The vegetation of the Sydney Basin, Australia, is highly flammable and subject to a wide range of fire regimes. Sclerophyllous shrubs and sedges are common and in some vegetation types up to 70 % of fuel consumed during a fire can be live. Research into fire behaviour and fuel dynamics has been minimal. To address this issue this thesis investigated the principal factor affecting the ease of ignition and rate of combustion of individual fuel particles and fuel beds in bushfires: dead fine fuel moisture (FFM). Two common Sydney Basin vegetation types, eucalypt woodland and heathland, each with a history of problematic fire management, were measured in the field for diurnal fluctuations in FFM following rain, under conditions similar to when prescribed burns are conducted. The FFM components of current operational fire behaviour models were found to be inadequate for predictions of FFM and fire behaviour under these conditions. The equilibrium moisture content (EMC) of five fuel types from the field site was investigated in a laboratory study. An existing function describing EMC as a function of temperature and relative humidity was evaluated and found to be very accurate for these fuels. Two FFM predictive models incorporating this function were evaluated on the field data and the laboratory results were shown to be applicable to the estimation of FFM in the field. One model gave very accurate predictions of FFM below fibre saturation point, but its accuracy was reduced when screen level conditions were used instead of those measured at fuel level. A recent process-based model that accounts for rainfall showed promise for predicting when fuel is < 25 % FFM. Systematic problems with the radiation budget of this model reduced the accuracy of predictions and further refinement is required. Live fine fuel moisture content (LFMC) of common heathland shrubs and sedge was investigated over two years and found to be both seasonal and influenced by phenology. LFMC minima occurred in late winter and spring (August to October), and maxima were in summer (December to February) when new growth was recorded. The dominant near-surface fuel in mature heath was sedge. It was found to have little seasonal variation in its??? percentage dead but the percentage dead maxima occured at the same time as the LFMC minima of shrubs and sedge in both years. Simple instantaneous models for duff moisture content in woodland and heathland and LFMC and the percentage dead sedge in heathland were developed. The information gained by this study will form the basis for future development of fuel moisture models for prescribed burning guidelines and fire spread models specific to the vegetation communities of the Sydney Basin.

Seeds of seven alpine and subalpine Australian shrub species (Acacia alpina,A. obliquinervia, Bossiaea foliosa, Hovea montana, Oxylobium ellipticum,Grevillea australis & Pimelea ligustrina) with potential to colonise in badly disturbed alpine and subalpine sites had a range of treatments (scarification,stratification, leaching, chemical soaks, freezing & diurnally fluctuating temperatures) applied to them to enhance germination success. Seeds of the hard seeded legumes responded well to scarification and stratification treatments. Acacia obliquinervia was scarified with boiling water which resulted in enhanced germination success. The scarification treatment with the best result was nicking for the other four legumes. The use of hot-watersoaks for these other legumes, of a minute or less showed some potential as a useful scarification treatment Stratification periods between 8 to 14 weeks for Acacia alpina, 12 to 14 weeks for Bossiaea foliosa, 2 to 8 weeks for Hoveamontana and 4 to 6 weeks for Oxylobium ellipticum gave significantly enhanced germination. Grevillea australis did not respond to germinationpre-treatments, except for an isolated case of nicking and stratification for 6weeks. The same treatment of older seed did not result in significantgermination. Pimelea ligustrina did not reliably respond to germination pretreatments.Germination trial results were then applied to one of the legumespeCIes (Bossiaea foliosa) as a guide to how these seeds respond to apretreatment before sowing on a disturbed site at the Bogong High Plains.The treatment of 30s in water @ l00°C and 14 weeks stratification before sowing in autumn was found to significantly enhance the field establishment success of Bossiaea foliosa.

Thesis (M. Sc.)--University of Alberta, 1990. / Submitted to the Faculty of Graduate Studies and Research in partial fulfilment of the requirements for the degree of Master of Science, Department of Botany. Includes bibliographical references. Available also in electronic format on the Internet.

Thesis (Ph. D.)--Oregon State University, . / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.Sc. (Environmental Science)) - Rhodes University, 2009.

