AbstractAshmore Reef Nature Reserve is an Australian External Territory on the outer edge of the Sahul Shelf in the East Indian Ocean. The islands and waters of the reserve are environmentally significant, supporting large concentrations of breeding seabirds and providing an important staging point for migratory waders. The dominant shrub species on Ashmore's islands is Argusia argentea. Argusia typically grows as a shoreline fringing species and is highly adapted to the harsh environmental conditions experienced in these habitats.
Little is known about Argusia argentea despite its importance to the ecology andstability of Ashmore Reef and islands throughout the Pacific and Indian Oceans. On Ashmore Reef, Argusia is heavily used by nesting sea birds and turtles. In recent years, concern has been expressed by the managers of Ashmore that little or no recruitment of Argusia is occurring, and the species is declining in abundance on all of Ashmore's islands. This project aimed to investigate the ecological and environmental processes that affect Argusia recruitment on Ashmore Reef, and determine the most effective method of propagation and establishment.
Two trips were made to Ashmore Reef, in November 1999 and May 2000, to collect data on seed banks, seedling recruitment, asexual recruitment, and to assess the impact of birds and turtles. Planting trials were established on West Island using seed and potted seedlings. Seed was collected from West Island for germination trials conducted in Darwin under shade house conditions. Germination trials investigated the treating of seed with aerated salt I freshwater for varying periods, and the comparison of germinability of Argusia fruits of several ages and provenances.
Argusia maintains an extensive but low-germinability seed bank, which together with the harsh environment, greatly restricts seedling recruitment. Seedling recruitment on West Island is minimal, though asexual recruitment is common in the inland regions of the island. No seedling recruitment is occurring on the other islands.
The primary factor in the successful propagation of Argusia from seed is age of the fruit. Using young, mature (yellow) fruit removes the necessity for pre-sowing treatments such as salt water soaking. Seed age has not previously been shown to be important in germination of Argusia, and the same can be said of asexual reproduction, despite its importance to recruitment in the inland regions of the islands.
Potted seedlings were successfully established on West Island during trials and this shows that restoration of the islands is possible. Ashmore's managers now have the information to enable the propagation of large numbers of Argusia seedlings in pots for replanting on the islands. The knowledge gained in this project on appropriate seed pre-treatments, seed age selection, and methods of seedling establishment are sufficient to achieve successful revegetation on Ashmore's islands. Middle and East Islands require extensive revegetation, but the success of planting seedlings into these bird rookery areas is yet to be determined. The high impact of nesting birds on seedling recruitment remains an area requiring further research. The only successful method available to re-establish Argusia on Ashmore Reef is via potted seedlings; to date all direct seeding trials have been unsuccessful.
In light of the study findings that using the younger yellow fruits can greatly improve germinability, further research is needed into the development of direct seeding methods, particularly since the findings on seed age were never able to be tested in the field.
|Date of Award||Dec 2000|
|Supervisor||Samantha Setterfield (Supervisor) & Michael Douglas (Supervisor)|