AN ANALYSIS OF LAND USE WITHIN THE LIMITS OF LANDSCAPE UNITS. A CASE STUDY OF THE NORTH-WESTERN
PART OF THE GEFARA PLAIN IN LIBYA Yousef S. Kajalik
Zawia University, Libya
The interaction between humans and their living-space should be approached as a system consisting of two sub-systems: natural and socio-economic. The system has been studied by various specialists, including geographers and ecologists. Various approaches are used in the studies, including an analysis of the way of land use within the limits of landscape units characterised by a definite potential. The method has been developed quite recently and it has not been used so far with respect to the territory of Libya.
This study focuses on the north-western part of the Gefara Plain within the boundaries of the administrative sub-unit (branch of municipality) of Zuwarah. In the west, the area is bounded by the state frontier between Libya and Tunisia. The area covers approximately 5830 square kilometres. Its population amounts to 181,785, which constitutes 12% of the whole Gefara Plain population, according to the population census of 1984. The area under study was chosen due to its natural differentiation and socio-economic features.
The purpose of the study was to grasp the relationship between the potential of landscape units and land use as well as to formulate conclusions aimed at optimisation of land use in the area under investigation. The study was based on an in-depth analysis of the data available in various sources as well as on the author’s own fieldwork. The satellite and air photos were also used. First, the basic components of the natural environment were distinguished and characterised. Then, the landscape units were delimited and next land use was analysed and the map of landscape use was elaborated.
The basic components of the natural environment encompass: relief, lithology, vegetation, climate, soil cover and water conditions. The analysis of the above- mentioned components allowed us to characterise the differentiation of the natural environment of the north-western part of the Gefara Plain.
Relief
The altitude rises steadily from the sea coast towards the east and south. The maximum elevation is found in the south and it amounts to some 120 metres above sea level. The
basic types of relief consist of:
(1) hills;
(2) marshes or Sebkha areas;
(3) plains;
(4) valleys or Wadis (bottom plains and depressions).
From the point of view of relief, three distinct zones may be distinguished:
1. Coastal zone, which rises gently towards the south to an altitude of some 20 metres above sea level. Its width ranges from 10 km in the east to 20 km in the west.
2. Central zone, which rises gradually to an altitude of approximately 80 metres above sea level. Its maximum width is 60 km in the south-east.
3. The southern zone with the altitudes rising from 30 to 60 metres above sea level and the width ranging from 15 to 20 km.
Fig. 1. Relief of the investigation area.
The relief is presented in the hypsometric map (see Fig.1) compiled from thirteen sheets of topographic maps of 1:50,000.
The surface formations are related to the morphological history of the area, which emerged from the sea in the late Miocene, when the entire area of Tripolitania was uplifted. Synthesis of a large number of geological investigations of this area was presented in the geological map of 1: 250,000 (see Fig. 2). Prevalent formations are the Quartenary Holocene and Pleistocene Sediments as well as sediments of the Upper Pliocene underlain by the Miocene and Mesozoic rocks.
The Holocene is represented by loose sands and gravels, aeolian sands as well as silts and alluvia.
Among Pleistocene formations there prevail carbonate fine-grained sands and sandstones with fragments of shells; lenticular insertions of silts are found and there also occur carbonate clays (Gargaresh formation), as well as sands, silts and local accumulations of pebbles, gravel and gypsum (Gefara formation). Pebbles and varied
Fig. 2. Geological map of the Northwestern part of Gefara Plain
series of deluvial and alluvial sediments and conglomerates (Qaser al Haj formation) are also found.
Formations of the Upper Pliocene are represented by gravels, sands and gypsum (Al-Assah formation). Upper Triassic and Middle Jurassic period comprise gypsum, anhydrite and dolomitic limestones (Bir al Ghanam formation). The Upper Triassic period is represented by continental sandstones, limestones with fossils and red sandstone (Abu-Shaybah formation).
