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

Plant competition can be a potent force influencing the success or fai lure of pasture establishment and hence the financial viability of pas ture development. Perennial legumes, including tree legumes, are parti cularly vulnerable to competition because of their slow seedling growt h rate. This paper reviews the effects of plant competition during pas ture establishment in subtropical and tropical areas of northern Austr alia and advances the hypothesis that gaps in the existing pasture of adequate size are needed for reliable and effective establishment. Roo t competition is generally more important than shoot competition for t he growth and survival of seedlings. Variation in requirements for nut rients and the ability to form symbioses with rhizobium bacteria and, in some cases, vesicular-arbuscular mycorrhiza, enable legumes to comp ete successfully with, and establish in native grasslands on low ferti lity soils; grass establishment usually fails under such conditions. T his paper discusses the need for a greater understanding of how the ef fects of root competition vary according to the amount and distributio n of rainfall, and how the effects of fire and grazing might affect ro ot competition in different climatic regions.