Sudan is endowed with a great diversity of tree species; nevertheless the utilization of wood resources has traditionally concentrated on a few species only. Despite of the richness of Sudan in most of basic factors required to establish forest based industries it still almost entirely dependent on imports to satisfy its needs of the products of such industries. There is an urgent need to assess the suitability of the local fibrous raw materials for industrial utilization, this would not only reduce imports, but they would also provide an economic incentive to the forestry and industrial sectors of Sudan. Sudan has a wide variation of climatic zones, thus; great variations are expected in the anatomical and physical properties between and within species grown in each zone. This variation needs to be fully explored in order to suggest best uses for the species. The present study was carried out to assess the suitability of Acacia seyal var. seyal Del and Balanites aegyptiaca (L.) Delile wood for pulp and paper making (PPM) and flooring industry, as well as to investigate the effect of rainfall zones on selected wood properties. For this purpose, a total of thirty trees per species were collected from four states in Sudan, namely: Blue Nile, North Kordofan, South Kordofan and White Nile. The study areas located in two precipitation zones. Zone one with 273 mm mean annual rainfall, and zone two with 701 mm mean annual rainfall. Wood samples in form of disc were obtained from two heights within each tree, which are 10 % and 90 % from the tree merchantable height. Anatomical, physical and mechanical investigations were conducted in order to test the wood properties of the study species. The studied anatomical properties were: fibre and vessel diameter, lumen diameter and wall thickness. In addition to fibre length and three fibre derived values, namely: flexibility coefficient, Runkel ratio and slenderness ratio. The trend of fiber length from pith to bark was determined. The anatomical composition was described. Wood density was investigated as a main physical property. Basic density as well as air dry density were measured in the current study. Additionally, the density was measured using X-ray densitometry method in order to assess its suitability as a valid tool for the study species density determination. The trend of wood basic density from pith to bark was also determined. Brinell hardness strength was measured in the transverse and radial sections. According to the study results, the fibre length of both species considered as medium (900 -1600 μm). However, Acacia seyal has longer fiber. Acacia seyal wood density considered heavy (≥ 720 kg/m³) while that of Balanites aegyptiaca is medium (500 - < 720 kg/m³). Depending upon the mean values of hardness strength in transverse as well as radial sections, the wood of both species can be classified as very hard (up to 146 N/mm2 hardness strength). Fibre length and wood density for both species followed the increase trend from the pith to the bark. The X-ray densitometry technique is considered as a valid tool for wood density determination for both species. For each species, some wood properties (in mature wood) were significantly affected by the water stress in the drier zone. For instance, Acacia seyal fibre length was negatively affected, while vessel wall thickness, basic density as well as hardness strength of the radial section were positively affected. In case of Balanites aegyptiaca the following properties were affected: vessel dimensions (negatively) and basic density (positively). However, the water stress did not affect Acacia seyal fibre and vessel diameter and lumen diameter, fiber wall thickness, flexibility coefficient, Runkel ratio and hardness strength in transverse section. Balanites aegyptiaca fibre characteristics and hardness strength did not show any response to water stress as well. In general, the overall wood properties of the study species considered compatible for PPM and flooring industry. However, trees growing in the more humid zone are preferable for both industries, due to their lower wood density and longer fibres in case of Acacia seyal and lower density in case of Balanites aegyptiaca.

Eine wissenschaftliche Exkursion in den Blue Nile State der Republik Sudan im Jahr 2011 vermittelte einen Überblick über die forst- und holzwirtschaftliche Situation der Region. In den verbliebenen Naturwäldern führt der Nutzungsdruck seitens der örtlichen Bevölkerung zu einer starken Degradierung. Hauptbaumart der Wirtschaftswälder ist Acacia nilotica. Die Sägeindustrie des Landes konzentriert sich auf die Verarbeitung dieses Holzes zu Eisenbahnschwellen. Im Bereich Möbeltischlerei spielen einheimische Laubholzarten eine gewisse Rolle. Daneben wird europäisches Nadelholz importiert. Um die Entwicklung der Region zu fördern, muss das Ziel der weiteren Forschungsarbeit eine zielgerichtete und nachhaltige Bewirtschaftung und Nutzung der forstlichen Ressourcen sein.

