Dans un contexte de destruction des zones humides à l’échelle mondiale, conséquence des activités d’origine anthropique, la restauration écologique de ces milieux et de leurs fonctions est devenue un enjeu écologique et sociétal. L’objectif de ce projet est de recréer des prairies humides à vocation agricole aux caractéristiques pédologiques et floristiques aussi proches que possible de celles des prairies totalement détruites par l’exploitation de matériaux alluvionnaires. L’étude présentée ici se focalise sur l’incidence des matériaux pédologiques utilisés pour la recréation de quatre sols sur les fonctions du sol et les cortèges floristiques associés. L’hypothèse principale est que la recréation d’un sol morphologiquement proche de celui détruit devrait permettre d’orienter la restauration écologique.L’hypothèse sous-jacente est qu’en utilisant différents matériaux pédologiques locaux, on hérite de leurs caractéristiques physico-chimiques et biologiques ce qui permettait de conserver les fonctions pédologiques qui leur sont associées et favorisait le retour d’un cortège floristique compatible avec un usage agricole. La première partie est consacrée à l’étude de deux fonctions remplies par les sols de zones humides à savoir le stockage du carbone organique et la dénitrification. Deux années et demi après la fin des travaux de comblement de ballastières, ces deux fonctions sont conservées au sein des quatre types de sols recréés. Les principaux résultats montrent un niveau d’efficience des matériaux pédologiques testés, fonction de leur sol origine et de leurs caractéristiques physico-chimiques. La deuxième partie est consacrée à l’étude des mécanismes de structuration des communautés végétales. Le suivi de la colonisation spontanée de la végétation a permis d’appréhender la forte contribution de la banque de graines issue des matériaux pédologiques locaux. Malgré la mise en évidence d’un début de trajectoires dynamiques au sein des quatre sols recréés, la similarité entre les communautés obtenues et les communautés cibles des prairies de référence n’excède pas 50 %. Les productions de biomasses aériennes associées à ces communautés sont comparables en quantité à celles des prairies de référence mais pas en qualité. La mise en place d’une gestion par semis associée à une fauche montre dès la première année une production de biomasses de qualité se rapprochant de celles des prairies locales.La dernière partie de ce manuscrit est consacrée à l’effet de trois niveaux d’engorgement des sols sur le processus de dénitrification et sur les traits de réponse d’une espèce prairiale, Holcus lanatus. Placer les quatre matériaux pédologiques dans des conditions identiques d’engorgement permet de souligner l’importance de l’héritage des communautés bactériennes dénitrifiantes sur le processus de dénitrification. Parallèlement, ces conditions expérimentales permettent de mettre en évidence les traits de réponses morphologiques et fonctionnels de l’espèce considérée. À l’issue de ces suivis, le meilleur compromis de restauration alliant sol, végétation et coûts économiques doit prendre en considération l’origine et l’histoire (i.e. gestion) des matériaux utilisés lors de la recréation écologique. / In a worldwide context of wetland destruction, a consequence of anthropic activities, ecological restoration of such habitats and their functions has become a societal and ecological issue. The objective of this project is to recreate agriculture-oriented wet grasslands with pedological and floristical properties as similar as possible to typical grasslands destroyed by alluvial materials extraction. The study presented here focuses on the impact of pedological materials, used in the re-creation of four soils, on soil functions and associated floristic processions. The main hypothesis is that re-creation of a soil morphologically similar to the previously destroyed one should drive ecological restoration. The underlying hypothesis is that different local pedological materials inherit their previous physicochemical and biological properties. This should conserve associated pedological functions and favor the return of a floristic procession compatible with agricultural exploitation. The first part is dedicated to the study of carbon storage and denitrification, two wetlands soils functions. These two functions are retained within the four re-created soils two and a half year after gravel-pit filling. Main results highlight functional efficiency levels of tested pedological material inherited from their respective initial topsoil physico-chemical properties. The second part is devoted to the study of mechanisms structuring plant communities. The high contribution of local pedological materials seed bank during the colonization process and its impact on aforementioned mechanisms was highlighted from our monitoring. Despite demonstration of the start of a dynamic trajectory in the four created soils similarity between obtained and target communities never exceeds 50%. Aerial biomass production associated to these communities is comparable to the production in reference wet grasslands in terms of quantity, but not quality. Implementation of management (sowing and mowing) shows biomass production of comparable quality to reference grassland from the first year onwards. The last part focuses on the effect of three soil waterlogging levels on the denitrification process and the response traits of Holcus lanatus, a meadow species. Pedological materials placement in identical waterlogging conditions highlights the importance of denitrifying bacteria communities inheritance on the denitrification process. These experimental conditions also enabled us to highlight the considered species morphological and functional response traits. To conclude and following our monitoring the best compromise for concurrent restoration of soil and vegetation while considering cost-effectiveness needs to account for topsoils origin and history (i.e. management).

