Volume 27, 302

Tropical Grasslands (1993) Volume 27, 302–313

Tropical pasture establishment.
4. Population dynamics of sown species in developing pastures

J.G. McIVOR¹, R.M. JONES² and J.A. TAYLOR²

¹Division of Tropical Crops and Pastures, CSIRO, Townsville, and
²Brisbane, Queensland, Australia

Abstract

The persistence of introduced species in pastures depends on the survival of plants from the original sowing, and the recruitment of new plants to maintain or increase population size. Recruitment can be by vegetative expansion but in many species it is by seedlings.
The population dynamics of 4 legume species (Stylosanthes hamata, S. scabra, Macroptilium atropurpureum and Cassia rotundifolia) are outlined, and the importance of seed production and soil seed banks for persistence of these species is highlighted. The effects, of management (grazing, fertiliser, fire, pests and diseases) on survival, soil seed levels and recruitment are outlined, and examples are given of how these effects are reflected in changes in pasture composition. Some management guidelines based on the understanding derived from these demographic studies are presented.
Most paddocks are not uniform, and the influence of variation 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.