Acacia species producing gum Arabic are of great (socio)-economic, and ecological importance in Sudan. Insect attacks are one of the main causal agents in the decline in the gum Arabic yielding trees. Infested trees are almost totally damaged if the infestation is left untreated. The beetle family Cerambycidae is one of the largest groups of insects. Commonly referred to as long-horned beetles, these pests destroy host trees, having a great affect during times of drought. Many studies have been completed about the effect of long-horned beetles in various global settings. However, in Sudan, there is limited information about the insects’ ecological, biological, and even basic, profile. Thus, in this dissertation I study the spectrum, relative abundance, and phenology of the long-horned beetle species that are infesting Acacia species in Kordofan region (Sudan). Seven species were recorded using interception traps. These included Anthracocentrus arabicus (Thomson, 1877), Crossotus strigifrons (Fairmaire, 1886), Crossotus subocellatus subocellatus (Fairmaire, 1886), Doesus telephoroides Pascoe, 1862, Gasponia gaurani Fairmaire, 1892, Titoceres jaspideus (Serville, 1835) and Tithoes sp.. Two species were recorded using ground - photoeclectors: Crossotus albicollis (Guérin, 1844) and Coelodon servum White, 1853. Most of the species are known from other Arabian and African countries. However Coelodon servum White, 1853, Doesus telephoroides Pascoe, 1862, and Gasponia gaurani Fairmaire, 1892 were recorded in this study for the first time in Sudan. Results from flight interception traps indicated peak activity density of long-horned beetles during the rainy season (June – September), with maximum occurrence in June and peak occurrence in August. All study sites showed infestations of long-horned beetles, but the level of infestation varied between sites and Acacia species. The El Demokeya reserve forest indicated the highest percentage of infestation out of all the sites surveyed in this study. The infestation ranged between 57.1% and 100.0% for Acacia senegal, between 5.9% and 26.7% for Acacia mellifera, and 0% to 23.1% for Acacia seyal study sites. Acacia species differed also with respect to the spatial infestation pattern. Results indicated the maximum (95.5%) presence of holes of infestation in the branches of A. senegal when compared to the trunk. Holes of infestation were recorded in all directions, with a minimal occurrence on the south side (18.2%). Opposite results were obtained for A. mellifera with the maximum number of holes in the trunks (46.2%), while branches were less affected. In addition results obtained showed no presence of holes in the branches of A. seyal. Moreover, this study focuses on the assessment of tree characteristics that may trigger the infestation. Logistic regression indicated that tree age was the only predictor for the infestation with long-horned beetles – at least for Acacia senegal. A significance difference was obtained for the stand height curve between non-infested and infested trees of Acacia species, except A. senegal stands at El Demokeya. The study was supplemented by qualitative data, produced from a survey of gum landowners. This questionnaire indicated the level of awareness that gum landowners had with regard to long-horned beetles and their infestations. The results of this survey denoted that 95.0% of gum farmers were aware of the long-horned beetles, while 49.2% indicated an awareness about infestations, mentioning the emergence holes as damage characteristics.

Ziele der Arbeit sind die Bestimmung der dominanten Landnutzungsarten im Untersuchungsgebiet von Edd Al Fursan (Sudan) sowie die Kartierung und Analyse der Veränderungen der Landnutzung im Zeitraum 1972 bis 2008 mit Hilfe von multi-temporalen Satellitenbildern (Landsat MSS, TM und ETM sowie Terra ASTER). Des weiteren erfolgt eine Evaluierung des Einflusses von Veränderungen der Landnutzung auf die Lebensbedingungen der ländlichen Bevölkerung in Hinblick auf die Verfügbarkeit von Ressourcen mit Hilfe von quantitativen Untersuchungsmethoden. Um diese Aussagen treffen zu können, werden drei Methoden der Bestimmung von Veränderungen der Landnutzung angewandt, und zwar Post Classification Comparison (PCC), Change Vector Analysis (CVA) basierend auf Tasseled Cap Transformation (TCT) sowie Iteratively Reweighted Multivariate Alteration Detection (IR-MAD) mittels Maximum Autocorrelation Factor (MAF). Neben den fernerkundlichen Untersuchungen wurde eine sozio-ökonomische Feldstudie durchgeführt, die vorstrukturierte Fragenkataloge, Interviews und Gruppendiskussionen mit Personen in regionalen und lokalen Schlüsselpositionen und mit älteren Menschen durchgeführt. Fünf Klassen der Landnutzung und Landbedeckung ergeben sich aus einer Klassifikation der Satellitenbilder mit der Methode der größten Wahrscheinlichkeit (Maximum Likelihood), explizit die Klassen Grasland, Waldland, Brachland, bebautes und landwirtschaftlich nicht genutztes Land. Die Klassifikation schafft eine genaue Grundlage für die Kartierung, Quantifizierung und Analyse der Änderungen. Die Gesamtgenauigkeit der Flächenermittlung beträgt 83% für die Jahre 1972 und 1984, 85% für 1989, 87% für 1999 und 92% für 2008. Die Untersuchungen zeigen, dass die Post Classification Comparison (PCC) eine vollinhaltlich geeignete und leicht anzuwendende Methode der Flächenanalyse darstellt. Change Vector Analysis (CVA) beruhend auf Tasseled Cap Transformation (TCT) wird ebenfalls für die Kartierung und Bestimmung von Landnutzungsänderungen verwendet. Durch TCT wird der spektrale Bildinhalt in die Komponenten Greeness und Brightness transformiert sowie in dem dadurch neu definierten Koordinatensystem die CVA durchgeführt. Die Ergebnisse