INTERFERENCE IN POPULATIONS OF 3 WEED SPECIES

Interference between individuals was investigated in monocultures and mixtures of 3 weed species, Bidens chinensis, Eleutheranthera ruderalis and Tridax procumbens. Increasing density induced greater mortality and a considerable plastic reduction in the size and reproductive potential of the individuals of all 3 spp. In mixed cultures, B. chinensis suppressed the other 2 spp. while E. ruderalis suppressed T. procumbens. The growth of B. chinensis and T. procumbens in monocultures, and relative success of these 2 spp. in mixtures, was greatly influenced by the soil surface heterogeneity. Survival and plant size of both species was greater in hollows than on hummocks. In mixtures, the species occupying hummocks was always suppressed by the species occupying hollows. However, when the 2 spp. were grown evenly on hummocks and in hollows, neither species had an overall competitive advantage over the other. The results are discussed in relation to the natural regulation of populations of these species in the field.