Natural vegetation
It belongs to the Mediterranean and semi-Mediterranean type. Steppe and semi-desert vegetation can be found too. According to the climatic conditions and type of soil, as well as human management, the following types of vegetation may be distinguished in the area under investigation:
1. Limited growth of separated communities of forests and brushwood.
2. Small communities of shrubs and scrubs.
3. Communities of semi-shrubs and meadows.
4. Dwarf semi-shrubs.
5. Grasses.
6. Patches of grass and dwarf semi-shrubs of halophilous type.
7. Growth of some weeds alongside cultivated vegetation.
Climate of the studied area is moderate. It is characterised by windy, mild and humid winters and hot, dry summers as well as two short transition periods (spring and autumn). The annual average air temperature amounts to 19-20o C, and the average amount of annual rainfall ranges from 100 to 250 mm. In the autumn and winter, there westerly, northerly and north-western winds prevail, while in spring and summer easterly, north-eastern and sometimes southerly winds are predominant.
Soil cover
Within the north-western part of the Gefara Plain, the following types of soil are found: calcic xerosols (Xk), calcic yermosols (Yk), gypsic yermosols (Yy) and orthic solonchaks (Zo). According to the soil map of the world drawn in scale of 1:5,000,000 and published in 1977 by FAO as well as according to the research carried out in western Libya by Selkoz Promezport in 1980, the following types can be distinguished in the above-mentioned groups of soils: reddish brown arid soils, alluvial soils, saline soils and solonchaks, crust soils and non-soil formations.
Water relations
These are determined both by atmospheric rainfall and groundwater availability. These are two sources of water supply not only in this area but also in the whole country.
An analysis of annual rainfall distribution shows that the entire area receives more than 100 mm of rainfall, but also much higher values, amounting to 220 and 230
mm, have been recorded. Although rainfall is generally low and varies from year to year, in the years more abounding in precipitation, the area receives sufficient amount of water for agricultural crops and growth of plants in the vegetation period.
Groundwater in the studied area comes from both shallow and deep water- bearing formations. Water from shallow aquifers represented by the Quaternary, Piocene and Upper Miocene sediments exhibits disturbed balance which is the result of the lowering water level and worsening water quality. This is specially the case of the coastal zone. The reason for this should be sought in sea-water intrusions and increasing water exploitation, which is related to the increasing population, development of water supply systems, rising life standards and expansion of agriculture that requires water.
The feasibility of the use of water coming from deep aquifers which are represented by the Middle and Lower Miocene as well as the Triassic period, are limited due to great depth and low quality of the water. It should be said that consumption water is also received by sea-water desalination. Appropriate installations are found in several places in the investigated area.
Landscae units
Fig. 3. Landscape types in the Northwestern part of Gefara Plain
Delimitation of landscape units was an important stage of the work. A landscape unit is perceived as a smaller “entity” – geocomplex subordinated to a “bigger entity” – a landscape. Landscape units are defined as parts of geographical landscape, characterised by specific acquisition of properties and the way of functioning. Landscape units are relatively homogenous and their character is determined both by natural resources and by human activity. Each unit is described through dominant components of the natural environment and is an entity being the result of the interaction of many components.
For the purpose of the elaboration, a map of the natural landscape types was drawn by comparing the kinds of geological structure and relief forms but other components of the natural environment were also taken into account. A map of the natural landscape types was compiled in scale 1:250,000, and shown as a map in reduced scale in Fig. 3.
The principal components which were taken into consideration (relief, lithology, altitude above sea level, natural vegetation) determine other less important components, such as soil and water. The interaction of all those components affects the kind and value of natural potential of the unit.
Fig .4. Land use in the Northwestern part of Gefara Plain
It may be observed that the units linked up with the forms of Sebkha or marshes occupy a vast part of the littoral areas. These areas lie across the Wadi lowlands, which can be seen particularly in the west of the lowland. The Sebkha units which occur in the entire investigated area are characteristic and make it different from the rest of the country. However, they are not dominant in respect of the size of the area. The largest areas are occupied by sand lowlands and their proportion increases towards the south and towards the east.
