Thesis (Ph. D).--Oregon State University, 1988. / Typescript (photocopy). Includes bibliographical references (leaves 46-49). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 1985. / Typescript (photocopy). Includes bibliographical references (leaves 71-74). Also available on the World Wide Web.

No description available.

Abstract Although nodulated legumes have been used by indigenous peoples in Africa for centuries, their full potential has never been realized. With modern technology there is scope for rapid improvement of both plant and microbial germplasm. This review gives examples of some recent developments in the form of case studies; these range from multipurpose human food crops, such as cowpea (Vigna unguiculata (L.) Walp.), through to beverages (teas) that are also income-generating such as rooibos (Aspalathus linearis (Burm. f.) R. Dahlgren, honeybush (Cyclopia Vent. spp.), and the widely used food additive gum arabic (Acacia senegal (L.) Willd.). These and other potential crops are welladapted to the many different soil and climatic conditions of Africa, in particular, drought and low nutrients. All can nodulate and fix nitrogen, with varying degrees of effectiveness and using a range of bacterial symbionts. The further development of these and other species is essential, not only for African use, but also to retain the agricultural diversity that is essential for a changing world that is being increasingly dominated by a few crops such as soybean.

Gum arabic is a natural gummy exudate from acacia trees and exhibits natural built-in variations commonly associated with hydrocolloids. This study is concerned with the determination of factors which could influence its properties and functionality. These factors include origin (location, soil type, rainfall), different collections, age of the trees and storage condition. Previous studies acknowledged the influence of some of these factors but somehow lack providing definitive answers to questions being asked by the end user and required for the development of Gum arabic industry in Sudan. Local knowledge as well as the various stages of gum collection and processing were reviewed in order to provide a clear background and the justification for the experimental design. In this study samples were collected from six plantations located in the west and east regions in Sudan. Samples were collected from trees of different age (5, 10, 15 and 20 years old) and also from different picking interval (1-4). Each sample was divided into three portions (UK, Khartoum and Port Sudan) and stored for 5 years in order to determine the effect of the respective location. Various analytical parameters (% loss on drying, Optical rotation, % protein, intrinsic viscosity, molecular weight and molecular weight distribution) were measured to fully characterise the gum samples and to determine their functionality (emulsification). The results obtained for all samples were consistent with those previously reported in the literature (see Chapter 4). The only exception, identified in a number of samples from the western region, is the high proportion (~30%) of high molecular weight fraction termed arabinogalactan-protein complex (AGP). The results clearly demonstrated significant variations between plantations located in western region compared with the eastern region. However, the variations between the plantations within the same region are statistically not significant. High values of % protein, viscosity, Mw and % AGP were obtained from the 1st pick, from both regions, and then significantly decreased thereafter to the fourth pick. Samples from west region in Sudan, from 1st and 2nd pick and from tree age (15) years gave the highest viscosity, molecular weight, % AGP and superior emulsification performance compared to other samples from different tree ages. The regression statistical analysis for the physiochemical properties correlation with emulsification performance demonstrated the role of % AGP to be the most influential factor followed by viscosity. The major finding of this study is the effect of storage condition on the properties and functionality of Acacia senegal. An increase in the molecular weight for all stored samples (for 5 years) irrespective of region was evident and statically significant. However, this increase was more prominent for samples from the western region compared to the eastern region. The AGP fraction was increased by the storage treatment up to 40% in Port-Sudan, 20% in Khartoum-Sudan and 15% in UK. The result clearly demonstrated that the temperature and humidity are the crucial factors to induce the natural maturation process in acacia gums. Statistical analysis (linear regression) suggested statistically significant models and equations to predict and explain the variations in the physiochemical and functional properties based on the environmental factors, picking set and age of the tree.

Thèse de doctorat : Sciences physique et de l'ingénieur. Sciences du bois : Bordeaux 1 : 2008. Thèse de doctorat : Sciences physique et de l'ingénieur. Sciences du bois : Université Cheikh Anta Diop de Dakar : 2008. / Titre provenant de l'écran-titre.

