Sustainable grazing systems for the Central Tablelands of New South Wales. 1. Agronomic implications of vegetation - environment associations within a naturalised temperate perennial grassland

Temperate perennial grass-based pastures dominate the high rainfall zone of south-eastern Australia and support a major livestock production industry. This area has experienced a recent change in overall pasture condition, however, typified by a reduction in the abundance of perennial grasses and an increasingly prominent winter-annual grass weed component. Improving the condition and productivity of these pastures can be achieved by improved management but this requires better knowledge of the interactions between management options and pasture species composition and of the interaction between pasture vegetation and the complex effects of a heterogeneous landscape. This paper reports the results of an intensive survey of a 60-ha paddock that was designed to identify the species present, determine their patterns of distribution and examine the relationships between pasture vegetation and the environment. The survey of species present in late summer was supplemented by the identification of seedlings that later emerged from extracted soil cores and by soil physical and chemical analyses. Data were analysed using ordination and interpreted with GIS software so that topographic features could be considered. The most frequently identified taxa were Hypochaeris radicata, Austrodanthonia spp. and Bothriochloa spp. (in late summer) and Vulpia spp., Bromus molliformis and Trifolium subterraneum (winter-annual species). Austrodanthonia spp. were commonly found on the drier ridges and more acid soils with lower phosphate levels. These were also the areas dominated in spring by Vulpia spp. and were generally lower in plant species richness overall. The most species-rich areas occurred downslope where soil fertility was higher and less moisture stress was presumably experienced. The measured environmental factors explained a substantial proportion of the variation in the vegetation dataset, which underlined the importance of considering landscape effects in the management of typical tablelands pastures.