Neste trabalho, avaliamos como arbustos pioneiros regulam comunidades lenhosas em uma restinga subtropical. Arbustos têm grande capacidade de modificar ecossistemas, pois alteram o fluxo de nutrientes e água do solo, aprisionam sementes transportadas por água ou vento sob suas copas, e oferecem recursos a dispersores. A combinação desses processos leva ao surgimento de ilhas de fertilidade em áreas de vegetação herbácea, aumentando a diversidade local. Interações biológicas são fatores determinantes na coexistência de espécies nessas ilhas arbustivas. Portanto, utilizamos atributos vegetativos de arbustos e distância filogenética média (MPD) entre as espécies para avaliar como a riqueza, a abundância e a diversidade (i.e. Entropia Quadrática de Rao, EQR) são reguladas em moitas de restinga. Também comparamos esses mesmos parâmetros nas áreas de vegetação predominantemente herbácea circundantes às ilhas arbustivas. A fim de entender a estruturação filogenética nesse ambiente, calculamos o net relatedness index (NRI) de cada moita. Nossos dados reforçam a importância de arbustos pioneiros sobre a vegetação de áreas predominantemente campestres devido à sua capacidade de modificar o micro-habitat sob suas copas e pelas interações com espécies que colonizam as ilhas arbustivas. / In this work we tested how pioneer shrubs regulate community structure in woody islands of a subtropical sand-dune (restinga) environment. Shrubby species show a great ability to modify ecosystems, since they change the flux of nutrients and water in the soil, they retain under their crowns seeds carried by water or wind, and the seeds in turn attract new dispersers. The combination of these processes leads to the formation of fertility islands in areas with herbaceous vegetation, increasing the local diversity. Biological interactions are determinant factors in the coexistence of species in these shrubby islands. So we used vegetative traits of shrubs and mean phylogenetic distance (MPD) between species to evaluate how richness, abundance and diversity, i.e., Rao‟s quadratic entropy (RQE), are regulated in sand-dune woody islands. We also evaluated the same parameters in the surrounding areas with predominantly herbaceous vegetation. In order to understand the phylogenetic structuring in this environment we estimated the net relatedness index (NRI) in each woody thicket. Our data reinforce the importance of pioneer shrubs in a matrix of the predominantly open grassland vegetation because of their ability to modify the microhabitat under their crowns and their interactions with other species which colonize the shrubby islands.

A alelopatia, na qual uma espécie causa efeitos negativos sobre outra através da liberação de substâncias químicas, é um fenômeno que pode afetar comunidades vegetais. Em alguns casos, o estabelecimento de arbustos aromáticos em formações densas, com apenas poucas espécies ocorrendo em suas proximidades, é um padrão que tem sido relacionado aos efeitos fitotóxicos dos voláteis que os mesmos liberam. Em campos dos sul do Brasil, esse padrão de estabelecimento frequentemente ocorre para as espécies arbustivas aromáticas Heterothalamus psiadioides Less e Baccharis patens Baker, indicando a possibilidade de alelopatia. Dessa forma, o presente estudo teve como objetivo determinar se H. psiadioides e B. patens são fitotóxicas e se isso implica em efeitos negativos sobre a comunidade vegetal na qual os arbustos ocorrem. Em ensaios em laboratório, os efeitos dos voláteis liberados diretamente das folhas frescas e secas de H. psiadioides e B. patens foram testados sobre a germinação e o crescimento das plantas-alvo alface e cebola nas quatro estações do ano. Em um estudo em campo, foram avaliadas cobertura e biomassa vegetal, número de mudas, diversidade, riqueza, e variáveis de estrutura da vegetação no entorno de ambas as espécies arbustivas e onde não havia arbustos. Nos bioensaios, os voláteis de H. psiadioides e B. patens causaram inibição na porcentagem e velocidade de germinação e redução no tamanho da raiz e da parte aérea das plantas-alvo, sendo que folhas frescas apresentaram maior fitotoxidez. Esses parâmetros foram mais afetados por H. psiadioides que por B. patens em todas as estações, e os efeitos de ambas foram menores no verão. Em relação à investigação em campo, que objetivou avaliar os efeitos da espécie muito fitotóxica H. psiadioides sobre a comunidade vegetal, não foram observadas evidências de alelopatia. Houve maior riqueza e diversidade próximo a H. psiadioides, devido à menor cobertura de gramíneas dominantes. Variáveis de estrutura da vegetação e intensidade de luz explicaram os padrões observados de forma mais conclusiva que alelopatia. Esse estudo sugere que o potencial alelopático de plantas pode ser superestimado em bioensaios e que estudos em campo são necessários para demonstrar se efeitos alelopáticos são realmente relevantes em comunidades vegetais. Ainda, o trabalho ressalta a importância de conduzir estudos mais realistas em laboratório e de utilizar controles em estudos em campo. / Allelopathy, in which a species causes negative effects on another through the release of chemical substances, is a phenomenon that may affect plant communities. In some cases, the establishment of aromatic shrubs in dense stands, with few other species occurring in their surroundings, has been related to the phytotoxic effects of volatiles released by these shrubs. In South Brazilian grasslands, this pattern of establishment often occurs for the aromatic shrub species Heterothalamus psiadioides Less and Baccharis patens Baker, indicating the possibility of allelopathy. Thus, this study aimed to determine if H. psiadioides and B. patens are phytotoxic and if this implicates in negative effects on the plant community in which the shrubs occur. In laboratory assays, the effects of the volatiles released directly from fresh and dry leaves of H. psiadioides and B. patens on germination and growth of the target plants lettuce and onion were evaluated in four seasons. A field study was carried out, in which vegetation cover and biomass, number of seedlings, diversity, richness, and variables of vegetation structure were evaluated in the surroundings of both species and where there were not shrubs. In the bioassays, H. psiadioides and B. patens volatiles inhibited the germination rate and speed of germination and reduced the root and shoot length of the target plants, with fresh leaves showing higher phytotoxicity. These parameters were more strongly affected by H. psiadioides than by B. patens in all seasons, and effects of the both shrubs were lower in summer. In relation to the field investigation that aimed to quantify the effects of the highly phytotoxic H. psiadioides on the plant community, no evidences of allelopathy were found. Richness and diversity were higher near H. psiadioides, due to lower cover of dominant grasses. Variables of vegetation structure and light intensity explained vegetation patterns more conclusively than allelopathy. This study emphasizes that the allelopathic potential of plants can be overestimated in bioassays, and that field studies are necessary to elucidate if allelopathic effects are in fact significant in plant communities. Still, the relevance of conducting more realistic laboratory studies and of using controls in field studies is highlighted.