(Cartografia morfopedológica e de ocupação das terras como subsídio à avaliação ecológica: o caso dos campos de planalto em Itararé, SP). Duas abordagens cartográficas pouco utilizadas no Brasil, morfopedológica e de ocupação das terras, foram aplicadas como parte de um projeto de análise florística, fitogeográfica, ecológica e de conservação dos remanescentes de campos de planalto, na porção sul do município de Itararé, São Paulo (escala 1:50.000). As duas abordagens traduzem em termos ecológicos a paisagem. A carta morfopedológica mapeia unidades cuja evolução, estrutura e problemática sejam correlacionadas, correspondendo a interações específicas entre o material, o modelado, a morfogênese e a pedogênese sob condições climáticas precisas; a carta de ocupação das terras mapeia uma combinação entre as formações vegetais e a influência humana em um território. Ambas as abordagens têm um potencial pouco explorado na gestão da paisagem e no ordenamento territorial no Brasil. (Análise florística e fitogeográfica dos campos de Itararé, São Paulo). A região de Itararé, no sudoeste do estado de São Paulo, junto à divisa do estado do Paraná, possui uma considerável diversidade climática, geológica, pedológica, florística e paisagística, onde ainda podem ser encontrados remanescentes significativos e bem preservados de campos de planalto, uma formação singular e pouco conhecida no estado de São Paulo. Como um primeiro passo para estudar a ecologia dos campos de planalto de Itararé e subsidiar um plano para sua conservação, a flora dos campos foi analisada. Um intensivo levantamento possibilitou a preparação de uma lista florística com 1.000 espécies em 120 famílias, dentre as quais 23 espécies são novas ocorrências para o estado de São Paulo, 71 são consideradas espécies vulneráveis e 22 em perigo, segundo a lista de plantas ameaçadas do estado de São Paulo. As oito famílias que mais contribuem para a riqueza de espécies são: Asteraceae (17,8 %); Poaceae (9,7 %); Fabaceae (7,0 %); Myrtaceae (4,1 %); Cyperaceae (3,9 %); Melastomataceae (3,9 %); Rubiaceae (3,2 %) e Apocynaceae (2,9 %). Uma análise de agrupamento foi efetuda para avaliar o posicionamento fitogeográfico dos campos de planalto de Itararé entre 47 listas florísticas disponíveis para localidades das regiões Sul e Sudeste e dos estados da Bahia, Goiás e Distrito Federal. Uma análise de correspondência canônica indicou as variáveis isotermalidade, sazonalidade térmica e precipitação do mês mais úmido como as mais correlacionadas com a distribuição das espécies dos campos. (Estrutura dos campos e suas relações com o ambiente em Itararé, SP). A estrutura ecológica dos campos na região sul de Itararé, sudoeste do estado de São Paulo, Brasil, foi estudada em uma área de 32.697 ha. Esses fragmentos de campo ainda estão relativamente preservados. O objetivo deste trabalho é diferenciar os tipos de campos existentes na região de Itararé e caracterizar suas relações com variáveis ecológicas. Foi empregada a estratégia de amostragem estratificada aleatória. O critério de estratificação da paisagem foi produzido por meio da interseção do mapa morfopedológico com zonas de influência microclimáticas. A composição florística e sua abundância/cobertura, junto com descritores sobre o meio físico e a estrutura da vegetação, foram obtidos em 115 levantamentos distribuídos pelas unidades de amostragem. Através da aplicação de métodos de estatística multivariada (análise de agrupamentos, de espécies indicadoras e ordenações) foram identificados 