures. Similar effects were found for high and low levels of P. Therefore resource availability can have a strong influence on the interactions and growth of mixtures. The productivity of mixtures may only be increased on sites where the resource for which competition is reduced in mixture is a major limiting growth resource. For example, if N is not a limiting growth factor then an increase in N availability from N-fixation may not increase growth, and the N-fixing species may compete for other resources such as soil P, moisture or light. This study has shown that mixtures containing a N-fixing trees and a non-N-fixing trees can be more productive than monocultures, but that this increase in productivity will only occur on certain sites. Examination of the growth, interactions and processes that occurred in mixtures in this study provide useful information that can aid the selection of species combinations and sites.

The overall aim of the study was to investigate re-vegetation of disturbed sites, using nursery grown plugs (from seedling trays) of Themeda triandra, Heteropogon contortus and Hyparrhenia dregeana in order to reach practical management guidelines for re-vegetation using indigenous grass plugs. A number of field trials were set up at Kamberg Nature Reserve (29°24'S, 29°40'E) on a site that was clear felled of A. mearnsii in October 1997. The trials were established in January 1998 and January 1999. A total of approximately 52 ,000 nursery raised plugs of T. triandra, H. contortus and H. dregeana were planted into an area of approximately 7,000 m2 . In the planting density trial , plugs of H. dregeana only and a combination of T. triandra/H. contortus were planted at 15 cm and 30 cm spacings. The T. triandra/H. contortus combination at 30 spacing showed the greatest survival and lateral plant growth (tiller number and basal area) and this combination is thus recommended. In the over-sowing trials, the H. dregeana and T. triandra/H. contortus combination at both 15 cm and 30 cm spacing were over-sown with E. curvula. The survival and lateral growth of the T. triandra/ H. contortus combination at 30 cm was again greater than the other treatments. Over-sowing with E. curvula suppressed the survival and lateral growth of the planted plugs across all treatments compared to not over-sowing. The over-sown conditions showed a significant decrease in the diversity of the plots, both in the number of species present and the Shannon diversity index. An area that had been cleared of A. mearnsii and sown to E. curvula 25 years previously was shown to have a lower number of species than the neighbouring veld. Nursery raised plugs of T. triandra were planted into the mature E. curvula in an attempt to improve the biodiversity of these areas. To re-introduce T. triandra into these E. curvula swards the plugs must be planted into the centre of a gap rather than around the base of an E. curvula plant. For improved survival of the plugs the E. curvula tufts must be clipped, while for best lateral growth the E. curvula tufts must be sprayed with a glyphosate herbicide three months prior to planting and clipping. However, the added expense of spraying and clipping is not warranted as the clipped treatments also showed good growth. Transplant shock is common when planting nursery raised plugs out into the field, as there is a relatively small root volume in the plug compared to the above ground leaf biomass. Alleviation of moisture stress at planting using a starch based polymer with high water holding capacity (Terrasorb®) and a white, needle punched geo-fabric (Agrilen®) to provide a seven day period of artificial shade after planting did not show significant improvements over the control with regards to survival or plant growth. Thus these methods of moisture amelioration are not recommended in revegetation through planting of plugs at this study site. A trial was established to investigate the biomass production of six different treatments to determine their potential to support a fire. The total biomass for the plots which were over-sown by E. tef and planted to only H. dregeana were on average sufficient for a fire, but there was a discontinuous fuel load across these plots, especially in the replications that had very low survival rates and thus these plots could not be burnt. The control and herbicide sprayed plots also showed sufficient fuel load for a fire, but this fuel load was made up of A. mearnsii saplings and bramble with very little grass cover and thus a fire would not have burnt