The gum arabic belt in Sudan plays a significant role in environmental, social and economical aspects. The belt has suffered from deforestation and degradation due to natural hazards and human activities. This research was conducted in North Kordofan State, which is affected by modifications in conditions and composition of vegetation cover trends in the gum arabic belt as in the rest of the Sahelian Sudan zone. The application of remote sensing, geographical information system and satellites imageries with multi-temporal and spatial analysis of land use land cover provides the land managers with current and improved data for the purposes of effective management of natural resources in the gum arabic belt. This research investigated the possibility of identification, monitoring and mapping of the land use land cover changes and dynamics in the gum arabic belt during the last 35 years. Also a newly approach of object-based classification was applied for image classification. Additionally, the study elaborated the integration of conventional forest inventory with satellite imagery for Acacia senegal stands. The study used imageries from different satellites (Landsat and ASTER) and multi-temporal dates (MSS 1972, TM 1985, ETM+ 1999 and ASTER 2007) acquired in dry season (November). The imageries were geo-referenced and radiometrically corrected by using ENVI-FLAASH software. Image classification (pixel-based and object-based), post-classification change detection, 2x2 and 3x3 pixel windows and accuracy assessment were applied. A total of 47 field samples were inventoried for Acacia senegal tree’s variables in Elhemmaria forest. Three areas were selected and distributed along the gum arabic belt. Regression method analysis was applied to study the relationship between forest attributes and the ASTER imagery. Application of multi-temporal remote sensing data in gum arabic belt demonstrated successfully the identification and mapping of land use land cover into five main classes. Also NDVI categorisation provided a consistent method for land use land cover stratification and mapping. Forest dominated by Acacia senegal class was separated covering an area of 21% and 24% in the year 2007 for areas A and B, respectively. The land use land cover structure in the gum arabic belt has obvious changes and reciprocal conversions between the classes indicating the trends and conditions caused by the human interventions as well as ecological impacts on Acacia senegal trees. The study revealed a drastic loss of Acacia senegal cover by 25% during the period of 1972 to 2007.The results of the study revealed to a significant correlation (p ≤ 0.05) between the ASTER bands (VNIR) and vegetation indices (NDVI, SAVI, RVI) with stand density, volume, crown area and basal area of Acacia senegal trees. The derived 2x2 and 3x3 pixel windows methods successfully extracted the spectral reflectance of Acacia senegal trees from ASTER imagery. Four equations were developed and could be widely used and applied for monitoring the stand density, volume, basal area and crown area of Acacia senegal trees in the gum arabic belt considering the similarity between the selected areas. The pixel-based approach performed slightly better than the object-based approach in land use land cover classification in the gum arabic belt. The study come out with some valuable recommendations and comments which could contribute positively in using remotely sensed imagery and GIS techniques to explore management tools of Acacia senegal stands in order to maintain the tree component in the farming and the land use systems in the gum arabic belt.

