Integration of Remote Sensing and GIS in Studying Vegetation Trends and Conditions in the Gum Arabic Belt in North Kordofan, Sudan

Band 8 der Reihe „Fernerkundung und angewandte Geoinformatik“

Hassan Elnour Adam
ISBN: 978-3-941216-58-7
Veröffentlicht: Mai 2011, 1. Auflage, Einband: Broschur, Seiten 158, Format 17,6 x 25,0 cm, Gewicht 0.32 kg
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Integration of Remote Sensing and GIS in Studying Vegetation Trends and Conditions in the Gum Arabic Belt in North Kordofan, Sudan

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Hassan Elnour Adam

Integration of Remote Sensing and GIS in Studying Vegetation Trends and Conditions in the Gum Arabic Belt in North Kordofan, Sudan

Band 8 der Reihe „Fernerkundung und angewandte Geoinformatik“. Herausgegeben von Univ. Prof. Dr. habil. Elmar Csaplovics, Lehrstuhl Remote Sensing, FR Geowissenschaften, TU Dresden

158 Seiten. Format B5. Broschur. Zahlreiche, auch farbige Abbildungen. Preis: 28,00 Euro. ISBN 978-3-941216-58-7. Rhombos-Verlag, Berlin 2011.


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. Data bases of land cover and vegetation can be used to develop maps of habitat suitability (digital vegetation map) including information on forest cover and canopy structure. Remote sensing offers a quick and efficient approach to the classification and mapping of land use land cover in a basis for future planning. This study used remotely sensed imagery to identify and delineate various land use land cover categories and types of vegetation cover present in the gum arabic belt in Kordofan region using recent methodologies of classification such as sub-pixel approach using object-based approach. Also, the integration of terrestrial forest inventory and remotely sensed data for the estimation of forest stand parameters of Acacia senegal trees was tested. The study integrated data from different sources and used different methods and approaches to analyse the long term land use land cover changes and trends during the previous three decades in the gum arabic belt in Kordofan State. The approach includes imageries from different satellites (Landsat and TERRA) for multi-temporal dates and integrated to fieldwork (forest inventory).
A vegetation maps are derived as an approach for vegetation evaluation, which is required for the effective management of natural resources in Kordofan region. The land cover modifications in condition and composition of vegetation cover as important aspects of change are considered in current research, as well as providing forest managers with more current and improved data for the purposes of forest inventory. The research contributes to the fundamental concerns of resources management including forestry and land use with developed approaches and methodologies using remote sensing and GIS and providing useful information for specific purposes.


The author

Hassan Elnour Adam was born in 1970 in Elobeid, Sudan. He graduated from Faculty of Forestry, University of Khartoum with B.Sc. (Hons.). He has been working as a teaching assistant since 1995 in the Forestry and Range Sciences Department, University of Kordofan. In 2000 he obtained his MSc. (Tropical Forestry) at the Technology University of Dresden, where he also completed his PhD degree (2011) at the Institute of Photogrammetry and Remote Sensing. Currently he is working as assistant professor at University of Kordofan, Sudan. Mr. Adam E. Hassan is an expert in the area of application of remote sensing and GIS in sustainable forest management and land use land cover analysis. He presented his research in many international conferences. Also he enrolled in supervision of MSc. students, lecturing and teaching of practical courses in the field of remote sensing and applied geoinformation analysis. Mr. Adam E. Hassan is able to accomplish a broad spectrum of tasks related to the fields of his study.

Der Herausgeber:
Prof. Dr. techn. habil. Elmar Csaplovics leitet den Lehrstuhl Geofernerkundung am Institut für Photogrammetrie und Fernerkundung der Technischen Universitaet Dresden

TU Dresden, Institut für Photogrammetrie und Fernerkundung, Helmholtzstraße 10, 01062 Dresden
Prof. Dr. Elmar Csaplovics: "In loser Folge sollen in dieser Schriftenreihe wissenschaftliche Arbeiten, die am Lehrstuhl für Fernerkundung bearbeitet und betreut werden, in ansprechender Form veröffentlicht werden. Wir glauben, dass dadurch das Spektrum von Literatur zum Themenkreis projektorientierter angewandter fernerkundlicher Forschung nachhaltig bereichert werden kann und wünschen uns demgemäß eine kritikfreudige Schar von Leserinnen und Lesern." >Professur Geofernerkundung