Neste trabalho, avaliamos como arbustos pioneiros regulam comunidades lenhosas em uma restinga subtropical. Arbustos têm grande capacidade de modificar ecossistemas, pois alteram o fluxo de nutrientes e água do solo, aprisionam sementes transportadas por água ou vento sob suas copas, e oferecem recursos a dispersores. A combinação desses processos leva ao surgimento de ilhas de fertilidade em áreas de vegetação herbácea, aumentando a diversidade local. Interações biológicas são fatores determinantes na coexistência de espécies nessas ilhas arbustivas. Portanto, utilizamos atributos vegetativos de arbustos e distância filogenética média (MPD) entre as espécies para avaliar como a riqueza, a abundância e a diversidade (i.e. Entropia Quadrática de Rao, EQR) são reguladas em moitas de restinga. Também comparamos esses mesmos parâmetros nas áreas de vegetação predominantemente herbácea circundantes às ilhas arbustivas. A fim de entender a estruturação filogenética nesse ambiente, calculamos o net relatedness index (NRI) de cada moita. Nossos dados reforçam a importância de arbustos pioneiros sobre a vegetação de áreas predominantemente campestres devido à sua capacidade de modificar o micro-habitat sob suas copas e pelas interações com espécies que colonizam as ilhas arbustivas. / In this work we tested how pioneer shrubs regulate community structure in woody islands of a subtropical sand-dune (restinga) environment. Shrubby species show a great ability to modify ecosystems, since they change the flux of nutrients and water in the soil, they retain under their crowns seeds carried by water or wind, and the seeds in turn attract new dispersers. The combination of these processes leads to the formation of fertility islands in areas with herbaceous vegetation, increasing the local diversity. Biological interactions are determinant factors in the coexistence of species in these shrubby islands. So we used vegetative traits of shrubs and mean phylogenetic distance (MPD) between species to evaluate how richness, abundance and diversity, i.e., Rao‟s quadratic entropy (RQE), are regulated in sand-dune woody islands. We also evaluated the same parameters in the surrounding areas with predominantly herbaceous vegetation. In order to understand the phylogenetic structuring in this environment we estimated the net relatedness index (NRI) in each woody thicket. Our data reinforce the importance of pioneer shrubs in a matrix of the predominantly open grassland vegetation because of their ability to modify the microhabitat under their crowns and their interactions with other species which colonize the shrubby islands.

