Botanic Gardens Trust, Sydney, Australia


Wallaroos vs Weedy Invaders

With the scale of urban development in south-west Sydney continuing to gather pace, the Australian Botanic Garden, Mount Annan has become a precious haven for local flora and fauna. One of the more conspicuous native animals that calls Australia’s largest botanic garden home is the common wallaroo (Macropus robustus). These animals can be seen grazing in the open grassland areas of the Garden and are always a welcome sight for visitors.

Consultants were recently engaged to complete a study of the wallaroo population at the Garden, and specifically their habitat preferences. The aim of this study was to provide advice on wallaroo management and the potential impacts of the Garden’s African olive removal program on the wallaroo population. 

African olive (Olea europaea ssp cuspidata) is a highly invasive evergreen tree which creates a dense canopy, dramatically changing the ecosystem and preventing the regeneration of understorey plants. Through a control program sponsored by Endeavour Energy, great progress is being made to eradicate more than 40 hectares of dense olive forest from the Garden. However, the time arrived where we needed to asses the impact of large scale olive removal on the Garden’s wildlife.

Methodology for the study included the use of motion sensitive infrared cameras, faecal pellet counts and spotlight surveys in a range of habitats including native woodland, olive forest, cleared olive sites and open grassland.

The study revealed a healthy, breeding population of the regionally significant common wallaroo residing within the Garden, a population considered to be one of the last remaining of this species in the Sydney metropolitan area. The population was estimated at 52, which is considered maximum carrying capacity for the site. The study also showed that a small population of eastern grey kangaroos is now present in the Garden.

It was identified that the wallaroos were using a range of habitats and no apparent differences between occupation of native and woodland areas were seen. The highest density of wallaroos observed was in the mechanically cleared olive areas.

The study showed that further removal of dense olive can proceed without impacting the wallaroo population and small ‘habitat islands’ of olive are to be retained in large scale cleared olive areas.

Future planning for the African olive control program will continue to incorporate the retention of habitat islands, as well as planting and natural regeneration of woodlands in designated conservation areas. Thought is now being given to fencing options for the Garden, which will include fauna underpasses in some sectors and fauna exclusion in other areas adjacent to major roads. Maintaining the green vision for the Garden and particularly wildlife management at the urban interface will continue to provide conservation planning challenges, but the result is an important part of the visitor experience.