The classification of landscape units within the limits of the Gefara Plain was carried out by use of the system proposed by Kondracki and Richling for the purpose of elaboration of typology of Poland’s natural landscape. In accordance with the assumptions made, four classes, eight sub-classes, eleven types and twenty-six sorts of landscape were distinguished.
In the littoral zone, an impact of the sea upon the natural landscape is very strong. The origin of the forms of relief is connected with the processes caused by the sea. Thus, natural units are determined by their marine origin and constant impact of the sea. In the map of natural landscape most of the units types in the littoral zone correspond to the areas of Sebkha or littoral hummocks (dunes) to which meadows, brushwood and forests may be attached. The areas of Sebkha cover salt marshes, lagoons and alluvial plains. The shape and height of the dunes vary. Dependence of those areas on the sea is expressed i.a. by high humidity. The increasing salinity of soil and groundwater is also of great importance. Sea water penetrates the littoral areas through tidal phenomena and underground intrusions of salt water occur.
In the remaining parts of the area, where the natural environment gradually turns from marine to continental other types of landscape units prevail. They encompass hummocks and hills, sandy plains and rolling plains, marshes and Wadi valleys.
Surface erosion and accumulation processes are prevalent there.
Land use
It is most often analysed only as the effect of socio-economic activity and is regarded as an expression of human impact on the natural systems. One should say, however, that land use is usually connected with the resources of a given habitat, that is with the landscape potential. That is why the major types of land use were distinguished on the basis of the dominant form of land use, but also taking into consideration physiognomic and ecological features of the area and with regard to the natural environment potential, which, in turn, also depends on spatial variability and impact of human activities.
Types of land use were divided into two groups: agricultural and forest land use as well as urban and industrial use. The map of land use types was drawn, just as in the previous case, in scale of 1:250,000 (see Fig. 4). Types were distinguished based on satellite and air photos, as well as data available in the various sources. The following types were distinguished: settlements, orchards, agricultural areas, forests, urban areas, industrial areas and recreation areas. In addition to the above-mentioned areas, the map shows areas under intensive and extensive cultivation, intensive and extensive pastoral economy and areas with the mixed form of land use – agricultural-pastoral. Salt marshes and barren land were also marked. The analysis of the map shows that most
of the area under investigation has mixed types of land use. The map also allows us to determine the main forms of socio-economic activities and it was used for the mapping of land use.
The compilation of the landscape use map was the most important stage of the work. This map was drawn in the same scale as the previous maps (see Fig. 5) and it resembles studies conducted in other countries, especially in Europe; its methodology was developed and improved in Poland.
The map of landscape use of the north-western part of the Gefara Plain was drawn by correlating two previously elaborated maps: typology of natural landscape and of land use types. The map shows the aforesaid types of land use which were analysed within the limits of the following types of landscape units:
I. Dune areas:
1. Sand beaches.
2. Littoral dunes.
3. Inland dunes . 4. Mobile sand fields.
II. Hummocks and ridges
5. Crusty hummocks and ridges.
6. Alluvium and eolian hummocks.
7. Sand hummocks with poor vegetation.
III. Sebkha areas
8. Salt marshes and damp swamps.
9. Humid meadows.
IV. Sebkha plains with hummocks
10. Sebkha plains with hummocks not covered by vegetation.
11. Sebkha plains with hummocks covered by vegetation.
V. Flat sand plains
12. Flat sand plains of low level.
13. Flat sand plains of higher levels.
VI. Rolling sand plains
14. Rolling sand plains of low levels.
15. Rolling sand plains of higher levels.
VII. Lowlands and Wadi forms
16. Lowlands with clear-cut limits.
17. Lowlands with unclear limits.
The map of landscape use was regarded as a cartographic presentation of the interaction between the structure of the natural environment shown as geocomplexes with different potential and the structure of land use closely related to the natural predisposition of the terrain. The map in question can be used for various purposes, including the management of the environment, evaluation of anthropopressure intensity, landscape protection and management, and spatial planning. By analysing the elaborated map of the part of the Gefara Plain attempts were made to arrive at conclusions which might contribute to the improvement of the way of spatial
management. In particular, attempts were made to distinguish areas marked by specific features, areas utilised in accordance with the natural tendency, and those of mismanagement. In case of the latter, the possibility of replacing the existing form of land use by a different one or of expansion of the existing forms of land use was considered. The study of the distribution of land use types within the landscape units also allowed to grasp those properties of the natural environment which affect the system of land use. An analysis of the map also helps to capture the conflicting areas which are threatened with degradation processes. As it seems, the results obtained may constitute a good basis for solving definite problems and should be utilised to elaborate the programme of further development of the investigated area.
