Intra- and inter-specific competition between seedlings of Acacia etbaica and a perennial grass (Hyparrenia hirta)

Intra- and inter-specific competition between seedlings of Acacia etbaica Schweinf. and the grass Hyparrenia hirta (L.) Stapf. was studied to evaluate the influence of the perennial grass on the establishment of the tree seedlings. The experiment was conducted using a replacement series in which plants were grown in a greenhouse at an overall density of six individuals per pot, providing combinations of the two species from 0:6 and 6:0. Indices of intra- and inter-specific competition, relative crowding coefficients and relative yield totals (RYTs) were calculated from the dry weight data. For both shoots and roots, the crowding coefficient of Hyparrenia towards Acacia was five- to ten-fold that of Acacia towards Hyparrenia, which indicated a high competitive strength for the grass species. RYT values of the two species averaged 1.25, indicating some degree of resource complimentarity. Both species had comparable intra-specific competition based on shoot yield. However, based on the root yield, intra-specific competition of Hyparrenia was slightly lower than that of Acacia. Inter-specific competition of Hyparrenia on the root yield of Acacia was more than five times greater than vice versa. With more crowding, shoot/root ratio decreased more in Hyparrenia than in Acacia for pure stands as well as for mixtures which indicated that Hyparrenia could adjust biomass allocation. In general, the results indicated that Hyparrenia was competitively aggressive towards Acacia and may inhibit the growth of tree seedlings when the latter are planted within the grass community. Implications of the findings in terms of land reclamation efforts are discussed.