4 tipos de campos com suas respectivas espécies indicadoras. O gradiente mais importante presente na matriz de dados está relacionado com o fator umidade. / Two cartographic approaches little used in Brazil, morphopedologic and land occupation, have been applied as part of a project to analyze the flora, phytogeography, ecology and conservation of grassland fragments of the southern portion of the Itararé county in São Paulo State. Both approaches translate the landscape in ecological terms. The morphopedologic theme maps units whose evolution, structure and problematic are correlated, corresponding to specific interactions between the material, the relief, morphogenesis and pedogenesis under precise climatic conditions. The land occupation theme maps the combination between the plant formations and the human influence in a territory. Both approaches have a potential little explored in landscape management and in land zoning in Brazil. ¶ (Floristic and phytogeography of the grasslands of Itararé, São Paulo). The region of Itararé, in southwestern of São Paulo state, at the border with the state of the Paraná, has a considerable climatic, geologic, pedologic, floristic and landscape diversity, where it\'s possible to find significative and well preserved grassland fragments, a singular and little known vegetation type in state of São Paulo. As a first step to study the ecology of the Itararé grasslands and to underpin a conservation plan, the flora of the fields was analyzed. An intensive survey made possible to prepare a floristic list with 1.000 species in 120 families, amongst them 23 new records for the State of São Paulo, 71 vulnerable and 22 endangered species according the Red List of São Paulo State. The eight families with major contributions to the species richness are: Asteraceae (17,8 %); Poaceae (9,7 %); Fabaceae (7,0 %); Myrtaceae (4,1 %); Cyperaceae (3,9 %); Melastomataceae (3,9 %); Rubiaceae (3,2 %) and Apocynaceae (2,9 %). A cluster analysis was performed to evaluate the phytogeographic position of the Itararé grasslands among 47 floristic lists available for South and Southeastern Brazil, as well for the states of Bahia, Goiás and Federal District. A canonical correspondence analysis indicated the climatic variables isothermality, temperature seasonality and precipitation of wettest month as the most correlated with species distribution of grasslands.¶ (Grasslands structure and relations with environment in Itararé, SP). The ecological structure of the grassland in the South region of Itararé, located in southwest of São Paulo state, Brazil, was studied over an area of 32.697 ha. These grassland fragments are still relatively well preserved. The goal of this paper is to distinguish the types of grassland present in the Itararé region and to characterize their relationship with ecological variables. A stratified random sampling strategy was used and the landscape stratification criterion was produced by an intersection of the morphopedologic map with a microclimatic zones layer. Species composition and cover/abundance, together with structural and abiotic parameters were recorded in 115 relevés distributed throughout the sampling units. By the application of multivariate statistical analysis methods - such as cluster analysis, indicator species analyses, and ordination techniques - four grasslands vegetation types were identified with its diagnostic species. The most important ecological gradient present in the data matrix is related with humidity.