Neste trabalho, avaliamos como arbustos pioneiros regulam comunidades lenhosas em uma restinga subtropical. Arbustos têm grande capacidade de modificar ecossistemas, pois alteram o fluxo de nutrientes e água do solo, aprisionam sementes transportadas por água ou vento sob suas copas, e oferecem recursos a dispersores. A combinação desses processos leva ao surgimento de ilhas de fertilidade em áreas de vegetação herbácea, aumentando a diversidade local. Interações biológicas são fatores determinantes na coexistência de espécies nessas ilhas arbustivas. Portanto, utilizamos atributos vegetativos de arbustos e distância filogenética média (MPD) entre as espécies para avaliar como a riqueza, a abundância e a diversidade (i.e. Entropia Quadrática de Rao, EQR) são reguladas em moitas de restinga. Também comparamos esses mesmos parâmetros nas áreas de vegetação predominantemente herbácea circundantes às ilhas arbustivas. A fim de entender a estruturação filogenética nesse ambiente, calculamos o net relatedness index (NRI) de cada moita. Nossos dados reforçam a importância de arbustos pioneiros sobre a vegetação de áreas predominantemente campestres devido à sua capacidade de modificar o micro-habitat sob suas copas e pelas interações com espécies que colonizam as ilhas arbustivas. / In this work we tested how pioneer shrubs regulate community structure in woody islands of a subtropical sand-dune (restinga) environment. Shrubby species show a great ability to modify ecosystems, since they change the flux of nutrients and water in the soil, they retain under their crowns seeds carried by water or wind, and the seeds in turn attract new dispersers. The combination of these processes leads to the formation of fertility islands in areas with herbaceous vegetation, increasing the local diversity. Biological interactions are determinant factors in the coexistence of species in these shrubby islands. So we used vegetative traits of shrubs and mean phylogenetic distance (MPD) between species to evaluate how richness, abundance and diversity, i.e., Rao‟s quadratic entropy (RQE), are regulated in sand-dune woody islands. We also evaluated the same parameters in the surrounding areas with predominantly herbaceous vegetation. In order to understand the phylogenetic structuring in this environment we estimated the net relatedness index (NRI) in each woody thicket. Our data reinforce the importance of pioneer shrubs in a matrix of the predominantly open grassland vegetation because of their ability to modify the microhabitat under their crowns and their interactions with other species which colonize the shrubby islands.

Subtropical Thicket is the dominant vegetation biome in the Eastern Cape, and extends through to parts of the Western Cape. It is dominated by Portulacaria afra (spekboom), a woody succulent plant recognised for its importance as an ecosystem engineer and its carbon sequestration potential. Due to excessive grazing from domestic stock, spekboom has been completely removed from some areas. The Subtropical Thicket Restoration Programme (STRP) initiated a large scale restoration programme of planting spekboom cuttings in these degraded areas. Their efforts have been met with varying levels of success and improvement of the programme relies on continuous monitoring and scientific evaluation. I investigated the influence of selected soil properties on spekboom growth, mortality and landscape distribution, at both restoration sites and natural intact areas, and through experiments. Site or location was the most important factor influencing spekboom success at restoration plots, whereby sites in the eastern end of spekboom distribution perform better. Moving westwards slope orientation emerged as an important factor, whereby north facing slopes are preferred by spekboom. Although high levels of soil salinity (NaCl) restricted spekboom growth and affected its health, it could tolerate the levels it was exposed too. Soil pH, above 7, and phosphorous concentration, above 70 mg.kg-1, were the only limiting factors to spekboom survival found in the restoration sites. This preference for acidic soils was mirrored in intact Thicket. However in general, soil is not a major factor influencing spekboom growth and distribution, and spekboom is tolerant of a wide range of soil conditions. Spekbooms constraint is most likely a function of climate, which varies greatly across the biome. This study answered some vital questions regarding the possible influence of soil in spekboom growth and distribution. It disapproved the theory that a catena effect may be responsible for the lack of spekboom growing in bottomland areas. The study also indicates and supports the versatility of spekboom as a plant for restoring degraded lands across a range of different geologies and soil types. To maximise spekboom survival rates, restoration efforts should be focussed towards the eastern end of its distribution and to avoid planting in soils with pH levels higher than 7.