Naturalne warunki rozwoju uprawy roślin na pograniczu lasu i sawanny w Afryce

The fundamental assumption of the work is the relation between the geographical environment of the border zone of the equatorial forest and savannah in Africa, and the cultivation of plants. The problem suggiests original though very general views of some agriculture historians who consider the areas of differentiated environment the probable cradle of mankind, the place of the beginning and important development stages of the man's economic activity. The paper words a working hypothesis that the differentiation of the geographical environment, expressed in the border line of the equatorial forest and savannah, is one of the significant factors of plant cultivation. To check this hypothesis the relation was analyzed between the geographical environment and the initiation of plant cultivation as well as its contemporary features and development. Theoretically the work was based on the assumption that elements selected for analysis are parts of a larger system in the functional and spatial sense. The analysis availed of research results dispersed in the literature on paleography, physical geography, archaeology, history and broadly conceived geography of man. Employed was the comparative analysis of the mechanism of mutual relationship of selected elements of the geographical envirorunent and plant cultivation in the zone of forest, savannah and in the zone of the forest and savannah border line. Only in few cases the material allowed for quantitative approach of the analyzed phenomena. The heterogeneity of source materiał frequently compelled to cautions wording of conclusions. Natural conditions of initiatilon of plant cultivation were considered from the point of view of two general opinions about the beginnings of agriculture adopted in the form of assumptions. The first states, that the existence of intensive collecting forms is an indispensable condition of starting plant cultivation. According to the second view, the primary heterogeneity of wildly growing species related with cultivated plants is such an indispensable condition. The above assumptions were investigated by means of analyzing spatial differentiation and changes in time of three elements of the geographical environment: (a) climate, particularly of selected limiting factors of plant growth; (b) soils, paricularly their fertility; (c) vegetation, mainly its productivity and species composition. The domestication of plants in the forest-savannah boundary zone wais examined also on the basis of ecological requirements of african cultigens and the distribution of wild growing species closely related with the cultivated plants. Due to the analysis based on quantitative assessment of the climate factors limiting the growth of plants in terms of the J. Phillips method (1959) modified for the purpose of this work, the conformity of spatial differentiation of the mentioned factors of climate, soil and natural vegetation was stated. It was determined that a greater natural productivity and richer flora conditioned by climate and soils were the specific feature of the geographical environment in the forest-savannah boundary zone at the time of the beginnings of agriculture. A richer vegetation of the forest-savannah boundary zone guaranteed to the man better possibilities of finding plants serving as nourishment at the same time contributing to the survival of a greater number of population there. This conclusion is confirmed by the reconstruction of the African continent's population at the end of Pleistocene carried out by archaelogists who located the zone of intensive collecting at the outskirts of a dense forest complex. As far as some cultivated plants of African origin are concerned it was anticipated that the border zone of equatorial forest and savannah was the most probable place of initiation thieir cultivation. They include: the group of Guinean jams, pearl millet and oil palm. Moreover, the zone of forest and savannah border line is an area of overlapping ranges of the occurrence of majority of basic cultivated plants of African origin and of wild growing species related with them. The results of the analysis became the basis for the shifting of G. P. Murdock's independent center of origin of agriculture from the Mande region to the eastern part of West African section of the forest-savannah boundary zone wher african yams had been domesticated. One of the most important generalizing conclusions of this part of the work consisted in the statement, that the zone of forest and savannah border was an area mostly favouring the early development of plant cultivation due to more favourable conditions of the geographical environment mainly conditioned by its diversirty. A similar tendency may be noticed also with regard to contemporary plant cultivation. The differentiation of the envirionment through crops structures and yield of plants creates conditions for a bigger concentration of population which in turn accelerates the evolution of traditional systems of plant cultivation. Three types of man's „responses” were recorded to natural possibilities of the zone of forest and savannah border. In the first case, tribes living in the zone of forest and savannah border farm only in savannah, in the second - only in the forest, and in the third - they utilize both environments. Relatively developed plant cultivation accompanied by a bigger population density occurs most frequently in the case of those tribes which utilize both forest and savannah environment. The analysis carried out in this part of the work enabled the author to take a stand with regard to the existing contradictory views concerning the relation between the distribution of population and the border line of the equatorial forest. The analysis states, that the main advantage of the geographical environment of the equatorial forest border are conditions favouring the occurrence of diversified crops structure and correlated agricultural production. The existence of a relationship between population distribution and forest border is confirmed by denser population in its vicinity, settlements both in the forest and the savannah, but with the possibility of agricultural utilization of both environments. The results of the analysis throw also a new light on the broadly discussed problem of the so-called „middle belt”. One of the reasons of the occurrence of a belt of smaller population density in the vicinify of primary border of the equatorial forest and the contemporary border between the derived savannah and South Guinean savannah, called the „middle belt”, is, apart from other reasons, also the long duration of the influence of intensive cultivation pression which caused the retreat of the forest's border and gradual degradation of the environment. Due to taking into account two rather distant stages of plant growing development it was possible to determine the permanence of the differentiated environment's influence upon the man's activity though the mechanism of this relationship and its effects are in both cases different. The natural potential itself of the equatorial forest border zone is the most essential factor of initiation plant cultivation. Whereas in the contemporary evolution agriculture more importance is gained by the method of utilizing this potential by the man.