NEIGHBORHOOD ANALYSIS OF COMPETITION BETWEEN 2 NAMAQUALAND EPHEMERAL PLANT-SPECIES

By using attributes of neighbours, such as number, size and distance, investigators have developed neighbourhood competition models that are able to predict plant performance of an individual in a plant populat ion. A non-linear neighbourhood model proposed by Silander & Pacala (1 985) was applied to performance data (i.e. total above-ground dry mass ) of Dimorphotheca sinuata and Ursinia cakilefolia, two Namaqualand ep hemeral species. The best neighbourhood size was sought by varying the neighbourhood size and plotting an interference index against dry mas s. The non-linear model was then fitted to the data and the r(2) value s determined for each neighbourhood. Correlations between performance (total above-ground dry mass) and different interference indices were much higher in mixtures than in monocultures for both species. Number of neighbours seemed to be the best predictor of performance for both D. sinuata and U. cakilefolia in mixtures. In monoculture, the best co rrelations were obtained when the distance of the neighbours was also taken into account. Even so, these correlations accounted for less tha n 50% of the variation in plant mass. Although these neighbourhood mod els may be useful in describing the inter-individual effects of interf erence on Namaqualand ephemeral species, it may be difficult to apply these results in the field.