Die Invloed van besoedelde lug op basbewonende ligene in Pretoria (Volume I)

Abstract

The distribution of macroscopic corticolous lichen species against northern and southern fronts of the trunks of Jacaranda mimosifolia was determined by means of transects. The vertical distribution of lichens against phorophytes in the study area was graphically shown. Differences in terms of species composition and other factors between the northern and southern fronts were highlighted. Mapping of the horizontal distribution of lichens in the study area showed the inverse relationship which existed between polluted air and lichen growth. Diversity indexes for releves representing lichen growth along the northern and southern fronts of phorophytes were calculated according to the formulae of Simpson and Shannon-Wiener. Index of Atmospheric Purity values were also calculated for the different releves. Correspondence between results obtained from calculations of the different indexing techniques was investigated. Zones of similar species diversity were mapped in order to determine the distribution of isotoxic zones. A Braun-Blanquet survey was made of lichen growth which occurred at a height of 300mm and 1,3m against the northern, southern, eastern and western fronts of phorophytes. The sociological tables, representing lichen growth in each of the different micro-habitats were compiled. These tables showed the ecological/ sociological differences present in the different micro-habitats. By means of the sociological tables the existence of a sensitivity gradient in terms of air pollution could be shown for the different lichen species. The distribution of isotoxic zones in the study area could be determined by mapping the distribution of the different associations. Interspecific associations between different combinations of species were mathematically determined for lichens found in the different micro-habitats. The degree of similarity between lichen growth associated with the different micro-habitats was determined by means of Spatz's index of similarity.