Showing papers on "Biodiversity published in 1973"

Ecological investigations of forest communities in the eastern orange free state and the adjacent natal drakensberg

Abstract: Small ravine forests which are found as an extrazonal vegetation in the grassveld country of the eastern Orange Free State have been investigated. Special attention has been paid to the microclimate, the soils, floristics, and synecology of these small evergreen forests. The data obtained indicate the important shielding effect of the forest canopy on the humidity, radiation, temperature conditions and consequently on the soil formation. Soil samples collected in the forests were studied on their texture classes, pH, conductivity, organic matter content and determinations were made of their replaceable ion content. In contrast with the soils of the surrounding areas the organic content of the forest soil is extremely high. Synecological surveys were made according to the method ofBraun-Blanquet. Two distinct plant associations have been described: the Ehrharto-Eucleetum crispae and the Peperomio-Carissetum. In the first, three subassociations could be distinguished. The geographical distribution of these associations is correlated with a humidity gradient and differences in soil characteristics. The geographical distribution of a number of woody species of the ravine forests was studied for the whole of Africa. The patterns indicate that these forests are closely related to the biome of montane-temperate forests which are spread throughout Africa, from West and East Africa down to the coast of the Cape Province. The possible origin and palaeobiogeography of these forests is shortly discussed.

Habitat features and vegetation of deserts and semi-deserts in egypt

Abstract: Egypt forms the north-eastern corner of Africa and embraces a total area of almost exactly a million square kilometres. Desert conditions prevail throughout the country, and the population of nearly 34 millions is mainly concentrated in an area of some 355oo sq. kin. The cultivated area amounts to about 25oo sq. km. Without the Nile, Egypt would be the harshest desert all over the world. The Nile traverses the country from south to north for a distance of 15oo kin. A glance to the map of Egypt (Fig. I), with the cultivated lands coloured green and the deserts in shades of brown, will show that the cultivated land has the shape of a lotus plant. The Nile represents the stem, the Delta is the flower and Fayioum depression is the bud. Egypt, due to its peculiar situation, has been considered to belong to more than one floral region. The northern coastal region adjacent to the Mediterranean sea belongs to the Mediterranean region and forms a natural extention of the Algerian-Tunisian flora. While the major part of the country belongs to the African-Indian desert region. Relics of the western and central Asiatic flora are met with in Sinai. In the southeastern corner of Egypt viz. Gebel Elba, the flora of the Sudanese Park Steppe is found. Egypt occupies a key position between the Asiatic and African continents, and its floristic composition shows affinities in different directions.

Succession and stability in biological communities

Abstract: An analysis of community structures in relation to applicability of various measures of diversity is undertaken. Structural changes in natural communities are examined with respect to succession. It is concluded that in general, diversity, however measured, can be expected to increase, at least initially with time over a successional gradient. The relationship between structural diversity, biological diversity and succession is investigated and it is concluded that in the case of marine fouling communities the former attribute of a substrate generates increased biological diversity whereas the latter characteristic is restrictively determining of future associations. This paper consists of two parts of which this, the first deals with relationships between structural and species diversity in conjunction with community development. The second section concerns relationships between community development and organization.