TROPICAL PASTURE ESTABLISHMENT .4. POPULATION-DYNAMICS OF SOWN SPECIES IN DEVELOPING PASTURES

The persistence of introduced species in pastures depends on the survi val of plants from the original sowing, and the recruitment of new pla nts to maintain or increase population size. Recruitment can be by veg etative expansion but in many species it is by seedlings. The populati on dynamics of 4 legume species (Stylosanthes hamata, S. scabra, Macro ptilium atropurpureum and Cassia rotundifolia) are outlined, and the i mportance of seed production and soil seed banks for persistence of th ese species is highlighted. The effects of management (grazing, fertil iser, fire, pests and diseases) on survival, soil seed levels and recr uitment are outlined, and examples are given of how these effects are reflected in changes in pasture composition. Some management guideline s based on the understanding derived from these demographic studies ar e presented. Most paddocks are not uniform, and the influence of varia tion across landscapes on the development and dynamics of pastures is also considered. Recruitment and mortality vary across landscapes with management and seasonal conditions. Examples are presented of success and failure in different parts of a paddock, and of temporary loss of a species at the quadrat level but survival at the paddock scale.