Indivíduos, populações e espécies tendem a usar e selecionar habitats de modo não-aleatório. Consequentemente, a perda e a degradação de habitats geram impactos distintos sobre os organismos dependendo de seus atributos. Os efeitos da perda de habitat são claros – os organismos são eliminados ou desalojados por falta de habitat ou baixo sucesso reprodutivo. As consequências da degradação de habitat são mais sutis, e resultam na incapacidade de um ecossistema sustentar determinadas espécies. Como a perda e a degradação de habitat reduzem a disponibilidade de nichos, espera-se que táxons ecologicamente especializados e com requerimentos estreitos de nicho sejam mais propensos à extinção que generalistas. Organismos que são negativamente afetados por perda e degradação de habitat em geral exibem porte muito grande ou muito pequeno, baixa mobilidade, baixa fecundidade, reduzido recrutamento e estreitos requerimentos de nicho. Campos temperados constituem ambientes particularmente afetados por perda e degradação de habitat. No sudeste da América do Sul, como em muitas outras regiões do planeta, a expansão da agricultura e silvicultura são os principais responsáveis pela perda de habitat campestre. Os remanescentes de vegetação natural são usados para criação de gado, estando sujeitos à degradação pelo sobrepastejo, pisoteio e técnicas de manejo. Avaliar como a perda e degradação de habitat afetam a diversidade de organismos campestres é vital para o desenvolvimento de estratégias de conservação e manejo. A presente tese tem por objetivo investigar como a degradação e perda de habitat induzidas pela pecuária e silvicultura afetam a diversidade e a composição das comunidades de aves. Inicialmente, exploramos as relações entre variáveis de habitat e a composição da comunidade de aves num gradiente de altura da vegetação determinado por pastejo em campos litorâneos do Rio Grande do Sul. Posteriormente, avaliamos como variações no relevo interagem com variáveis de habitat e afetam a diversidade de aves em áreas de pecuária na Campanha gaúcha. Finalmente, avaliamos de que forma a perda de habitat resultante do estabelecimento de plantações industriais de celulose em áreas de campo afeta a composição de comunidades de aves campestres. Nossos resultados demonstram que a degradação de habitat decorrente do manejo de gado em campo nativo afeta a comunidade de aves de forma diferencial. Aves adaptadas a campos ralos ou generalistas tendem a ser beneficiadas pelo pastejo, ao passo que as espécies associadas à vegetação alta e densa são desfavorecidas. As variações na topografia reduzem os impactos da degradação de habitat nos campos. Essas variações interagem com o habitat e afetam de forma diferencial os distintos componentes da diversidade. Por outro lado, a perda de habitat decorrente da silvicultura gera um impacto de maior magnitude, alterando a composição das comunidades de aves e favorecendo aves não-campestres. Nesse contexto, impedir que novas áreas de campo nativo sejam convertidas em plantações de árvores passa a ser imperativo. Embora o manejo do gado aumente a diversidade em nível de paisagem ao criar um mosaico de manchas de vegetação de alturas distintas, maior atenção deve ser dada à manutenção e recuperação de formações densas de herbáceas de grande porte. Isso somente pode ser assegurado através de mudanças no regime do pastejo ou do desenvolvimento de técnicas de manejo alternativas. / Individuals, populations and species tend to select habitats in a non-random way. Consequently, habitat loss and degradation will have different impacts on organisms according to their traits. The effects of habitat loss are straightforward – organisms are eliminated or displaced because of the inexistence of adequate habitat or of low breeding success. Effects of habitat degradation are more subtle and result in the reduction of the capacity of an ecosystem to support some subsets of species. Since habitat loss and degradation reduce niche availability, ecologically specialized taxa with narrow niche requirements are expected to be more extinction prone than habitat generalists. Temperate grasslands have been strongly impacted by habitat loss and degradation. In southeastern South America, the expansion of agriculture and industrial pulpwood plantations are the main sources of habitat loss. Remnants of natural grassland vegetation are used for livestock ranching, being subject to habitat degradation from overgrazing, trampling and inadequate management techniques. The evaluation of how habitat loss and degradation affect the diversity of grassland organisms is vital for the development of management and conservation techniques. The main goal of this thesis is to evaluate how habitat degradation and loss related to cattle ranching and pulpwood plantations affect the diversity and composition of bird communities. We began by exploring the relationship between habitat variables and the composition of the bird community along a gradient of vegetation height determined by grazing in coastal grasslands of the state of Rio Grande do Sul. We then assessed how variations in the relief interact with habitat variables e affect the diversity of birds in rangelands of the Campanha gaúcha. Finally, we evaluated how habitat loss related with grassland afforestation for pulpwood plantations affects the composition of grassland bird communities. Our results demonstrate that habitat degradation resulting from livestock ranching in natural grasslands affects bird communities in a differential way. Birds adapted to stunted grasslands or habitat generalists tend to benefit from grazing, whereas tall-grass specialists are negatively affected. Variations in topography are responsible for reducing the impacts of habitat degradation in grasslands. These variations interact with habitat and have a differential effect on distinct components of diversity. On the other hand, the magnitude of the impact of habitat loss from afforestation is larger, altering the composition of bird communities and favoring a series of non-grassland species. In this sense, protecting remaining grasslands from afforestation is imperative. Although cattle ranching increases diversity at the landscape level by creating a mosaic of vegetation patches of different height, more attention should be given in maintaining and recovering dense formations of tall grassland plants. This can only be achieved by changing grazing regimes or developing alternative management techniques.

