TROPICAL PASTURE ESTABLISHMENT .3. IMPACT OF PLANT COMPETITION ON SEEDLING GROWTH AND SURVIVAL

Plant competition can be a potent force influencing the success or failure of pasture establishment and hence the financial viability of pasture development. Perennial legumes, including tree legumes, are particularly vulnerable to competition because of their slow seedling growth rate. This paper reviews the effects of plant competition during pasture establishment in subtropical and tropical areas of northern Australia and advances the hypothesis that gaps in the existing pasture of adequate size are needed for reliable and effective establishment. Root competition is generally more important than shoot competition for the growth and survival of seedlings. Variation in requirements for nutrients and the ability to form symbioses with rhizobium bacteria and, in some cases, vesicular-arbuscular mycorrhiza, enable legumes to compete successfully with, and establish in native grasslands on low fertility soils; grass establishment usually fails under such conditions. This paper discusses the need for a greater understanding of how the effects of root competition vary according to the amount and distribution of rainfall, and how the effects of fire and grazing might affect root competition in different climatic regions.