through these plots either. The T. triandra/H. contortus combination did not produce sufficient fuel load, due to poor survival. Thus only the plots over-sown with E. curvula were able to burn in this trial and as a burning trial per se the trial was abandoned. Seed bearing hay (thatch) was collected in early summer (December 1997) and late summer (April 1998). Both times of year of harvesting proved to be successful in terms of grass cover, although the early harvested thatch had a greater number of species per plot. The Shannon diversity indexes of the two treatments were not significantly different. The multi-response permutation procedure technique confirmed that there was a compositional difference between the treatments. By the end of the trial Harpochloa falx and T. triandra and H. dregeana were indicators for the early and the late harvested thatch respectively. Comparing the thatching trial and the planting density trial indicated that the T. triandra/H. contortus combination at 30 cm spacing would be recommended to maximize biodiversity. The summer months have been shown to be the best time to plant the plugs, although the actual success will be dependant on the conditions within a particular year. The plugs should not be kept in the nursery for longer than three months and larger plugs (96 seedlings per tray) should be used. Nursery raised plugs of T. triandra and H. contortus were planted in an equal mix in an area that was cleared of A. mearnsii in 1996. By June 1998 661 H. contortus seedlings and 14 T. triandra seedlings had germinated naturally. The November 1998 population consisted of 418 H. contortus seedlings and 18 T. triandra seedlings. By May 2000 the June 1998 population showed a survival of 78.4% and the November 1998 population showed a survival of 91 .1 %. In the various trials, the ability of the nursery raised plugs used for re-vegetation to suppress the regrowth of A. mearnsii was investigated by determining the number of A. mearnsii seedlings per metre squared. The plant spacing and species of plugs used did not have a significant effect on the number of A. mearnsii seedlings per metre squared. Over-sowing with E. curvula did, however, significantly suppress the wattle re-growth. In the thatching trial the early harvested plots showed lower numbers of A. mearnsii per metre squared than the late harvest plots, as they were covered with a thick layer of thatch soon after the A. mearnsii was cleared which suppressed the A. mearnsii re-growth. Although E. curvula is able to produce a high biomass and suppress the A. meansii seedlings, it has a detrimental effect on the biodiversity of the area. Therefore, in conservation areas, where biodiversity is of great importance the planted plugs (at 30 cm spacing) or seed bearing hay must be used in preference to sowing E. curvula , although it must be remembered that greater follow up control is likely to be needed with planted plugs or seed bearing hay. The area must be planted or thatched as soon as possible after clear felling to provide competition for the A. mearnsii seedlings. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

Thesis (MScFor)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Several studies have shown that stands of invasive alien plants in the natural forest environment can facilitate the rehabilitation and recovery of such forests and challenged the general and global perception that such invasive species threaten the biodiversity and functioning of natural vegetation systems. The aim of this study was to develop an understanding of the dynamics of the spread and establishment of natural forest species in a large stand of the invasive alien plant species Acacia mearnsii (Black wattle) along the Buffeljagsrivier, Western Cape, South Africa. Several patches of Moist forest, Dry forest and Riparian forest occur along the Buffeljagsrivier, above the Buffeljagsrivier dam. The stand of Black wattle consists of 90 ha for a distance of 3.12 km. The main objective was pursued through four specific objectives: (i) to map and assess the patterns in the distribution, size and species composition of the natural forest clusters within the Black wattle stand; (ii) to determine the relationship between natural forest clusters establishing within the Black wattle stand and the neighboring natural forest patches as potential seed sources for the developing forest clusters; (iii) to determine the subsequent spread of natural forest species from the developing forest clusters into the rest of the Black wattle