Among the most useful trees growing without cultivation, must be reckoned: the gum-tree, the tamarind, the beautiful tabaldi (note: Adansonia digitata), and the egelit (note: Balanities aegyptiaca) before mentioned. The gum-tree (Mimosa nilotica) as it is termed in books, merits a different denomination in Kordofan, for the shape of the tree, its leaves and spines, differ materially from those of the mimosa Nilotica, properly so called. The latter tree yields common gum only, whereas that of Kordofan is of the finest description, so that it is erroneously distinguished by the name of gum-Arabic. In some parts of the country, the mimosa forms whole forests of vast extent; but the district of Bara furnishes the largest quantity of gum. The harvest is modified by the annual fall of rain, for, if it rain much, the trees sweat the more. The gum exudes from the bark of the stem and large branches, nearly in the same manner as the resinous exudation from the cherry-trees of Europe. In digging for a beetle, I casually observed that the gum proceeds from the root also. Sennaar, which is situated under the same degree of latitude as Kordofan, yields a far less quantity of this product. The gathering takes place a few months after the rain, in the months of December, January, and February. It is an exceedingly profitable affair to the government, and therefore a monopoly. But even in this undertaking, the Egyptians act with unparalleled neglect, and do not interfere when they see whole forests of gum-trees hewn down, and the ground converted into dockn (note: dochen in the German original, i.e. pearl millet Pennisetum glaucum) fields, although immense tracts of the country far better adapted for arable land remain uncultivated, by making use of which, the gum-trees would be spared. But the government does not trouble itself about such trifles, it merely scrapes together that which comes within its reach without paying the slightest attention to ulterior consequences. Of the plantation of young trees and the extirpation of such as are unprofitable, it has no idea, nature must attend to that business.
(Ignaz Pallme, Travels in Kordofan. Embracing a Description of that Province of Egypt, and of Some Bordering Countries, with a Review of the Present State of Commerce in those Countries, of the Habits and Customs of the Inhabitants, as also an Account on the Slave-Hunts Taking Place under the Government of Mehemed Ali, By Ignatius Pallme, from Notes Collected during a Residence of Nearly Two Years in Kordofan. J.Madden and Co. London, 1844, chapter XIII Products, pp 225-226)
The garrat (note: local name of Acacia nilotica in some parts of Western Sudan, comm. by Hassan Elnour and Abdelnasir Hanno) whose pod is employed in tanning, and the tamarisk (Tamarindus Indica) are likewise frequently seen in the province, but not in the same abundance as the gum-tree. The pods of the tamarind are collected and trodden into the form of cakes, which are dried, and either kept for domestic use or converted into commodity. A large quantity of this production is consumed in” the country. This tree suffers greatly by the locusts; for sometimes the inflorescence, sometimes the fruit, is totally devoured by these destructive insects, and in those years, there is, of course, a scarcity of this fruit in many villages.
(ibidem, chapter XIII Products, p 226-227)
Kordofan was since ever famous for its abundant resources in gum arabic. This richness was one of the reasons of the Turkish-Egypt invasion in 1820. Al-Ubayyid fell on 20 August 1821. The Egyptians immediately set up a monopoly on the gum trade thus taking over control and centralising the accumulating benefit of the trade in the hands of a few, though some traders still were allowed to organise their trade deliberately. Anyhow, only after international pressure the Egyptians were forced to give up the monopolies in 1849. Immediately afterwards international merchants set up to buy gum and to transfer it to and sell it in Cairo or Alexandria with expectation of extremely high profit rates. The export of gum arabic increased from around 1800 till the mid-century from approximately 150 tons to 900 tons p.a. After the Mahdist state once more monopolised the gum trade in the 1880s and was abolished by the Anglo-Egyptian invasion the re-establishment of an extended trade in gum which led to an increase from under 2000 tons in 1899 to 19.500 tons in 1912 was stimulated. Gum provided then about 43% of the total export income. The following decades saw the greatest flourishing of the gum trade when export reached 27000 tons in the early 1930s and nearly 50.000 tons in the 1960s. After the severe drought periods in the early 1970s and early 1980s the gum trade broke down and less than 20000 tons p.a. was traded to Port Sudan (Stiansen 1998). Today the exports by Sudan’s government-controlled Gum Arabic Company are extremely low due to impacts of political instability (2006: 9000 tons p.a.!) especially with regard to the Darfur conflict. Revenues are more and more driven by swings in production and dropped from USD 5000,- to an average of appr. USD 2000,-. Interesting to realise that nowadays revenue from Sudan’s gum arabic totals less than $80 million a year, far less than the $4 billion to $6 billion the country receives from oil production.
Kordofan is struggling with climatic impacts, periods of drought and periods of strong winds, with human impact, misuse of the land, overgrazing and overbrowsing, with ethnic conflicts pushed by the southward movement of nomads and transhumants, and of the northward movement of sedentary farmers at the same time, as well as with socio-ethnic and socio-political conflicts destabilising the western parts of the gum arabic belt in the Darfur region. The spatio-temporal dynamics of regional and local patterns of various intensities of impacts, of heterogeneous causes and reasons, and the effects both destructive as devastating have to be coped.
