Effects of time-since-fire on the tussock dynamics of a dominant grass (Themeda triandra) in a temperate Australian grassland Original Research Article

Changes in tussock attributes and sward structure with time-since-fire were documented for the dominant tussock grass, Themeda triandra, at the Derrimut Grassland Reserve in southern Victoria, Australia. When the inter-fire interval exceeded 6 yr, the number of tillers per tussock and the total number of tussocks declined, and by 11 yr, few live tillers or tussocks remained in the sward. Below-ground biomass was also substantially lower at this time. With increasing time-since-fire, the canopy of live leaves was elevated high above the soil surface and dead leaves accumulated around and over the tussock bases. Productivity declined in long unburnt areas and by 11 yr without disturbance, the canopy “collapsed” upon itself, forming a thick layer of dead thatch over the soil surface. A single fire in an area previously unburnt for 12 yr did not immediately return the tussocks to a state more characteristic of a site with a 4 yr inter-fire interval burnt at the same time. Inter-fire intervals of less-than-or-equals, slant5 yr would appear necessary to maintain the health and competitiveness of Themeda triandra. These findings have important implications for the maintenance of faunal habitat and the potential for weed invasion into remnant grasslands.