The study undertaken was carried out in the montane tussock grassland region which in the South Island comprises some six million acres. Field trials were established at Mt Somers, Mid Canterbury. This study attempts to elucidate some of the factors connected with the sulphur nutrition of grasses. For the particular trial area it was hoped to determine four key aspects ; 1. Whether the response of the grass to nitrogen is governed by the sulphur level available. 2. A determination of what level of nitrogen was likely to be provided by clover fixation and transferred to the grass component under improved grassland conditions in the area. 3. What the optimum level of sulphur for the association is, allowing adequate sulphur for maximum possible nitrogen fixation as well as for utilization by the grass of the nitrogen transferred. 4. The effects of nitrogen and sulphur on plant chemical composition and any possible relationships between plant and soil as infuenced by these factors. Following a review of literature, a summary of experimental work is presented, with results, discussion and conclusions.

Social dilemmas constitute a broad class of quandaries, including, for example, common pool resource (CPR) dilemmas and public good (PG) dilemmas. CPR's are characterized by non-excludability and rivalry and are often associated with overexploitation. Through similar arguments, the features non-excludability and non-rivalry give rise to under-provision of PG's. The prevalence and inefficiencies often associated with CPR's have given rise to an extensive literature and the role of resource uncertainty has not been ignored. Uncertainty combined with rivalry is often said to augment users' incentive to overexploit. However, underlying most of the theoretical research is an explicit or implicit assumption of symmetric information, or a symmetric lack of information. In reality, people generally have access to different sources of information and they may differ in their abilities to process information. In the first two papers of this thesis, the assumption of symmetry is relaxed and both papers demonstrate that from a welfare perspective, the distribution of uncertainty is also of importance. Many CPR's and PG's are natural, which can complicate the situation. In the traditional resource management literature, the exploited resource is often assumed to be properly characterized by some concave growth function. Today, there is extensive empirical evidence suggesting that many ecosystems have more complex, often non-linear dynamics. Management of such resources can be quite challenging as the non-linear dynamics can make the ecosystem flip between alternate stable states, and even marginal changes can cause radical transformations of such ecosystems. Most of the CPR models assume the shared resource to be of fixed size or to be able to generate a constant flow of services. In the third paper we aim at providing a more complete picture of the overexploitation of a common resource, by combining the institutional structure with complex ecological dynamics. We manage to raise questions and doubts about the standard assumptions. Another feature of convex-concave resources is that a state can become highly robust and sometimes an ecosystem change may even be irreversible. This is problematic if, for example, we wish to restore a degraded ecosystem. The aim of the fourth paper is to empirically analyze this question, by eliciting peoples' preferences through a hypothetical referendum on the issue. / Diss. Stockholm : Handelshögskolan, 2005

Invasive exotic species threaten biodiversity and ecosystem functions globally, creating need for and encumbering ecological restoration. When restoring exotic plant-dominated ecosystems, reinvasion pressure is the rate of new exotic recruitment following mature exotic removal. It can vary broadly among similarly invaded habitats and is crucial to restoration outcomes and costs, but is difficult to predict and poorly understood. Initial results from the experimental restoration of a wetland dominated by Triadica sebifera led us to develop the ‘outgrow the stress’ hypothesis. It holds: (1) Variation in reinvasion pressure is driven by differences in propagule abundance and spatiotemporal availability of realized recruitment windows, which are defined by abiotic conditions and biotic interactions. (2) Differences in reinvasion pressure become masked by exotic dominance when increases in niche breadth during development enable exotic persistence across sites where recruitment windows range from frequent to episodic. We validated this hypothesis. First, we used greenhouse and field experiments to quantify Triadica’s moisture niche early in development. By two months post-germination, seedling tolerances broadened to include conditions