A better understanding of the variations of interactions of man and nature, of land use and eco-climatic constraints, of ethnic conflicts and political arbitrariness is needed in order to set up stringent land management strategies all over the globe in general and in the Kordofan in particular. Knowledge about the heterogeneous driving forces affecting land use systems under semi-arid to arid conditions, systems squeezed by peoples forced into migration, systems still able to recover under certain circumstances as proven by specific regional research, is still low compared to the urgent needs for implementation of sustainable socio-ecological and socio-economical planning and development. Why is spatio-temporal monitoring of land use and land cover by means of space-borne earth observation if not anymore elitist and expensive as in former decades still a black box for the governmental stakeholders from national to regional level? Why are management practices and strategies of regional development still paperwork but not appropriate tools for decentralised and participative action in the affected regions?
The PhD thesis of Hassan Elnour Adam Zakaria focuses on research on the values of space-borne remote sensing for monitoring the gum arabic belt in the Kordofan in order to thoroughly assess and analyse quantitative and qualitative parameters of land cover and land use change. Research is urgently needed to develop and provide a sound methodology for periodical assessment of the spatio-temporal patterns of regional climatic and human impact on the respective land use system of Acacia senegal (and Acacia seyal) forest stands with special regard to significant trends of decrease of tree stands all over the belt due to human pressure. One fifth of the Sudanese population lives and two thirds of the livestock population are raised in the gum arabic belt. Conflicts of different and often contrary land use interests are obvious. Earth observation allows for a large-coverage accurate detection of trends in land use and land cover change in the belt and of specific variations in the distribution and density of Acacia senegal stands in particular. Nevertheless intensive research is needed to develop, amend and analyse various qualities of data, different approaches to image classification as well as of strategies to combine terrestrial (in-situ-verified) sampling data with remotely sensed data in order to allow for an estimation of forest stand parameters in relation to spectral information provided by imagery.
Sound research on innovative approaches of combination of satellite image analysis both pixel- as well as object-based, and of the application of regression models for estimation of Hashab forest stand parameters from spectral information of satellite imagery is provided. A clear perspective for the implementation of remote sensing forestry in efforts to set up long-term monitoring programmes for assessment of state and dynamics of change of Acacia senegal forest in the gum arabic belt in Kordofan is given. Several minor omissions concern inconsistencies in the methodological and textual representation of details of image analysis by segmentation and feature extraction, in the lay-out of the strategies of in-situ sampling and related statistical analysis as well as in the assessment of image elements allowing for the visual interpretation of specific patterns of land use and land cover as a precondition for selection of reliable land use and land cover categories for further classification. A more detailed representation and discussion of image features versus in-situ photographic documentation and description would have been valuable.  The value of the research is evidently based on its thorough integrative structural approach to multi-sensor and multi-temporal image analysis as well as on its strong effort to imply strategies of in-situ sampling of quantitative inventory parameters towards their statistical evaluation via spectral analysis. The appropriate design of the data input as well as the data interpretation and classification based on spectral, object and field parameters builds a novel hybrid strategy of monitoring and assessment of Acacia senegal forests. It is strongly recommended to further operationalise the approach and to implement it in the activities of the Gum Research Centre at University of Kordofan, al-Ubayyid, being the home university of Hassan Elnour Adam Zakaria.
The research study of Hassan Elnour Adam Zakaria is a most valuable and important contribution to building and putting into operation sound strategies of regional planning and management in the Sub-Saharan fringe of the semi-arid lands of Kordofan with special regard to the sustainable development and management of natural resources of  the world-wide unique gum arabic belt of the Kordofan, a cultural landscape which underlay transformations since thousands of years and still provides resources to people and herds on the one hand, and inherits a unique cultural and natural heritage on the other hand.
Endre Stiansen, The gum arabic trade in Kordofan in the mid-nineteenth century, in: Michael Kevane, Endre Stiansen (eds), Kordofan invaded – peripheral incorporation and social transformation in Islamic Africa. Brill, Leiden Boston, 1998, pp 60-85
Ignaz Pallme, Travels in Kordofan .. . Madden, London, 1844 (Translated From the German original, Ignaz Pallme, Beschreibung von Kordofan und einigen angränzenden Ländern .. . Cotta Stuttgart, 1843)