stand; and (iv) to synthesize the information on the dynamics of the spread and establishment of natural forest species into the Black wattle stand as a basis for developing general guidelines for the conversion of invasive alien plant stands in the forest environment towards regrowing natural forest. In total, 329 clusters of natural forest species were GPS recorded and mapped (Arc-GIS) in three zones (Proximal, Intermediate and Distant in relation to the forest patches) within the Black wattle stand: 266 small clusters (one to three reproductively mature trees), 36 medium sized clusters (four to nine trees) and 27 large clusters (more than 10 trees). Large clusters were abundant in the zone close to the natural forest patches and the number of small clusters increased with increasing distance from the forest patches. A total of 28 species of 20 families were recorded. Natural forest species are therefore able to establish within a Black wattle stand. The relationship between natural forest clusters establishing within the Black wattle stand and the natural forest patches as potential seed sources was studied by sampling the stand composition along transects through the stands. A total of 55 rectangular plots (20 m x 10 m, 200 m2) were sampled across forest patches and forest clusters. Hierarchical clustering analysis, using number of stems of a species per plot, identified three main groups and 10 sub-groups. All the sampled forest clusters were included in four of the five Riparian forest sub-groups. Most Moist and Dry forest species were absent from the forest clusters. The three main forest types differed in their general characteristics and site conditions, and this was supported by the ordination analyses: aspect, slope and canopy closure. The developing forest clusters within the Black wattle stand related more to the Riparian forest in terms of similar very gentle south-westerly slope and mean stem diameter. This suggested Riparian forest to be the primary seed source of the establishing forest clusters within the Black wattle stand. However, the large-sized stems of common species were not significantly different between Riparian forest patches and forest clusters, suggesting that large-sized stems in the forest clusters could be part of remnant forest patches, which could act as local seed sources. Detailed evaluation of species importance values and stem diameter distributions showed that some important Moist and Dry forest species are present in the forest clusters. The conclusion was that every type of forest patch contributes to a greater or lesser degree to the development of forest clusters within the Black wattle stand. Seven large clusters were selected to sample the regeneration of natural forest species within 18 m from the forest cluster boundary. Two species lists were generated; one of species from adjacent natural forest patches, and another from 59 forest clusters of all sizes sampled throughout the wattle stand. The results indicated that (1) Mature trees of well-established forest clusters were the main seed sources for the cluster expansion in all directions; (2) Three different patterns were observed in terms of the distance of expansion of regeneration from the clusters: a decrease in regeneration with increasing distance from the cluster margin; increasing regeneration with increasing distance from the cluster; and no distinct pattern with a lack of regeneration of the dominant species of a forest cluster. The 40 species recorded within the Buffeljagsrivier site include a wide range of fruit and seed characteristics. Four main groups of woody species were identified, based on their presence/absence in forest patches and forest clusters. The presence/absence of most species can be explained in terms of their fruit/seed characteristics and dispersal mechanisms. The majority of recorded woody species were most likely dispersed by birds and mammal, particularly Rameron pigeons and baboons. In conclusion, a conceptual framework was developed to guide the rehabilitation of stands of light demanding invasive stands in the forest environment. Several topics for further research were identified. / AFRIKAANSE OPSOMMING: Verskeie studies het gewys dat opstande van uitheemse indringerplante in die woudomgewing kan die rehabilitasie en herstel van sulke woude fasiliteer, en daag die algemene en globale persepsie uit dat sulke indringerplantspecies die biodiversiteit en funksionering van natuurlike plantegroeisisteme bedreig. Die doel van hierdie studie was om ‘n beter