unsuitable for germination. This clearly demonstrated a rapid ontogenetic niche expansion, which could decouple mature Triadica density and average reinvasion pressure. Second, we used a greenhouse mesocosm experiment to quantify how recruitment window duration, competition and fertility impacted population-level Triadica establishment in stressful environments. As ‘outgrow the stress’ predicts, longer windows increased Triadica success and multi-factor interactions were common, with competition and fertility effects varying among environmental contexts. Third, we substantiated predictions of ‘outgrow the stress’ regarding propagule availability and soil moisture by manipulating these in a multi-site field experiment spanning eleven experimental restorations of Triadica-dominated habitats along a moisture gradient. Triadica reinvasion pressure varied broadly among sites but correlated with moisture and fertility. Propagule availability drove reinvasion in favorable environments, but availability of suitable conditions trumped propagules in extreme environments. Competition reduced Triadica performance and sometimes survival. Triadica prevalence reduced native plant prevalence. Six restorations require minimal Triadica management for success. This work advances our understanding and enables better predictions of reinvasion pressure and invasions in general. Accurate predictions enhance restoration efficiency by informing site selection and optimal management strategies.

Disputats. Rheinische Friedrick-Wilhelms-Universität, 2001. / Haves kun i elektronisk udg.

No description available.

Global environmental changes, especially land-use changes, have profound effects on both ecosystem functioning and biodiversity, having already altered many ecosystem services. These losses emphasize the need to preserve what remains; however when conservation programs are not sufficient, restoring areas that have been destroyed or disturbed can improve conservation efforts and mitigate damages. This work focuses on campos rupestres, Neotropical grasslands found at altitudes, which are part of the Cerrado (Brazilian savannas). They host a great biodiversity with a high level of endemism and, like other mountain ecosystems, provide valuable ecosystem services, such as water purification and recreational services. They have been and still are being impacted by human activities, such as civil engineering construction, quarrying or mining. The first objective of this thesis was to describe the reference ecosystem in order to aim for a clear restoration target and to monitor progress and success. We show that campos rupestres are composed of at least two distinct plant communities (i.e. sandy and stony grasslands), each having a specific composition and structure, hosting a great biodiversity. Several phenological patterns occur among the herbaceous communities: the majority of species flowers and fruits appear during the rainy season but other patterns can be observed. During our 2-year survey, some dominant species belonging to Poaceae, among others, were not observed reproducing, which implies limited chances to disperse on degraded areas. Campo rupestre vegetation is not resilient following a strong disturbance: several years after the disturbance, almost no native species are encountered on the degraded areas, soils are completely altered and seed bank recomposes only with non-target ruderal species. According to the filter model, a local community is a subset of the regional species pool determined by a set of dispersal, abiotic and biotic filters. Acting on the different filters to influence the plant community was the core of our restoration interventions. We then applied three in-situ restoration protocols (hay transfer, species translocation and turf translocation) to restore both kinds of grassland. Hay transfer does not allow the restoration of campo rupestre vegetation because of soil alteration and mainly because of poor seed quality. Indeed, germination studies show that, while some Xyridaceae and Velloziaceae have a high germinability, some dominant Poaceae, Cyperaceae or Asteraceae species have embryoless, unviable or dormant seeds, which makes seeding less efficient. There is no evidence that fire-related cues enhance germination in campos rupestres. Species translocation is successful for only one species, Paspalum erianthum; for the others, root damages probably impede survival. Finally, turf translocation is the most successful method, since numerous species are re-introduced on degraded areas. However due to the low resilience of pristine campos rupestres where turfs are taken from, turf translocation can only be considered in the case of habitat rescue, in circumstances when complete habitat destruction is otherwise unavoidable. Face to the difficulty to restore these peculiar grasslands, the protection and the conservation of campos rupestres must be made a high priority

