Inter-Specific Competition Between Seedlings of Pinus radiata, Eucalyptus regnans and Acacia melanoxylon

Abstract

A replacement series experiment was carried out to determine the competitive aggressiveness of three species, P. radiata, E. regnans and A. melanonylon towards each other at seedling stage. Seedlings of the three species were grown at an overall density of six plants per pot for each species combination, providing all combinations of two species from 0:6 to 6:O. In addition, seedlings were grown in pure stands from one plant to six plants per pot for the three species. The relative crowding coefficient, the relative yield total, the relative effects of intra- and inter-specific competition on the yield of each species were the four indices calculated. Acacia melanoxylon was the most aggressive species, followed by P. radiata then E. regnans. In comparison with their corresponding monoculture, A. melanonylon in mixtures showed the smallest decrease in shoot/root ratio, whilst P. radiata had a greater decrease and E. regnans showed the greatest reduction. The average relative yield total of E. regnans and A. melanoxylon was close to 1 for both shoots and roots, indicating an almost complete overlap in resource use between the two native species. The relative yield total of P. radiata and E. regnans was 1.27 for shoots and 1.48 for roots, suggesting a possible difference in resource use between them. The results of this experiment provide a valuable qualitative insight into the relative magnitudes of the effects of inter- and intra-specific competition between the seedlings of the three species.