The invasion of African olive at the Australian Botanic Garden Mount Annan remains an ongoing challenge, but progress with clearing and regeneration is slowly restoring the natural ecosystem.
Horticulturists at the Garden continue to work at clearing weeds and invasive species across the Garden’s 416 hectares of diverse land, with African olive (Olea europaea subsp. cuspidata) being the prime offender.
African olive covers a large area of Cumberland plain woodland and Western Sydney Dry Rainforest at the Garden, along with a handful of resilient Acacia and eucalypts. Originally introduced to Australia as a hedging plant, this woody weed grows up to 15 metres high and can live for 100 years or more.
Tackling invasive species
Its canopy blankets the ground, prohibiting plant life and decimating wildlife habitat. African olive trees are so dense that heavy mulching machines need to be brought in to grind and chop them down to ground level. Even with this equipment, tearing down this invasive weed is a slow and tedious job.
Over the last 15 years, 55 hectares of African olive have has been removed. While the invasion front is being pushed away from the woodland, and the number of seeds spreading has reduced, there is still a lot of work to be done. About 30 hectares remains across the Garden.
This is only a fraction of the 4,000 hectares of African olive throughout Sydney’s south-west. With one tree producing more than 25,000 seeds per year, which are dispersed through bird droppings, every tree removed at the Garden ultimately contributes to plant diversity in the area.