begrip te ontwikkel van die dinamika vir die verspreiding en vestiging van inheemse woudspesies binne ‘n omvangryke opstand van die uitheemse indringerplant, Acacia mearnsii (swartwattel), langs die Buffeljagsrivier, Wes-Kaap, Suid Afrika. Verskeie kolle (‘patches’) van Vogtige, Droë- en Oewerwoud kom langs die Buffeljagsrivier voor. Die swartwattel opstand van ongeveer 90 ha groei langs die Buffeljagsrivier oor ‘n afstand van 3.12 km, tussen die dam en die woudkolle aan die stroom-op kant van die swartwattelopstand. Die hoofdoel is nagevolg deur vier spesifieke doelwitte: (i) om die groepies (‘clusters’) vestigende inheemse houtagtige plantsoorte binne die swartwattelbos te karteer en die patrone in hul verspreiding, grootte en spesies samestelling binne die swartwattelopstand te evalueer; (ii) om die verwantskap tussen natuurlike woudgroepies wat binne die swartwattelopstand vestig en die aangrensende woudkolle as potensiële saadbronne vir die ontwikkelende woudgroepies te bepaal; (iii) om die daaropvolgende verspreiding van inheemse woudspesies vanaf die ontwikkelende woudgroepies binne die res van die swartwattelopstand te bepaal; en (iv) om die inligting oor die dinamika van die verspreiding en vestiging van die woudspesies binne-in die swartwattelopstand saam te vat as ‘n basis vir die ontwikkeling van algemene riglyne vir die omskepping van uitheemse indringerplantopstande in die woudomgewing na hergroeiende inheemse woud. In totaal is 329 groepies van inheemse woudspesies aangeteken (via GPS) en gekarteer (Arc-GIS) in drie sones (nabygeleë, intermediêre en afgeleë) binne die swartwattel opstand: 266 klein groepies (een tot drie voortplantingsvolwasse bome), 36 medium-grootte groepies (vier tot nege bome) en 27 groot groepies (10 of meer bome). Groot groepies was volop in die sone naby aan die woudkolle en die aantal klein groepies het toegeneem met toenemende afstand vanaf die woudkolle. ‘n Totaal van 28 species van 20 families is aangeteken, en spesies soos Canthium inerme, Celtis africana, Gymnosporia buxifolia, Rapanea melanophloeos en Vepris lanceolata was algemeen binne die swartwattelopstand. Dit is daarom moontlik vir inheemse woudspesies om binne die swartwattelopstand te vestig. Die verhouding tussen inheemse woudgroepies wat binne die swartwattelopstand vestig en die woudkolle as potensiële saadbronne is bestudeer deur die opstandsamestelling langs transekte deur die opstande te bemonster. ‘n Totaal van 55 reghoekige persele (20 x 10 m, 200 m2) is opgemeet: nege in Droeëwoudkolle, 17 in Vogtige woudkolle, 20 in Oewerwoudkolle, en nege in die woudgroepies binne the swartwattelopstand. Hiërargiese Groeperingsanalise, gebaseer op aantal stamme van ‘n spesies per plot, het drie hoofgroepe en 10 sub-groepe ge-identifiseer: Vogtige woud met drie sub-groepe, Oewerwoud met vyf sub-groepe, en Droeëwoud met twee sub-groepe. Al die gemete woudgroepies is in vier van die Oewerwoud sub-groepe ingesluit. Die meeste Vogtige en Droeëwoud spesies was afwesig van die woudgroepies. Die hoof woudtipes (Droog, Vogtig, Oewer) verskil in hul algemene eienskappe en groeiplektoestande, en dis ondersteun deur die ordinasie-analises: aspek, helling en kroonsluiting. Die ontwikkelende woudgroepies binne die swartwattelopstand was nouer verbonde met Oewerwoud in terme van soortglyke baie geleidelike suid-westelike helling en gemiddelde stamdeursneë. Dit veronderstel dat Oewerwoud is die primêre saadbron van die vestigende woudgroepies binne die swartwattelopstand. Baie inheemse woudspesies kom egter oor die verskillende groepe en sub-groepe voor, met goeie verjonging oor die gemeenskappe. Die stamdeursneë van goter stamme van algemene spesies was niebeduidend verskillend tussen die Oewerwoudkolle en die woudgroepies, en dit veronderstel dat die groter stamme in die woudgroepies kan deel wees van oorblywende woudkolle, wat as plaaslike saadbronne kan dien. Gedetaileerde ontleding van spesies belangrikheidswaardes en stamdeursneëklasverdelings het getoon dat sommige belangrike Vogtige en Droeëwoud spesies is wel teenwoordig in die woudgroepies. Die gevolgtrekking was dat elke tipe woudkol in a mindere of meerdere mate bydra tot die ontwikkeling van die woudgroepies binne die swartwattelopstand. Sewe groot woudgroepies is geselekteer om die woudverjonging binne 18 m vanaf die woudgroepierand te bemonster. Twee spesieslyste is saamgestel; een van spesies van die aangrensende woudkolle, en een van spesies van 59 woudgroepies van alle groottes wat deur die hele swartwattelopstand aangeteken is. Die resultate