Botanic Gardens Trust, Sydney, Australia
African Olive update June 2010
Stage One of contract African Olive control work has now been completed, at a total cost of $150,000. The main focus of the work done in the first half of 2010 was:
- Controlling the spread - a 10 hectare area in the eastern valley was spot sprayed to control small olive shrubs emerging in grassland areas. Several thousand shrubs were sprayed with selective herbicide (which doesn't affect grasses) to limit the spread of African Olive in this sector of the Garden. Area treated: 10 hectares. Contractor: Greening Australia.
- Mt Annan summit - freeing up surviving native trees. Mt Annan is covered in dense African Olive forest established over the past 20 years. Despite this dense invasion there are still some native trees surviving above the African Olive canopy. These important remnant native trees have been mapped using GPS by Garden's staff and transferred onto a digital map layer (GIS). Work in this first stage was to free up these native trees by controlling all African Olives within a 10 m radius of each tree. Olives were either removed by chainsaw/herbicide treated or drill/injected with herbicide. The cleared zone around each tree will ensure the tree's survival and encourage natural seedling regeneration. Access paths into the Mt Annan summit area were created to facilitate future work on this steep and difficult site. Area treated: 28 trees/1 hectare. Contractor: Toolijooa Pty Ltd.
- Maintaining previously treated sites - all bush regeneration projects require follow-up (secondary) work, particularly when large dense weed invasions have been cleared for this first time. Follow-up weed spraying was completed for sites mechanically cleared of olive in 2003 and 2007. Direct sown native grasses are establishing well at these locations. Area treated: 2.3 hectares. Contractor: Greening Australia
- Securing new conservation areas and fauna corridors - Good native woodland areas exist along a series of creeklines and gullies north of the Banksia Garden. This area has excellent native tree canopy and understorey with some African Olive invasion. Work in this area has now controlled the majority of olive invasion which will allow natural regeneration. This area, located in the southern sector of the Garden, is important as a fauna corridor linking south beyond the Garden boundary to the Nepean River. Area treated: 3 hectares. Contractor: The Bush Doctor.
- Early intervention: maintaining good bush - Good examples of Cumberland Plain Woodland can be seen by visitors as they travel around the Garden. The work in the woodland has focussed on controlling early olive invasion in bushland areas located in close proximity to Caley Drive. Bushland areas respond very quickly to this timely control of olive invasion. Area treated: 2 hectares. Contractor: The Good Bush People.
- Providing the seed resource for future regeneration: seed harvesting and production - The native vegetation of western Sydney is very resilient and in many cases able to regenerate from seed held in the soil seedbank. For areas that have been dominated by African Olive forest for many years, large amounts of native seed will be required to ‘kick start’ the regeneration of the native bushland. To meet this demand for seed, a dedicated native seed production area was established at the Mount Annan Botanic Garden nursery to provide high quality native grass seed for use in restoring areas once African Olive is cleared.