Grassland species response to soil disturbance and nutrient enrichment on the Northern Tablelands of New South Wales

An experiment was established in an area of long- grazed temperate grassland on the Northern Tablelands of New South Wales to investigate individual species response to mechanical soil disturbance and nutrient enrichment. Grazing was excluded for the duration of the experiment. The total species pool available in the experiment included 56 native and 24 exotic species recorded in the plots, as well as seven exotic species that were artificially introduced ( i. e. sowing treatment). Eighteen months after treatment, total species richness was significantly lower under high soil disturbance ( mean of 14.7 +/- 0.85 species m(-2)) than under low ( 21.1 +/- 0.67 species m(-2)) and moderately ( 21.7 +/- 0.77 species m(-2)) disturbed conditions. Total species richness was not significantly affected by nutrient enrichment or sowing. Most of the annuals analysed were exotic and their relative cover increased with nutrient enrichment ( Aira cupaniana Guss., Briza minor L. and Vulpia spp.), but was unresponsive to soil disturbance. Perennials showed varied responses, with the abundance of most decreasing with high soil disturbance and being unaffected by moderate soil disturbance levels. All four perennials favoured by high soil disturbance were exotic ( Dactylis glomerata L., Lolium perenne L., Hypochaeris radicata L. and Sanguisorba minor Scop.); three of these were sown. Most perennials showed no significant response to nutrient enrichment, although the occurrence of a small number was either reduced ( Aristida ramosa R. Br., A. warburgii Mez., H. radicata and S. minor) or increased ( Carex inversa R. Br., D. glomerata, Fimbristylis dichotoma ( L.) Vahl., Sporobolus creber De Nardi and Tricoryne elatior R. Br.). Most interactions ( i. e. species response to one experimental factor depends on another experimental factor) occurred because few individuals survived on the severely soil- disturbed plots to respond to nutrient enrichment. However, in this particular grassland, the short- term response of most species to soil disturbance was independent of the level of nutrient enrichment.