Response of a rare herb (Trioncinia retroflexa) from semi-arid tropical grassland to occasional fire and grazing

Trioncinia retroflexa (Asteraceae) is a rare perennial herb endemic to Dichanthium -dominated grasslands on basaltic soils in central Queensland. Trioncinia lives for approximately 5 years and some seed remains viable in the soil for at least 18 months. Population densities increased sixfold over 4 years, coinciding with recovery during a period of above-average rainfall after a 4-year drought preceding this study. The species' lifespan, which can exceed 5 years, coupled with its extended seed-bank viability ensures that populations can endure drought despite low levels of seedling recruitment. The restricted occurrence of the species to spasmodically grazed stock routes provides evidence that Trioncinia is sensitive to the continuous grazing that typically occurs in paddocks. The hypothesis that the species requires occasional disturbance for survival was experimentally tested. Recruitment was depressed with burning and inflorescence production enhanced with both burning and simulated intense spasmodic grazing after the first application of treatments. However, these effects were not evident after a second application of the treatments and there were no significant effects of treatment on population densities at the completion of the 4-year experiment. Although not requisite, sporadic dry-season grazing and burning of these areas would appear to be compatible with the survival of Trioncinia. This project highlights the value of stock routes for rare plant conservation.