'n Ekologiese studie van gifblaar, Dichapetalum cymosum [Hook] Engl. in die Pretoria-omgewing

Abstract

Although Gifblaar (Dichapetalum cymosum (Hook)Engl.) has been extensively studied from a biochemical viewpoint, comparatively little is known of the ecological relations of the plant, which is of considerable economic importance because of its poisonous effects on livestock in Southern Africa. The density, frequency of occurrence and ecological relations of Gifblaar were studied in a representative and varied area of about 2,400 sq. km around Pretoria. A strong correlation between the detailed distribution of Gifblaar and that of certain geological formations was found . The plant occurs only on acidic sedimentary formations and their residual soils and is absent from soils of igneous origen. It is correlated with a low range of calcium concentrations, low soil pH, well-drained, lithosolic, sandy loam and sandy soils.

The distribution limits of populations in the research area are linked with a climatic boundary due to minimum air temperature and, most likely, soil temperature . Semi-quantitative studies on species associates of Gifblaar show that Ochna pulchra and Burkea africana are the most reliable plants indicating the presence of Gifblaar. Reproduction studies revealed that under favourable climatic conditions during the

1968-'69 growth season the number of seeds produced by Gifblaar was only one thousandth of the potential seed formation. Viable seed planted in the veld did not germinate, whereas seed planted under experimentally simulated forest conditions of high humidities and in organic forest soil resulted in 97 percent germination . Methods to propagate Gifblaar successfully from seed and cuttings are described for the first time .