The analysis was based on tables containing the comparison of sub-classes, types and sorts of landscape with the types of land use occurring within their limits.
This dependence was also presented graphically by drawing appropriate charts.
It can be well seen that within the limits of the studied area several types of land use can be encountered. Generally, their variety corresponds to the potential
Fig. 5. Landscape use of the Northwestern part of Gefara Plain
of landscape units and population distribution. Low-lying plains and some alluvial lowlands within the limits of the forms of Sebhka are connected with the areas of highest density of population. Here, plains under agricultural use can also be found. The reason for greater intensity of land use in these areas is their situation in the vicinity of the sea coast. These areas are also marked by the greatest variety and intensity of forms of the impact of human management upon the natural environment.
In the eastern part of the area investigated, the following forms of land use are concentrated: urban development, orchards, intensive agriculture, intensive shepherding, forests, areas of mixed land use. Within the limits of urban areas, the following can be distinguished: built-up areas, transportation, recreation, services, trade and fishing areas. Agriculture includes vegetable and fruit cultivation in the conditions of constant irrigation. Intensive shepherding is connected with a sedentary life; these are usually small households in which vegetables and fruit are cultivated in addition to animal husbandry.
In the western part of the studied area, extensive agriculture is a prevalent one, though some fragments of the area are under intensive cultivation. They are concentrated around local centres of agriculture servicing. In addition to agriculture, in the western part of the area the mixed agricultural and pastoral land use is of importance; forests and bigger meadows can be found, too.
The southern part is entirely different. Here, apart from vast areas of barren land, extensive shepherding is the only form of land use.
All this shows that there is a close relationship between low-lying plains and intensive agriculture and fruit farming in the eastern part of the area. Extensive agriculture and intensive shepherding are connected with low-lying plains in the central part. In the south, extensive shepherding is closely connected with the rolling sand plains and with the plains occurring in the valley bottoms. The settlement in the littoral zone is in the majority of cases linked up with the Sebkha areas. The same areas are also characterised by ties with industry. The settlement is also related to inland plains (flat low-lying areas). Plains situated higher show correlation in the eastern part of the area with the mixed agricultural and pastoral land use. There is also a relationship between forests and low plains and with sand hummocks in the coastal zone.
Conclusions
To sum up, the following conclusions may be drawn:
1. Studies of land use in respect to the structure of natural environment are of great importance for environmental planning and management. That is why the research in the north-west of the Gefara Plain should be carried on, using more in- depth information that can be available as a result of detailed fieldwork. Such work should lead to the formulation of a substantiated forecast of the future status. Similar research should be carried out in other parts of the country.
2. Main problems that need solution in the north-west of the Gefara Plain include: counteracting erosion and soil salinity, increasing the soil fertility, water supply and water quality. There is also a need to prevent desertification process. The area is marked by the shortage of labour in agriculture. If all these problems are not
solved, this will lead to a future deterioration of the entire environmental system.
3. The majority of the area should be afforested. Forests composed of appropriate species should be planted in the form of longitudinal belts to create green zones.
4. Except for the areas in which salt or other raw materials for industry are received, the Sebhka areas should be treated with special care and investigated in detail in respect to the possibility of their future utilisation.
5. High technologies should be introduced in industry as they have a less negative impact on the natural environment.
6. Special emphasis should be on the development of recreation and appropriate maintenance of the areas of the highest recreation values. They encompass the sea coast and forest communities in the coastal strip, as well as the town of Sabratah.
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