in Form von Vektoren der Veränderung mit messbarer Richtung und messbarem Ausmass der Flächendynamik beweisen, dass die Methode für die Kartierung von Vegetationsbedeckung und insbesondere von Entwaldung und Wiederbewaldung geeignet ist. Durch die Anwendung der Multivariate Alteration Detection (MAD) in Kombination mit dem Maximum Autocorrelation Factor (MAF) werden Veränderungen der Landnutzungsklassen während des betrachteten Zeitraumes visualisiert. Die Ergebnisse beweisen, dass die MAD für die Veränderungsanalyse in multi-spektralen Satellitenbildern sehr gut geeignet ist. Darüber hinaus wird nachgewiesen, dass die Kombination mit dem MAF die Ergebnisse der MAD entscheidend verbessern kann, da Rauschen und geringfügige Änderungen unterdrückt und signifikante Änderungen klarer herausgestellt und damit besser interpretierbar werden. Um die Ursachen für die Veränderungen der Landnutzung und den Einfluss dieser Änderungen auf die Lebensbedingungen der ländlichen Bevölkerung im Projektgebiet zu identifizieren, wurde eine Befragung mittels vorstrukturiertem Fragenkatalog, Interviews und Gruppengesprächen mit 100 GesprächspartnerInnen im Alter zwischen 42 und 65 Jahren in vier nach dem Zufallsprinizip ausgewählten Dörfern ausgeführt. Die Auswertung der sozio-ökonomischen Daten erlaubt die Extraktion der Faktoren, die Landnutzung und deren Änderung beeinflussen, und die zu bestimmten Auswirkungen dieser Änderungen auf die Lebensbedingungen in den Dörfern in Hinsicht auf die Verfügbarkeit von Natur-Ressourcen führen. Die Ergebnisse der Forschungsarbeiten zeigen, dass Fernerkundung und sozio-ökonomische Datenanalyse effizient verknüpft werden können, um anthropogene Einflüsse auf Art und Dynamik von Landnutzung sichtbar zu machen. In bezug auf die gegenständliche Zeitreihe wird durch die Untersuchungen bewiesen, dass zunehmende Bevölkerungszahlen im Gebiet von Edd Al-Fursan in direktem Wirkungszusammenhang mit Veränderungen der Landnutzung stehen.

The present study was conducted in Umfakarin natural forest reserve, South Kordofan, Sudan. The main objective was to investigate the possibility of managing Acacia seyal Del. variety seyal for the production of gum talha. Three stand densities (strata), namely dense, medium, and slight, were distinguished based on the number of trees per hectare. During the sampling phase, the study adopted the method of identifying the competitors (neighboring trees) from the subject one (trees selected for gum production experiments). From the three stand densities, a total of 482 subject trees, covering variable diameter ranges (d= 9-11.5, 13.5-16, 18-20.5 and above 21 cm) were selected, based on the diameter at 0.25 m height (d0.25). In each stratum, competitor trees were identified within a radius equal to the height of subject tree multiplied by a factor (1.25). The diameter at breast height, height to crown base, height, crown radii, and tree coordinates were measured for each of the subject trees and its competitors. Subject trees were exposed to tapping on first of October, the fifteenth of October, and the first of November, using local tools (Sonki and Makmak). Additionally, untapped trees were used as controlling-variables. The initial gum collection was completed fifteen days after the tapping, while the subsequent (7-9 pickings) were done at an interval of fifteen days. Six stand height functions were tested and the results illustrated that the Michailow stand height function was suitable for predicting the height of Acacia seyal in Umfakarin natural forest. The predictive ability of this height function ranged from 19.3% to 24%. The volume function used in this study was able to predict the volume of standing trees with more than 92 percent accuracy. Competition among trees of Acacia seyal was assessed in terms of competition indices. Eight competition indices were quantified using the CroCom program. The relationship between these indices and tree dimensions (diameter at breast height, height and crown diameter) was tested using logarithmic models. Among these indices, the Hegyi_2 index is considered a suitable index to be applied for estimating the degree of competition in natural stands of A. seyal of dense stratum when using diameter at breast height as a predictor. About 70% of the total variability is explained by this logarithmic model. Gum yielded by each subject tree per season was obtained by summing up the gum samples collected from all pickings. Gum production per unit area was also determined. Regression tree, general linear model (GLM) and logistic regression techniques were used for analyzing the obtained data. The results of the study indicated that the gum yield is independent of stand density. Tapping has influence on gum yield. Trees tapped by sonki on the first of October at medium stand density have the highest gum with an average value of about 56 g/tree/season. Significant difference (p = 0.021) was detected between two groups of dates; the first of October and first of November in medium stand density. The results also revealed that the most important variable influencing gum production was found to be diameter at breast height with 23.95 cm threshold. Between 41-53 percent of subject trees produce gum less than 50 g/season. The results indicated that A. seyal species produces a very low quantity of gum talha (3.6-4.8 kg/ha) and for economic reasons, its tapping is not recommended. The findings of the regression analysis revealed to a model which could be used to estimate the yield of gum talha from A. seyal natural stands in the Umfakarin forest, South Kordofan, Sudan. Conducting experiments on the production of gum talha in permanent plot trials in different climatic regions of the Sudan is highly recommended.