published_or_final_version / Ecology and Biodiversity / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 100-117).

Michaux's sumac (Rhus michauxii) is a federally endangered rhizomatous shrub endemic to the southeastern United States, with two of the largest populations located at Maneuver Training Center--Fort Pickett, VA (Fort Pickett), and a nearby property, Deepwater. Michaux's sumac requires soil disturbance and fire to maintain healthy populations. Before being added to the endangered species list, 47% of populations were extirpated due to habitat loss, fire suppression, and hybridization with smooth sumac (Rhus glabra). Concerns with hybridization include hybrid swamping if hybrids are fertile, or outbreeding depression if hybrids display reduced fitness. I used genotyping-by-sequencing to estimate the extent of hybridization at Fort Pickett and Deepwater, and to assess how such hybridization may impact survival of Michaux's sumac as a distinct species at each of these locations. Additionally, population structure was examined using DAPC (discriminant analysis of principal components) and Admixture analyses to determine whether the colonies at Fort Pickett and Deepwater make up separate populations, meta-populations, or one large population. Analysis of 107,344 SNPs (single nucleotide polymorphisms) using Introgress and Admixture software suggested widespread hybridization at both Fort Pickett and Deepwater, with hybrids present in most of the sampled colonies. Population structure analyses revealed differentiation between the Fort Pickett and Deepwater populations, but little evidence of separate populations among the colonies sampled at Fort Pickett. These results are important for conservation planning to ensure the long-term survival of Michaux's sumac at Fort Pickett and Deepwater and can be used to help inform future management decisions. / Master of Science / Michaux's sumac (Rhus michauxii) is a small, federally endangered shrub endemic to the southeastern United States, with populations remaining in North Carolina, Virginia, and Georgia. To date, the largest known colonies of Michaux's sumac are in Virginia at Maneuver Training Center--Fort Pickett, VA (Fort Pickett), and at a nearby privately owned property called Deepwater. Michaux's sumac requires soil disturbance and fire to reduce competition and maintain healthy populations. It currently faces threats from habitat loss due to agricultural land use and fire suppression, and hybridization with a closely related species, smooth sumac (Rhus glabra). Hybridization is a threat to Michaux's sumac at Fort Pickett and Deepwater because it co-occurs with smooth sumac throughout the area. This study determined how much smooth sumac and Michaux's sumac are hybridizing in these locations and assessed whether hybridization is a threat to the long-term survival of the populations at each site. A secondary goal of the study was to gain a better understanding of how genetically similar the colonies within and between locations are to one another. Understanding the level of hybridization and the population structure of Michaux's sumac is important for making management decisions to protect the species. I found widespread hybridization between Michaux's and smooth sumac, with hybrid individuals at nearly all the colonies sampled. Additionally, there is evidence that Fort Pickett and Deepwater comprise two distinct populations, but the colonies inside each area are likely not separate populations. These results will inform future conservation management decisions for the species.

L’intégration des fibres naturelles cellulosiques de plantes annuelles ou de résidus agricoles ou agro-industriels dans l’élaboration de matériaux de structures composites et le développement de nouveaux liants biosourcés sont aujourd’hui un domaine de recherche d’intérêt croissant. La thèse s'est déroulée dans le cadre du programme « Eco-panneaux », dont les deux objectifs principaux furent tout d'abord de valoriser les fibres végétales d’origine tunisienne comme l’alfa, le jonc et les folioles de palme et ensuite d'évaluer le potentiel d'espèces végétales tunisiennes dont les écorces sont riches en tannins (fruit de grenade, racines du sumac et tronc de pin d’Alep). Les études de caractérisation des fibres ont montré que leurs masses volumiques sont inférieures à 1. Le calcul du point de saturation des fibres (FSP) montre des valeurs majoritairement comprises entre 60 et 100 %. Nous avons également pu caractériser la cinétique d'imprégnation d'eau pour chacune des fibres. L’imprégnation se stabilise après 24 h d’immersion. Riches en minéraux (concentrations supérieures à 1 %), les fibres ont montré des teneurs en cellulose, en lignines et en hémicellulose comparables à celles généralement rencontrées avec les fibres de bois. L’analyse thermogravimétrique (ATG) a permis de constater que les matrices végétales étudiées sont thermiquement stables pour des températures inférieures à 200°C. Le dosage colorimétrique pour étudier la composition en polyphénols des matrices tannifères, l’analyse infrarouge et l’étude structurale de l’extrait des tanins, ainsi que le calcul du « Stiasny number » , montrent la forte teneur de l’écorce de grenade en tanins hydrolysables et la richesse des écorces du tronc de pin d’Alep et des racines du sumac en tanins condensés. L’étude des propriétés thermiques des extraits de tanins par ATG montre que les tanins de pin d’Alep et du sumac sont thermiquement plus stables que ceux de la grenade. La colle formulée à partir d’hexamine et de tanins de pin d’Alep présente un module d’élasticité élevé. Alors que la colle à base de tanins de grenade forme le réseau le moins dense. Ces résultats ont été confirmés par l’étude de la résistance au cisaillement. L'étude réalisée sur les composites fibres-plâtre (mise en œuvre et caractérisation physico mécanique des composites) a montré que les fibres locales pourraient constituer une alternative aux fibres d'importation utilisées actuellement. Une première caractérisation de la conductivité thermique des panneaux isolants élaborés à partir des fibres locales et de colles de tanins montre une conductivité thermique moyenne de 0,106w/K.m. / The integration of natural cellulosic fibers from annual plants and agricultural residues and agro-industrial materials in the development of composite structures and the development of new bio-based adhesives, are now a research field with growing interest. The thesis was conducted within the framework of "Eco-panels" program, which its two main objectives were firstly, to enhance plant fibers of Tunisian origin as alfa, rush and palm leaflets and then to evaluate the potential of Tunisian plant species whose bark is rich in tannins (pomegranate fruit, sumac roots and Aleppo pine trunk). The characterization studies of fibers showed that their densities are less than 1. The calculation of the fiber saturation point (FSP) shows values mostly between 60 and 100 %. We were also able to characterize the impregnation kinetics of water for each of these fibers. The impregnation stabilizes after 24 h of immersion. Rich in minerals (concentrations greater than 1 %), the fibers showed levels of cellulose, lignin and hemicellulose comparable to those generally encountered with wood fibers. The thermogravimetric analysis (TGA) shows that the plant matrices are thermally stable for temperatures below 200 ° C. The colorimetric assay of the polyphenolic composition of tanniferous matrices, the infrared analysis and the structural study of the tannins extract, as well as the calculation of "Stiasny number" show the high content in hydrolysable tannins for pomegranate barks and richness of Aleppo pine trunk barks and sumac roots barks in condensed tannins. The study by TGA of the thermal properties of tannins extracts shows that Aleppo pine and sumac tannins are thermally more stable than those of pomegranate. The formulation made from hexamine and Aleppo pine tannins has the greatest elasticity modulus. While the formulation prepared from pomegranate tannins forms the least dense network. These results were confirmed by the study of the shear strength. The study conducted on fiber-plaster composites (implementation and physico-mechanical characterization of composites) showed that local fiber could be an alternative to imported fibers used currently. A first characterization of the thermal conductivity of insulation panels made from local plant fibers and tannins adhesives shows an average conductivity of 0,106 W / Km.