The gum arabic belt in Sudan plays a significant role in environmental, social and economical aspects. The belt has suffered from deforestation and degradation due to natural hazards and human activities. This research was conducted in North Kordofan State, which is affected by modifications in conditions and composition of vegetation cover trends in the gum arabic belt as in the rest of the Sahelian Sudan zone. The application of remote sensing, geographical information system and satellites imageries with multi-temporal and spatial analysis of land use land cover provides the land managers with current and improved data for the purposes of effective management of natural resources in the gum arabic belt. This research investigated the possibility of identification, monitoring and mapping of the land use land cover changes and dynamics in the gum arabic belt during the last 35 years. Also a newly approach of object-based classification was applied for image classification. Additionally, the study elaborated the integration of conventional forest inventory with satellite imagery for Acacia senegal stands. The study used imageries from different satellites (Landsat and ASTER) and multi-temporal dates (MSS 1972, TM 1985, ETM+ 1999 and ASTER 2007) acquired in dry season (November). The imageries were geo-referenced and radiometrically corrected by using ENVI-FLAASH software. Image classification (pixel-based and object-based), post-classification change detection, 2x2 and 3x3 pixel windows and accuracy assessment were applied. A total of 47 field samples were inventoried for Acacia senegal tree’s variables in Elhemmaria forest. Three areas were selected and distributed along the gum arabic belt. Regression method analysis was applied to study the relationship between forest attributes and the ASTER imagery. Application of multi-temporal remote sensing data in gum arabic belt demonstrated successfully the identification and mapping of land use land cover into five main classes. Also NDVI categorisation provided a consistent method for land use land cover stratification and mapping. Forest dominated by Acacia senegal class was separated covering an area of 21% and 24% in the year 2007 for areas A and B, respectively. The land use land cover structure in the gum arabic belt has obvious changes and reciprocal conversions between the classes indicating the trends and conditions caused by the human interventions as well as ecological impacts on Acacia senegal trees. The study revealed a drastic loss of Acacia senegal cover by 25% during the period of 1972 to 2007.The results of the study revealed to a significant correlation (p ≤ 0.05) between the ASTER bands (VNIR) and vegetation indices (NDVI, SAVI, RVI) with stand density, volume, crown area and basal area of Acacia senegal trees. The derived 2x2 and 3x3 pixel windows methods successfully extracted the spectral reflectance of Acacia senegal trees from ASTER imagery. Four equations were developed and could be widely used and applied for monitoring the stand density, volume, basal area and crown area of Acacia senegal trees in the gum arabic belt considering the similarity between the selected areas. The pixel-based approach performed slightly better than the object-based approach in land use land cover classification in the gum arabic belt. The study come out with some valuable recommendations and comments which could contribute positively in using remotely sensed imagery and GIS techniques to explore management tools of Acacia senegal stands in order to maintain the tree component in the farming and the land use systems in the gum arabic belt.

E Nord-Cameroun comme toutes les zones arides et semi-arides de l’Afrique subsaharienne est confronté à la désertification qui est causée par les aléas climatiques et la surexploitation des ressources naturelles. L’une des conséquences est la baisse des rendements des cultures due à la dégradation des sols cultivables. Dans cette situation, l’une des voies pour améliorer le niveau de vie paysan est de développer la plantation des ligneux à usages multiples. L’introduction de l’A. senegal dans les années 90 dans les exploitations agricoles avait l’optique de restaurer la fertilité des sols et de diversifier les sources de revenus des agriculteurs par la production de gomme arabique. Malgré la multifonctionnalité de cet arbre et les efforts des projets pour sa vulgarisation, les résultats et les réactions des populations pour sa plantation restent peu concluants et sélectifs. La thèse identifie et analyse les facteurs socio-économiques et leurs effets sur la décision paysanne à planter A. senegal. La méthode est basée sur les enquêtes et entretiens semi-directs. Les résultats montrent que la plus grande production en gomme obtenue par une exploitation est de seulement 50 kg/ha/an. Toutefois les recettes des ventes éventuelles des autres produits des plantations complètent celles de la gomme. Les planteurs n’ont pas tous disposé d’information ni de formation suffisantes. Une plate forme de concertation est à mettre en place pour redéfinir les rôles des acteurs de la filière gomme. Pour une gestion durable des plantations d’A. senegal, les projets de développement et les décideurs doivent faire respecter les normes de différentiation des prix de la gomme. / The North Cameroon like all arid and semi-arid zones of African sub-Saharan is facing desertification caused by climatic factors and over exploitation of natural resources.One of the consequences is the decline of crop yields due to degradation of arable land. In this situation, promotion of multipurpose trees plantations can improve the farmers’ livelihood. The introduction of A. senegal in the 90’s in agricultural farms had the aim to restore soil fertility and diversify sources of income for farmers through the production of arabic gum. Despite the multifunction aspect of this tree and the involvement of different development projects for its extension, the results and reactions of local people to its plantation remain inconclusive and selective. The thesis identifies and analyzes the socio-economic factors and their effects on the farmers decision to plant A. senegal. The method is based on surveys and semi-structured interviews. The results show that the best gum yield observed on the exploitation is 50 kg / ha / year. However, the revenue can be increased with the sale of byproducts of A. senegal. Not all farmers are sufficiently informed or trained. A platform for dialogue is to be set in order to redefine the roles of stakeholders in the market chain. For the sustainable management of A. senegal plantations, development projects and policy makers need to meet the standards of gum price differentiation.