publisher = {Selbstverl. d. Inst. f. Physische Geographie, FU, Berlin},

abstract = {[contains map: Geoecology of Ouarzazate] ; [contains map: Geology of Ouarzazate] ; Summary: The structural pattern of the small and large-scale, local and regional vegetation conditions in the Ouarzazate basin was investigated. The objective was to map the vegetation as an integrating indicator of the different geoecological site types and the structural units of relief. From these results a generalized model in the form of a catena and a map of the geoecological structural pattern were obtained. The main factor influencing the basin is its arid climate, causing a dry steppe vegetation and the almost total lack of soil formation. Results show that the uniformity of the vegetation in the study area is mainly due to anthropogenic influences (extensive goat and sheep pasturing). The Haloxylon articulatum - type of vegetation prevails on all the older, gently sloping glacis plains covered with mainly loamy sands containing much stony material. Neither the westeast differentiation of rainfall and temperature conditions, relief—linked climatic factors, age, various climate-genetic and tectogenetic processes during the formation of the glacis plains overlying the Mio—Pliocene basin sediments nor the sediments themselves produced any variation in this vegetation. The only differentiation in the Haloxylon articulatum vegetation was a decrease in density corresponding to increasing silt and clay content of the subsoil. However, this decrease ist not linked to geomorphological or geological basement structures. The main type of vegetation in the basin has only a limited pasture value and is only grazed by goats for lack of better fodder. The Ouarzazate basin thus possesses only a low potential as pasture land. Small-scale variations in the Haloxylon type of vegetation are mainly due to relief—based variations in habitat. Shallow drainage-ways and depressions filled with sandy-clayey to sandy-silty loam containing little stony material have a generally thick plant cover with Artemisia herba—alba predominating. Since this species has a higher grazing value and is often associated with numerous other shrubs these sites are the only abundant pasture areas on the glacis plains. Farsetia Hamiltom'i and Convolvulus Trabutianus predominate on slopes with gradients over 30, characterized by a coarse debris layer overlying the stony, sandy-silty layer and by greater edaphic aridity due to subsoil conditions and topographic Situation. There is no differentiation according to slope orientation. Neither species is important for pasturing. There are varieties of the Haloxylon-type that are due primarily to anthropogenic rather than relief factors. They are limited to the eastern part of the basin, cover only small areas, and their subsoil and relief conditions are comparable to those of the Haloxylon type: The Peganum Harmala-variety - a ruderal plant typical of overgrazed sites - occurs along the only easily accessible route from the Ouarzazate basin to Jbel Sarhro and the saharien South which is often used by the mountain population and the Berber nomads to reach the market village of Boumalne. The Helianthemum Lippii - Aristida obtusa – variety with its high proportion of good grazing plants is limited to the areas in the north-east of the basin where relief conditions render grazing almost impossible. The Artemisia herba-alba — variety occurs only on the glacis immediately adjacent to the mountain chains in the north and south. These glacis frequently have steeper slopes and a pronounced relief, due to the numerous run-off channels. This variety, prevalent on stony, often crustified sandy—clayey loams, is often degraded owing to its high fodder value and its use as a medicinal herb. Because it is not widespread its potential pasture value is limited. In contrast to the above-mentioned types the Farsetia Hamiltonii — variety of the Haloxylon - type and the Halophyte — type, both limited to the more recent plains, reveal a clear correlation to the geological conditions of the bedrock: The Farsetia Hamiltonii - variety is typical of sites with stony, sandy loams and (in contrast to the Haloxylon type) no subsoil crusts, i.e. an extensive Tensiftien plain with only moderate salinity in the centre of the Ouarzazate basin. The Halophyte - type, on the other hand, is restricted to the silty sands with low stone content found on the Soltanien plain and the Rharbien ”alluvions modernes” in the western part of the basin. Unlike the older plains, the sediments here are fine-grained and increasingly saline as the ground-water level of the generally lower-lying plains rises in the south, resulting in a prevalence of halophile species. In connection with this vegetation type a number of more valuable pasture plants occur, but only in small patches. Because they are situated in the most heavily grazed region, the west of the study area, there are clear traces of heavy overgrazing here too. The bigger wadis and dry valleys, which represent a further site type, have a more varied association of different shrubs and a higher proportion of phanerophytes, often linked to nebka formation. They belong to the most important grazing areas for extensive animal husbandry, frequently causing the range of species to shift towards the less popular species or those avoided entirely by grazing animals. The shrub vegetation is generally characterized by species adapted to the edaphic aridity of the sandy-loamy gravel deposits on the valley floors, whereas the phanerophytes mostly possess long roots extending down to the groundwater reserves in the bigger wadis. Those wadis with regular discharge or a high groundwater table and finegrained sediments as opposed to gravel accumulations are characterized by intensive cultivation. The limited distribution of good pasture vegetation, together with the semi-arid - arid conditions and overgrazing have led to a uniform vegetation of low fodder value. The continuous degradation of these low—species associations, intensified by the absence of annuals as in recent, relatively dry years, results in the extensive Hat areas of the Ouarzazate basin being increasingly denuded of any vegetation whatsoever. Thus the pressure caused by grazing is increased and the inevitable result will be the total degradation of the Haloxylon articulatum vegetation, thus completing the process of irreversible damage to the vegetation. Plant regeneration is only possible if the remaining, often only sparse vegetation is rigorously protected from overgrazing, use as fuel etc. However, this necessity is counterbalanced by a continuously increasing population, insufficient information and, above all, the lack or only slow improvement of infrastructure in southern Morocco.},
note = { \url {http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/7210}},
}