het aangetoon dat (1) volwasse bome van goed-gevestigde woudgroepies was die hoof saadbronne vir die uitbreiding van die woudgroepies in all rigtings; (2) drie verskillende patrone is waargeneem in terme van die afstand van uitbreiding van verjonging weg vanaf die woudgroepies: ‘n afname in verjonging met toenemende afstand vanaf die groepierand; toenemende verjonging met toenemende afstand vanaf die woudgroepie; en geen beduidende patroon met ‘n gebrek aan verjonging van die dominante spesies van die woudgroepie. Die 40 spesies wat binne die Buffeljagsrivierstudiegebied aangeteken is het ‘n wye reeks vrug- en saadeienskappe ingesluit. Vier hoofgroepe van houtagtige spesies is geïdentifiseer, gebaseer op hul aan- of afwesigheid in die woudgroepies and woudkolle: spesies algemeen in die woudkolle en teenwoordig in die woudgroepies; spesies spesifiek to bepaalde woudkolle en teenwoordig in die woudgroepies; spesies teenwoordig in die woudkolle maar afwesig van die woudgroepies; en spesies afwesig van die woudkolle maar teenwoordig in die woudgroepies. Die aan- of afwesigheid van die meeste spesies kan verduidelik word in terme van hul vrug/saadeienskappe en verspreidingsmeganismes. Die meerderheid van aangetekende houtagtige spesies was meeswaarskynlik deur voëls en soogdiere versprei, veral Geelbekbosduiwe en Bobbejane. Ten slotte, ‘n konsepsuele raamwerk is ontwikkel om die rehabilitasie van opstande van ligafhanklike indringerspesies in die woudomgewing te rig. Verskeie onderwerpe vir verdere navorsing is geïdentifiseer. / RESUME: Plusieurs études ont montré que les peuplements de plantes exotiques envahissantes dans le milieu de forêt naturelle peuvent favoriser la réhabilitation de ces forêts contestant par-là, la perception générale et globale que ces espèces envahissantes menacent la biodiversité et le fonctionnement des systèmes de végétation naturelle. L’objective de cet étude était de mieux comprendre le dynamisme d’établissement et de propagation dans une forêt naturelle des espèces forestières au sein d’un large peuplement de l'espèce de plantes exotiques envahissantes Acacia mearnsii (acacia noir) le long de Buffeljagsrivier, Western Cape, en Afrique du Sud afin d’élaborer des axes directives de réhabilitation relative aux recouvrements d’espèces invasive. La forêt de Buffeljagsrivier s’étale sur un gradient de petites parcelles de forêt allant de forêt sèche, humide et marécageux. Au milieu de ces parcelles de Buffeljagsrivier, on circonscrit un peuplement d’acacia noir estimé à 90 ha sur une distance de 3,12 km. L’objective principal s’est poursuit à travers quatre sous objectives à savoir: (i) cartographier et évaluer les formes d’ invasions dans la distribution, la taille et la composition des recouvrements des espèces de forêt naturelle à l’intérieur du recouvrement d’acacia noir servant comme preuve possible de l’existence et établissement des espèces de forêt naturelle sous un recouvrement d'une espèces invasive; (ii) de déterminer la relation entre les recouvrements de forêt naturelle s’établissant á l’intérieur du peuplement d’acacia noir et ceux de la forêt naturelle avoisinante humide, sèche et marécageuse pouvant être considéré comme sources potentiel de semences conduisant au développement des premiers recouvrement cités; (iii) de déterminer l’étalement subséquent des espèces de la forêt naturelle à partir des recouvrements d’ acacia noir se développant à l’intérieur du reste du peuplement de l’Acacia noir; (iv) Synthétiser les informations sur la dynamique de la propagation et l'établissement d'espèces forestières naturelles dans l’acacia noir comme une base pour l'élaboration des lignes directrices générales pour la conversion de peuplements de plantes exotiques envahissantes se trouvant dans l'environnement de la forêt vers des repousses des forêts naturelles. Au total, 329 recouvrements d'espèces forestières naturelles ont été GPS enregistrées et cartographiées (Arc -GIS) dans trois zones (Proximale, Intermédiaire et Eloignée par rapport aux parcelles de forêt avoisinantes) dans le peuplement de l'acacia noir: 266 petits recouvrements avaient un à trois arbres matures, 36 recouvrements de taille moyenne avaient quatre à neuf arbres matures et 27 larges recouvrements avaient plus de 10 arbres matures. La visualisation de la carte a révélé que les larges recouvrements de forêt mature étaient abondant dans la zone proche des parcelles de forêt naturelle avoisinantes et que de petits recouvrements de jeunes arbres de forêt naturelles croissaient en nombre à mesure