Dresden, March 2011
Professor Dr. habil. Elmar Csaplovics


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 stands 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 stands 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.


Table of Contents

List of Tables    XVI
List of Figures    XVIII
Abbreviations and acronyms    XX
Abstract    1
1    Introduction    3
1.1    Background    3
1.2    Forest Resources in Sudan    4
1.2.1    Overview    4
1.2.2    Gum arabic belt location and role    5
1.3    Problem Statement and Justification    7
1.4    Research Objectives    9
1.5    Research Hypotheses    10
2    Remote Sensing and GIS in Vegetation Mapping  and Monitoring    11
2.1    Historical Overview of Remote Sensing and GIS    11
2.2    Integration of Remote Sensing and GIS    12
2.3    Spectral Reflectance of Vegetation    13
2.4    Properties of Remotely Sensed Data    14
2.4.1    Spatial resolution    15
2.4.2    Spectral resolution    15
2.4.3    Radiometric resolution    15
2.4.4    Temporal resolution    15
2.5    Image Classification    15
2.5.1    Hard classification    16    Unsupervised classification    16    Supervised classification    16    Expert knowledge-based classification    17
2.5.2    Soft classification    17    Object oriented image analysis    18
2.6    Land Use and Land Cover    19
2.6.1    Definitions of land use and land cover    19
2.6.2    Vegetation mapping and monitoring    19    Methods of measuring vegetation condition    20
2.7    Application of Remote Sensing in Forest Inventory    22
2.7.1    Ground measurement    23
2.7.2    Airborne measurement    24
2.7.3    Satellites    24
2.7.4    Applications of models in forestry and remote sensing    25
2.7.5    Forest inventory in Sudan    25
3    Study Area and Research Methodology    27
3.1    Study Area Description    27
3.1.1    Geographical location    27
3.1.2    Climate conditions    27
3.1.3    Soil and geology    28
3.1.4    Description of vegetation cover    29
3.1.5    Land use    30
3.2    Material and Methods    31
3.2.1    Remotely sensed data    32    Landsat satellite imagery    34    ASTER satellite imagery    34
3.2.2    Field data collection    34    Ground truth survey    35    Forest inventory data    35
3.2.3    Ancillary data    38
3.2.4    Socioeconomic data    39
3.2.5    Image pre-processing    39    Atmospheric correction    39    Geometric correction    42
3.2.6    Masking of residential areas    43
3.2.7    Image classification    43    Maximum likelihood classification    43    Object-based classification    45
3.2.8    Classification accuracy assessment    45
3.2.9    Change detection    45
3.2.10    Data analysis methods    46    Land use land cover change analysis    46    Regression analysis    46    Paired samples t-test    48
4    Multi-temporal and Change Analysis of Land Use
    Land Cover in the Gum Arabic Belt in Kordofan    49
4.1    Introduction    49
4.2    Categorisation of Land Use land Cover in Gum Arabic Belt Using NDVI    49
4.3    Land Use Land Cover Classification in the Gum Arabic Belt    54
4.3.1    Land use land cover distribution    55
4.3.2    Land use land cover maps    56
4.4    Land Use Land Cover Change, Trends and Analysis in Gum Arabic Belt    59
4.5    Accuracy Assessment    65
4.6    Driving Forces of Land Use and land Cover Changes in Gum Arabic Belt    67
4.7    Discussion and Summary    69
5    Integration of Remote Sensing, GIS and Terrestrial Forest Inventory in
    Estimation of Acacia senegal stands Parameters    71
5.1    Overview    71
5.2    General Description of Elhemmaria Forest    71
5.3    Extraction of Forest Reflectance from Remote Sensing Data    74
5.3.1    Data transformation    74
5.3.2    Extraction of reflectance using 2x2 and 3x3 pixel windows methods    75
5.4    Estimation of Acacia senegal trees’ Parameters by Remotely Sensed Data    77
5.4.1    Model construction    77
5.4.2    Model evaluation and selection    78
5.4.3    Model validation    80
5.5    Discussion and Summary    82
6    A comparison of Pixel-based and Object-based Approaches for
    Land Use Land Cover Change Classification    85
6.1    Introduction    85
6.2    Image Segmentation    85
6.3    Image Classification    87
6.3.1    Object-based classification    87    Feature extraction    87    Nearest neighbour classification    89
6.3.2    Pixel-based classification    91
6.4    Accuracy Assessment    93
6.5    Discussion and Summary    95
7    Conclusions and Recommendation    97
7.1    Conclusions    97
7.1.1    Land use land cover analysis in the gum arabic belt    97
7.1.2    Integration of terrestrial forest inventory and remotely sensed data    98
7.1.3    Object-based and pixel-based approaches for image classification    99
7.2    Limitations of the Study    99
7.3    Recommendations and Future Outlooks    100
8    References    103
9     Appendices    121



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