THE EFFECT OF GRASSLAND GAP SIZE ON ESTABLISHMENT, GROWTH AND FLOWERING OF THE ENDANGERED RUTIDOSIS-LEPTORRHYNCHOIDES (ASTERACEAE)

1. To determine the effect of grassland gap size on patterns of seedli ng recruitment and juvenile establishment of the endangered composite Rutidosis leptorrhynchoides, seed and transplants were introduced irat e artificially created canopy gaps in both a 'short' and 'tail' temper ate Themeda triandra tussock grassland in southern Victoria, Australia . Square gaps of 0 sm (undisturbed control), 15 cm, 30 cm, 50 sm and 1 00 cm width were created by removing the dominant grass, and the emerg ence, survival and growth of R. leptorrhynchoides were followed for 1 year. Survival and performance were compared with light quantity at gr ound level and soil moisture differences between the gags. 2. Emergenc e of seedlings was greatest in large gaps (30 cm, 50 cm and 100 cm) bu t survival was restricted primarily to the 100-cm gaps in both grassla nds. 3. Survival of transplants to 1 year occurred in 30-cm, 50-cm and 100-cm gaps, suggesting that juvenile plants tolerate competition for resources better than germinating seedlings do. Survival, rate of gro wth and total number of inflorescences produced, however, was signific antly greater in 100-cm gaps. 4. There were few differences in the sea sonal pattern of soi moisture between gaps in bath grasslands. The amo unt of light at ground level was significantly greater in the short-gr asslands. and in large gaps (30 cm, 50 cm and 100 cm) at most times du ring the year. Differences between gaps in total soil moisture and lig ht levels, however, only partly explain the patterns of transplant sur vival and growth observed. Sail moisture variability is suggested to h ave been an important factor influencing transplant survival over summ er. 5. These results confirm that R. leptorrhynchoides is a gap-sensit ive species, with recruitment and survival unlikely to occur in canopy Sags less than 30-50 cm in diameter. Management of remnant population s needs to ensure that large canopy gaps are regularly maintained to m aximize successful seedling recruitment and maintain the standing popu lation. This may be achieved by burning the grassland at 3-year interv als. In the absence of the frequent burning of productive grasslands, localized extinction is likely. 6. Reintroduction of the species into secure grassland reserves is likely to be problematic given the paucit y of large Themeda-free gaps in these grasslands. Alternative stategie s for conserving the species include its introduction into grassy wood lands where gap closure rates are likely to be slower.