que la distance depuis les parcelles de forêts naturelles adjacentes s’élargissait. Un total de 28 espèces appartenant à 20 familles a été répertorié. Deux familles, Rubiaceae suivit de Anacardiaceae ont dominé l’echantillon. Les espèces forestières naturelles sont donc en mesure de s’établir dans un peuplement d'acacia noir. L’échantillon qui a servi à l’évaluation des sources de semences pour le développement des recouvrements de forêt naturelle à travers l’investigation de la relation entre les recouvrements de forêt naturels qui s’établissent à l’intérieur du peuplement d’acacia noir et les parcelles de forêt avoisinantes humide, sèche et marécageuse était constitué de 55 placettes rectangulaires de 200m2 le long de layons à travers le site d’étude. Une analyse hiérarchique des recouvrements réalisée sur la composition des espèces de l’échantillon a révèle que la forêt marécageuse concentre les espèces les plus fréquentes des recouvrements de forêts, et que la majorité des espèces présentes sur les parcelles des forêts sèches et humides étaient absente dans l’ensemble des recouvrements des forêts de l’acaci noir. Les trois principaux types de forêts différaient dans leurs caractéristiques générales et les conditions du site, et cela a été appuyé par l’analyse d’ordinants à partir de trois facteurs environnementaux, la pente, l’angle d’inclinaison par rapport au soleil, et la fermeture de la canopée. Les recouvrements de foret en développement au sein de l'acacia noir se sont trouvés davantage liés à la forêt marécageuse en termes de pente plate orientée sud-ouest et en diamètre moyen des arbres. Ces résultats ont désigné la forêt marécageuse comme la première source potentielle de semences permettant l’établissement des recouvrements de forêt à l’intérieur des peuplements d’acacia noir. Cependant, les souches d’arbres de grande taille des espèces communes entre les parcelles de forêts marécageuses et les recouvrements de forêt dans l’acaci noir n'étaient pas significativement différents, suggérant ainsi que ces arbres de grande taille trouves dans les recouvrements de foret pourraient faire parties des parcelles de forêt subsistantes de la dernière turbulence. Elles pourraient constituer des sources locales de semences. Par ailleurs, une évaluation détaillée des valeurs d'importance des espèces et des distributions des diamètres des souches d’arbres a montré que certaines espèces importantes de forêts humides et sèches sont présentes dans les recouvrements de foret. Finalement l’on conclue que chaque type de parcelles de forêt contribue plus ou moins à l’établissement des recouvrements de forêt dans le peuplement de l'acacia noir. Sept grands recouvrements de foret ont été sélectionnés pour étudier la régénération des espèces forestières naturelles sur un rayon de 18 m depuis la limite du recouvrement de foret. Deux listes d'espèces ont été générées, l'une des espèces de parcelles de forêt naturelle adjacentes, et une autre venant des 59 recouvrements de foret, toutes tailles confondues le long de l'acacia noir. Les résultats ont indiqué que (1) Les recouvrements de forêts, lorsque bien matures et bien établies devenaient les principales sources de semences pour leur expansion sur toutes les directions; (2) Trois allures différentes ont été observées en fonction de la distance de l'expansion de la régénération autour des recouvrements: une diminution de la régénération avec l'augmentation de la distance; une croissance de la régénération avec une distance croissante depuis les revcouvrements de foret, et pas d’allure particulaire voire une absence de régénération de certaines especes pourtant dominant dans les recouvrements de foret. Les 40 espèces recensées sur le site deBuffeljagsrivier comprennent un large éventail de caractéristiques de fruits et de graines. Quatre principaux groupes d'espèces ligneuses ont été identifiées, en fonction de leur présence / absence dans des parcelles de forêt et les recouvrements de forêt. De façon générale, la présence / absence de la plupart des espèces a pu être expliquée en termes de caractéristiques de leur fruits/graines et les mécanismes de dispersion. La majorité des espèces ligneuses enregistrées sont susceptibles d’être dispersées par les oiseaux et les mammifères, en particulier les pigeons rameron et les babouins vues sur le terrain. En conclusion, un cadre conceptuel a été élaboré pour guider la réhabilitation de peuplements envahissants de lumière en milieu forestier. Plusieurs sujets pour des recherches plus poussées ont été identifiés.