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sur le développement des zones arides et semi-arides

Titre : Variations Among Forests, Plots and Trees of Acacia tortilis (Forssk.) subsp. raddiana (Savi) in Above-ground Wood Biomass and Carbon Content of Tree Components and their Inter-relationships in Semi-Arid Zone of Central Sudan

Auteur : Hisham Saeed Abdeen Elzein

Université de soutenance : University of Khartoum

Grade : Doctor of Philosophy in Forestry (Wood Science) 2021

Résumé partiel
The study investigated a variation among A. tortilis subsp. radiana forests, plots within forests and trees within plots in four forests in semi-arid zone in Central Sudan. The study aimed to estimate aboveground volume (AGV), dry weight (DW), above ground biomass (AGB) and carbon content (CC) of tree, stems, and branches and their interrelationships. Data was collected from 36 variable-area sample plots randomly taken within the stocked area in each sample forest. For each tree in the plots, an average standing sample stem was divided into about 1-meter segments and their volumes were measured and the stump volume was added to obtain the volume of the sample stem and then multiplied by the number of stems per tree. Three branches of that stem were randomly selected and their volumes were calculated and the volume of branches per tree was then calculated. Above-ground wood volume of each tree was obtained by adding volumes of all stems and branches. Sample discs of 5 cm-thickness were cut from the felled sample stem, at the top of the stump and stem segments and the mid of branches (a total of 720 discs from all forests). From each disc, a wedge-shaped, 5 cm-thick piece of wood was used to determine the wood basic density and carbon ratio, and then dry AGB and CC were then estimated. The data were statistically analyzed using the Statistical Analysis System (SAS 1991) package. Tree (stems and branches) means and other basic statistics of the variables were computed (Proc Means) to describe the data obtained from sample trees and make statistical inference about the respective values of the population. Hence, 95% confidence intervals of the means were obtained for the population in the study area. The data was treated as a nested experiment and analysis of variance and variance components were conducted. Pearson correlation coefficient was obtained to investigate the linear association between all possible pairs of the studied variables. Plotting of the paired observations of all possible pairs of variables showed that the pattern of the relationships was linear. Simple linear regression analysis was performed for the paired variables that had strong correlations. Results of ANOVA showed that the sources of variation in all tree’s variables were significant (p≤0.0001). It is concluded that the tree volume mean in the population is between 0.041 and 0.042 m3. Forests revealed the greatest proportion of variation in volume (22%) and dry weight (17.9%), while plots explained the largest one in carbon content (17.5%). The estimates of AGWB per hectare of the forests was found to vary between 13.68 and 20.47 t ha-1, and that of CC between 5.883329 and 10.27402 t C ha-1. The results of the correlation of all possible pairs of the studied variables were highly significant (p ≤ 0.0001) and positive

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