The effects of fire and mechanical clearing were investigated for their potential in assisting with the eradication of Chromolaena odorata (previously Eupatorium odoratum). The study was divided into two focus areas, the first focused on mechanical clearing of dense stands of C. odorata on three sites and the second focused on the long term influences of a single burn on C. odorata plants in the different size categories. For mechanical clearing, two key issues were investigated; namely whether this type of clearing procedure was effective in dense C. odorata stands and whether rehabilitation was necessary in these cleared areas. The study was conducted from July 2002 to June 2004. The area was subject to a severe drought throughout the duration of the study. The severe drought had a large influence on the result in both focus areas. A bulldozer was found to be a very effective at clearing dense C. odorata stands. Results from the mechanical clearing study showed that there was still a large viable grass seed population in the areas that had been covered by a dense stand of C. odorata plants for over three years. Thus, indigenous plants were able to re-colonize the area after removal of C. odorata without human intervention, even thought the area was experiencing a severe drought. The density of C. odorata seedlings emerging in the cleared areas was far lower than expected. The C. odorata density in the permanent plots, for seedlings that germinated in the first season after clearing (SeptemberOctober 2002), was only 0.25,0.03 and 0.72 per 5 m2 in the three sites respectively by the end of the study in June 2004. For the C. odorata seedlings that germinated in the second season (September-October 2003) the density was, 0.5, 0.56 and 1.06 per 5 m2 in the three sites respectively by the end of the study in June 2004. It was suspected that the drought influenced seed germination. Unfortunately the number of C. odorata seedlings was so low, that no significant relationship could be found between grass and C. odorata seedling density. By the end of the study the grass fuel mass in all the rehabilitated sites was already over 3000 kg ha-1, even though the area was experiencing a severe drought. This grass fuel load, when burnt, will assist land managers in controlling C. odorata plants, especially seedlings. Very few other alien invasive plant species emerged in the cleared areas. At the Mhlosinga site, Senna pendula made up less than one percent of the herbaceous species composition and only a single Ricinus communis plant was recorded. No alien plant species were recorded on the other two sites. Results from the burning trials revealed that plants in all the size categories were affected by fire. Greater fuel masses and fire intensities were required to kill larger C. odorata plants relative to smaller ones. Fire was found to be very effective at eliminating small and medium size C. odorata plants. Fire applied as a once off treatment had a significant long-term effect on the C. odorata population. The following fuel loads were required to achieve 80% mortality in this 11 study: for small plants a fuel load of over 4000 kg ha-I, for medium plants a fuel load over 4200 kg ha-I and for large plants a fuel load over 4600 kg ha-I. Little difference could be detected between a head or a back burn, as both fire types had their own advantages and disadvantages. Although some of the C. odorata plants in the burnt plots had not perished by the time of the first investigation, following the burn (February 2003), by the time of the second investigation (June 2004), many of these plants had eventually succumbed. These results highlighted the fact that plants which are damaged by fire were more likely to persish during an extended droughts period, than plants which were not subjected to fire. Results from the control plots, in the burning trials, for medium and large plants showed dramatic increases in density over time. Tagged individuals from the control plots did reveal that some of the medium and large plants did die during the drought, although the amount was negligible when compared to the number of new plants growing into the new size categories. A large proportion of the small plants in the control plots also survived the drought with many of them even growing into the medium category. The difference between the control plots and the burnt plots was obvious and significant, especially once the fuel mass exceeded 3783 kg ha-I. Results from this study show that fire can be used as a very effective tool in assisting land managers to control C. odorata in open savanna bushveld. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.